Western Michigan University ScholarWorks at WMU

Master's Theses Graduate College

4-1979

The Origins and Functional Significance of Incest vA oidance

R. Daniel Murray

Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses

Part of the Social and Cultural Anthropology Commons

Recommended Citation Murray, R. Daniel, "The Origins and Functional Significance of Incest vA oidance" (1979). Master's Theses. 2044. https://scholarworks.wmich.edu/masters_theses/2044

This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. THE ORIGINS AND FUNCTIONAL SIGNIFICANCE OF INCEST AVOIDANCE

by

R. Daniel Murray

A Thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the Degree of Master of Arts

Western Michigan University Kalamazoo, Michigan April 1979

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

This thesis is a product of a long-term interest in the stud}7 of

human and non-human primate ethology. Initially I would like to thank

Robert P. Collins, Department of Biology, St. Clair County Community

College, for the enthusiastic introduction to the fields of anthropo­

logy and primatology he provided early in my undergraduate career.

During my graduate training, I have gained from the advice and encour­

agement of my major professor, Dr. Robert Jack Smith, as well as the

entire faculty of the Department of Anthropology at Western Michigan

University. The gratitude extended to those mentioned does not diminish

my full responsibility for the contents of this thesis.

R. Daniel Murray

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INFORMATION TO USERS

This was produced from a copy of a document sent to us for microfilming. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the material submitted.

The following explanation of techniques is provided to help you understand markings or notations which may appear on this reproduction.

1. The sign or “target” for pages apparently lacking from the document photographed is “Missing Page(s)”. If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting through an image and duplicating adjacent pages to assure you of complete continuity.

2. When an image on the film is obliterated with a round black mark it is an indication that the film inspector noticed either blurred copy because of movement during exposure, or duplicate copy. Unless we meant to delete copyrighted materials that should not have been filmed, you will find a good image of the page in the adjacent frame.

3. When a map, drawing or chart, etc., is part of the material being photo­ graphed the photographer has followed a definite method in “sectioning” the material. It is customary to begin filming at the upper left hand comer of a large sheet and to continue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again—beginning below the first row and continuing on until complete.

4. For any illustrations that cannot be reproduced satisfactorily by xerography, photographic prints can be purchased at additional cost and tipped into your xerographic copy. Requests can be made to our Dissertations Customer Services Department.

5. Some pages in any document may have indistinct print. In all cases we have filmed the best available copy.

Uni International 300 N ZEEB ROAD. ANN ARBOR. Ml 48106 18 BEDFORD ROW. LONDON WC1R 4EJ. ENGLAND

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1312980

MURRAY, R. DANIEL THE ORIGINS AND FUNCTIONAL SIGNIFICANCE OF INCEST AVOIDANCE.

WESTERN MICHIGAN UNIVERSITY, H.A., 1979

University Microfilms International 3 0 0n ztee road, ann arbor, mi 48io6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i i i

TABLE OF CONTENTS

CHAPTER PAGE

I INTRODUCTION ...... 1

II THEORETICAL BACKGROUND ...... 3

Sociocultural Explanations of Incest Avoidance and Exogamy ...... 5

Previous Biological Thought on the Origins of Outbreeding ...... 7

III EVIDENCE FOR A BIOLOGICAL BASIS OF INCEST AVOIDANCE ...... 12

Aversions to Incestuous Pairing in Primates and Other Mammals...... 12

Recent Support for the Westermarck H y p o t h e s i s ...... 17

IV THE GENETIC ADVANTAGES OF O U T B R E E D I N G ...... 24

Deleterious Recessives: A Cause or a Result of the Outbreeding Pattern ...... 25

The Selective Advantages of Variability...... 29

Problems of Small-Population Genetic D r i f t ...... 31

Outbreeding, Heterosis and Evolution ...... 34

V CONCLUSIONS ...... 39

VI REFERENCES CITED ...... 41

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION

The prohibition of incest, whether characterized by avoidance

behavior in non-humans or a cultural manifestation as taboo in human

groups, has recently occupied a considerable portion of the ethologi-

cal and anthropological literature. Following Fox (1972) and Parker

(1976), the incest taboo is regarded as strictly a cultural prohibi­

tion of mating between specific members of the consanguineous group,

while incest avoidance refers to the more basic mammalian behavioral

tendency to avoid mating with siblings, parents, and offspring.

The ethnographic literature covering a multitude of cultures leads

us to conclude that the presence of an incest taboo is probably uni­

versal in all human groups, although it is manifested in a variety of

ways in which precise mechanisms and functions appear at this time to

be elusive. If we are to understand fully the functional relationships

of any particular incest prohibition or its culturological implications,

we may first find it useful to assess the possible causal mechanisms

for the general pattern of incest avoidance among the social mammals,

with special attention to the order of primates.

Despite a strong tendency to relegate genetic influence to any

behavior that consistently transcends taxonomic boundaries, very little

attention has been devoted to those genetic and psychobiological in­

fluences that may underlie the inclination to outbreed. With the

recent documentation of non-human primate incest avoidance (Sade, 1968;

Tokuda, 1961-1962; Enomoto, 1978; van Lawick Goodall, 1968; Harcourt,

Stewart, and Fossey, 1976), kin selection theory (Hamilton, 1963; 1964; 1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2

Maynard Smith, 1964), and beneficial results of heterosis as a result

of outbreeding (Schrieder, 1978), it seems appropriate to return to

these issues to readdress the possible selective advantages of this

mammalian trait.

The purpose of this essay is to present an alternative functional

explanation for the origins of incest avoidance, specifically suggesting

a superimposition of human culture upon a biological substrate. For

heuristic purposes, special emphasis is placed upon the general incest

avoidance patterns among all primates and the interrelationship between

socialization and subsequent aversion to consanguineous sexual bonding.

Incest avoidance is viewed as an expression of the genome providing a

predisposition to avoid sexual contact with those with whom the indi­

vidual was socialized. Individual, rather than group genetic fitness

is emphasized in the discussion of the ontogeny of this pattern. The

existing neuro-physiological mechanisms of this sexual indifference

toward kin will be mentioned briefly, but are considered peripheral to

the primary genetic functional considerations.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THEORETICAL BACKGROUND

The problem of delineating the relative contributions of culture

and biology to human behavior has suffered a long history of little

reward in the social sciences. Indeed, many anthropologists, including

Kroeber and White, have attempted to separate the two, considering

culture a thing sui generis. As Parker (1976) has pointed out, the

reluctance to attribute a biological influence to human behavior may

be founded in fear of "rejection of sociocultural causation" (1976:286).

More importantly, the culture-biology distinction may stem from the

anthropocentric tendencies that dogmatically view a sharp distinction

between animal and human behavior - the latter to be attributed solely

to environment and learned behavior (culture), while the former is

relegated to a combination of social and bio-genetic forces (van den

Berghe, 1974).

The more recent use of sociobiology (Wilson, 1975; Barash, 1977)

to explain some human behavioral patterns has likewise met with consid­

erable criticisms within the field of anthropology. For Sahlins,

Sociobiology challenges the integrity of culture as a thing-in-itself, as a distinctive and symbolic human creation. In place of a social constitution of mean­ ings, it offers a biological determination of human interactions with a source primarily in the general evolutionary propensity of individual genotypes to maximize their reproductive success (1976:X).

Nevertheless, for the evolutionary biologists and an increasing

number of anthropologists, the sociobiological framework presents an

interesting, challenging, and testable approach to the study of human

behavior. Addressing the somewhat emotionally charged reactions of

3

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4

Sahlins, a recent article in the American Anthropologist states:

The strength of sociobiology derives... from its ability to order diverse facts about numerous other species, facts which are almost inexplicable in terms of any other theory. Regardless of how fashionable it may be in some circles to criticize sociobiology, it is important to remember that it fits species from seahorses to lemurs, from reptiles to gulls; can we fail to apply it to human behavior? Evolutionary biology's applicability to every species but our own is unchallenged; how do we claim that it is irrelevant to our own species (as does Sahlins, 1976) without camping out with the anti-evolutionary Creationists for whom man and beast must forever be separated by the latter's lack of a soul (Barkow, 1978:7).

The lack of attention to the behavioral similarities between man

and his closest relatives or cross-specific comparisons in the field

of anthropology (save Fox, DeVore, and Washburn, among others) has

persisted among most authors in spite of the discipline's commitment

to holism and adherence to cross-cultural comparisons. In addition,

two criteria for distinguishing between culture and nature, outlined

by Levi Strauss (1970), appear as undeclared guidelines: 1) establish­

ment of rules is a cultural attribute while natural behavior is spon­

taneous, and 2) culture depends on historical coincidence, while the

natural tendencies are observed to be universal (taken from Bischof,

1972). While this nature/nurture distinction expressed in this manner

may have developed from the deeper theoretical orientation of Levi-

Strauss, it reflects a widely held view of many anthropologists and

is particularly illuminating in terms of the consistent reformulation

and discussion of the incest question.

