SEXUAL SELECTION IN LANGUAGE,

MUSIC AND BIRDSONG œ COMMON

THEMES AND ISSUES

MSc Dissertation Sarah Fisher August 2006

1

Introduction

Sexual selection plays a major role in evolutionary biology, shaping some of nature‘s most spectacular beauties and intricate systems. The interplay between competition, display and choice is a major driving force in shaping the world around us.

Human beings are very sexual creatures, and display competition, selectiveness and jealousy when it comes to our partners. To what extent did sexual choice shape our evolutionary history?

Studies in the evolution of language have considered a role for sexual selection in the development of our most unique and mysterious trait, and more recently, in the emergence of music. However, the theories put forward are for the most part hesitant and conflicting. This study attempts to gather and assess some of these theories, while considering the insights available from another group of adept vocal learners and performers, the oscine songbirds.

2 CHAPTER ONE œ THEORIES OF SEXUAL

SELECTION

Sexual selection operates in two major ways œ firstly on traits that give advantage in intrasexual competition (for example antlers, claws), and secondly on traits that give advantage in choice by the opposite sex (for example bright plumage or attractive song) (Andersson 1994)

Surprisingly, though both modes of selection were mentioned by Darwin in the

Descent of Man (Darwin 1871), the latter was for the most part, disregarded until the mid to late 20th century.

Runaway Sexual Selection

R.A. Fisher (1915, 1930) is credited with the discovery of the —runaway sexual selection“ phenomenon œ a coevolution of male traits and female preferences.

Fisher suggested that both the male trait and the female preference were selected.

Females with adaptive preferences produce offspring that carry genes for a) the adaptive preference and b) the trait the preference is for. Therefore the trait and preference are genetically coupled through evolution. Fisher also noted that sexual selection might lead to sympatric speciation, as different trait/preference dyads escalated in different directions, ultimately segregating populations.

3 Fisher‘s work was apparently prompted by this intendedly sarcastic comment by

Morgan (1903) œ

—Shall we assume that still another process is going on, that those females whose taste has soared a little higher than that of the average … select males to correspond, and thus the two continue heaping up the ornaments on one side and the appreciation of these ornaments on the other? No doubt an interesting fiction could be built up along these lines, but would anyone believe it, and, if he did, could he prove it?“

Andersson (1994) suggests that sexually selected traits begin as having a selective advantage for the organism, e.g. a long tail conferring agility. The trait begins as a straightforward index of the individual‘s abilities. When it becomes attractive to the female (possibly as a trait they would like for their offspring) sexual selection begins to act on it and it becomes exaggerated.

Mortality from environmental disadvantages of the trait (for example, increased predation, reduced movement, difficulty foraging) eventually halts the cycle.

Therefore, sexual selection can act more freely on traits less likely to incur these problems. Song may be considered an example of one of these, as an individual can stop and start singing, whereas a physical, external feature, such as a bright tail, is a permanent fixture.

Zahavi & Zahavi (1997) complain that in Fisher‘s model, traits are arbitrary and that their exaggeration is in fact useless and detrimental. Their only function is to

4 pander to female choice. Females continue to choose these decorated, worse- quality males only for the indirect benefits of passing on the display qualities to their offspring. They describe Fisher‘s situation as a —catch 22“ from which neither the males nor females can escape; a male without the hampering display feature may in fact be better quality, but he will fail to attract any mates.

Similarly, the female who chooses a non-displaying male may have fit offspring, but they will themselves find it difficult to reproduce. Despite detriment to both parties, the system drives itself forward purely on its own momentum.

Zahavi and Zahavi (1997) identify one major problem with the Fisher idea.

Arbitrary traits may somehow become sexually attractive, but attraction is not the only function involved in sexual selection. Competition also plays a role. If individuals with the selected-for traits are in fact no fitter than those without, why do they consistently manage to deter their rivals? If the trait is in fact a burden on these individuals, they should be in a worse position than their undecorated contemporaries and be very likely to lose any competition they engaged in. It would only take one or two undecorated, undeterred males to mate with females and produce undeterred offspring, who would then proliferate in the population and outcompete the decorated opposition. The lack of substantiality behind the —signal“ would be unmasked.

The Handicap Principle

5 The Handicap Principle (Zahavi and Zahavi 1997) was only widely accepted in the

1990s.

—If we see a character which does not signal quality, then it must be a handicap.

The handicap principle lies at the heart of evolutionary signaling, and must therefore play a major role in our understanding of it.“

-Grafen 1990, p.5

—The male, like a good salesman, does whatever he can to impress females, while the goal of the female, like that of a shrewd customer, is to check the merchandise and accept only proven quality.“ œ Z&Z 1997

Zahavi and Zahavi (1997)‘s Handicap Principle follows on from Fisher‘s observation that female choice shapes male traits. However, they also go on to suggest that the nature of the traits may be the reason females are selecting for them. Certain aspects of a male‘s physiology or behaviour act as signals to the female, advertising his quality. However, in order for the signals to be un- fakeable, they must also be costly.

Though the Handicap Principle can be applied to many situations where signaling takes place between two individuals with opposing interests, the case of sexually selected signals is particularly complex and interesting. Individuals looking for a mate are interested in a wide range of qualities (unlike other signaling circumstances, where signals are often limited to messages about the

6 power of an adversary, or the potential escape-speed of prey). Sexual signals indicate the properties of a potential mate both in terms of heritable quality and care-giving ability.

Traits such as bright plumage do not have any immediate use for the individual bearing them. On the contrary, they may draw the unwanted attention of predators. Yet this is precisely why, in Zahavi and Zahavi‘s estimation, they are so attractive. Colours attract rivals and predators and are therefore a handicap and an honest signal of resistance to these threats. A male who can bear such a burden and still survive must have a high level of agility and resilience. In order to keep his plumage bright, he must have a good diet. And since the coloured markings on each side of his body are symmetrical, he probably has a stable developmental history.

Such tell-tale signs cannot be faked by a poor quality male œ his colours cannot be artificially brightened. A good male —wears“ colours well, whereas on a poor quality male the colours only show up the imperfections.

Even if a poor quality male could artificially enhance his plumage (see Saino et al.

1997, detailed below) he would quickly fall foul of the predation risks incurred and be eaten, curtailing his newfound career as a sexually attractive suitor before he had a chance to make good on the mating opportunities his markings afforded him. It is only those who can overcome a handicap who have the ability to wear it.

7 Arcteid and Danaid butterflies secrete a chemical signal derived from a poisonous alkaloid compound found in plants. This signal indicates that when they were larvae, they were able to eat poisonous plants to no detriment. The alkaloids are also passed to female and offspring once the male takes a mate œ they are useful against predators. (Eisner and Meinwald 1984)

Tern males feed their potential mate during courtship (Nisbet 1973), a transparent signal of their ability to collect food, and that that they are able to provide enough to share with the female and her potential offspring.

Additionally, this courtship technique is favourable to the female in a proximate sense, because she gains a meal. The amount of food provided is a direct reflection of the male‘s abilities, so the signal acts as a reliable index. The signal is honest because the male can only bring as much food as he can catch œ he cannot

—lie“ about his food-gathering abilities by conjuring an illusion œ the signal is made from the very substance it purports to. Food provision as a signal also limits his courtship to one female (unless he is a very prolific hunter).

The table below summarises some forms of handicap and they properties they may convey.

8 Handicap Function Example A large protruding Illustrates agility and Peacocks (Petrie and tail stamina œ this trait Halliday 1994) affects balance and adds weight Brightly coloured Attracts predators, Red backed fairy wren markings thereby showing that (Karubian 2002) the individual can escape or outwit them*, shows that individual is healthy and able to maintain appearance through good nutrition Complex song Shows a wealth of time Frog (Ryan et al. 1982) and mental resources to dedicate to learning and practicing the song. May indicate creativity, a transferable skill for problem-solving which may aid in parental care Symmetrical body Symmetry illustrates a Barn swallows (Moller stable developmental 1994) history, and an ability to resist disease and parasitism throughout life *NB. Bright colours do not always equal handicap. Conversely, some creatures use bright colours as a signal of toxicity and a warning to predators to stay away from them. These are also honest signals, but not aimed at potential mates.

A literal handicap is present in the case of the white pelican. Both males and females of this species grow a vision-obstructing bump between the eyes at the breeding season. Those individuals still able to hunt and fish with impaired vision are reliably demonstrating how their skills hold up under pressure. The bumps recede when mating has taken place in order to allow the pelicans to provide efficiently for their young (Brown & Urban 1969).

9

Time spent singing cannot be used for foraging. So if male can sing, his foraging and hunting skills must be excellent, or his territory very rich. Despite the fact that unlike colours, they can be discontinued at will, calls, like bright colours, also carry an increased risk of predation.

Ryan et al. 1982 showed that bats use the calls of frogs (Physalaemus pustolosus) to locate them for predation purposes. The male frogs produce two forms of signal, a —chuck“ sound and a —whine“. Females apparently prefer the

—chuck“ sound, which conveys information about male body size. However, males do not always —chuck“. In asking why the frogs would not opt to maximise their mating potential by —chucking“ at all times, Ryan et al. (1982) concluded that the

—chuck“ sounds also acted as a lure to predators, more specifically the frog-eating bat Trachops cirrhosus.

