Chapter 18 ......
Body Size and Intelligence in Hominoid ......
...... chapter Evolution ......
......
Carol Ward ......
Department of Anthropology – Department of Pathology and Anatomical Sciences ...... 107 Swallow Hall, University of Missouri ...... Columbia, MO 65211 USA ...... [email protected] ...... Mark Flinn ...... Department of Anthropology, 107 Swallow Hall, University of Missouri ...... Columbia, MO 65211 USA ...... [email protected] ...... David Begun ...... Department of Anthropology, University of Toronto ...... Toronto, ON M5S 3G3, Canada ...... [email protected] ......
...... Word count: text (6526)
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1218 of 1365
A-Head 1 Introduction ......
...... 2 Great apes and humans are the largest brained primates. Aside from a few ...... 3 extinct subfossil lemurs, they are also the largest in body mass. Body size ...... 4 is a key aspect of a species’ biology, a large organism having different ...... 5 energetic, ecological and physical constraints than a small one. Brain size, ...... 6 insofar as it determines abilities to acquire, process, and act on ...... 7 information, is also a key aspect of a species’ biology and is linked to body ...... 8 size. Large animals have different informational problems to solve than do ...... 9 small ones, hence their respective sensory organs and nervous systems are ...... 10 sized and organized differently...... 11 Mammalian body and brain size scale consistently with each other
...... c18fig001 12 (Figure 18.1). This relation is generally described by allometric exponents c18rfa014 ...... c18rfa015 13 that vary between 2/3 and 3/4 (e.g., Bauchot & Stephan 1966, 1969; c18rfa041 ...... c18rfa043 14 Hofman 1982; Jerison 1973; Lande 1979; Martin 1981; Martin & Harvey c18rfa053 ...... c18rfa057 15 1985; Stephan 1972). From a paleontological perspective, the body-brain ...... 16 size relation offers an appealing way to evaluate the cognitive abilities of c18rfa061 ...... c18rfa095 17 fossil taxa, a problem of particular importance for understanding hominid ...... 18 evolution...... Inset Figure 18.1 about here ......
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1 A convincing theoretical basis for this general allometric statistical ......
c18rfa040 2 pattern, however, remains elusive (Deacon 1997; Harvey & Krebs 1990)......
3 Body mass is not a strict determinant of brain size, as species of similar ......
4 size can have different brain sizes and cognitive abilities (Pagel & Harvey ......
c18rfa068 5 1989). In addition, comparative analyses indicate considerable variation ......
c18rfa068 6 among taxa from general mammalian patterns (Pagel & Harvey 1989)......
7 Hominid brains, for example, are double or more their expected size as ......
8 mammals. There are also phylogenetic differences in typical brain-body ......
9 size relations within primates that reflect grade shifts in encephalization ...... c18rfa007 c18rfa008 10 across taxa (Armstrong 1985a, b; Martin & Harvey 1983, Pagel & Harvey ...... c18rfa059
11 1989)......
c18rfa068 12 One reason for the lack of a universal brain-body size correlation ......
13 among mammalian species is that factors other than body mass or ......
14 metabolism, such as locomotion, diet, predation risk, social structure, and ......
15 life history, affect relations between body and brain size (see recent ......
c18rfa021 16 reviews in de Waal & Tyack 2003; other chapters in this volume). All of ......
17 these factors and others may contribute to selective pressures for cognitive ......
18 abilities. As such, allometric scaling models developed from analyses of ......
19 relations between physical variables such as metabolic rate and body mass ......
20 may not be appropriate models for relations between body and brain size......
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1 Evolving a large brain depends upon a complex balance of costs and ......
2 benefits, which vary from species to species. There are not likely to be ......
3 simple explanations based upon simple physical principles. Observed ......
4 correlations between brain size and body size, the variability in these ......
5 relations, and the reasons underlying phylogenetic differences, require ......
6 consideration of both direct and indirect influences. Direct influences ......
7 include structural and metabolic constraints on encephalization and ......
8 size-related needs: Large-bodied animals are better able to support large ......
9 crania and energetically expensive neural tissue than are small-bodied ......
10 animals, and larger bodies may require more neurons to control. If this ......
11 were all there was to the relation between body size and brain size, then we ......
12 would expect simple and consistent statistical associations. However ......
13 additional indirect influences can independently affect both body size and ......
14 intelligence, including the effects of selective pressures shaping other ......
15 aspects of a species’ biology, such as locomotion, diet, predation risk, ......
16 social interactions, and life history. If these indirect influences are ......
17 important for determining body size-brain size relations, then we expect ......
18 more complex and variable statistical patterns, as indicated by analyses of ......
c18rfa061 19 inter-taxa differences (Martin & Harvey 1985)......
20 Because of the apparent complexities of brain-body relations and ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1221 of 1365
1 neurobiological differences among extant mammals, simple consideration ......
2 of relative brain size provides only an incomplete picture of the cognitive ......
3 abilities of fossil species. To understand scaling relations among body size, ......
4 brain size, cognition and other aspects of a species’ adaptation, we need to ......
5 first understand the underlying selective pressures shaping cognitive ......