For Levi Strauss' first point, the establishment of rules to

indicate with whom an individual can mate exists in all human societies

while primates, despite incest avoiding patterns, are considered to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5

lack the cognitive development necessary for social proscription of

this type. While not contesting this established psychobiological

difference, the universal existence of the same types of behavior in

both humans and non-humans should, by virtue of his second point,

challenge the culture-causative explanations popular among many

anthropologists. Unless we wish to postulate that the emergence of

culture in protohominids extinguished the suggested biological "spon­

taneous" behavior and replaced them with the same behavior (i.e. incest

avoidance) of only cultural determinations, we should begin to address

the possible genetic substrate of these seemingly universal character­

istics.

Sociocultural Explanations of Incest Avoidance and Exogamy

The near-universal existence of some taboo for prohibiting marriage

between certain individuals has resulted in consideration of different

types of underlying features. Although this possibility is the primary

theme of Levi Strauss (1970), he regards the incest taboo as functioning

to promote alliances and communication between human groups in the form

of reciprocity or exchange of women. In this sense he neglects the

non-human primates and concludes that such specific patterns are of

little genetic import. This parallels to some degree the early position

of Tylor (1889), but they differ in the respect that Tylor stressed the

survival advantage of exogamy to avoid being "killed off" by competing

groups of men. Levi Strauss, on the other hand, is committed to the

basic structure of the mind and considers the reciprocity a product of

that structure (Harris, 1968).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6

Freud (1918), also without benefit of the ethological studies, was

probably the most influential individual in the formulations of views

on incest. The universal feature of the taboo, he believed, was evi­

dence of the natural tendency to inbreed. For without this natural

incestuous tendency, there would be no need for a law prohibiting such

relations. Sir James Frazer (1910) subscribed to this view, incorpor­

ating the following rationale.

It is not easy to see why any deep human instinct should need to be reinforced by law. There is no law commanding men to eat and drink or forbidding them to put their hands in the fire... The law only forbids men to do what their instincts incline them to do; what nature itself prohibits and punishes, it would be superfluous for the law to prohibit and punish... instead of assuming, therefore, from the legal prohibition of incest that there is a natural aversion to incest, we ought rather to assume that there is a natural instinct to favour it (1910:97).

In this same vein, White (1948) rejects the suggestion of a bio­

logical basis of the incest taboo based again upon the reasoning that

if such influence existed, there would be no reason for a cultural

taboo to suppress mating between closely related individuals. Both

Kroeber (1963) and Harris (1968, 1971) state that in view of the vari­

ability of cultural practices and attitudes toward incest, there is

little chance that a universal biological underpinning could account

for these behaviors. It should be pointed out however, that a number

of biologically based behaviors - reproduction, eating, defecation -

have a variety of cultural rituals associated with them. It would

indeed be impossible to deny the somatic foundation of these activities,

based on the variety in which these are carried out. Likewise, the

biological importance of outbreeding cannot be discarded simply because

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7

of a cross-cultural inconsistency in the rules governing activities

resulting in the same behavioral outcome.

Another popular idea for the explanation of the incest taboo was

presented by Starcke (1901) who felt that incestuous matings would dis­

rupt paternal authority. Mother-son or sibling pairing, in this manner,

might override the established dominance of the father. Both Malinowski

(1927) and Murdock (1949) also regard incest as potentially disruptive

to family life and follow the early suggestions of Starcke.

Aberle et al. (1963), Washburn and Moore (1974), and Campbell

(1966) suggest that the incest taboo in humans also functions to avoid

premature births within the family before the young male is economi­

cally stable or the girl is sufficiently mature to handle the responsi­

bilities of motherhood. As a reason for the cultural prohibition, this

appears inconsistent given the variety of patterns for the taboo. Turn­

bull (1968) has cited examples of premature unions of non-kin and general

sexually permissive traditions for children accompanied by strong incest

prohibitions that are not violated. Lenient early premarital sex ex­

ploration would seemingly not be allowed if a purpose of the incest

taboo was to avoid unwanted premature births.

Previous Biological Thought on the Origins of Outbreeding

Westermarck (1891) was among the first to postulate a biological

basis for incest avoidance by suggesting that close association of

children with parents and siblings cause a sexual repulsion at maturity.

...there is an innate aversion to sexual intercourse between

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8

persons living very closely together from early youth, and that, as such persons are in most cases related, this feeling displays itself chiefly as a horror of intercourse between near kin (1891:320).

The taboo, as Westermarck saw it, is an extension of an already

existing programmed behavior. He concluded that the patterns of out-

breeding preceded the human ability to symbolize, and functions to

avoid the negative biological effects of inbreeding.

The most notable criticisms of this position were the previously

mentioned writings of Sigmund Freud and Sir James Frazer, proposing

statements of direct contradiction. With an obvious incorporation of

the psychoanalytic viewpoint, Leslie White (1948) claims that

Westermarck's thesis...is not in accord with the facts in the first place and still would be inadequate if it were. Propinquity does not annihilate sexual desire, and if it did there would be no need for stringent prohibitions (1948:420).

Nonetheless, several more recent articles tend to lend credibility

to the Westermarck hypothesis (Wolf, 1970; Shepher, 1971), and this

early suggestion also appears to be upheld by the studies of animal

behavior (Daly and Wilson, 1978). Both Parker (1976) and Demarest (1977)

vindicate the position of Westermarck with an enlarged body of information

on human and non-human primates. They differ only in that Parker sees

the psychobiological basis of incest avoidance as adaptive in the respect

that it suppresses xenophobic aggression, which is neuro-physiologically

linked to sexual behavior. Demarest, on the other hand, emphasizes that

the sexual aversion to kin was a preselection to the sociality of higher

mammals and rose specifically to avoid the genetic "deleterious recessive"

effect of inbreeding. Parker makes serious mention of these effects as

a selective disadvantage, but adds the importance of curiosity and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9

exploration that promote survival advantages in inter-group relation­

ships.

The lethal and abnormal effects of deleterious recessive genes,

as a result of inbreeding, is an issue raised by many authors (Aberle

et al., 1963; Campbell, 1966; Fox, 1972; Parker, 1976) in discussions

of the possible functional considerations of the incest avoidance

pattern. There is yet considerable controversy as to whether inbreeding

promotes these deleterious recessive genetic defects or if they could,

indeed, be selected out by extensive and prolonged incestuous unions.

The possibility of defects would undoubtedly be influenced by the nature

and frequency of recessive genes in the original population. Whether

the higher death rate shown by Schull and Neel (1965) for incestuous

offspring would cause demographic difficulties in finding an appropriate

mate of the right age within the family has yet to be investigated.

Slater (1959) has proposed that mate acquisition in early hominid groups

would have posed a serious dilemma, and the pattern of exogamy and

incest avoidance developed from demographic necessity and later became

culturally normative from the experienced advantages of group alliance.

Robin Fox (1972) has produced one of the most recent biological

discussions on the origins of the incest taboo in humans. His theory,

which incorporates much of the previous work of Chance (1967), views

the incest taboo as having developed out of a state of chaos within

the consanguineous protohominid group, which resulted from strife and

competition for available kin-sex partners. The outcome, as Fox sees

it, was a change from hormonal to cortical control of these behaviors

(delaying gratification and introducing feelings of guilt), which

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10

concomitantly caused the subordinate males to seek mating outside the

family group. Fox argues that the incest taboo was the primordial

"rule" among humans and that it may have catalyzed "the whole process."

A linear hierarchy of dominance is conceptualized by Fox as the under­

lying model of this organization - the dominant or alpha male having

total sexual access to the females, to the exclusion of the other males

within the troop.

It is certainly questionable, first of all, that the protohominid

groups were organized as troops as are those of baboons or macaques.

It is more conceivable that the loosely arranged social organization of

the chimpanzee should be used as a model of early hominid group compo­

sition (Reynolds, 1966; Kortlandt and Kooij, 1963). Second, more

recent analysis of macaque behavior has challenged the suggested rela­

tionship between dominance and impregnation of females (Eaton, 1974;

Modahl and Eaton, 1977; Enomoto, 1974). The unilinear and unidimen­

sional dominance, as assumed by Fox, has also met considerable criti­

cism. Chalmers (1973), for one, has asserted that no single model of

dominance can operate for all species of animals, while Bernstein (1970)

has argued that the agonistic encounters, mounting sequences, and

grooming relations used as criteria of dominance do not always corre­

late and are not derived from any single social mechanism.

The most troublesome issue, however, is that Fox's "feelings of

guilt" presupposes the existence of culture as a mechanism to avoid

incestuous pairing in protohominid groups. If incest prohibition was

a "preadaptation" to human culture, it is tautological to presume that

this mechanism consisted of guilt feelings which are thought to accompany

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the advent of culture Itself. Although Fox's paper does contain many

original and noteworthy considerations, it most conspicuously lacks

any discussion of the specific genetic features involved in the origin

of the panmammalian characteristic to outbreed.