Playback experiments using flight cages and also in the field showed that the bats were preferentially attracted to the more complex frog-calls containing —chuck“ sounds.

Ryan et al. (1982) view the variable modality of frog calls as a compromise between attraction and predation risk. However, from a Zahavian point of view, the predation risk actually enhances the effectiveness of the signal, as it offers the male frogs a chance to show that they are resilient enough to —chuck“ even in the presence of danger.

The peacock (Pavo cristatus)‘s tail is the classic example of a sexually selected trait. It is one of the most flamboyant and visually impressive display structures

10 known, and has become almost symbolic of the theory of sexual selection

(Gadagkar 2003), featuring in many popular accounts of the theory (for example,

Helena Cronin‘s —The Ant and the Peacock“ (Cronin 1991). However, experimental evidence of the tail‘s function was only provided relatively recently by Petrie and Halliday (1994). They manipulated the tails of peacocks (Pavo cristatus) to demonstrate the effect these structures have on female choice.

Peacocks from a free-ranging population in Whipsnade, UK, were monitored and photographed over 2 breeding seasons between 1993 and 1994. The experimenters removed the eye-spots (occeli) from some of the tail feathers of full-trained males. They compared the mating success of these males to a control group, and found that number of eye-spots correlated with the number of copulations achieved by each male per mating season. Peacocks are lekking birds

- the males display in a circular area dedicated for this purpose, and gathered females choose from the suitors. The results suggest that the tails are likely to be signals of good genes, since the females choose them preferentially. However, the choices may also at least partially be for direct benefits offered to the females, who may be choosing high-quality males for the protection and status offered by them in the short term, rather than for genetic benefits to their offspring.

Honest signals in action

Following the observation that males most frequently involved in extra pair copulations (EPC) were those with longer tails, Saino et al. (1997) manipulated

11 the length of tail feathers in the barn swallow (Hirundo rustica) in order to test the relationship between paternity and tail length. Though the species is socially monogamous, EPCs mean that male birds can continue to benefit from advertisement of their qualities by achieving multiple copulatory partners, and females can still be selective across the population even when the best quality males are already mated. EPC males will be selected purely for the indirect benefits they confer on the female‘s offspring, rather than for any parental care they may offer. Therefore, despite the barn swallow being a monogamous species, this extra-pair dynamic accounts for the sexual dimorphism in the tail feathers of this species.

The tail of the male barn swallow acts as a signal both of strength and agility and of a good developmental history. As a structure, the large tail acts as a literal handicap on the movement of the creature, requiring extra balance and stamina to support it in the air. The symmetry of the tails is also important. The ability to produce a bilaterally symmetrical structure relies on a robust state throughout life. Illness and poor condition during an individual‘s life history are reflected by some degree of fluctuating asymmetry (FA) in the body structures, which betrays a lack of ability in coping with environmental and genetic stress (Moller and

Pomiankowski 1993). Fluctuating asymmetry is particularly apparent in sexually selected traits, occurring at a significantly higher rate than it does in ordinary morphological structures in an individual (Moller 1994). These structures will be subject to increased variance as they are not essential for the individual‘s survival, which is precisely why they work as sexual indicators. A structure that

12 needs to be of good quality in order for the individual to survive, such as a leg or respiratory system, would not be able to vary widely enough to allow for a range of female choice. Less physiologically essential structures, such as tail plumes, can vary widely without the individual‘s survival being jeopardised as much.

Saino et al. (1997) experimentally shortened the tails of some male barn swallows and lengthened those of others (by means of scissors and glue). The birds with the shortened tails had reduced levels of paternity (proportion of biological offspring in broods and across the population, determined by blood tests of the chicks) compared to controls. The artificially enhanced males fathered more of the chicks in their broods than the controls, to a degree similar to the naturally long-tailed individuals. However, neither of these findings were statistically significant.

A similar experiment by Smith et al. (1991) conducted on the same species in

Ontario, Canada showed that although the artificially enhanced males did succeed in mating early alongside the naturally long-tailed males, only 59% of the offspring in the resulting nests belonged to them. The artificial tails were —too much of a burden for males not fit to carry them“ (Zahavi & Zahavi 1997), and they were consequently unable to guard their mates to prevent cuckoldry. In contrast, the artificially shortened males fathered 96% of the chicks in their brood.

13 These findings illustrate that while manipulating a signal may have short-term benefits for a cheater (albeit an inadvertent one), the cost of the signal will soon begin to tell on the bearer unfit to carry it, resulting ultimately in a loss to that individual. The relative cost of a handicap signal will always be higher for a low quality individual than a high one.

As Zahavi & Zahavi (1997) point out, sexual selection often produces multiple signals in males, allowing a female to gauge the male‘s quality across several modalities. Each adaptation may highlight a certain trait, for example stamina, developmental stability, foraging skill, and ability to fend off aggressors. This means that any signal is interacting with several others at any one time, and does not need to account for all aspects of fitness. For example, while a song shows cognitive skills, a long tail present in the same individual may indicate physical strength and the ability to move freely despite this impediment.

Testing the Handicap Principle

The Handicap Principle in its first, 1970s incarnation (Zahavi 1975) came under criticism from population geneticists (e.g. Kirkpatrick 1986, Maynard-Smith

1976) who build models which seemed to illustrate that the Handicap Principle could not persist in populations. They preferred Fisher‘s version of events, in which the display trait had no significance in and of itself, and was an arbitrary convention held in place only by the relationship between female choice and reproductive success. The somewhat broad and anecdotal manner in which the

14 theory had been presented left the Zahavis open to criticism by those seeking hard evidence of the mechanics of it.

Grafen (1990) Lent considerable support to Zahavi‘s then-contested Handicap

Principle theory with the use of game theoretic models. These showed that an

Evolutionary Stable Strategy (ESS) could be achieved with honest signaling, and that costly signaling is key to the function of the stable system. The models deal specifically with mate choice.

—One can conclude from the evolutionary stability of signals that they are honest, costly and costly in a way that relates to the true quality revealed“

-Grafen p5

—The handicap models of sexual selection clearly demonstrate that the single reason for an increase in optimal display rate in relation to individual quality is that low-quality individuals pay a relatively higher cost per unit of display than high quality individuals“ œ Moller 1994 p170

In Grafen‘s model, males have free choice over the degree of advertising they show to the females, but their quality is fixed. The female perception of the quality of the males is based only on their advertising. There is a discrepancy between the perceived and actual quality of the males, and this is an overall measure of female fallibility of judgment. The verdict of the female is vital for male fitness.

15 Under these assumptions, a male‘s fitness is greater when he advertises in keeping with his quality. Similarly, a female does best with the assessment strategy where she judges the males‘ quality by the degree of their advertising.

Other strategies are ruled out as being unstable, since all other strategies are open to cheating.

It is essential to the operation of the system that the signal is costly, and that it is proportionately more costly to the lower quality individual than the higher one.

The benefits of advertising a higher level of quality than one possesses must be outweighed by the cost of the signal.

Parental Investment

The role of parental investment in sexual selection was outlined by Trivers (1972) in a groundbreaking paper.

Bateman (1948, reported by Trivers 1972) identified three major sexual differences based on the observation of a small number of Drosophila in lab conditions;

1) Male reproductive success varies a lot more than female reproductive

success œ females can almost always have babies if they are physically

capable.

2) Female reproductive success is not limited by an ability to attract males.

All females are courted. Male success is limited by their ability to attract

females.

16 3) Higher number of copulations did not correspond to higher reproductive

success in females. For males, however, there was a linear increase in

reproductive success with numbers of matings.

Taken as a whole, these results reflect the fact that female reproductive investment is in the production of egg cells and the ability to gestate offspring, whereas the male‘s main investment is in maximising his mating opportunities.

Trivers defines parental investment as —any investment by the parent in an individual offspring that increases the offspring‘s chance of surviving (and hence reproductive success) at the cost of the parent‘s ability to invest in other offspring“ (Trivers 1972 p139)

Notably, although it includes the energy invested in the sex cells themselves, parental investment does not include the effort expended in finding partners of the opposite sex to mate with. A male‘s courtship attempts or a female‘s mate preferences (i.e. the mechanics of sexual selection) are not counted as parental investment, as these do not directly contribute to the survival of the offspring.

Differing reproductive strategies in the two sexes lead to increased choosiness in the sex with greater investment per offspring, nearly always the female. This effect is thought to stem ultimately from anisogamy œ the differential size and number of male and female gametes, an ancient evolutionary trait found across many species.

17 Animals have a limited amount of resources. There is a maximum level of parental investment per offspring that a parent can make before the investment is spread so thin it ceases to be useful œ an optimum clutch size. The sex who invests most per offspring will have a smaller optimum clutch size. Given that the reproductive success of one sex is equal to that of the other, the sex whose investment is greater becomes a limiting resource for the less-investing sex. The less-investing sex will compete among themselves for access to this finite resource.