6 function and related variables. Complex models involving ecological and ......
7 social factors are required. Such models may provide new insights into the ......
8 causal relations underlying statistical associations between body and brain ......
9 size. This chapter first examines the interrelations among multiple relevant ......
10 variables and their relations with cognitive capacities and brain size that ......
11 apply generally in primates, especially those linked with body size. This ......
12 puts us in a stronger position to interpret the cognitive capabilities of ......
13 extinct taxa, and therefore to understand the evolution of intelligence in the ......
14 hominids......
......
A-Head 15 Previous hypotheses relating body mass to intelligence ......
16 Logarithmic scaling between brain size and body size in mammals is often ......
17 interpreted to suggest that increases in body size result in increases in brain ......
18 mass in the absence of any selection for a particular brain function ......
......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1222 of 1365 c18rfa042 c18rfa043 c18rfa057 1 (Hofman 1983; Jerison 1973; Martin 1981, 1983) (Figure 18.1). The ...... c18rfa059 c18fig001 2 scatter about the line is interpreted as a change in brain mass that must be ......
3 explained by some other factors. The questions to be answered are: (1) why ......
4 do these observed scaling relations exist and (2) why do some species ......
5 depart from them? ......
......
B-Head 6 Somatic factors: size, scaling and metabolism ......
7 A possible answer to the first question is that having a larger body with ......
8 more sensory receptors sending input and more motor units to control ......
9 requires greater processing power, hence larger brain size. This appears ......
10 unlikely, however, because animals of similar size can vary dramatically in ......
11 brain-body size relations. As an example among catarrhines, Theropithecus ......
12 oswaldi,alarge fossil papionin, was similar in body size to chimpanzees ......
13 and female gorillas, with estimates ranging from about 20 to 128 kg ......
c18rfa023 14 (Delson et al. 2000; Martin 1993; and unpublished data (CVW)). Direct ...... c18rfa060
15 estimates of the cranial capacity of three specimens with body sizes ......
c18rfa060 16 ranging from 32–70 kg are 154, 155 and 200 cc (Martin 1993)......
17 Chimpanzees and gorillas of about the same body mass range, on the other ......
c18rfa098 18 hand, have brain sizes of roughly 275–580 cc (Tobias 1971). This ......
19 variability, and the grade shifts in this relation evident among taxa (Begun ......
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1 &Kordos this volume), undermine the interpretation that brain size and ......
2 body size are related by simple physical or physiological laws......
3 A related possibility is that somatic brain regions, which govern ......
4 somatic and autonomic sensorimotor function, should scale with body size ......
5 because larger bodies with their greater number of cells might need more ......
c18rfa001 6 neurons to receive input and send output (Aboitiz 1996; Fox & Wilczynski ......
c18rfa034 7 1986). In contrast, extrasomatic regions of the brain concerned with higher ......
8 cognitive processing, such as the neocortex, are expected not to follow any ......
9 fixed scaling pattern. Somatic regions of the brain correlate weakly with ......
10 body size (r = 0.5), suggesting that a larger body does not require a larger ......
c18rfa085 11 somatic brain (Rilling & Insel 1998). Non-somatic regions show even ......
12 weaker correlations......
13 A frequently cited explanation for observed brain-body size ......
14 correlations is metabolic rate of either the individual or its mother (Jerison ......
c18rfa043 15 1973; Martin 1983). Smaller animals have higher metabolic rates, limiting ...... c18rfa059
16 the size of metabolically expensive brain tissue. There are significant ......
17 problems with this hypothesis, however. Taxa do not always scale as ......
18 predicted. Metabolic rate is not always correlated with adult brain size ......
c18rfa040 19 (Harvey & Krebs 1990) or neonatal brain size (Pagel & Harvey 1988)...... c18rfa067
20 Furthermore, taxa with similar metabolic structures and body masses can ......
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1 have markedly different trajectories of postnatal brain growth (Periera & ......
c18rfa075 2 Leigh 2002). Maternal or individual metabolic rates do not seem to ......
3 constrain brain size tightly......
4 A small-bodied organism faces stricter structural, metabolic, and other ......
5 constraints on attaining large brain size than a large-bodied one. A large ......
c18rfa026 6 body is necessary for attaining large brain size (Dunbar 1993). Smaller ......
7 animals are usually subject to higher extrinsic mortality rates than are ......
8 larger ones, decreasing the selective advantages of growing a larger brain at ......
9 the expense of rapid generational turnover times. They also tend to have ......
c18rfa050 10 relatively faster metabolisms than do larger animals (Kleiber 1932), so ......
11 maintaining a large brain would pose a relatively greater burden on them......
12 Large body size results in both a slower metabolism and less predation ......
13 risk, decreasing costs associated with growing and maintaining a large ......
14 brain. Therefore, one mechanism for being able to afford a large brain in ......
15 the presence of cognitive selection pressures would be to increase body ......
c18rfa026 16 size (Dunbar 1993). This would alter the cost/benefit ratio of increasing ......
17 brain size by decreasing metabolic costs, and accordingly facilitate brain ......
18 expansion. In addition, selection for slower life history or increased body ......
19 size would decrease constraints imposed by life history and metabolism on ......