In spite of the many explanations that have been posited for the

origins and functions of the human incest taboo, as reviewed above,

the problem still remains unresolved for its existence in one form or

another in almost all species of primates. The primary intent of this

paper is to provide an explanation for the general panmammalian char­

acteristic to outbreed and thus to provide some insight regarding the

possible biological basis for this behavior among humans. In order to

address the mechanisms for this, we shall turn first to the variability

in this outbreeding pattern.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EVIDENCE FOR A BIOLOGICAL BASIS OF INCEST AVOIDANCE

Ethological and ethnological research has disclosed significant

evidence of a biological basis of incest avoidance. The documented

transfer of individuals between troops in many species of non-human

primates, as a form of exogamy, has begun to suppress the erroneous

notion that incest avoidance is a uniquely human characteristic.

Further research has indicated that confined troops of primates (in­

cluding humans lacking a cultural incest taboo) exhibit a general aver­

sion to mate with individuals of close familial association.

Aversions to Incestuous Pairing in Primates and Other Mammals

There are two principal manners in which animals avoid sexual con­

tact with those of the same brood. The most widely practiced method

among the mammals involves a spatial separation of potential incest

partners by differing mechanisms of family dissolution. These types

of behaviors are most characteristic of the social animals which generally

require prolonged periods of parental care and sibling association.

Bischof (1972) has outlined four mechanisms by which spatial separations

take place, summarized here with supplemental data.

1) Isolation of individuals from the natal group after weaning

in mammals would reduce the chance of incestual unions to the random

level. Segregation of both young males and females from their siblings

and parents before sexual maturity has been shown to occur in rodents

(Eisenberg, 1966; Eibl-Eibesfeldt, 1970), the opossum (Reynolds, 1952),

12

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13

the tiger (Schaller, 1967), and the red fox (Tembrock, 1957). Also,

cases of only the male leaving the pride and finding mates not of kin

were observed in both the coati (Kaufmann, 1962) and the European wild

boar (Gundlach, 1968). Bischof has pointed out that these dissolutions

with only the male leaving the family group reduces the possibility of

incest to the same degree as dispersion of both sexes. It is plausible

that this type of early avoidance of incestual mating by isolation

exists in many of the unstudied lower mammalian taxa.

2) Change of object. The more social mammals are character­

ized by sharing a need for social attachment through their lives. Raised

within a family-like grouping, such species requiring prolonged parental

care may undergo a change of object or shifting focus of attention at

sexual maturity, or at the onset of the rutting season. At this time,

social contact is switched from the uterine group to unfamiliar indi­

viduals. The possible psychobiological mechanisms involved with this

behavior are not completely understood, although hormonal activation

could very well induce aggressive as well as sexual activity, which in

turn may suppress xenophobic tendencies and promote exploration.

In the first of three forms of object shift, males often

form all-male groups rather than remain with their home kinship network.

During the mating season or as females become available (for mammals

without a defined season), the males will then disperse to seek attach­

ment in female groups for the duration of breeding activity. This type

of organization is observed in the wapiti (Altmann, 1963), the red deer

(Darling, 1951; Etkin, 1964; Eisenberg, 1966), and the African elephant

(Nicholson, 1955; Ewer, 1968).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14

The second form of shift involves a double set of object

changes with males, that eventually lead to sexual bonding outside the

natal group. Initially, the males from several groups join together

to form a fraternity as described previously. These males split up,

however, during the female estrous period to form a permanent conjugal

union and do not return to either the natal or all-male groups. Bischof

adds that these unions appear as intense as the original family bonding.

This type of early-adult double change is characteristic of both one-

male and multi-male group organizations and is the most typical among

the non-human primates. Polygynous or one-male groups of primates that

exhibit this type of family dissolution include the hamadryas baboon

(Kummer, 1968; 1971), the Hanuman langur (Jay, 1965; Sugiyama, 1967;

Yoshiba, 1968; Blaffer-Hrdy, 1977), and the patas monkey (Hall, 1968).

The polygamous or multi-male group organizations of this type are repre­

sented by over ten species of macaques (Koford, 1963; Imanishi, 1957,

Simonds, 1965; 1974), the gorilla (Schaller, 1963), and to some degree

the chimpanzee (Reynolds and Reynolds, 1965; Goodall, 1965; 1967; van

Lawick-Goodall, 1971).

The final type of object shift omits the unisexual grouping

in that maturing members leave the family-type organization and join

a new group directly. This form of rearrangement exists to the greatest

extent with monogamous species such as the gibbon (Carpenter, 1940;

Ellefson, 1968) and Callicebus groups (Mason, 1968), although in many

respects it is difficult to determine the extent of voluntary behavior.

Nonetheless, in some species of antelope the males reportedly leave their

uterine group without expulsion (Hendricks and Hendricks, 1971).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15

3) Abduct ion. Whereby the males leave and therefore avoid

incestuous unions via both former types of mechanisms, separation of

females from their father can occur by abduction of females from the

family group by outside males. This has been documented in both mono­

gamous species by an active emancipation by the female or in polygynous

animals by outside males abducting the maturing females.

Species exhibiting this type of pattern with the females

may have, in addition, a different form of family dissolution for the

abducting male such as change of object or expulsion. Bischof has

pointed out that abduction of females may or may not be accompanied by

aggressive interactions between males. Abduction in the hamadryas baboon

takes place before the females sexual maturity and occurs with only

passive interest on the part of the troop's dominant male (Kummer, 1968).

Female transference in the gorilla, on the other hand, is done with con­

frontations sometimes resulting in open wounds (Harcourt, Stewart, and

Fcssey, 1976; Fossey, personal communication).

4) Expuls ion. In addition to the above mechanisms, family

dissolution for mating purposes may result from a growing intolerance

and expulsion of the maturing sub-adult. In most cases, this is a

combination of waxing aggressiveness by the adult parent of the same

sex in a monogamous union and growing emancipatory tendencies on the

part of the rejected individual. Therefore, both change of object and

expulsion may operate in the separation of parents from their sexually-

maturing offspring. Carpenter (1940) and Ellefson (1968) have reported

expulsion of both males and females in the white-handed gibbon and males

have been expelled from their group at maturity in the howler monkey

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16

(Carpenter, 1965) and rhesus macaque (Carpenter, 1942). In the case

of the rhesus, however, there is not total agreement, since Sade (1968)

considers the departure of the young males voluntary and lacking any

parental pressure (Bischof, 1972:2-4).

In addition to dispersal of the familial unit, the social mammals

have exhibited an obviously accurate recognition of close consanguineous

associates and refrain from mating with them. This has been documented

in confined groups of primates in which dispersion of maturing indivi­

duals is not possible. The likelihood of incestuous mating under these

circumstances would seemingly be random and identical to any other sexual

union between non-kin. On the contrary, few instances of son-mother or

sibling completed copulations have been documented for over 20 troops

of Japanese macaques in 25 years of observations (Enomoto, 1974; Hanby,

Robertson, and Phoenix, 1971; Eaton, 1974). Among the rhesus, Sade

(1968) has reported only one incestuous son-mother pair among 363 cop­

ulations at Cayo Santiago. This latter single instance was atypical,

since it involved the unusual reversal of the mother-son dominance re­

lationship (Sade, 1968). In addition to the incest avoidance afforded

by the mechanisms of "change of object" through transference in feral

or unconfined populations, there appears an underlying psychological

mechanism that tends to extinguish sexual motivation between kin. In

all probability, this same psychological phenomenon is the foundation

for the previously mentioned mechanisms of dissolution which combine

as an integral aspect of the social organization.

The recognition of relatives may be limited to the social animals

whose periods of sibling and parental associations are prolonged. This

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17

type of incest avoidance is most typical among the primates whose non-

sexual association in uterine groups may exist throughout their lives

(Murray and Mayer-Murdoch, 1977). The increased probability of-incest,

as a potential genetic disadvantage to sociality, is necessarily cir­

cumvented by a psychobiological avoidance mechanism in these animals.

For most asocial mammals, however, mating between closely-related

kin presents no problem. The early family dissolution, unlike the social

primates, takes place before sexual maturity and no substantial loss of

genetic fitness or inbreeding depression is possible. The lack of

social complexity in these animals, therefore, may not require a further

elaboration of mechanisms for the suppression of mating between kin.

Regarding these mechanisms, considerable attention has been devoted

to discussions of the sexual aversion to kin displayed by the primates

and most other social mammals. There are sufficient examples from human

and non-human behavioral studies suggesting that the mechanisms which

promote sexual avoidance within the consanguineous group are directly

linked to familial closeness during socialization. These examples

support the early positions of Westermarck (1891) and Hobhouse (1912),

who were among the first to counter the untenable "voice of the blood"

theories (i.e. a genotypic recognition of kin) by suggesting that fam­

iliarity within the kin-group may foster sexual disinterest.

Recent Support for the Westermarck Hypothesis

In the Israeli communal kibbutz, age peer children are reared to­

gether in one location. They, in effect, are sociological siblings,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18

dressing, bathing, sleeping, and eating communally until the age of

about 12 or 13. One surrogate housemother is in charge of the unit

and tends to most of their needs.

Although intra-kibbutz marriage is allowed, and in many cases

encouraged, Talmon (1964) has observed no cases of post-pubescent sex­

uality or marriages between members of the same age-peer group. At

maturity there is a growing avoidance of the opposite sex within the

unit. Young maturing females are embarrassed by the closeness within

the kibbutz and turn their attention to males outside the group. Males

report no interest in their ’’siblings” because they know them too well.