As a general rule, a lower level of investment in a sex results in a higher level of competition within that sex.

In practical terms, it tends to be the female who becomes a limiting resource for the male.

—What governs the operation of sexual selection is the relative parental investment of the sexes in their offspring“ (Trivers 1972 p141)

Under these conditions, it seems obvious that the optimum strategy for males is to copulate as promiscuously as possible and not to invest in his offspring at all post-conception.

18 CHAPTER 2 - MONOGAMY AND

DIMORPHISM

Sexual selection, monogamy and monomorphism

A major stumbling block for assigning sexual selection a role in the evolution of music and language is the lack of sexual dimorphism in our species, contrary to the typical pattern of sexually selected traits appearing in only the displaying gender.

Human females, as well as males, display jealousy, vanity, competitiveness, mate guarding and intra-sex aggression. However, the general view of sexually selected traits within animal biology is that they will tend to be dimorphic œ with a displaying sex and a receptive sex.

While some data from evolutionary psychology studies (e.g. Miller 2000, Bale et al. 2005) suggests that males have the edge with regard to linguistic —display“, it can intuitively be observed that male and female language abilities are very similar. This is the dimorphism problem; the dimorphism, or lack thereof, in human language abilities. It is an argument often held up against a role for sexual selection in language evolution, e.g.

19 —It is logically possible, but probably unlikely, that sexually selected trait could be non-dimorphic so that selection on one sex resulted in evolution in both sexes“

œSnowdon, 2004

—Sexual selection predicts strong dimorphism. Whenever we observe a characteristic shared by males and females, sexual selection cannot be considered a valid explanation“

- Dessalles 1999

However, sexual monomorphism is found in many species, particularly in monogamous bird species where both partners invest similar resources in raising offspring. In these species, males and females display and compete for mates.

Preference and selection occurs due to a variation in parenting and resource- holding ability in both genders. The behaviour also seems to be associated with lekking birds, and with communal and social species. Some, e.g. the crested auklet, show sexual display structures in both males and females.

The simplest explanation for monomorphism is —that competition over mates, or other social competition, is similar in the two sexes“ (Andersson 1994). If individuals of both genders play similar roles, but e.g. their parenting ability varies widely, fierce sexual competition/selective mate choice can still occur.

20 In humans, sociality and the ability to self-promote and integrate in social situations are equally important to both sexes, and (according to e.g. Miller

2000) very closely linked to reproductive success.

Female song

Langmore et al. (1996) conducted a study on accentors (Prunella collaris).

The female of this alpine songbird species produces complex song, and furthermore, uses it for mate attraction.

The birds live in male/female groups of about 8 in large, undefended home ranges. They are polygynandrous (meaning that both sexes have multiple partners). The population in this study lived in the French Pyrenees.

Females opt to breed with multiple males in order to ensure help with parental care. Mixed paternity for a brood means that if one —father“ is unavailable, another may also be motivated to help. There is a conflict of interests between females and males, since males prefer exclusive paternity and will attempt mate guarding.

Fertility synchrony among the females means that a given male may not be certain to help with a brood he has fathered, as other broods will also be demanding his attention.

21 The overlap between female periods of fertility sets up a pressure towards attracting maximum numbers of mates in a limited time. Females compete and sing to attract the maximum number of mates within their period of reproductive opportunity, so as to ensure a good chance of paternal care.

The complexity of the songs is hypothesised to reflect female age and hence quality (older females sing more complex songs, and produce more offspring per brood).

The authors suggest that the evolution of the female song may have been fostered by the sparse mountainous terrain and scarcity of prey which necessitates large groups and overlapping ranges. This leads to mate competition in both sexes.

The pressure of finding food seems unlikely to have been one of the more pressing ones faced by the savannah dwelling early modern humans, especially after they started developing technologies to access food resources more easily.

However, this example does show that under certain environmental circumstances, the neural song equipment latent in the female can be pressed into service.

The link between monogamy, sociality and shared raising of offspring suggest parallels between the bird and human lineages that seem to present a possible solution to the —lack of dimorphism“ problem. Additionally, a correlation between large group size, synchronized fertility and female competition does tally with some human lifestyles.

22

Duets œ male and female joint song

Duets occurring between paired birds were commonly thought to be a territorial measure, as they are observed during conflicts with neighbouring couples, and can be elicited by playbacks of other birds‘ calls (Langmore 1998). The duet may be suited to defensive contexts because the male part of the duet deters other males, and the female‘s deters other females. Or the two birds may simply make more noise and cover more area than one, making the duet more effective than a solo call.

Another hypothesis raised here is that duets may be a mutual form of mate guarding. The interruption of the song by that of the mate advertises to surrounding competitors that both individuals are already mated. This was borne out by removal experiments by Levin (1996) on the bay wren showing that females sang to deter other females in a territory defence context, while males sang both for mate guarding and for territory defence. She also showed that female birds almost always initiated duets in this monomorphic species.

Social vs. sexual monogamy

Social monogamy (also termed sociospatial monogamy) does not necessarily go hand in hand with reproductive monogamy, as recent genetic analyses of creatures have shown.

23 EPCs (extra pair copulations) add scope for sexual selection even within a socially monogamous society. Choice criteria and competition for EPC mates may work on quite different bases to those for long-term partners.

Geary (2005) broadly divides reproductive strategies into —mating“ and

—parenting“ types. The sex with the higher resource investment per offspring will focus on parenting, whereas the lower investing sex will prioritise mating opportunities. Typically, the —parenting“ sex is the female, particularly in mammalian species, which typically have long gestation times and a need for care during infancy.

However, Geary also notes that social and ecological differences such as shared territorial defence and female on female aggression can —negate this physiologically based sex difference and result in monogamy and high levels of paternal investment.“

The phenomenon of male parental care seems to arise under particular circumstances where the —standard“ male strategy of mating with as many females as possible becomes impractical unprofitable.

Successful pairings between the —male“ (mating focussed) and —female“

(parenting focussed) strategies requires —a co-evolving compromise (Geary 1998).

Paternal investment is important as it increases the choosiness of males. As they make greater investments, they will become pickier about their mate choices.

24 It is worth keeping in mind that the distinction between direct (caretaking) and indirect (genetic) parental investment is blurred slightly by environment-gene interactions in the individual œ for example, the genetic compliment may supply a particular talent for nest-building, which is an environmental factor.

While human paternal investment is facultative (i.e. its occurrence is context- dependent), some species have obligate paternal investment, meaning that the offspring cannot survive without the father‘s care whatever the proximate circumstances.

Facultative investment seems to be more likely when there is a high degree of paternity certainty for the male. (He does not want to risk investing energy in another male‘s offspring.)

In order for paternal investment to evolve, the benefits must outweigh those of being able to mate with multiple females. Factors promoting paternal investment are outlined by Geary (1998) as follows;

-monogamous society

Not only does this mean that most females will be mated already and unreceptive to male advances, it can also mean a penalty for extra-pair mating from other members of the society. This phenomenon is certainly present in humans as well as other primates.

25 -large litters

Offspring clustered in one litter are easier to care for and the reproductive payoff of limiting himself to one female is greater.

-prolonged infant dependency

Offspring who require more care will benefit more from paternal investment

-geographically dispersed females

Increase the amount of effort males must exert to find multiple mates, and therefore makes a promiscuous strategy less desirable.

-female-on-female aggression

Females drive away any potential rivals for the male. Some consider this to be a primary mechanism in promoting monogamy (—[female on female aggression] may be the most parsimonious explanation for socially monogamous males in many species“ œ P Gowaty 1994).

-concealed ovulation

This female adaptation is thought to promote pair-bonding, as the male needs to remain near the female over time to ensure he mates with her at her most fertile phase. Synchronised ovulation also promotes monogamy by reducing male opportunities for mating to a small temporal window. As discussed above, a co- incidence of female fertility periods may also result in competition among females for paternal investment.

26

Mixed male strategies may exist in some species œ a male invests materially in the offspring he has with one female, but continues also to impregnate and then abandon other females. Different choice criteria exist for these different types of partner. With the female he raises his offspring alongside, he should be choosy in terms of her parenting ability and general health, as she is towards him. With the females he only mates with, he is likely to be indiscriminate and eager for sex.

The adoption of mixed strategies varies individual to individual according to male quality, mate availability, female quality and also some genetic bases in the male.

Social status within a society also plays a role.

Mixed strategy may, for example, occur when paternity uncertainty is low and mating opportunities are high.

In species where social monogamy occurs alongside promiscuous extra-pair mating, sexually selected traits can appear due to male competition for short- term encounters, even when mutual selection for long-term parenting skills occurs according to different criteria.

Sexual selection in birdsong

Acoustic signals are those most frequently shown to be sexually selected

(Andersson 1994). Songs can function both as mate-attracting signals and as territorial markers.

27 Evidence that song affects breeding in birds has been experimentally demonstrated. For example, the number of songs sung in a population of sedge warblers peaks shortly before eggs are laid (Searcy 1992), and males quit singing once they have found a mate.