......
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c18rfa099 1 brain size (van Schaik & Deaner 2003; Kelley, van Schaik et al. this ......
2 volume), easing constraints on brain expansion in species facing selection ......
3 for increased intelligence......
4 Because the brain is so metabolically expensive, consuming up to ......
5 10% of calories for most mammals and up to 20% for modern humans ......
c18rfa009 6 (Armstrong 1990), it should be as small as possible for a given body mass ......
c18rfa035 7 and set of species-specific cognitive demands (Geary & Huffman 2002)......
8 The only way for an expanded brain to be retained by selection is if the ......
9 benefits to the individual of improved cognitive processing outweigh the ......
10 metabolic and structural costs. The expensive nature of brain tissue may ......
11 partially explain why brain regions expand differentially in taxa responding ......
c18rfa002 12 to different information processing demands (e.g., Adolphs 2003; ...... c18rfa008 c18rfa103 13 Armstrong 1985b; Barton & Harvey 2000; MacLeod, this volume; Purves ...... c18rfa081 c18rfa092 14 1994; Semendeferi & Damasio 2000; Whiting & Barton 2003; de Winter & ...... c18rfa103 c18rfa030 15 Oxnard 2001; contra Finlay & Darlington 1995, Finlay et al. 2001; Rakic ...... c18rfa031 c18rfa022 16 1988; 1995b): it is too costly to sustain expansions that are not strictly ......
17 necessary. c18rfa082...... c18rfa083 18 Another factor arguing against evolution of large, unspecified cortex ......
c18rfa030 19 of the sort proposed by Finlay and Darlington (1995), Finlay et al. (2001) ...... c18rfa031 ......
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c18rfa011 1 or Barton (1999) is the energetic costs of maintaining a large brain would ......
2 not necessarily be balanced by significant functional improvements ......
c18rfa001 3 (Aboitiz 1996; cf. La Cerra & Bingham 2002). To expand the brain, ......
4 neurons must increase in number rather than size to maintain conduction ......
5 speed, as dendrite breadth must increase with the square power of length to ......
c18rfa045 6 maintain conduction velocity (Kaas 2000). With more neurons, each ......
7 neuron will communicate with absolutely more but proportionately fewer ......
8 neurons than before. Clusters of specialized neurons should appear with ......
9 cortical expansion to permit fine-tuned processing of information, or there ......
10 can be relatively little improvement in cognitive sophistication (Geary & ...... c18rfa035 c18rfa045 11 Huffman 2002; Kaas 2000; Nimchinsky et al. 2002; and see MacLeod this ......
12 volume). For these reasons, areal specializations alongside greater ......
13 interconnectedness both characterize the human and probably the great ape ......
14 cortex (MacLeod this volume). Great apes and humans have larger ......
15 neocortices, the area primarily responsible for flexible problem solving, ...... c18rfa002 c18rfa010 16 than less socially complex species (Adolphs 2003; Barton 1996; Clark et ...... c18rfa018 c18rfa026 17 al. 2001; Dunbar 1993; Dunbar & Bever 1998; Preuss 2001; Sawaguchi ...... c18rfa028 c18rfa080 18 1997; de Winter & Oxnard 2001), and also have augmented neocerebellar ......
19 structures compared to other anthropoids that may be related to their ...... c18rfa091 c18rfa022 20 especially complex behavioral challenges (MacLeod this volume)......
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1 Variation among mammal species in relative brain size and cognitive ......
2 potential suggests that selection for overall or regional brain size increase ......
3 affects metabolic rate or metabolic tradeoffs within an organism. A species ......
4 under selective pressure to increase its cognitive complexity may ......
5 experience selection to modify diet, altering calorie or nutrient intake to ......
6 support brain expansion. Metabolic rate can also vary among mammalian ......
7 species of similar body size, so it can also be modified by selection. For ......
8 example, platyrrhines have higher rates of oxygen metabolism than do ......
c18rfa009 9 strepsirhines of similar sizes (Armstrong 1990). This appears to have ......
10 happened in the evolution of Homo, which reduced its gut size, diverting ......
c18rfa003 11 more metabolic energy to the brain (Aiello & Wheeler 1995). That the ......
12 extra energy from a reduced gut was devoted to the brain and not to ......
13 increasing reproductive output or some other reproductively valuable ......
14 function can only be explained if brain size, and by inference intelligence, ......
15 was under strong selective pressure......
......
B-Head 16 Locomotion ......
c18rfa078 17 Povinelli and Cant (1995) argued that great apes, as large-bodied arboreal ......
18 primates, face unique challenges in negotiating arboreal substrates due to ......
19 increased substrate unpredictability and compliance, and face severe costs ......
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1 of failing to support their body weight high in the trees. These conditions ......
2 would pose selective pressures for especially flexible and complex mental ......
3 calculations during locomotion that would have survival and therefore ......
4 reproductive consequences, and could have resulted in selection for ......
5 negotiating safer movement in an arboreal setting. This led, they propose, ......
6 to the evolution of self-concept and its supporting mental representation ......
7 capabilities in the great ape lineage. However, as noted by Begun, Gebo, ......