One informant summarized the attitude of males toward the females in

the group in the following statement: "We are like an open book to

each other. We have read the story in the book over and over again

and know all about it" (1964:504). Joseph Shepher (1971), addressing

this same phenomenon, has noted that among 2769 marriages between second

generation kibbutzniks, there were no instances of unions between two

individuals of the same age-peer group. In addition, no cases of

heterosexual activity were reported to Shepher during the study, and

sexual avoidance within the group appeared to be completely voluntary.

On the other hand, both males and females actively sought friends of the

opposite sex outside their kibbutz group.

Seymour Parker has provided three general observations regarding

outbreeding based on interviews with young adult kibbutzniks:

1) Marriage does not occur in spite of early sexual exploration and experimentation. 2) There is no existing taboo regarding sexual relationships among community members. Young adults do not believe there is anything "wrong" or "strange" with intra-kibbutz sexuality, if so desired.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19

3) Although there is no taboo, the lack of novelty and excitement and not being "turned on" by one another were consistently provided as reasons for the lack of intra-group relationships (Parker, 1976:291-292).

Likewise, Wolf (1966, 1968, 1970), in discussions of adopted-daughter

Chinese (northern Taiwan) marriages, has characterized these unions as

having a high degree of sexual and marital dissatisfaction. In these

"minor" unions, children are betrothed at the adoption of the daughter

and the future affines are raised as siblings by the male's parents

until the time of marriage. These early and prolonged childhood asso­

ciations before wedlock differ from the "major" or other form of marriage

in Taiwan in which the two betrothed individuals are relatively un­

familiar with one another.

Testing the validity of the Westermarck hypothesis, Wolf (1970)

has indicated contrasting rates of birth and divorce between these two

types of marriages. Despite stronger conjugal ties between the male's

parents and the adopted daughter that would tend to encourage marital

stability and productivity, minor marriages produced fewer children and

incurred higher rates of divorce than the major and more popular form

of union. Further investigations revealed that adultery, as an indicator

of marital dissatisfaction, in minor marriages was over five times that

of the major form. Drawing from these data, Wolf postulates that the

early childhood association in adopted daughter marriages depresses

erotic sexual desire which in turn promotes marital dissatisfaction

and infidelity. He vindicates the early position of Westermarck by con­

cluding that "there is some aspect of childhood association sufficient

to preclude or inhibit sexual desire" (1970:515). The Chinese adopted-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20

daughter marriages, like the Israeli kibbutzim, offer considerable evi­

dence that intra-familial sexuality is suppressed by closeness during

socialization, and that psychological suppression of desire may operate

in the absence of any cultural sanction enforcing it.

Popular accounts of non-human primates raised by humans also offer

evidence of the same type of sexual avoidance at the onset of the "foster

child's" sexual maturity. Temerlin (1972) gives an interesting and

amusing account of the change in a young female chimpanzee's behavior

at menarche toward himself as her human father. All affection and

physical contact toward Temerlin and his adolescent son totally van­

ished at the onset of each monthly estrous period, although sexually

gregarious behavior was exhibited to unwary outside visitors and nude-

male magazine foldouts. The young female chimp would elicit screams

at any attempt by Temerlin to make contact during these periods. On

the other hand, no general avoidance behaviors were exhibited at any

time toward females.

Although this isolated example does not, by itself, offer proof

of the Westermarckian hypothesis, it may provide insight that could con­

tribute to our understanding of the basis of incest avoidance. The lack

of any abstract inter-specific communication regarding proscription of

mating solicitation is immediately apparent.

Wild female chimpanzees have also exhibited these same types of

behaviors (screams, threats, retreat) toward siblings when mounting

attempts were made during estrous (van Lawick-Goodall, 1971). The

same females that denied sexuality to a brother would actively seek

males of casual aquaintance. Pre-pubescent sexual play among siblings

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21

in chimpanzees is quite common although repulsion by the female at

estrous prevent brother-sister and son-mother matings in these ani­

mals (1971:188).

In an evaluation of this general avoidance tendency, Kcrtmulder

(1968) suggests that bonding behavior of any type is usually associated

with considerable fear and aggressive reactions. He suggests that the

early family bonding necessitates a reduction of these behaviors that

also tend to inhibit sexual desires. It is postulated, therefore, that

there may exist an optimum level of aggression, exploration, and novelty

that would act as prerequisites of sexual arousal.

Parker (1976), in a discussion of these relationships, has referred

to studies by Goldstein and Jacoby (1955) and Barfield and Sachs (1968)

who found that marked increases in sexual behavior could be induced in

rats by mild convulsive shocks. These studies indicate a strong link

between sex and aggressive arousal since behaviors such as feeding,

drinking, gnawing, and nest-building were seemingly unaffected while

heightened sexual behaviors were obviously exhibited (Parker, 1976).

Barclay and Haber (1965), and Clark (1952) have revealed a positive

correlation between the initiation of sexual arousal and subsequent

aggressive behavior in human subjects. The experimental reversal of

these arousal links appear to produce the same relationship since Bar­

clay (1971) has noted that the inducement of aggressive behavior would

similarly elicit sexual excitement. During these experiments, aggression

promoted sexual behavior exclusively, since general needs for affilia­

tion and attachment were not suggested by the thematic apperception test.

This dismisses the possibility of a "general arousal" and indicates a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22

specific relationship between xenophobic aggression and sexual moti­

vation. The familial associations characterizing the social mammals

seemingly necessitates a suppression of the former with a resulting

sexual aversion to these same familial individuals. Parker (1976)

supports this view and suggests that this psychobiological mechanism

is the foundation of all incest prohibition.

...long-term socialization in the human or non-human family necessitates an inhibition of (overt) aggressive behavior among family members and results in a low level of hostility and fear. As a consequence of the association of sexual and agonistic responses, sexual arousal is reduced among family members. The social-behavioral system of the family, involving as it does close association between its members, acts on a pre-existing biologically based tendency for incest avoidance (1976:293-294).

Another possible explanation may rest with the habituation or

stimulus satiation that would occur within a family-like condition.

This accordingly would promote exploratory behavior, causing the indi­

viduals to seek new mates. In any case, the "outsider" will elicit a

heightened sexual response and, depending on availability of mates,

promote a sexual rejection of individuals within the kin group. It is

plausible that the duration and intensity of socialization are important

determinants i.i the degree of sexual repulsion to kin.

It is concluded, therefore, that the aversion to incestuous mating

is probably derived from a psychobiological underpinning and manifests

itself by a general lack of sexual motivation to those with whom the

individual was socialized. The psychobiological foundation is evidenced

not only among the social mammals, but operates in human groups in the

absence of a cultural proscription of courtship and marriage. The selec­

tive and adaptive features are herein believed to be of genetic origin

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and function to assure the reproductive success of the individual and

the evolutionary success of the organism.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE GENETIC ADVANTAGES OF OUTBREEDING

Having outlined manners in which animals refrain from consanguin­

eous pairing, and suggested a probable mechanism for this general incest

avoidance, what is the adaptive value or genetic advantage of an out-

breeding pattern? The relinquishing of available kin mates to other

individuals, as a seemingly altruistic act, would need to be offset by

a concomitant increase in fitness that would be inherent in non-incest-

uous matings. While fitness gain for any behavioral manifestation is

only relative to all alternative fitness-limiting behaviors, the adap­

tiveness of any behavioral feature can be demonstrated by a recognition

of its dysfunctional alternative. Indeed, negative genetic and evolu­

tion-limiting aspects of incest do exist. These may result from in-

breeding depression or loss of genetic variability through stochastic

processes. Outbreeding, on the other hand, guarantees continual vari­

ability through gene flow as an agent of evolutionary change. This

variability and resulting heterozygosity are selected attributes favored

in the evolution of biparental or sexual reproduction.

One of the most troublesome aspects of postulating a genetic contri­

bution to behavior rests with the yet undetermined mechanics of gene

action. The question of how the genotype in an individual will unfold

to phenotypic behavioral expression is a monumental task for biologists

who for now must assume a one-to-one mapping between a single polypetide

chain and a somatic characteristic (Lewontin, 1971).

Since the initial thrust of behavioral genetics by Calvin Hall (1951),

the inheritance of behavioral traits has been documented for several

24

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25

species of animals, including human and non-human primates (Kurland,

1977). The genetic inheritance of the hamadryas baboon's hording

behavior, as it relates to selection and retention of mates, is parti­

cularly illuminating (Kummer, Goetz, and Angst, 1970). The hamadryas

baboon male was shown to possess a genetically controlled behavior to

herd females which contributes as an intrinsic aspect of their social

organization. In this case, genetic influence is species and gender

specific, but indicates, nonetheless, the extent of genotypic contri­

bution to sexual behavior in higher primates.

Likewise, the previously postulated psychobiological basis of

incest avoidance is believed to be represented as a genetic manifesta­

tion in all mammals. The variation of social organization, including

the adaptive reinforcement of this behavioral tendency in the form of

a cultural taboo, are products of this underlying structure. The nature

of this genetic basis and the evolutionary necessity of a mechanism to

assure outbreeding are now reviewed.