Attraction songs seem longer and more complicated than territorial songs in many species, though not all œ in some cases, the same song is used for both purposes; suggesting that the attractiveness of the song to females may have begun as a simple index of territory size and/or quality.

One of the first studies into the effect of song repertoire size on attractiveness to females was done on canaries (Kroodsma 1976). This laboratory study showed that a higher male song repertoire was positively linked to a greater amount of eggs laid and early nesting in females. The —males“ in question, however, were song recordings rather than actual males.

Lambrechts and Dhont (1988) suggested that a wide song repertoire actually worked to the male‘s advantage in that it was less exhausting mentally and vocally than a repetitive call. However, most studies seem to focus on repertoire as a signal of male quality and as a handicap rather than a help to the male.

28

CHAPTER THREE œ COMMONALITIES

BEWTEEN THE SPECIES

—Songbirds“ in the popular sense (e.g. nightingales, starlings, canaries) belong to the oscine group, which is itself a subdivision of the passerine group, which also contains the hummingbird and parrot lineages in which song seems to have evolved independently.

It is the oscine passerines which have been most frequently studied with regard to song.

Oscines produce a range of syllables, or notes, sometimes in a range of up to several thousand in some species. The notes are stereotyped, meaning that they retain the same form when they are repeated.

The vocal organ in birds is the syrinx, a specialised structure possessed in addition to the larynx. While birds have larynxes, they do not seem to use them in making sounds (Fitch 2006). The oscine syrinx is located at the base of the trachea, and produces sounds when expiratory air is channelled through it. It has two separately functioning sound producing elements, each independently receiving airflow from one of the two bronchii. This means that one bird can

29 produce two notes at once, massively increasing its scope for novel sound production. Additionally, fine motor control of the respiratory tract, pharynx and beak allow further modification of sound.

Breathing in birds is markedly different from that of humans in that the resting state for the avian sternum is midway between expiration and inhalation, so that both are active processes. The co-ordination of both requires several dedicated muscles.

It would seem that the bird‘s vocal tract is considerably more specialised for sound production than that of modern humans. In fact, the syrinx has been described as —arguably the most sophisticated vocal instrument known“ (Fitch

2006).

However, there are some deviations from the standard primate vocal tract plan that have led some (e.g. Lierberman, 1994) to suggest that the human vocal tract is physically specialised for vocal language.

Another obvious commonality between birdsong and human language is the vital role played by auditory feedback. (This is not exclusive to birds and humans, however, bats and other mammals also require it.) In order to learn and produce song successfully, birds must be able to hear themselves sing.

30 Birdsong and language are analogous, rather than homologous traits. This means that they do not share a genetic basis - the common ancestor birds and apes share was not a singing species.

Rather, their similarity results from the adaptation of two separate lineages to a similar set of adaptive pressures. The vocal-auditory channel, plasticity and learnability they share suggest that these traits are geared for a similar function.

Yet apes and birds are, phylogenetically, profoundly different kinds of animal. So given the evolutionary distance between them, their similarities are even more telling when we come to compare them from a functional basis.

Vocal learning (i.e. learning to produce a vocal output) is a distinctive and vital feature in both birdsong and language. Both share a close, almost mutually dependent relationship between the perceptual and productive mechanisms.

Human infants and baby birds cannot learn to speak or sing unless they are exposed to the vocal output of adult members of their species. Chicks raised in isolation produce abnormal songs (Thorpe 1958), and the few children known to have been raised in social isolation have dramatically reduced language ability

(Fromkin et al. 1974). Such dependency on learning is unusual in animals (Doupe and Kuhl 1999), though it is also known to occur in cetaceans (McCowan and

Reiss 1997). Self-inspection and auditory feedback is also important (Suthers

1999) œ it is important that an individual can hear their own vocal output.

Congenitally deaf children do not learn a vocal language (Doupe and Kuhl 1999).

31 Likewise, infant birds must be able to hear their own vocalisations in order to produce and maintain normal song.

The benefits of learning a song, rather than inheriting it as part of a genetic complement, may lie in the adaptability of such a system. Change can occur rapidly through cultural evolution, allowing songs to develop and change over a very short period of time. From a human point of view, this feature is invaluable because of the quantities of information we are able to convey. For birds, however, the songs do not contain meanings other than that of handicap signals.

The energy and effort required to learn a song grammar after birth may tie in to that function œ ability to learn a song may be a reliable indicator of developmental stability and a sound cognitive faculty.

Song may also have a group defining property that benefits from it being a learned system. Birds have been shown to have dialects, with birds of different locales singing different song types (e.g. Mundinger 1975). These may act as a marker of group identity.

Both birds and humans begin their journey to full adult song or language by producing jumbles of meaningless sound units, often repetitively œ babbling in humans, and a similar phenomenon known as subsong in birds (Doupe and Kuhl

1999). The subsong period can range from 1month up to 8 months in songbird species, and is followed by a phase of —plastic“ song before the song becomes crystallised (i.e. full, fixed adult song), see Fig.1 (Marler & Slabbekoorn 2004).

32

Figure1 Subsong, plastic song and crystallized song phases in different oscine species. Taken from Marler and Slabbekoorn 2004

This process can be thought of as an initial —practice“ of all the elements that will be used in language or song. The fundamental, meaningless small units are learned and stereotyped, and will as a result be reliably uniform in that individual when they are used within more structured patterns of output. It also ensures that the infant has determined the distinctiveness of each unit, and can tell it apart from other phonemes.

33 A critical period, as defined by Lenneberg (1967) is a phase of development in which an individual has a heightened ability to learn certain skills, and is particularly sensitive to certain stimuli. The critical period for language learning in humans appears to span from birth until just before puberty, with a steady decline in receptivity during the later years.

Hurford (2005) questions why language appears so early in a child‘s development. He suggests that if language is a sexual signal, it would be likely to arrive at puberty alongside other secondary sexual characteristics.

—A more telling objection to sexual selection in language evolution is the fact that language is acquired in infancy and childhood, before puberty. Traits associated with sexual attraction come onstream around puberty, with sexual maturity. To attract sexual partners before one is able to reproduce would be a waste of effort and potentially harmful. The most prominent sexually dimorphic feature in human language, the typical pitch of the voice, comes onstream around puberty, when the male voice ”breaks‘. This lowering of pitch in the male signal is well known as a sexually selected feature in a number of animals. But human babies start showing signs of language learning around one year of age, and they are probably busy absorbing a lot well before that age, even in the womb, and language acquisition proceeds rapidly in children during their pre- pubertal years. Clearly the adaptive uses to which babies and children put language do not include the attraction of mates“

(Hurford 2005 p172)

34

However, it may also be said that songbirds, who certainly do use their songs as a sexual signal, begin learning and producing them before sexual maturity (Marler and Slabbekoorn 2004). The end of the critical period in humans however, may be said to coincide with the onset of puberty. The pre-pubescent period during which children have greater language acquisition ability can be considered a kind of learning phase before the fully developed faculty emerges, —fixed“, alongside the other sexual characteristics (such as the change in male pitch that Hurford describes).

It is true that most children are fully articulate well before puberty. Modern language has important communicative functions which exist alongside any possible sexual utility, and these are useful whether or not one is sexually mature.

If, as Okanoya (2002) suggests, there existed a learned, pre-linguistic, non- meaningful syntactic song in early humans, then the initial skills and learning necessary for full adult display may have occurred in this plastic pre-pubescent period. It is true that language as a sexual signal is not at all useful for babies and small children. However, after the structural element had acquired semantics and become a tool for communication, it would have become very useful, which may have put those who were able to use it early in their development at an adaptive advantage, though not a reproductive one. The heightened learning ability of pre- pubescent children may be an evolutionary hangover from this prelinguistic time, originally suited to the learning and development of a sexually-selected song.

35 Miller (2000a) holds a similar view of puberty as a —training period“ for linguistic mate display, suggesting the run-up to puberty as a Haeckelian

—recapitulation“ of our courtship abilities through evolutionary time;

—The awkward, uneven, sometimes witty verbal courtship of teenagers may not be such a bad model for the verbal courtship of our ancestors during the evolution of language.“ (Miller 2000a, p352)

However, if we believe that vocal output was a sexual signal throughout our history, this analogy appears to imply that our ancestors were less good at attracting mates than modern humans are. If that were the case, surely they would not have proliferated in quite such a dramatic way.

Neural similarities between bird brains and human brains with regard to vocal song

Vocal learning (the acquisition of a song through hearing others perform it) occurs in humans, bats and some cetaceans, as well as songbirds, hummingbirds and parrots.

There are 7 interconnected brain nuclei common to all song-learning birds, 3 forming an —anterior“ pathway, and 4 the —posterior“ one, all of which are active during vocal learning. The 7 nuclei are present also in many non-song learning birds, however they are not interconnected.

36 In humans, equivalent structures have been suggested which also appear to form anterior and posterior pathways, in addition to an auditory pathway in the brain.