8 Hunt and Russon-a (this volume), large bodied arboreal hominoids can be ......
9 small brained (Oreopithecus), self-concepts may occur in mainly terrestrial ......
10 hominids (Gorilla), and travel on highly compliant branches with ......
11 deliberate, slow, non-stereotypical clambering occurs in small primates as ......
12 well (some prosimians)......
......
B-Head 13 Diet ......
14 Diet and body size are associated in primates (Clutton-Brock & Harvey ......
c18rfa019 15 1977; Milton & LeMay 1976). Because larger animals tend to have ...... c18rfa064 c18rfa050 16 relatively slower metabolic rates than smaller ones (Kleiber 1932), ......
17 however, body size can affect the types and amounts of food in which a ......
18 species will specialize. Very small primates are insectivorous, large ones ......
......
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c18rfa046 1 folivorous, and frugivores typically intermediate in size (Kay 1984). When ......
2 size and phylogenetic factors are controlled for, there is no set relation ......
3 between diet and metabolism in primates, with folivores and frugivores ......
c18rfa029 4 often having similar metabolic rates (Elgar & Harvey 1987). There is also ......
5 no correlation between encephalization and dietary quality or challenge, as ......
6 measured by percent fruit in diet (Ross this volume) or seasonality (Parker ......
c18rfa070 7 & Gibson 1977, 1979), or between extractive foraging and neocortex size ...... c18rfa071 c18rfa025 8 in primates (Dunbar 1992; Barton & Dunbar 1997). Identifying dietary ...... c18rfa012
9 features related to intelligence, however, may require more specific dietary ......
c18rfa089 10 measures (Ross & Jones 1999). Neither of these diet measures considers ......
11 the particular form of frugivory in which great apes specialize, which is ......
12 extended to include foods higher in protein and fat and non-fruit fallback ......
13 foods on a seasonal basis to survive recurrent periods of fruit scarcity ......
14 (Yamagiwa this volume). Even so, dietary pressures alone are unlikely to ......
15 explain the evolution of enhanced intelligence in the great apes......
......
B-Head 16 Social complexity ......
17 As a consequence of selection to cope with ecological pressures, most ......
c18rfa105 18 primates live in social groups (Wrangham 1980). Resource distribution ......
19 affects the cost-benefit equation of living in groups, so dietary ......
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c18rfa004 1 specializations can affect grouping size and patterns (Alexander 1974)......
2 Body size also affects social systems by altering susceptibility to predators, ......
3 conspecific competition, resource availability and distribution, and habitat ......
4 use......
5 The social brain hypothesis proposes that cognitive enhancements in ......
6 anthropoid primates are associated with social complexity and is supported ......
c18rfa012 7 broadly across primates by comparative analyses (Barton & Dunbar 1997; ......
c18rfa025 8 Dunbar 1992; review in van Schaik et al. this volume). These analyses ......
9 typically find that group size and proxy measures for brain size (e.g., ......
10 cranial capacity, neocortex ratios) are associated in a wide range of ......
c18rfa051 11 primates (e.g., Kudo & Dunbar 2001; Pawlowski et al. 1998; van Schaik & ...... c18rfa074 c18rfa099 12 Deaner 2003). The social brain hypothesis as initially presented, however, ......
13 fails to explain why primates with great ape-like social systems, such as ......
c18rfa079 14 capuchins and macaques (Preuschoft & van Schaik 2000; Thierry et al......
c18rfa097 15 1989; Perry 2003), are not as intelligent as great apes or why great apes, ...... c18rfa076
16 with group sizes typical of other anthropoids, consistently show more ......
17 complex cognition than all other anthropoids (in this volume, see Russon ......
18 a). Closer examination, however, reveals that despite apparent social ......
19 similarities, living great apes face more dynamic social problems than ......
20 other nonhuman primates (van Schaik et al. this volume), and so ancestral ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1231 of 1365
1 hominids may have been under stronger selective pressure to become ......
c18rfa027 2 better equipped for flexible social problem-solving abilities (Dunbar 1996; ......
c18rfa102 3 van Schaik et al. this volume; Whiten 1997). Why great apes are more ......
4 complex socially has not been made clear by the social brain model......
5 Social complexity may be related to patterns of sexual dimorphism in ......
6 body size. Males are selected to grow to large size in taxa for which size is ......
7 an advantage in male-male competitions that affect mating success, and ......
8 this makes for rigid social structures. In monogamous primates where ......
9 mating competition is minimal (e.g., gibbons), or where male-male ......
10 coalitions are a significant component of their competition (e.g., Pan, ......
11 hominins, capuchins), body size dimorphism is reduced. Gibbons are not ......
12 relatively more intelligent than other primates so reduced size dimorphism ......
13 alone is not directly correlated with greater intelligence. In species in ......
14 which decreased body size dimorphism is related to coalitionary behavior, ......
15 however, the situation may be different. The social complexities of ......
16 building and maintaining effective kin and non-kin coalitions, as ......
17 documented among humans, male chimpanzees and capuchin monkeys ......
c18rfa074 18 (Boehm 1999; Pawlowski et al. 1998; Wrangham 1999), may have selected ......