Deleterious Recessives: A Cause or a Result of the Outbreeding Pattern

The "deleterious recessive" explanation of the biological foundation

of incest avoidance differs from the posited "inbreeding depression"

statement above, inasmuch as the latter is concerned with the out-

breeding tendency as a genetical programmed prerequisite of sexual

behavior in general. Most earlier models concerned with problems of

inbreeding, however, have considered only the lethal and abnormal effects

resulting from increased expression of recessive deleterious genes.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26

Inbreeding would permit these deleterious recessives to pair frequently

since kin mates, by virtue of their genetic relationship to one another,

have a greater likelihood of possess still another identical deleter­

ious recessive at that locus. In normal exogamous mating patterns,

these rarely express themselves because of the expanded variability in

the gene pool. Dysfunctional recessives are most often masked by the

dominant normal gene, and phenotypic expression is limited to the rare

and truly random occurrences of recessive homozygosity.

Morgan (1377) and Westermarck (1891) were among the first concerned

with the "deleterious recessive" problem, and this major theme has

flourished in both the scientific literature and in popular Western

folk belief throughout the last several decades. The more recent

essays on this issue, including Demarest (1977) and Parker (1976), con­

sider this hypothesis as a foundation for their models addressing both

the function and origin of outbreeding patterns among primates. These

authors suggest that the chance of homozygosity for dysfunctional re­

cessive genes provides a biological basis cf the behavior to avoid in­

dividuals within the consanguineous group and, therefore, selection

pressures have promoted social mechanisms to assure non-incestuous mating.

Although I seriously question any relationship between deleterious re­

cessives and the origins and functions of incest avoidance, I will

briefly review the evidence and controversies associated with its use.

There is little disagreement that incestuous unions do promote

problems that may otherwise be overridden in the genome by the contri­

bution of an outside mate. Indeed, Adams and Neel (1967, Schull and

Neel (1965), Seemanova (1971), and Carter (1967), studying the products

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27

of incest among humans, indicate a high mortality and abnormality for

children of father-daughter and sibling incest. The problem of these

defects is envisioned as the combining of recessive deleterious genes

in greater frequencies as a result of the shared-genes among individuals

closely related.

Criticisms of this popular position often point to the fact that

the deleterious recessive genes would be offset by the presence of ad­

vantageous recessives that would also receive full expression. In

this manner, it is argued that no advantage or disadvantage would be

conferred upon individuals with any particular proscription of mating.

Apart from the fact that this criticism may indicate a misunderstanding

of the origin and function of these genes, several previous observa­

tions just mentioned disqualify this assertion. Addressing this con­

troversy, Aberle et al. (1963), utilizing the research of L e m e r (1958)

and Morton (1961), argue that the potential disadvantage of incest,

promoting homozygous deleterious recessives, could not be offset by

any advantages of functional recessives pairing in the genome.

...it has become clear that the ratio of deleterious and lethal recessive genes to selectively advantageous genes is very high indeed...as we move from (biologically defined) second cousin matings to first cousin matings to parent-child or sibling matings, both the models of population genetics and the experi­ mental and observational evidence from animals indicate that the reduction of heterozygosity increased rapidly, and hence that the percentage of individuals homozygous for lethal or deleterious recessive genes also rises sharply (Aberle et al., 1963:256).

Presenting still another popular criticism, Livingston (1969) main­

tains that incestuous unions would probably decrease, rather than in­

crease, the number of homozygous recessive lethal genes by removing

them from the gene pool by natural selection. In this manner, he

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28

believes that outbreeding is less adaptive since it tends to retain

lethals that would otherwise cease to exist through simple selective

processes. This argument, however, addresses the question of genetic

or group fitness only in respect to dysfunctional homozygous recessives.

Since individual fitness advantages in reproductive success exists

with the outbreeding pattern, sorting out dysfunctional or lethal

genes by inbreeding would only result in diminishing heterosis, with

other concomitant disadvantages that will be discussed later.

While there are known advantages of heterozygosity and biparental

reproduction, the disadvantages previously suggested for inbreeding

focus upon deleterious genes as a cause rather than a result of an

evolutionary sequence of outbreeding patterns. The genetic diversity,

as a product of biparental reproduction and outbreeding, has obviously

allowed for the existence of many dysfunctional genes in all populations.

Because of the recombinal non-incestuous pattern of reproduction, the

probability of these dysfunctional or deleterious genes combining at

one locus is retained well below the random level. In other words, if

the pattern of outbreeding had never existed, there would undeniably

be a lower concentration of deleterious recessives. Therefore, we

must bear in mind that outbreeding itself has allowed this high frequency

of these genes to be present without detriment to most individuals.

It is, therefore, tautological to conclude that the existence of these

deleterious genes had provided an evolutionary foundation for the out-

breeding pattern.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29

The Selective Advantages of Variability

While I believe it is doubtful that the problems resulting from

the combining of recessive deleterious genes will shed any light upon

the origins and functions of incest avoidance, another aforementioned

genetic disadvantage of inbreeding depression or loss of variability

is present. Bischof (1972), in a more general theoretical framework,

states:

A species which allowed the obligatory mating of siblings only would retain almost all of the disadvantages of biparental generation, without being able to profit from a single one of its advantages. Its variety would sink to the low level of self fertilization, and its evolutionary rate would accordingly be so halting that it could stand up against competition only under highly favorable conditions of life; as a general rule the lack of adaptive plasticity would act as a death warrant (1972:24).

Two obviously important advantages of heterozygosity over homozy-

osity exist: it provides the individual with greater evolutionary

plasticity and improved biochemical versatility (Demarest, 1977).

Heterozygosity in biparental reproduction offers a greater assortment

of genes to a changing environment. When both parents are heterozygous

for a particular two allele trait, there are obviously three possible

genotypic expressions for offspring. However, when one parent is homo­

zygous, only two expressions are possible, and when both parents are

homozygous, there is only a single possible resultant. Heterosis

clearly allows greater phenotypic variety and is an important requisite

in the establishment of a predictive measure of evolutionary success

(Slobodkin and Rapoport, 1974).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30

The variability afforded by sexual reproduction does not in itself

cause evolution or change the gene frequencies in populations. However,

while any frequency may remain relatively stable, reproduction by the

union of haploid gametes will form new combinations of genes in each

successive generation. Without the effects of mutation, meiotic drive,

gene flow, genetic drift, and selection, the gene pool would remain

stable and evolution would not occur despite the retention of vari­

ability in each successive generation of organisms as a result of re­

combination. In the presence of these agents, the degree of variability

in any population, offering a wider assortment of phenotypes for selec­

tion, will allow evolution to occur by a change in gene frequency.

Through differing rates of reproductive success, a gene pool may under­

go an increase in the frequency of genes for an adaptive behavior and

a decrease or extinction of genes influencing a maladaptive one. Most

importantly, this plasticity is directly related to the degree of genetic

variability since selection, and hence evolution, can only occur in the

presence of polymorphisms.

An agent that is capable of producing changes and promoting vari­

ability may also, by virtue of demographic limitations, negatively

affect a population and reduce variability. Most of the evolutionary

agents mentioned, such as mutation, meiotic drive, and selection, tend

to remain stable irrespective of population size but are more highly

influenced by other outside environmental factors. In this essay,

however, we are interested with only those evolutionary agents whose

rates of evolutionary change are altered by the size reduction of the

effective breeding population, promoting inbreeding depression as a

detrimental loss of variability from within the gene pool.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31

Problems of Small-Population Genetic Drift

Genetic drift is one primary evolutionary agent in which change

in gene frequency can take place in a population. Since genetic drift

results from sampling error, and the amount of error is proportional

to the size of population, any discussion of the negative effects of

inbreeding (i.e. a reduction of effective breeding population) should

necessarily begin with an explanation of the mechanisms and effects of

continuous drift. For large populations, the two allele Mendelian

system will produce a large number of gametes whose gene frequency

will closely match, but not be identical to, that of the parents.

However, when the number of parents in the population is small, random

errors in gene frequency tend to be relatively greater and the ultimate

fate of sampling errors' "random walk" (in probability theory) may

ultimately result in homozygosity at any particular locus from these

stochastic processes alone.

The impact of this potentially dramatic reduction in gene frequency

through drift in small breeding populations such as a familial incest­

uous unit can best be contrasted with the relative genetic stability

in large populations by an example. If we envision a 1:1 ratio of black

and red marbles in a container (representing a hypothetical distri­

bution of alleles p & q at any locus), the chances of randomly choosing

an all black or all red sample of marbles (an elimination of either p

or q) diminishes with increased sample size. A probability of .008

exists for an elimination of one color in a choice of eight marbles,

while the chances on a one-color representation among a hundred marbles

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32

-3 0 chosen at random are 1.58 x 10 . The greater the sample (popula­

tion), the less chance of sampling error and reduction in variability

through fixation or loss of an allele. The gain and losses of any

allele in a two-allele Mendelian system will conform to the central

limit theorem of probability which indicates that as the population (N)

becomes large, the change in gene frequency ( A p) will be -normally

distributed with a mean of zero (Wilson, 1975). This occurs as a

result of the distribution of A p for interbreeding sub-units so

that the gains and losses from sampling error offset one another. The

sum of A p in the negative direction (losses in the frequency of p)

will be equal to the A p in the positive direction (gains in the fre­

quency of p). In other words, the sampling errors would tend to off­

set one another in large populations, whereas the effects of sampling

errors in a population the size of a family could eventually extinguish

genetic variability at any locus from accumulative random errors alone.