The posterior pathway is connected to facial structures and mediates vocal control, and is connected to the anterior loop which incorporates a —language strip“ (Jarvis 1994) involving Broca‘s area and the basal ganglia and thalamus.

See Fig. 2.

Neural similarities between vocal learning bird and human species may be due to convergent evolution under tight genetic and epigenetic constraints, or a parallel exaggeration of structures present in a common ancestor due to similar evolutionary pressures in both bird and human lineages.

Brain anatomy in humans, oscines and passerine species. Taken from Jarvis 2004.

37 CHAPTER FOUR œ SEXUAL SELECTION

THEORIES IN LANGUAGE EVOLUTION

Okanoya‘s Syntactic theory

Okanoya‘s account of sexual selection‘s role in language evolution is summed up by the following quote;

—What was gradual was the evolution of syntax in sexual display and what was catastrophic was the appropriation of syntactical form for semantic purposes.“

- Okanoya 2002 p. 46

Okanoya suggests that sexual selection played a kind of supporting role in the evolution of language œ providing us with a syntactic capability that was then exapted for use in conveying propositional information. This theory is drawn from observation of birdsong, which has properties of complex syntax which is apparently without any semantic element. Okanoya suggests that syntax and semantics evolved separately, in parallel, and were then unified in a sudden step

(see Figure 3).

38 This is a stark contrast to theories such as those of Bickerton (1990), who introduced the concept of protolanguage œ a rudimentary pre-linguistic form consisting of single semantic tokens for everyday objects and occurrences.

According to Bickerton‘s theory, these tokens were then combined in a rudimentary order-based arrangement as they became more frequent. The increase in number of symbols and the sophistication of the concepts they were used to express caused a form of syntax to arise in order to eliminate ambiguity.

—Sexual selection is good at shaping complex, arbitrary behaviour that lacks survival significance“ (Okanoya 2002 p. 47)

Presenting syntax as a sexually selected trait lifts the obligation to present an adaptive value for syntax in early protolanguage, as well as the need for evolutionary explanations to apparently counter-adaptive properties such as subjacency (a feature of grammar which prevents related elements in a phrase being too far apart from each other)

The Bengalese Finch (Lonchuria striata var. domestica) has a song that can be described by a finite-state syntax (FSS). Each male‘s repertoire of song elements is produced in —chunks“ which are further organised into phrases governed by a

FSS. Therefore, while the potential number of songs the male can produce is infinite, they will each conform to a pathway through the finite-state machine.

39 Human language is described by a context-free grammar, which allows self- embedding structures. This is a more powerful grammar than the finite-state grammar shown in Bengalese Finch song (according to the Chomsky Hierarchy, see Note 1.1). Explaining how a context free grammar might have developed from a finite-state grammar is a problem that Okanoya acknowledges, though he suggests that a finite-state grammar would have sufficed for early language, and that an —elaborate finite-state syntax could establish a communicative and representational ability close to that of a context free grammar“ (Okanoya 2002 p55). The latter assertion does raise the question of why we have a context-free grammar at all, if a finite-state grammar could have sufficed for our needs. This explanation appears to deny the selective advantage of evolving a context free grammar, rather than explaining how we did so.

The song of the Bengalese Finch (Lonchuria striata var. domestica) is notably much more complex than that of the white backed munia (Lonchuria striata), its near relative. Okanoya attributes the difference in song to a 250 year domestication of the Bengalese Finch by Japanese aviarists. 250 years equates to about 1,000 generations. During this time, via some combination of cultural and biological evolution, the males of the species were able to develop a finite-state syntax to their songs, due to a lack of environmental pressures such as predation risk and the cost of foraging. Their day to day lives required less resource

1 The Chomsky Hierarchy (Chomky 1965) is a classification system for languages and grammars, both human and machine. The more powerful grammars are less restricted by conditions for their production. Context-free grammars rank above finite-state grammars in the hierarchy.

40 expenditure, so they were able to concentrate their energies on developing more and more baroque sexually attractive signals.

Okanoya tested his supposition by splicing notes from a male munia‘s song together to form a new song organised with Bengalese Finch syntax. Female munias responded to the artificial song with increased nesting behaviour (when compared to behaviour after exposure to the regular munia song). This suggests that the Bengalese Finch song is a more developed form of munia song, and that the female preference is for increased complexity.

Figure 3 Okanoya‘s model of converging semantic and syntactic evolutionary pathways. Taken from Okanoya 2002.

It seems important to acknowledge that the function of the Bengalese Finch‘s signals in terms of handicap would have been different to that of the white

41 backed munia. The male munia‘s song indicates that he is resilient and cognitively capable, and that he can withstand the risks and demands that singing brings. For the Bengalese finch, these pressures have been removed, or at least reduced so much that the handicap caused by singing is negligible. Can the

Bengalese Finch‘s song still be viewed as a handicap, or is it merely a display of quality? I suggest that there may have been some degree of competition between males for food, and disease risk in the caged birds. Possibly the songs still acted as a handicap, but the bar was set considerably higher. Figure 4 is a graphic representation of the effect of environmental demands on the development of song. Assuming each bird has a limited —budget“ of resources, the pressures of the environment decree how much he has left over to —spend“ on his display once his survival expenditure has been taken care of. The —budget“ will vary from bird to bird, hence the variation in song quality that allows females to select between them.

Figure 4. Graphic representation of the resources available to a domesticated bird species and a wild bird species for investment in sexual song displays.

42 Okanoya‘s idea of domestication facilitating song complexity is also applied to early humans. In developing tool technologies and the use of fire, he suggests that our ancestors performed a kind of —self domestication“ œ manipulating their own selection pressures and freeing up their resources for sexually selected displays.

The fact that birdsong contains no propositional meaning was key to its development, in Okanoya‘s view. Following Knight (1998)‘s assertion that —apes are too clever for words“, he reasons that a meaningful language must also be open to the possibility of deceit. A language-like signal, with semantic content, must be able to be removed from the context to which it refers. Otherwise the signal is a reaction to, rather than a referential token about the event or object it describes. Such reactions, for example a cry of pain or fear, are under the control of the limbic system, and are involuntary. The semantic signal must be under cognitive, voluntary control, as the signaller can choose when to make it. The voluntary element introduces the possibility of deceit, and therefore the signal can no longer be honest.

A meaningless signal, such as the birdsong described here, does not convey semantic information and therefore can be judged on its form rather than its content. A semantic element would hamper this, according to Okanoya.

"[I]t is this very process of grounding that ties the signals down and prevents them from evolving into more various and elaborate forms over time. By freeing signals from any concrete reference, other than the fact that a particular

43 organism is able to produce that signal, sexual selection allows them to change continuously and fairly rapidly over time."

- Werner and Todd 1997

Like Okanoya (2002), Werner and Todd (1997) reason that the need to convey meaning hampers the development of complicated form. Referentiality demands that a signal must be standardised across many individuals and across some length of time in order to survive as a useful tool to a population.

However, as Franks and Rigby (2005) have suggested (see below), a signal may operate on more than one level. It is quite possible that the semantic information in a signal could exist alongside other properties such as the delivery, pitch, tone, enunciation and vocabulary, that delivered another form of information about the speaker, possibly not even on a conscious or voluntary level. This information could still be honest, while the information content need not be.

Franks and Rigby illustrate the four orthogonal truth possibilities of such an utterance in a table (see Fig.)

Meaning may still hamper syntactic innovation, however, in that once tokens become meaningful, —it matters how they are arranged“ (Okanoya p58). Syntax must conform to the needs of semantics. This suggests a discrepancy between syntax and semantics that must have been resolved before they were unified in

44 the way Okanoya suggests. If syntax had developed under sexual pressures, with no constraint on the arrangements or frequencies of its elements, it must have undergone some changes once it was welded onto semantics, and took on the additional constraints needed for meaningful expression. Thus the form of syntax we currently see in human language is probably quite different to any possible pre-linguistic syntax-only song form. It is possible that such a change in the function of the syntax could have provided the selection pressure necessary to make the leap from a finite-state grammar to a context-free one.

Ritchie and Kirby (2005) modelled the effect of domestication, or masking of selection pressures, as a factor in the development of certain traits. They used a population of agents with properties drawn from that of the white-backed munia and Bengalese Finch, transmitting information between generations in an

Iterated Learning scenario (Kirby and Hurford 2002). The agents were born with a genetic —song filter“ which was used to determine the probability that a song is that of the bird‘s own species. The filter determined which adult songs they learned during their lifespans. Adults were scored for fitness according to their ability to recognise members of their own species from songs. Ritchie and Kirby concluded that domestication alone may have a powerful enough influence to cause certain traits to proliferate in a population, without the need for sexual selection as a driver.

Miller (2000a) is a major champion of sexual selection as a driving force in all aspects of human evolution, language included.

45 Focusing on modern human contexts, he points out that language is a vital tool in courtship, with vocabulary choice, tone, pitch and enunciation all being criteria for judgment by a potential mate. This may be so, but the same could be said of job interviews, academic presentations, or meeting new friends in a social context. Language is common to all our interactions, and is our primary interface with one another. To point out that it plays a role in our courtship is hardly revelatory.