19 for increased cognitive capacities (van Schaik et al. this volume)......
20 This particular combination of body mass and social factors may in ......
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1 part explain encephalization in Pan and Homo,but it does not explain the ......
2 roughly equal levels of encephalization in Gorilla, Pongo, and probably ......
3 Dryopithecus, Sivapithecus and Australopithecus, all of which were ......
c18rfa016 4 strongly sexually dimorphic (Begun 2002; Kelley 2002; McHenry 1982)...... c18rfa049 c18rfa063 5 The combination of unusually complex coalitionary behavior and ......
6 reduction of body size dimorphism may have happened independently in ......
7 Pan and Homo, since Australopithecus, which is more closely related to ......
8 Homo, lacks at least some of these features (Ward et al. 1999). While ......
9 complex coalitionary behavior represents an aspect of social complexity ......
10 that may select for intelligence, it is not the sole factor influencing ......
11 selection for enhanced intelligence in hominids because encephalization ......
12 preceded reduction in sexual dimorphism in hominids......
......
B-Head 13 Life history ......
14 Body size is related to brain size via life history in several ways, in addition ......
15 to easing metabolic constraints on brain growth as outlined above. Large ......
16 body size tends to decrease extrinsic mortality by reducing susceptibility to ......
c18rfa104 17 predators (Williams 1957; and see recent reviews in van Schaik & Deaner ......
c18rfa099 18 2003; van Schaik et al.inpress). Large bodies take longer to grow, and a ......
19 longer growth period may favor relatively larger brains by prolonging brain ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1233 of 1365
1 growth and programming (Barton 1993; Kelley this volume; Ross this ......
c18rfa099 2 volume; van Schaik & Deaner, 2003). Slow life histories have been ......
3 hypothesized to allow longer time for brain growth or the learning involved ......
c18rfa024 4 to become a successful adult in humans (Dobzhansky 1962; Hallowell ...... c18rfa038 c18rfa054 5 1963; Mann 1975) and nonhumans (Joffe 1997; van Schaik & Deaner ...... c18rfa044 c18rfa099 6 2003; and see Ross this volume). However, time to reproductive maturity is ......
7 not tightly related to rate or timing of brain development. Primates with the ......
8 longest juvenile periods (humans), complete most of their brain size ......
9 growth in infancy, well before the most complex learning tasks are tackled ......
c18rfa075 10 (Periera & Leigh 2002; Ross this volume). Thus, prolonged juvenility may ......
11 allow for brain growth, brain maintenance, experiential learning or all ......
12 three, depending on the species. While life history is an important correlate ......
13 of intelligence and body size, slowing life history alone will not ......
14 automatically result in increases in brain size and encephalization, but will ......
15 only provide a conditions necessary for doing so when there is a fitness ......
16 advantage to increased intelligence (see Kelley this volume)......
......
......
......
......
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1 A synthesis to explain brain-body size relations in the ......
A-Head 2 hominoids ...... 3 We suggest that body size and brain size coevolved in significant but ...... 4 complex ways during hominid evolutionary history. Observed correlations ...... 5 between body and brain size are real. Allometry, however, does not signify ...... 6 a single universal constraint or scaling law. Instead, observed relations ...... 7 reflect a multi-factorial and often mutually reinforcing set of selective ...... 8 pressures. The specific allometric relation for each taxon depends on its ...... 9 phylogenetic history and its particular ecological and social circumstances...... 10 Considering only one or a subset of these circumstances will contribute to ...... 11 unsatisfying explanations for the relation between body and brain sizes...... 12 Observed brain-body size scaling relations in hominids, as in other ...... 13 primates and non-primate mammals, result from parallel selection on both ...... 14 brain size and body size. Because selection for body size is related to ...... 15 selection for many other aspects of a species’ biology, such as metabolism, ...... 16 diet, habitat, life history and social behavior, selection can produce similar ...... 17 combinations of traits. Situations favoring increased intelligence are often ...... 18 similar to those favoring increased body size. This would produce ...... 19 correlations independent of direct causal relations. Because closely related ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1235 of 1365
1 taxa share other adaptations that can affect and be affected by size, and ......
2 these sets of adaptations often co-evolve, common patterns across taxa ......
3 could result in the general relations generated by allometric analyses. One ......
4 would not expect all taxa to share exactly the same relations, given ......
5 different selective pressures and adaptive constraints faced by each......
6 Species therefore should vary about a statistically derived line (as in Figure ......
c18fig001 7 18.1). Only by elucidating patterns of selection shaping many parts of a ......
8 species’ biology and behavior can we hope to determine these relations and ......
9 predict why and how variables are interrelated, and hence why observed ......
10 scaling relations occur......
11 Selection pressures for enhancing cognition derive from situations ......
12 that require increased flexibility and complexity in behavior and ......
c18rfa035 13 problem-solving (Geary & Huffman 2002). They concern biotic more than ......
14 abiotic situations because the former are generally more variable, complex, ......
15 and unpredictable. Broadly speaking, the most challenging may be ......
16 predator-prey interactions and dynamic situations within social groups ......
c18rfa035 17 (Geary & Huffman 2002; West Eberhard 2003). The more complex these ......