In addition, changes in gene frequency from drift in a population are

often offset by gene flow from another. Without the outbreeding pattern

however, there would be no gene flow and therefore, drift in any pop­

ulation could not possibly be offset by the variability in other pop­

ulations. In normal patterns of outbreeding, genetic drift and gene

flow are interrelated; both have foundations with the origins and evolu­

tion of biparental reproduction.

Genetic drift is, therefore, an appropriate term for the changes

in gene frequency due to chance alone. These stochastic processes are

dependent upon the size of the population and may be cumulative in the

respect that they may ultimately lead to total loss of genetic variability

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33

in a small effective breeding population. Sewall Wright (1969) main­

tains that in the absence of any other evolutionary agent that could

promote new variability, fixation or loss of an allele will occur at

the average rate of 1/ 4(N) per locus, per generation. Therefore, for

any given mean familial population of six, for example, it will take

only 24 generations on the average for homozygosity to occur at any

particular locus.

Summarizing this position, inbreeding in effect would limit the

size of the effective breeding population to levels conducive to con­

tinuous, uncontrolled genetic drift. The loss of heterozygosity would

have a great effect on evolutionary change and reproductive success in

the face of environmental fluctuation or increased competition. Indi­

viduals would have otherwise tended to maximize inclusive fitness by

an adoption of behaviors for outbreeding that would have promoted con­

tinual genetic variability.

Where dispersion of the non-social animals assures a continual

genetic variability by virtue of the expanded size of the effective

breeding population, the social primates without benefit of a parti­

cular genetic basis of sexual repulsion toward kin would, in effect,

limit the size of the breeding population to disadvantageous levels.

It is unlikely that social behavior evolved in these animals without

genetic selection of a behavior to assure the same degree of genetic

variability as their asocial ancestors. Indeed, social behavior could

not have evolved, given the principles of evolutionary biology, if

it was accompanied by a loss of genetic fitness to those individuals.

More importantly, the framework presented is supported by both

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34

observational and experimental data on outbreeding behavior previously

discussed.

Outbreeding, Heterosis and Evolution

The beneficial effects of increasing heterozygosity or hybrid

vigour brought about by outbreeding are well documented in both the

animal and plant kingdoms (Pirchner, 1969). To what extent this pheno­

menon exists in the higher primates is more difficult to determine due

to experimental difficulties in lengthy developmental rates, and the

ethical and logistic problems of experimental control. Nevertheless,

several researchers have begun to disclose increasing evidence of a

heterotic effect on human intelligence, body size, infant survival, eco-

sensitivity, and general acceleration of growth and development.

Comparing survival rates for offspring of exogamous and endogamous

unions, Wolanski (1975) has noted a 10% increase in a survival index

for the former, with minor increases in ecosensitivity. The heterosis,

as a result of exogamous unions, provided the progeny with increased

stature and growth rates under adequate living standards. These data

concur with those of Nikityuk and Filippov (1977) who demonstrated a

positive correlation between a number of biological parameters (stature,

shoulder breadth, and dolichocephalization) and the increasing grade of

exogamy in Ukrainian communities. These studies, among others (Hulse,

1957; Lasker, 1960; Schrieder, 1978), suggests that the secular growth

trend during this century may in fact be a result of increasing hetero­

sis from relocation of human groups, rather than simply the product of

improved nutrition and standards of living (Tanner, 1962; Schrieder, 1978).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. More importantly, if heterosis is partially responsible for the early

protohominid growth trend as evidenced from the fossil record, it would,

by virtue of implied outbreeding, tend to refute the "incestuous horde"

concept of organization indicated by some previous authors (Fox, 1972;

Levi Strauss, 1970). The data undeniably point out that outbreeding

may have played a significant role in human evolution and that hetero­

sis as a result of this pattern continually promoted the development of

intelligence and cognitive abilities necessary for culture. In this

sense, the pattern of outbreeding predisposed the advent of culture as

an adaptive fitness maximizing strategy.

Substantiating this proposition, Beals and Kelso (1975) have reported

a marked increase in the degree of heterosis through each stage of socio­

cultural complexity. Moving from band level through tribal, chiefdom,

and state level societies, the average frequency of heterozygosity in­

creases 3% per evolutionary stage. The authors indicate that the dis­

tribution of heterozygosity is strongly dependent on cultural evolution.

Lacking any empirical method of determining these dependencies, the

aforementioned effects of heterosis suggest that the reverse may as

likely be true; cultural evolution may be dependent to some degree on

the distribution of heterozygosity within populations. Although the

documented relationship between heterosis and developing cultural com­

plexity is not clear, it may prove useful to consider an interplay between

these two phenomena. Such an alternative viewpoint may be of heuristic

value in addressing the unanswered problems concerning the rise of civi­

lization, which in many cases do not correspond to environmental causa­

tive explanation. Present models dealing with the rise of state level

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36

societies have simply concentrated upon the cultural innovations brought

about by contacts, and environmental conditions conducive to agricul­

tural and hydrau _ organizational growth. On the other hand, cultural

activities such as exchange, invasion, and migration could provide new

genetic variability to a population while this resulting heterosis may

foster a biological vigor that may indeed promote further cultural

elaboration.

Limited by the existing degree of biological variation or hetero­

sis in the population, an organism tends to maximize its own reproductive

success through a continued evolutionary selection of behavioral strate­

gies that tend to assure that the greatest amount of the individual's

genes will be passed to subsequent generations. Behaviors to enhance

reproductive success such as outbreeding, courtship, or parental care

are directly selected upon at the individual inclusive level and are,

therefore, retained within the gene pool at the expense of the less-fit

segment of the population. The sociobiological model expressed in this

form suggests that the result of selection for reproductive success,

through the use of these strategies, reflects a purpose of direction

in the course of evolutionary change.

The theoretical development of the "new evolutionary biology" has

developed independently but paralleling other earlier teleological

explanations of biological evolution, which did not incorporate repro­

ductive success as the all-important propensity influencing the direc­

tion of biological change. Harold Blum (1968), referring to the Second

Law of Thermodynamics, claims that biological and cultural change is

an expression of this thermodynamic process that rims counter to the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37

Second Law. Rather than a breakdown and disorganization in the phy­

sical world as an entropic tendency, the biological and cultural pro­

cesses are a movement "toward greater organization, greater differen­

tiation of structure, increased specialization of function, higher

levels of integration, and greater degrees of energy concentration"

(White 1949:367).

Again using the negentropy concept for his teleological explanation

of change, Blum states:

When we accept the idea that living organisms as well as non­ living evolve in a general direction pointed by time's arrow we see some reason for an appearance of purposiveness. That is, evolution goes only one way in time, and at the point to which it has led us we see greater fitness than has character­ ized the past (1968:196).

The evolution of behavior to assure the direction of "time's arrow"

has been supplemented, but to some degree supplanted, by the develop­

ment and evolution of culture as an extended behavioral strategy of

evolutionary success.

Boehm (1978) has argued that "rational preselection" or rational

decision making has enabled hominids to select, to some degree, their

destinies by choosing from a number of available evolutionary alterna­

tives. In this manner, the direction of time's arrow may, in fact, be

influenced by decisions based upon social advantages of an exogamous

pattern in accord with the fitness-maximizing blind teleonomic selec­

tion for the biologically based behavior. Given a psychological pro­

pensity to avoid mating with those of close familial association, it

appears that decisions on the part of individuals, acting in accord

with such a basis, have resulted in a strategic adoption of specific

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38

exogamous practices that would prove advantageous under a given set

of demographic and environmental circumstances. The adoption of rules

to indicate with whom an individual can marry, as a cultural attri­

bute, would necessarily follow processes of culture change identical

to the selection and retention of any other cultural attribute. In

any instance, however, the cultural manifestation must operate depen-

dently and in accord with the biologically based fitness-maximizing

strategy selected throughout the course of the evolutionary process.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONCLUSIONS

In addition to the genetic functions presented, there undeniably

exists a multitude of sociological functions of the incest taboo and

patterns of exogamy among human groups. The question of primary con­

cern here has been whether any of these sociocultural explanations that

have been posited over the years can account for the origins of incest

avoidance, or if they are simply additional social advantages rendered

by this general pattern. The cross-cultural variability in the rules

of marriage and exogamy suggests that rational selection of specific

patterns in each culture has occurred in accord with the psychobiolo­

gical propensity to outbreed.

The alliances between human groups fostered by an exchange of women

or exogamy (Levi Strauss, 1970) not only appears to be a plausible sup­

plementary function, but it also conforms to modem genetical theory on

kin selection (Hamilton, 1963; 1964). Since exogamous groups possess

a genetic investment in one another by virtue of shared genes, altruism

or inter-group cooperative behavior is predictable. The extent of al­

truistic behavior under these circumstances would be in direct relation­

ship with the degree of genetic relationship between any two groups.