While not implicating sexual selection in the first stages of language evolution,

Miller suggests that a rudimentary linguistic ability could have been accelerated and sharpened by a runaway sexual selection process, with language acting as an indicator of fitness, due to it being —costly and difficult“, although the precise nature of these costs and difficulties is not defined. Presumably the costs are in the mental processing necessary to conform to the grammar of a language, and the developmental investment involved in learning that language.

For example, he suggests that the romantic appeal of traditional poetry derives from the added handicap of conforming to metre, rhyme and rhythm when writing a poem œ additional constraints that require more mental processing for the poet who must conform to them in his writing.

According to Miller, viewing language as a sexual display explains why people compete to have their turn in conversation, and why interruption and overlap is so common. However, while sexual success may result from conversational dominance, it could equally be an indirect effect, following from perceived social status.

46 Interestingly, Miller explains the perhaps stereotypical notion of the monosyllabic married male, and the twittering, verbose female, in parental investment terms. While the male must be charming and eloquent to gain sexual access to the female in the first instance, he can then afford to lapse in his efforts once his mating opportunity has been secured. By contrast, the female feels the need to continue her display over time in order to encourage paternal investment.

This rather generalised reasoning runs counter to the idea that humans are fairly monomorphic when it comes to sexual display and competition, due to the degree of monogamy and paternal investment present in our species.

Meaning and Deception

The areas in which we might expect to see evidence of sexual selection will be in language‘s creativity, novelty and complexity, as these are traits that indicate cognitive skills. However, the display element and the creativity will be curtailed by other pressures such as the need for consistency across communicating populations, and the fact that words refer (i.e. the need for language to make sense).

Much is made of the fact that honest signals remain honest in nature because the message they convey is equivalent to the medium in which it is communicated.

The resources required to produce, for example, a large plumed tail, must be present in order for the tail to exist. The tail is a message to onlookers that the

47 individual possesses the resources to produce it. One cannot produce a tail from nothing œ therefore one cannot lie when speaking in the medium of tail- possession.

Human language, however, certainly does allow for the possibility of deception.

Humans can, and frequently do, lie about themselves to others.

Franks & Rigby present a possible solution to this problem œ they analyse the hearer‘s treatment of utterances as occurring on two levels. One is a semantic level, in which utterances can be analysed as true or false, while the other is a non-semantic, sexual display level which is treated rather differently by the hearer.

—Surface semantics may express a communicative act that indirectly indicates the genetic quality of the male, though the semantics does not describe the genetic qualities.“

- Franks and Rigby (2005)

Franks and Rigby (2005) suggest that the capacity to differentiate honest from dishonest communications is rooted in mate choice. This capacity is important for language. They theorise that language developed by means of a coevolutionary arms race. Creativity in (linguistic) mate-attracting displays, increased the deceptive power of language. Countering this, the species also develops an ability to discern dishonesty in signals so as to avoid being deceived.

48 The costs and benefits associated with the success or failure of these two strategies is predicted to add to the likelihood of attempted deception œ putting the effort in to deceive another must result in a payoff, or nobody would do it.

Likewise avoiding deception œ the deceived party must have something to lose by being deceived.

Mate choice is a prime example of a scenario with such high stakes œ the reproductive fitness of an individual can depend on the ability to outsmart another.

They investigate potential sex-differences in creativity using an empirical study on human participants. Each individual is given a novel two-word —concept combination“ e.g. —fork-scarf“ and asked to provide a definition for it. The responses were classed as either relation-linking or property-mapping, the latter being deemed more creative. The participants were —motivated“ by producing their responses in the presence of a —young an attractive“ member of the opposite sex, or as a control, in the presence of a member of his or her own sex.

A deceptive attempt to show creativity was characterised by a response that bore no semantic relation to the concept types, or that fitted into neither of the two categories.

Relevance Theory of pragmatics (Sperber & Wilson 1986) weighs up the costs and benefits of listening to a given utterance in a quantitative way. A trade-off is

49 outlined between the cognitive effort needed to interpret the utterance, the informativeness (i.e. worthwhileness) of hearing it.

There are two layers in play, ostensiveness of information (the fact that it‘s being pointed out because it‘s relevant) and the content of the information itself.

Hearers generally assume that if something is being said it is pertinent, though there will be contextual variation on that assumption œ e.g. when hearing someone who has already been established as unreliable, or with an ulterior agenda, such as a salesperson.

They posit a hearer sifting-mechanism for determining truth, which deals with the semantic content of the utterance, but also the non-semantic information being presented œ e.g. the display of fitness by a potential mate. This two-layer system means that utterances carry more than one meaning, and can

(surprisingly) both lie and tell the truth at the same time. (Facts may be correct, but information on genetic fitness may be incorrect and vice versa)

—The main implication [of the 2-level system of truth/falsehood in statements] is

that communicating as a descriptive device is only one of the potential evolved

functions of language; language use as an indicator of genetic fitness in mate

display is a further possibility.“

œ Franks and Rigby (2005)

50 There are opposing pressures for an indicative trait to be overt and straightforward enough to be received and understood by females, and yet complex enough not to be easily faked.

There is also a degree of —creativity“ that is so extreme in its novelty that it can no longer be considered a sign of fitness œ Franks and Rigby emphasise that creativity must conform to certain parameters such as intelligibility, relevance to conversational topic. There is a window of acceptability somewhere along the continuum that exists between monotony and bizarre extravagance.

Franks and Rigby‘s test results show that males produce more property-linked interpretations of novel concept-phrases with a young female interpreter than a post-menopausal one (i.e. one deemed to have no reproductive allure). They also produce more of them when speaking to a young male interpreter, which may be an indication of intra-sex competition.

Females, however, produced a similar number of property-linked interpretations with young males and females as they did with the post-menopausal female

—baseline“.

This leads the authors to conclude that there is a dimorphism between the sexes when it comes to creative language œ but only in a sexual display context. The fact that females also produce creative language (viz. the many successful female comics, authors and poets) need not disrupt this hypothesis, provided we bear in mind that creativity can have more than one purpose and can be used in different ways.

51 CHAPTER FIVE œ INNOVATION AND

CONFORMITY

Female neophilia is a driving force in the complexity of sexually selected song.

But what is the complementary balancing, degrading force that keeps it in a stable state? Handicap effects such as increased predation? Genetic mutation?

Transmission error in song?

Werner and Todd's (1997) model attempts to address this query. Their population has "female" agents with "local" and "global" transition male song- scoring preferences œ and additionally, a preference for being surprised. Initially, male songs are random, and female preferences are based on some folk tunes, intended to create some human-like basis for the simulation.

The first two scoring methods involve comparing "observed" song note transitions with "expected"/"preferred" values stored in her memory a. The

"expected" values are drawn from a running total she keeps from the transition frequencies in the song as a whole. The final score criterion goes directly against these œ what is unexpected is in these cases preferred. The female scores a male more highly when he surprises her with an off-the-wall transition.

52 "Note that it will not result in the males singing random songs{in order to get a high surprise score, a song must first build up expectations, by making transitions to notes that have highly expected notes following them, and then violate those expectations, by not using the highly expected note. Thus there is a constant tug-of-war between doing what is expected and what is unexpected in each song."

- Werner and Todd 1997

This setup allows a mechanism that prevents a descent into total randomness.

Werner and Todd predict a population effect œ operational sex ratio (OSR) skew affecting the strength of selection. Strongest selection occurs when 1 female selects from lots of males. However, this prediction was not met œ change occurred most rapidly when 2 males sang to a female. This was because their offspring were all "mixed up" œ a well-matched parental dyad would have offspring very similar to themselves. Additionally, good matching meant that neither songs or preferences needed to be adjusted all that much. With a poorer match, more —compromise“ occurred both with female selection and with male song.

This bottleneck enforcing compromise and therefore changes in the songs and preferences speeded up the rate of change in the population as a whole. It also meant that a larger population facilitated a greater rate of evolutionary change.

53 Complexity, randomness, and monotony.

Complex birdsong is attractive. Monotonous birdsong, and random birdsong, are not. In a continuum with monotony at one end, and randomness at the other, the attractive sort of song is represented by a region in the middle.

This window of acceptability is defined by the hearer‘s preference.

(—hearer“=female, and —displayer“=male, for simplicity‘s sake).

The female will not mate with males who produce a very monotonous song, e.g. all one note at a constant rhythm. Nor will she mate with a male whose song is so complex and unusual it appears to be random. Why?

The song must convey to the female that the male has the cognitive powers to learn and adhere to a complex grammar œ including some note combinations and orders, excluding others. A simple song follows a grammar, but not one that requires very much in the way of ability (for example S
a). A random song also follows a very simple grammar (S
[anything]).

An extremely complex song may have an extremely complex grammar, but appear to female ears as something random, because she does not grasp the grammar it adheres to, or cannot hear enough of the song at one time to deduce the grammar. The song is not attractive, because the female is unable to tell it apart from an arbitrary order of notes.

54

The simple example below illustrates this.