18 become, the more complex and flexible cognition must be. Extant ......
19 hominids face the most complex foraging challenges and the most ......
20 sophisticated social interactions and relationships known in nonhuman ......
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1 primates (see many contributions in this volume) ......
2 Body size affects the cost-benefit ratio of evolving enhanced cognitive ......
3 capacities by affecting susceptibility to predators and conspecific ......
4 competitors, as well as diet, habitat use, the social system broadly, and life ......
5 history’ it also alters physical influences on brain size. Body size is ......
c18rfa005 6 associated with ecological dominance (Alexander 1989, 1990), a situation ...... c18rfa006
7 in which Darwin’s traditional hostile forces of nature (predation risk, food ......
8 shortages, disease, and climate) decrease in their effects on differential ......
9 reproduction relative to competition with conspecifics. Ecological ......
10 dominance is accomplished in different ways by different species, but large ......
11 body size is a common avenue. It represents a gradient, with some taxa ......
12 being more ecologically dominant than others. An increase in body size ......
13 reduces susceptibility to predation and lowers metabolic rate, potentially ......
14 increasing ecological dominance, as well as relaxing energetic constraints ......
15 on encephalization. Increases in intelligence can also increase ecological ......
16 dominance, as they render individuals better able to locate and obtain food ......
17 resources, evade predators, and otherwise modify their environments. The ......
18 relative reduction in differential reproduction due to decreased ......
19 extra-specific costs also effectively increases the fitness value of ......
20 sophisticated social problem solving abilities, in species for which sociality ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1237 of 1365
1 is most relevant to reproductive success......
2 This spiral of ecological dominance and increased social competition ......
3 may have contributed to the evolution of the human grade of cognitive ......
c18rfa033 4 abilities (Alexander 1990; Flinn et al.inprep). Examples of nonhuman ...... c18rfa006
5 species with relatively high ecological dominance include elephants, ......
6 dolphins, orcas, sperm whales, lions, and the great apes. Intraspecific ......
7 interactions have significant fitness effects on individuals in most primate ......
c18rfa033 8 species (Alexander 1990; Flinn et al.inprep), providing an initial ...... c18rfa006
9 condition in which an increase in ecological dominance will increase social ......
10 competition and lead to more intense intraspecific arms races in social ......
11 intelligence......
12 When social competition has significant fitness effects, relatively ......
13 intelligent individuals who are able to negotiate their social and ......
14 environmental settings better then their less cognitively sophisticated ......
15 conspecifics stand to achieve higher net fertility. If a species’ social and ......
16 physical environments are such that greater intelligence does not have ......
17 significant fitness benefits, then large brains are not expected. Examples of ......
18 long-lived, relatively large, relatively asocial, but not particularly ......
19 encephalized species include Galapagos tortoises and rhinoceroses. One ......
20 apparent exception to this rule, orangutans, who are often characterized as ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1238 of 1365
1 asocial yet highly intelligent, are actually more social than often supposed ......
2 and show social complexity comparable to other great apes (see van Schaik ......
3 et al. this volume); they also share other key cognitive challenges with ......
4 other great apes, such as especially complex foraging problems (see ......
5 Yamagiwa this volume)......
6 In terms of the model proposed here, Oreopithecus may be an ......
7 exception that proves the rule. Oreopithecus probably was highly ......
8 folivorous (Singleton this volume) and insular, and probably experienced ......
9 little ecological competition or predator pressure due to its island habitat ......
c18rfa037 10 (Harrison & Rook 1997). Although it fits the large size-low predation ......
11 pattern, its folivorous diet would have made it difficult to obtain adequate ......
12 caloric and other nutrient resources to maintain a large brain. This and its ......
13 comparatively unchallenging ecology would have made a large brain an ......
14 attribute that it neither needed nor could afford, resulting in selection for a ......
15 smaller brain, and correspondingly, reduced cognitive abilities. Outside of ......
16 primates, river dolphins and male angler fish are other examples suggesting ......
17 that evolution can act to diminish brain size in the absence of positive ......
18 selective pressures......
19 Most anthropoid primates tend to be frugivorous and experience ......
20 social competition, although some taxa have undergone stronger selective ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1239 of 1365
1 pressure to negotiate more complex social systems than others. Great apes, ......
2 because of their size and largely frugivorous diets, live in societies that ......
3 tend to especially flexible fission-fusion with relatively high subordinate ......
4 leverage and complex non-kin social relations that can affect social and ......
5 therefore reproductive success (review in van Schaik et al. this volume)......
6 This social complexity could favor enhanced cognitive abilities, and ......
7 presumably brain size, until these increases are in turn constrained by other ......
8 factors, and individuals are then selected to allocate energy to other efforts ......
9 like parental effort. This arms race is species-specific, because different ......
10 ecological conditions and phylogenetic histories affect different species, ......
11 and it explains phylogenetic differences in scaling patterns. Capuchin ......
12 monkeys may share many aspects of their social system with chimpanzees, ......
13 butacapuchin is only selected to out-compete other capuchin monkeys. It ......
14 does not have to be as intelligent as a chimpanzee, reflecting its different ......