.Another secondary advantage or supplementary function of the pattern

of outbreeding is the ease and expediency of mate acquisition (Slater,

1959). Since the number of available mates within an extended family

is limited, there are definite fitness advantages in relinquishing kin

to other neighboring groups, thereby allowing oneself access to a variety

of potential mates of the appropriate age and social compatability from

39

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the outside nexus. While such functions are probably not of primary

importance in the origin of exogamy, the relinquishing of kin to others

is explicable in terms of present theory of reciprocal altruism (Trivers,

1971). This results in a net gain in fitness from a greater availability

of mates in adjacent groups, irrespective of the initial loss of repro­

ductive potential by forfeiture of kin to others. It is stressed that

the principal of reciprocal altruism is necessarily limited to rational

decisions believed to be limited to humans, since they necessitate the

adoption of cooperative behavior through specific rules of mating. In the

absence of evidence for this phenomenon among the other social mammals,

demographic necessity can only be used as an additional and uniquely

human function for the culturological taboo and not a function for the

general pattern of incest avoidance among other animals.

This essay suggests that the primary function of incest avoidance

is rooted in the origins of biparental reproduction and that it serves

to maximize genetic variability necessary for biological change or adap­

tation. In accord, the human incest taboo is an extention of the bio­

logical predisposition, but serves a multitude of additional social

functions that have been addressed previously by several authors. While

these earlier suggestions have adequately substantiated the importance

of exogamy for human groups today, we must understand their inade­

quacy for revealing the basis of the panmammalian tendency to outbreed

and the universal existence of the human incest taboo as a product of

that same basis.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCES CITED

Aberle, D. F., et al. 1963 The Incest Taboo and the Mating Patterns of Animals. American Anthropologist 65:253-265.

Adams, M., and J. V. Neel 1967 Children of Incest. Pediatrics 40:55-61.

Altmann, M. 1963 Naturalistic Studies of Maternal Care in Moose and Elk. In Maternal Behavior in Mammals. H. L. Rheingold, ed. Pp. 233-253. New York: Wiley.

Barash, D. P. 1977 Sociobiology and Behavior. New York: Elsevier.

Barclay, A. M. 1971 Linking Sexual and Aggressive Motives: Contributions of "Irrelevant" Arrousals. Journal of Personality 39:481-492.

Barclay, A. M., and R. N. Haber 1965 The Relation of Aggressive to Sexual Motivation. Journal of Personality 33:462-475.

Barfield, R. J., and B. D. Sachs 1968 Sexual Behavior: Stimulation by Painful Electric Shock to Skin in Male Rats. Science 161:392-393.

Barkow, J. H. 1978 Culture and Sociobiology. American Anthropologist 80:5-20.

Beals, K. L., and A. J. Kelso 1975 Genetic Variation and Cultural Evolution. American Anthro­ pologist 77:566-579.

Bernstein, I. S. 1970 Primate Status Hierarchies. Hi Primate Behavior. L. A. Rosenblum, ed. Pp. 71-109. New York: Academic Press.

Bischof, N. 1972 The Biological Foundations of the Incest Taboo. Social Science Information 11:7-36.

Blaffer Hrdy, S. 1977 Infanticide as a Primate Reproductive Strategy. American Scientist 65:40-49.

41

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42

Blum, H. F. 1968 Time's Arrow and Evolution, 3rd ed. Princeton N. J.: Princeton University Press.

Boehm, C. 1978 Rational Preselection from Hamadryas to Homo sapiens: The Place of Decisions in Adaptive Process. American Anthropologist 80:265-296.

Campbell, B. 1966 Human Evolution. Chicago: Aldine.

Carpenter, C. R. 1940 A Field Study in Siam of the Behavior and Social Relations of the Gibbon. Comparative Psychology Monographs, Vol. 16, No. 5. Baltimore, Md.: John Hopkins Press.

1942 Sexual Behavior of Free-Ranging Rhesus Monkeys. Journal of Comparative Psychology 33:113-162.

1965 The Howlers of Barro Colorado Islands. In Primate Behavior. I. DeVore, ed. Pp. 250-291. New York: Holt, Rinehart and Winston.

Carter, C. 0. 1967 Risk of Offspring of Incest. Lancet 1:436.

Chalmers, N. R. 1973 Differences in Behavior between Some Arboreal and Terrestrial Species of African Monkeys. In Comparative Ecology and Behavior of Primates. R. P. Michael and J. H. Crook, eds. Pp. 69-100. New York: Wiley.

Chance, M. R. A. 1967 Attention Structure as the Basis of Primate Rank Orders. Man 2:503-518.

Clark, R. A. 1952 The Projective Measurement of Experimentally Induced levels of Sexual Motivation. Journal of Experimental Psychology 44:391-3^9.

Daly, M., and M. Wilson 1978 Sex, Evolution and Biology. Belmont, Calif.: Duxbury Press.

Darling, F. F. 1951 A Herd of Red Deer. London: Oxford University Press.

Demarest, W. J. 1977 Incest Avoidance among Human and Non-Human Primates. In Primate Bio-Social Development: Biological, Social, and Ecological Determinants. S. Chevalier-Skolnikoff and F. E. Poirier, eds. pp. 323-342. New York: Garland.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43

Eaton, G. G. 1974 Male Dominance and Aggression in Japanese Macaque Reproduction. In Advances in Behavioral Biology, Vol II: Reproductive Behavior. W. Montagna and W. A. Sadler, eds. Pp. 287-297. New York: Plenum Press.

Eibl-Eibesfeldt, I. 1970 Ethology: The Biology of Behavior. Erich Klinghammer, trans. New York: Holt, Rinehart and Winston.

Eisenberg, J. F. 1966 The Social Organization of Mammals. Handbuch der Zoologie 8(10/7). Lieferung 39:1-92. (English abstract).

Ellefson, J. 0. 1968 Territorial Behavior in the Common White-Handed Gibbon, Hylo- bates lar. In Primates: Studies in Adaptation and Variability. P. C. Jay, ed. Pp. 180-199. New York: Holt, Rinehart, and Winston.

Enomoto, T. 1974 The Sexual Behavior of Japanese Monkeys. Journal of Human Evolution 3:351-372.

1978 On Social Preference in Sexual Behavior of Japanese Monkeys (Macaca fuscata). Journal of Human Evolution 7:283-293.

Etkin, W. (ed.) 1964 Social Behavior and Organization among Vertebrates. Chicago: University of Chicago Press.

Ewer, R. F. 1968 Ethology of Mammals. London: Logos Press.

Fox, R. 1972 Alliance and Constraint: Sexual Selection in the Evolution of Human Kinship Systems. In Sexual Selection and the Descent of Man. Bernard Campbell, ed. Pp. 282-331. Chicago: Aldine.

Frazer, J. 1910 Totemism and Exogamy, Vol. 4. London: Macmillan.

Freud, S. 1918 Totem and Taboo. A. A. Brill, trans. New York: Moffat, Yard.

Goldstein, A. C., and G. A. Jacoby 1955 Effects of Electroconvulsive Shock on Sexual Behavior in Male Rats. Journal of Comparative Physiological Psychology 48:173-179.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44

Goodall, J. 1965 Chimpanzees of the Gombe Stream Preserve. In Primate Behavior I. DeVore, ed. Pp. 53-110. New York: Holt, Rinehart, and Winston.

1967 My Friends the Wild Chimpanzees. Washington D. C.: The National Geographic Society.

Gundlach, H. 1968 Brutfursorge, Verhaltensontogenese und Tagesperiodik beim europaishen Wildschwein. Zeitschrift fur Tierpsychologie 25:955-995.

Hall, C. S. 1951 The Genetics of Behavior. In Handbook of Experimental Psycho­ logy. S. S. Stevens, ed. Pp. 304-329. New York: Wiley.

Hall, K. R. L. 1968 Behaviour and Ecology of the Wild Patas Monkey. In Primates: Studies in Adaptation and Variability. P. C. Jay, ed. Pp. 32-119. New York: Holt, Rinehart, and Winston.

Hamilton, W. D. 1963 The Evolution of Altruistic Behavior. The American Naturalist 97:354-356.

1964 The Genetical Evolution of Social Behaviour, I & II. J. Theoret. Biology 7:1-52.

Hanby, J. P., L. T. Robertson, and C. H. Phoenix 1971 The Sexual Behavior of a Continued Troop of Japanese Macaques, folia Primatologica 16:123-143.

Harcourt, A. H., K. S. Stewart, and D. Fossey 1976 Male Emigration and Female Transfer in the Wild Mountain Gorilla. Nature 263:226-227.

Harris, M. 1968 The Rise cf Anthropological Theory. New York: Thomas Y. Crowell.

1971 Culture, Man, and Nature. New York: Thomas Y. Crowell.

Hendricks. H., and U. Hendricks 1971 Dikdik und Elefanten. Munich: Piper.

Hobhouse, L. 1912 Morals in Evolution. London: Chapman and Hall.