The following strings are legal sentences in Grammar 1 (below)

S
abcdbcdbcadbcda

S
bcbcdbcadbcda

S
adbcadbcda a bc

a bcd bca dbc

b dbca abcd da

Grammar 1.

However, they are also adequately described by the much more simple Grammar

2.

a

d b

c Grammar 2

55

Grammar 2 allows any combination of the four symbols a,b,c and d. Grammar 1 allows only certain combinations, but the possibilities allowed by Grammar 1 mean that a female has to listen to a number of songs in order to deduce the patterns.

Grammar 3 is more complicated than Grammar 3, but less so than Grammar 1.

abcd a

b

c Grammar 3

Legal strings from Grammar 3;

S
abcdaabcddabcdaabcdc

S
abcddabcdcabcdbabcdaaa

S
abcabcabcabcdabcdabcd

A female bird might find it easier to determine that songs produced from

Grammar 3 are non-random, despite them being less complex. There is still some scope for creativity within Grammar 3, allowing male songs to vary within it.

56 Time, and female cognition and auditory perception act as constraints on the maximum complexity of the song, while competition among males and female choice prevent it from simplifying.

Could such constraints also have played a role in the development of human language? There are those who make a case for large vocabulary and the ability to speak eloquently as sexually attractive signals (Miller 2000), and it is also true that those whose ideas and thoughts are expressed in such exclusive, sometimes specialist terms are often simply not understood at all œ hence expressions such as —That was all Greek to me“ or —he may as well have been speaking gibberish“.

However, these misunderstood geniuses who cast their pearls before swine do not seem to —die out“, unlike the bird with the overly complex song. They are present in each human generation, and indeed the range of specialist terms and neologisms seems to grow with time. If language were purely a sexual signal, and if the fate of humanity hung upon it as in the case of songbirds, we might see a different, and more stringent set of constraints on our language.

57 CHAPTER SIX œ MUSIC AND SONG

The closest equivalent to a meaningless yet complex performance in humans is music. The near-universal ability to perceive and enjoy music, to judge a tuneful from a cacophonous melody and the ability to reproduce (with varying quality) the tunes that we hear in a hum or a whistle, all point to a deep and enduring relationship between humans and music. The fact that it does appear to be so universal suggests that it may have a biological basis. As to its function, some conclude that it has none (Pinker 1994), and is simply a cultural artefact retained because it happens to give us pleasure. Others (e.g. Fitch 2006) do not rule out a functional basis, but cite a lack of evidence for any particular hypothesis. The similarities between birdsong and music, such as the ordering of a repertoire of vocal elements, and cultural transmission (Fitch 2005) make a sexual selection hypothesis for music‘s origins a tempting one œ phenomena with such similarities in very distantly related species suggests a possibility of co-evolution for a similar function.

Miller (2000b- paper on music/sex) follows Darwin (1871) in considering music to be a sexually selected trait, and a means of mate-attraction. Musicians such as

Jimi Hendrix, he suggests, were sexually successful because of their musical skill.

Music is, to an extent, something we are born with a propensity to learn and enjoy;

58 [Music] is easy and fun for humans but very hard for artificial intelligence programs (suggesting that its function is objectively very complex and difficult, though seemingly effortless).“ (Miller 2000b)

This assertion, however, is a rather sweeping one, and the claim to objectivity is dubious given that artificial intelligence programs are in fact designed by human minds.

Despite the universality of musical appreciation, Miller notes that there is considerable variation in performance aptitude. Variation of this type would be congruent with music as a sexual signal, especially if high aptitude could be shown to be correlated with other qualities that made the musician a good mate.

Meanwhile, most of us are able to appreciate and judge music in terms of its quality, just as most members of a species are able to accurately interpret the sexual signals of a displaying male.

One of Miller‘s major reasons for classing music as a sexually selected signal is that it does not seem to have any survival value. (If it is not adaptive, then it must be sexual.) Along with music, he also places art, language and ideology in this

—sexually selected“ category. This line of reasoning appears to discount any non- biological element to human nature. Dividing every aspect of modern human life into either —natural“ or —sexual“ seems worryingly simplistic. It fails to take account of the cultural and social phenomena we have built up over the last several thousand years, and their complex interactions with our biology, environment and technologies.

59 One notable aspect of music is its emotional impact. Music has the ability to move us in a powerful, wordless way, conveying a range of emotions from sorrow to joy to anger and fear (Mithen 2005). An emotionally affective element is not a prerequisite for a sexual signal. In fact, the judging of a potential mate is ideally a shrewd, intellectual assessment, to which an emotional influence would probably be detrimental. Though emotions are a vital part of pair bonding and relationships, and beholding one‘s perfect mate may result in a rush of joy or excitement, the stirring of emotions with an initial signal, especially one designed only to promote copulation, does not seem particularly useful. Additionally, the negative emotions music can excite, such as fear, tension and aggression, are not readily associated with sexual attraction.

Fitch (2006) carries the multiple-component approach he takes with language evolution (Fitch 2005, HCF 2002) to his view of the evolution of music. As a faculty made up of diverse components both ancient and recent in evolutionary history, music as a biological phenomenon will have no —straightforward“ explanation.

Similarly, the roles of music and its antecedents are varied œ bonding, mate attraction, group cohesion are some examples Fitch offers.

—Thus, questions like —When did music evolve?“ or —What is music for?“ seem unlikely to have simple unitary answers.“ œ Fitch (2006)

60 Despite the lack of a clear answer to the —function“ question, Fitch advocates research into the —mechanistic, developmental and phylogenetic questions“ involved in the evolution of music.

In addressing the dimorphism problem, Fitch (2006) points out that the prevalence of female song has been generally underestimated in the literature due to an emphasis on the study of birds in the temperate regions. Tropical bird species show less dimorphism with regard to song, and females of temperate species have recently been shown to be more likely to sing than was at first assumed.

Fitch acknowledges that —the function of music in human courtship has considerable intuitive appeal“ but notes that the relationship between music and romantic entanglement is one seated in tradition and literature, rather than clearly established via scientific testing. While dubious of a role for human music in sexual selection based on the current state of the evidence, he doesn‘t rule it out entirely, instead calling for more empirical tests to confirm or deny its presence.

Hauser and McDermott (2003) also advocate a comparative approach to researching the evolutionary origins of music. They draw certain parallels with language. Music, they say, is like language in that everybody effortlessly "gets" it without being taught it. Even if you can't play an instrument or sing in tune, you

61 can appreciate music, tell good music from bad, you hum in the shower, you whistle while you work etc.

It seems to be a universal human faculty, which seems to suggest genetic basis with some innate constraints.

Hauser and McDermott suggest that one such constraint may be the organization of musical elements into octaves œ transposable "units" of 5-7 notes. The octave is a phenomenon that seems to be common to many human cultures.

The principle behind Hauser and McDermott's proposed comparative experiments is summed up here; œ "If animals reared without exposure to music develop features of human music perception, there is good reason to assume they are innate features of the brain". œ Hauser and McDermott 2003

By testing primate subjects in this way, Hauser and McDermott would seek to filter out human cultural artefacts of music from the innate "bare bones" of the music faculty. In selecting animals who do not produce or hear music in their wild contexts, they reason that any perceptual ability in their subjects arose for reasons other than music, and was exapted or co-opted for music at a later date by humans, rather than being evolved for the purpose.

They report a study by Wright et al. (2000) on rhesus monkeys that seems to show generalisation over transposition - they, like humans, recognise tunes

62 transposed up 1 octave as the "same", but 1.5 or .05 octaves are judged as non- same. Therefore the perception of the octave seems to have a significant status in the primate brain. Additionally, this octave generalisation seemed to be shown for tonal but not atonal melodies, suggesting that perception of "tunefulness" is also not an exclusively human characteristic.

These findings raise the question - If these properties are pre-human

(homologous), what is their adaptive function in other (non-singing) primates?

How is an octave useful to an ape?

Hauser and McDermott state that the octave transposition property exists in non- human primates, but not in songbirds. If the primate octave-transposition attribute is homologous with our own, then the analogy between birdsong and human music is weakened somewhat. The octave generalisation ability seems likely to have evolved for some pressure that exists for primates but not for birds.

Hauser & McDermott offer criticism of the Wright et al. 2000 study œ that the monkeys might have been watching TV in their enclosures at the university they lived at and picked up some of the trends in Western music via theme tunes and music programmes they had seen.

Additionally, it is pointed out that human infants are much less sensitive to certain note transitions than adults, lending weight to the importance of learning and therefore a cultural rather than innate basis for musical perceptual abilities.

63

Hauser and McDermott state that animal music is different from human music in that it has purely a communicative function œ that there is no aspect of enjoyment or practised performance.

"… although animal song may modulate the emotions of its listeners, its sole function is communicative, with no evidence of solo performances, practice or productions for entertainment. Human singing, though clearly communicative, is notably different in that it is characteristically produced for pure enjoyment. "

- Hauser and McDermott (2003)

I would suggest that this is less a matter of qualitative difference and more a matter of environmental context.