15 phylogenetic heritage. The the immediate ancestor of chimpanzees was ......
16 already more encephalized than capuchins, and presumably more socially ......
17 complex. Differences in such evolutionary starting points of intraspecific ......
18 arms races, coupled with other constraints on different taxa, affects their ......
19 ultimate trajectories......
20 The multiple covariates of selection may explain the lack of a tight ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1240 of 1365
1 correlation with social complexity and brain size. Because competition is ......
2 relative to species, one should not predict equivalence in encephalization ......
3 (i.e., EQ or neocortical index) or intelligence between taxa as mediated ......
c18rfa074 4 solely by social systems (e.g., Pawlowski et al. 1998; Preuschoft & van ......
c18rfa079 5 Schaik 2000; van Schaik et al. this volume). Instead, among close ......
6 phylogenetic relatives, we should see more socially complex species ......
7 having relatively larger brains (or neocortices and associated structures)......
8 Living catarrhines are generally more encephalized than platyrrhines and ......
9 tend to have more complex social systems, though the most encephalized ......
10 platyrrhines share some complex social features with cercopithecids......
11 Among catarrhines, papionins are generally more encephalized than other ......
12 cercopithecines, and hominids are more encephalized than hylobatids, after ......
c18rfa036 13 accounting for body mass (Gibson et al. 2001; Begun & Kordos this ......
14 volume). Generally, their higher encephalization levels are associated with ......
15 greater social complexity, with levels of social complexity broadly tracking ......
c18rfa027 16 these encephalization differences (e.g., Dunbar 1996)......
17 The neocortex is the primary site of learning and higher level ......
18 cognitive processing, although other components such as the amygdala ......
c18rfa002 19 have supportive functions (Adolphs 2003; Siegal & Varley 2002). The ...... c18rfa093
20 cerebellum is also important, appearing to coordinate with the cortex to ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1241 of 1365
c18rfa085 1 produce complex cognition (Rilling & Insel 1998; and see MacLeod this ......
2 volume). The neocortex and the cerebellum are the two largest regions of ......
3 the primate brain (MacLeod, this volume); the cerebellum is ......
4 disproportionately enlarged in apes over other nonhuman anthropoids and ......
5 both enlarge at greater rates relative to the brain as a whole than more ......
6 conservative components (see MacLeod this volume). Expansion of the ......
7 brain to achieve enhanced cortical and cerebellar function would result in ......
8 greater increases in overall brain size than would expansion driven by the ......
9 functions of other regions. Doubling the neocortex results in a larger brain ......
10 than doubling the hippocampus, for example. This is an important reason ......
11 for the generally high association between behavioral complexities and ......
12 brain size, with both social and ecological problems being important ......
13 sources for these complexities......
14 In summary, particular combinations of diet, life history, social ......
15 system, intelligence and body size are likely to co-evolve, resulting in ......
16 broad allometry between body and brain size. Some combinations appear ......
17 unlikely. Large brains are costly for small-bodied primates, which are ......
18 usually under selection for a high reproductive rate and fast life history due ......
19 to high extrinsic mortality rates. Small primates are more likely to rely on ......
20 insects for food, and coupled with high predation risks, this results in ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1242 of 1365
1 increased costs of grouping and thus solitary life or small groups. Similarly, ......
2 large primates are not expected to be relatively small-brained. For primates, ......
3 large size reduces predation risk, enabling flexibility in foraging party size......
4 In great apes, even the comparatively solitary orangutan, it enables ......
5 unusually flexible fission-fusion societies with high subordinate leverage ......
6 and complex kin and non-kin interactions, all of which require exceptional ......
7 cognitive sophistication (van Schaik et al. this volume). Foraging patterns ......
8 in great apes also tend to be especially complex. During hominoid ......
9 evolution, constraints lifted by increasing body mass, combined with ......
10 concomitant increases in ecological dominance in inherently social species, ......
11 contributed to selecting for increased social and cognitive complexity......
......
A-Head 12 Implications for the evolution of hominid intelligence ......
13 Our ability to infer the cognitive capacities of fossil primates depends on ......
14 the assessment of brain size, body size, dimorphism, diet, life history, and ......
15 social system. The evolution of body mass in fossil apes is somewhat ......
16 difficult to assess given uncertainties in determining phylogenetic relations ......
17 of some taxa, and the diverse range of sizes of Miocene apes. Extant great ......
c18rfa094 18 apes range from about 33 to 170 kg in body mass (Smith & Jungers 1997)......
19 Basal catarrhines were considerably smaller, with propliopithecids ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1243 of 1365
c18rfa032 1 (including Aegyptopithecus zeuxis) ranging from 5–7 kg (Fleagle 1999)......
2 Thus, it is likely that hominoids evolved from fairly small-bodied ancestors......
3 Proconsul,astem hominoid with no direct evolutionary relation with ......
c18rfa017 4 extant apes (Begun et al. 1997), ranged in size from about 9 to 60 ......
c18tab001 5 kilograms (Table 18.1). Other apparently stem hominoids (Afropithecus, ......