Hulse, F. S. 1957 Exogamie et Heterosis. Arch. Suiss. Anthrop. gen. 22:103-125.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45

Imanishi, K. 1957 Social Behavior in Japanese Monkeys, Macaca fuscata. Psycho- logia 1:47-54.

Jay, P. 1965 The Common Langur of Northern Indian. In Primate Behavior. I. DeVore, ed. Pp. 197-249. New York: Holt, Rinehart, and Winston.

Kaufmann, J. H. 1962 Ecology and Social Behavior of the Coati (Nasua narica) on Barro Colorado Islands, Panama. University of California Publi­ cations in Zoology 60:95-222.

Koford, C. B. 1963 Rank of Mother and Sons in Bands of Rhesus Monkeys. Science 141:356-357.

Kortlandt, A., and M. Kooij 1963 Protohominid Behavior in Primates, (Preliminary Communication). Symposia of the Zoological Society of London 10:61-88.

Kortmulder, K. 1968 An ethological theory of the incest taboo and exogamy. Current Anthropology 9:437-449.

Kroeber, A. L. 1963 Anthropology: Culture Patterns and Processes. New York: Harcourt, Brace, and World.

Kummer, H. 1968 Social Organization of Hamadryas Baboons. Basel: S. Karger.

1971 Primate Societies. Chicago: Aldine.

Kummer, H., W. Goetz, and W. Angst 1970 Cross-Species Modifications of Social Behavior in Baboons. In Old World Monkeys: Evolution, Systematics, and Behavior. J. R. Napier and P. H. Napier, eds. Pp. 351-363. New York: Academic Press.

Kurland, J. A. 1977 Kin Selection in the Japanese Monkey. Basel: S. Karger.

Lasker, G. W. 1960 Variances of Bodily Measurements in the Offspring of Natives and of Immigrants to Three Peruvian Towns. American Journal of Physical Anthropology 18:257-261.

Lemer, M. I. 1958 The Genetic Basis of Selection. New York: Wiley.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46

Levi-Strauss C. 1970 The Elementary Structures of Kinship. Oxford: Alden Press.

Lewontin, R. C. 1971 The Effect of Genetic Linkage on the Mean Fitness of a Popu­ lation. Proceedings of the National Academy of Science USA 68: 984-986.

Livingstone, F. B. 1969 Genetics, Ecology and the Origins of Incest and Exogamy. Current Anthropology 10:45-63.

Malinowski, B. 1927 Sex and Repression in Savage Society. London: Kegan Paul.

Mason, W. A. 1968 Use of Space by Callicebus Groups. In Primates: Studies in Adaptation and Variability. P. C. Jay, ed. Pp. 200-216. New York: Holt, Rinehart, and Winston.

Modahl, K. B., and G. G. Eaton 1977 Display Behaviour in a Confined Troop of Japanese Macaques (Macaca fuscata). Animal Behaviour 25:525-535.

Morgan, L. H. 1877 Systems of Consanguinity and Affinity in the Human Family. Washington, D. C.: Smithsonian Institution.

Morton, N. E. 1961 Morbidity of Children from Consanguineous Marriages. In Progress in Medical Genetics, Vol. I. A. G. Steinberg, ed. Pp. 261- 291. New York: Grune & Stratton.

Murdock, G. P. 1949 Social Structure. New York: Macmillan.

Murray, R. D., and K. Mayer-Murdoch 1977 Mother Infant Dyad Behavior in the Oregon Troop of Japanese Macaques. Primates 18:815-842.

Nicholson, B. D. 1955 The African Elephant. African Wildlife 9:31-40.

Nikityuk, B. A., and V. I. Filippov 1977 Heterosis as One of the Factors of Acceleration of Growth and Development. Journal of Human Evolution 6:745-749.

Parker, S . 1976 The Precultural Basis of the Incest Taboo: Toward a Biosocial Theory. American Anthropologist 78:285-305.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47

Pirchner, F. 1969 Population Genetics in Animal Breeding. San Francisco, Calif.: Freeman.

Reynolds, H. C. 1952 Studies on Reproduction of the Opossum (Didelphis Virginiana). University of California Publications in Zoology 52:223.

Reynolds, V. 1966 Open Groups in Hominid Evolution. Man 1:441-452.

Reynolds, V., and F. Reynolds 1965 Chimpanzees of the Budongo Forest. In Primate Behavior. I. DeVore, ed. Pp. 368-425. New York: Holt, Rinehart, and Winston.

Sade, D. S. 1968 Inhibition of Son-Mother Mating Among Free-Ranging Rhesus Monkeys. Science and Psychoanalysis 12:18-38.

Sahlins, M. 1976 The Use and Abuse of Biology: An Anthropological Critique of Sociobiology. Ann Arbor, Michigan: University of Michigan Press.

Schaller, G. B. 1963 The Mountain Gorilla. Chicago: University of Chicago Press.

1967 The Deer and the Tiger. Chicago: University of Chicago Press.

Schreider, E. 1978 Consanguinity and Biological Variations in Man. Journal of Human Evolution 7:547-549.

Schull, W. J., and J. V. Neel 1965 The Effects of Inbreeding on Japanese Children. New York: Harper & Row.

Seemanova, E. 1971 A Study of Children of Incestuous Matings. Human Heredity 21:108-128.

Shepher, J. 1971 Mate Selection among Second Generation Kibbutz Adolescents and Adults: Incest Avoidance and Negative Imprinting. Archives of Sexual Behavior 1:293-307.

Simonds, P. E. 1965 The Bonnet Macaque in South India. In Primate Behavior. I. DeVore, ed. Pp. 175-196. New York: Holt, Rinehard, and Winston.

1974 The Social Primates. New York: Harper & Row.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48

Slater, M. K. 1959 Ecological Factors in the Origin of Incest. American Anthro­ pologist 61:1042-1059.

Slobodkin, L. B., and A. Rapoport 1974 An Optimal Strategy of Evolution. The Quarterly Review of Biology 49:181-200.

Smith, J. Maynard 1964 Group Selection and Kin Selection. Nature 201:1145-1147.

Starcke, C. N. 1901 The Primitive Family in Its Origins and Development. New York: D. Appleton.

Sugiyama, Y. 1967 Social Organization of Hanuman Langurs. Ill Social Communication among Primates. S. Altmann, ed. Pp. 221-236. Chicago: University of Chicago Press.

Talmon, Y. 1964 Mate Selection in Collective Settlements. American Socio­ logical Review 29:491-508.

Tanner, J . M. 1962 Growth of Adolescence. London: Blackwell Scientific Publ.

Temberlin, M. K. 1972 Lucy: Growing Up Human. Palo Alto, Calif.: Science and Behavior Books.

Tembrock, G. 1957 Zur Ethologie des Rotfuchses. Der zoologische Garten 23:289- 532 (English abstract).

Tokuda, K. 1961- A Study on the Sexual Behavior in the Japanese Monkey Troop. 1962 Primates 3:1-40.

Trivers, R. L. 1971 The Evolution of Reciprocal Altruism. The Quarterly Review of Biology 46:35-57.

Turnbull, C. 1968 C. A. Comment to: K. Kortmulder. An Ethological Theory of the Incest Taboo and Exogamy. Current Anthropology 9:445-446.

Tylor, E. B. 1889 On a Method of Investigating the Development of Institutions; Applied to Laws of Marriage and Descent. Journal of the Royal Anthropological Institute 18:245-269.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49

van den Berghe, P. L. 1974 Bringing the Beast Back in: Toward a Biosocial Theory of Aggression. American Sociological Review 39:777-787.

van Lawick-Goodall, J. 1968 The Behavior of Free Living Chimpanzees in the Gombe Stream Reserve. Animal Behavior Monographs 1:3.

1971 In the Shadow of Man. New York: Dell.

Washburn, S. L., and R. Moore 1974 Ape into Man: A Study of Human Evolution. Boston: Little, Brown.

Westermarck, E. 1891 The History of Human Marriage. London: Macmillan.

White, L. A. 1943 The Definition and Prohibition of Incest. American Anthro­ pologist 50:416-435.

1949 Energy and the Evolution of Culture. In The Science of Culture. L. A. White, ed. Pp. 363-393. New York: Farrar Straus and Cudahy.

Wilson, E. 0. 1975 Sociobiology: The New Synthesis. Cambridge, Mass.: Belknap Press.

Wolanski, N. 1975 Heterozygosity and Human Evolution. Journal of Human Evolu­ tion 4:565-571.

Wolf, A. P. 1966 Childhood Association, Sexual Attraction, and the Incest Taboo, A Chinese Case. American Anthropologist 68:883-898.

1968 Adopt a daughter-in-law, Marry a Sister: A Chinese Solution to the Problem of the Incest Taboo. American Anthropologist 70:864-874.

1970 Childhood Association and Sexual Attraction: A Further Test of the Westermarck Hypothesis. American Anthropologist 72:503-515.

Wright, S. 1969 Evolution and the Genetics of Populations, Vol. 2: The Theory of Gene Frequency. Chicago: University of Chicago Press.

Yoshiba, K. 1968 An Ecological Study of Hanuman Langurs, Presbytis entellus. Primates 8:12 7-154.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.