Activities which benefit creatures are also enjoyable in many cases. An example is sexual intercourse. Another is grooming. Another, very simple one, is eating rich, high-energy foods such as fat. It makes sense, in evolutionary terms, for an animal to derive enjoyment from activities that increase its reproductive fitness or chances of survival. Such proximate motivations are as valid as the ultimate fitness-related ones in keeping the trait going. Alcock (1998) illustrates this point with the example of capuchin monkeys who apply citrus fruit oils to their skins.

"At a proximate level, monkeys may derive pleasure from applying certain scents to their bodies because, at an ultimate level, the behaviour in the past had

64 medicinal benefits that translated into increased reproductive success. The full analysis of any behaviour involves both proximate and ultimate features, with the one complimenting the other, not excluding it." (Alcock 1998 p5)

In a self-domesticated (see Okanoya 2002) situation where predation risks are low and environmental stress is reduced, there is less constraint on the expression of certain traits. In the case of Okanoya's captive-bred Bengalese

Finch, the trait is song, which becomes increasingly complex. As the external pressures go down, the individuals in the population have more "spare" time and energy resources to devote to activities that increase sexual success, or which they find pleasurable (or both).

Arguments against evolutionary bases for music (and language) that suggest they cannot be adaptive because they have no obvious purpose, and we merely derive enjoyment from them, are not necessarily valid. An example is Pinker (1997) who very quotably stated that music was —auditory cheesecake“ œ a spandrel of other traits that just happened to —tickle the sensitive spots“ of our perceptive mechanisms. A frivolity existing outside of the mechanics of selection and adaptation.

However, the very fact that we enjoy something may have a relevance of its own in tracing the evolutionary history of that activity. The activity need not even have a current adaptive function. The desire to eat foods high in fat and salt and the enjoyment humans derive from them can be related to a time in our history when food was scarce and high-energy items were valuable resources. While this

65 preference is no longer to our advantage, it remains, despite the fact that in modern society, the hunger for fat is a major cause of illness and death.

Given its affective properties, commonality among all cultures and races, and tendency to be performed and enjoyed in groups (Miller 2000b), I would view social bonding and the assertion of social status as an important role for musical performance in evolutionary history. As Mithen (2005) points out, cooperation would have been an important factor in ensuring survival for our Pleistocene ancestors. Music performed in groups could promote cooperation by inducing shared emotional states, and the cooperation illustrated by individuals all singing the same tune might have acted as an indicator of willingness to cooperate in other, more vital situations.

Music in modern contexts is often associated with group unity and co-operation.

Military tattoos and marching songs, national anthems, the tribe-like following acquired by rock bands, and the chanting on football terraces are all examples.

It is also the case that music, pop music in particular, tends to have a romantic and/or sexual focus. However, such an emphasis can be found in many cultural forms, such as theatre, literature, television, internet and art. Sexuality is simply central to human nature.

While social status may indirectly connect musical ability with sexual success, I don‘t think there is anything inherently sexy about the ability to produce music, and agree with Fitch (2006) that while sexual selection may have played a role in the evolution of music, it is unlikely to have been a major driving force.

66

How could sexually selected song be united with conceptual meaning?

Assuming a hypothesis like that of Okanoya (2002) in which syntax evolved independently of semantics, it follows that an explanation of how the two came together must be provided.

The role of segmentation ability is put forward as a vital tool for this process

(Okanoya and Merker in press, Sasahara et al. 2006). Analytic reduction of strings into segments according to their context, singling out patterns found in strings, according to statistical cues. Sasahara et al. (2006) used recurrent neural networks to model a population with agents uttering strings, and information flowing from —parent“ to —child“ in dyadic interactions. The strings were initially random. They found that the agents to single out commonly occurring patterns, or —words“ in their interactions by virtue of their statistical ability.

Given a population with meaningless strings, statistical ability and a social organisation, the authors suppose that commonly occurring sound patterns and commonly occurring events or situations may be —mutually segmenting“ œ the common contexts and common sound patterns begin to share a meaning. Ever- more specific segmenting and association with precise contexts could lead to something like meaningful language.

67 Okanoya and Merker (in press) present a similar theory, holding vocal learning as a highly important part of the process. They envision the pre-linguistic human ancestor as a —singing ape“ who developed a complex song display which acted as a handicap, illustrating fitness. The song —tokens“ were shared among group members due to imitation, in a process similar to that of the Iterated Learning

Model (Kirby and Hurford 2002). Gradually, the songs began to vary with context, occurring not just as sexual displays. Sub-parts of the songs became associated with certain behavioural contexts, and over many generations, the songs changed as they were transmitted and linguistic structures emerged.

Analysis of long strings into smaller ones according to contexts is also a feature of

Alison Wray‘s holistic protolanguage hypothesis (Wray 2000), although in her account there is no element of sexual selection.

Vocal learning is defined by Okanoya and Merker as the acquisition of a novel vocal ability after birth, based on hearing a sound and learning to produce it.

Segmentation ability, which can be defined as the ability to separate a continuous stream of sensory input into smaller functional units, is quite a basic property of living things. Taken in a broad sense, it is almost a prerequisite for survival in any creature œ the ability to segregate pain from non-pain, food from non-food and to tell living things apart from their non-living environment. It is also, as Okanoya and Merker point out, —the very first step in acquiring semantics“.

68 The ability for vocal learning occurs rarely in animals (cetaceans, bats, humans and certain types of birds), and in disparate lineages. A common ancestor seems unlikely. Okanoya & Merker suggest that the neural apparatus for vocal learning must be developed from basic neural structures which are common to all these species, evolved independently under similar selection pressures.

Bats, birds and whales all require voluntary breath control for flying, and in the case of whales, when submerged in water. A situation in which humans required voluntary breath control is hard to envisage (although see Morgan 1982, who put forward a theory that humans went through an aquatic phase).

Hihara et al (2003) tested the context segmentation ability of monkeys. The monkeys were presented with three different situations by the experimenters.

Initially, a piece of food was placed at a distance from the monkeys‘ cage when they made a call. On the production of another call, the monkeys were offered a rake with which to retrieve the far away piece of food. In a final training situation, they were supplied with the rake, and when they called, the food was placed down for them to rake up. These three scenarios were designed as three different rudimentary —contexts“, each changing when the monkeys produced a sound of some kind. Although the experimenters made no distinction between the kinds of calls the monkeys made during their training, the animals soon began to make a different sound for each situation.

69 Okanoya and Merker (2006) attribute this behaviour to context segmentation in the monkeys‘ brains. Each situation produced a different emotional state, and the calls differed accordingly. As the monkeys learned to categorise the three different situations, they also categorised the calls, changing them from emotionally-based responses to categorical labels for the different tool/food scenarios.

70 CONCLUSION

I suggest that while language, or facets of it, may have had a sexually-motivated element in its development (something like the complexity developed in birdsong), it cannot be appealed to as an explanation without taking other factors into consideration.

Selection pressures do not occur sequentially œ they are always in parallel, nor do traits always serve a single purpose in an organism.

Finding evidence for sexual selection in language (in its modern form) may be a misguided pursuit. Language performs so many roles for us, and probably did for our ancestors, that teasing out a sexual/display function from the social, communicative and thought-actualising roles language plays for us will prove very difficult.

While language can act as a channel for sexual display, it also has adaptive value in the communication of useful behaviours, non-sexual bonding, and the organisation of multiple individuals for tasks.

Linguistic displays (i.e. those with a sexual motivation) will be those that act as a signal of mate quality œ of intelligence (i.e. cognitive resources) of education (i.e. socioeconomic resources) and of creativity (which might translate to innovation,

71 initiative and problem-solving abilities as well as the cognitive capacity to learn and manipulate a system of calls/symbols).

The similarities between music and language, namely their universality among humans, the combination of discrete elements into phrases and strings that can be judged —correct“ or —incorrect“ (or —tuneful“ or —nontuneful“) by most normal humans, and the ability to learn to parse and produce them easily at a young age suggest that they at least have some brain mechanisms in common, and probably some shared evolutionary history. The historical function or functions of music, like that of language, is difficult to disentangle. It could be that music represents the kind of meaningless display system language may have been had it not been

—hijacked“ by semantics after a syntactic stage. However, though it lacks the descriptive power of language, music is not without communicative power. The deep emotive force of music lends weight to the idea that it has functioned in our history as a means of bonding and drawing individuals together in groups, either socially or to motivate cooperation for tasks.

Birdsong, however, has been shown to be a sexually selected signal. It has enough in common with human language for it to be reasonable to suggest that human language once resembled it, and also had a sexual function. However, any resemblances to it in modern language are mere traces. While structures in the two systems resemble one another, any functional commonalities are too far in the past to ever really get a satisfactory grip on.

72 Despite this, the opposing pressures for simplification through repetition, and increased complexity through either female choice or communicative power (or both) are one commonality that bears fruitful analysis, as both systems seem to operate in similar ways.

Acknowledgements

Thanks to Dr. Simon Kirby, Prof. Jim Hurford, Graham Ritchie, Thom Scott Phillips and Nathan Oesch for help and advice.

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