6 Morotopithecus) are also within this range, though toward the upper end......
7 While a few possible stem hominoids (e.g., Micropithecus) are as small or ......
8 smaller than gibbons, most stem hominoids are larger than siamangs, and it ......
9 is likely that hylobatids are phylogenetic dwarfs (Begun this volume). This ......
10 range does not follow any temporal or spatial patterning, however, and no ......
11 trends are readily apparent. Among extant hominoids and their fossil ......
12 relatives, only hylobatids are less than 20 kg in body mass. Dryopithecus, ......
13 suggested to share a particularly close phylogenetic relation with hominids, ......
14 is known from four species that all tend to be slightly smaller than ......
c18rfa016 15 chimpanzees in size (Begun 2002). Their 25–45 kg range is the likely ......
16 ancestral condition for African hominoids, as australopithecine females ......
17 also fall within this range. This is interesting, as Pan female body mass ......
c18rfa094 18 means range from 33.2–45.8 kg (Smith & Jungers 1997), suggesting that ......
19 loss of significant body mass dimorphism in Pan may have involved ......
20 females increasing size in addition to or even instead of males decreasing ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1244 of 1365
1 in size......
Inset Table 18.1 about here ......
2 Most hominoid taxa, living and fossil, are primarily frugivorous, ......
3 although different species had relatively higher dependence on leaves (Kay ......
c18rfa047 4 & Ungar 1997) and some show use of hard foods (Singleton this volume)......
5 All extant hominids have anatomical and behavioral adaptations for ......
6 processing especially challenging foods, often used as fallback resources in ......
7 times of primary food scarcity (Bryne, Russon & Begun, Yamagiwa this ......
8 volume). Most fossil hominids also have anatomical indications of an ......
9 enhanced ability to exploit fall back foods, either in the form of large or ......
10 specialized anterior teeth or large, thickly enameled molars and robust jaws ......
11 (Russon & Begun, Singleton this volume)......
12 Early Miocene stem hominoids were not suspensory like extant ......
13 hominoids, though a possible case has been made for Morotopithecus ......
14 (Gebo this volume). Among middle and late Miocene hominids ......
15 Dryopithecus had a clearly extant hominoid-like below branch adaptation ......
16 conceivably associated with the shift to a great ape sized brain and ......
c18rfa078 17 intelligence (i.e., Povinelli & Cant 1995). Sivapithecus,however, did not ......
18 have had the same type of below-branch positional behavior characteristic ......
......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1245 of 1365
c18rfa088 1 of extant great apes (reviews in Rose 1997; Ward 1997) and Oreopithecus ...... c18rfa101
2 was highly suspensory but small brained. This diversity suggests that ......
3 locomotor pattern alone is not correlated in a straightforward manner with ......
4 the evolution of intelligence......
5 The prolonged life histories and period of immaturity characteristic of ......
6 modern apes first appeared in the Miocene. The only basal hominoid for ......
7 which evidence is available is Proconsul heseloni, which appears to have ......
8 had a developmental trajectory, defined using timing of the eruption of the ......
9 first molar, more like that of a hylobatid than a hominid (Beynon et al......
c18rfa048 10 1998; Kelley 1997). Life history evolution seems to parallel the evolution ......
11 of encephalization in hominoids. Proconsul heseloni, the only basal ......
12 hominoid for which data are available, had a relative cranial capacity ......
13 roughly like that of a similarly sized cercopithecids (Begun & Kordos this ......
14 volume; Walker et al. 1993). We have no information, however, on brain ......
15 size or life history of larger sized basal hominoids with which to explore ......
16 variation in these parameters. Dryopithecus has a further delayed age of ......
17 first molar eruption, a life history change correlated to increased brain size, ......
18 and is known to have had great ape-sized brain (Begun & Kordos, Kelley ......
19 this volume). Sivapithecus also had a delayed age at first molar eruption ......
20 though no direct evidence of brain size exists in this otherwise well known ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1246 of 1365
c18rfa048 1 taxon (Kelley 1997, this volume)......
2 All living and fossil hominoids for which there are data available are ......
3 highly sexually dimorphic in body mass except for hylobatids, Pan and ......
4 Homo, implying intense mate competition and some level of group ......
c18rfa077 5 complexity (Plavcan 2001; Yamagiwa this volume). This suggests that ......
6 polygynous mating systems with fairly high levels of male-male ......
7 competition for access to females represent the ancestral hominoid ......
8 condition. Reduced size body mass dimorphism is associated with ......
9 monogamy in hylobatids. Pan and Homo have independently reduced body ......
10 mass dimorphism levels yet increased (perhaps both) or at least maintained ......
11 (in Pan) significant levels of encephalization, suggesting that their ......
12 male-male coalitionary behavior is associated with the dimorphism ......
13 changes......
14 In addition to coalitionary behavior, chimpanzees, orangutans and ......
15 Homo share the traits of tool use and manufacture. If chimpanzees and ......
16 orangutans are more intelligent than other apes, this would involve some as ......
17 yet undetected brain attribute other than mass to account for cognitive ......
18 differences, because brain mass alone does not distinguish among great ......
19 apes, and no significant cognitive differences have been documented. This ......
20 has profound implication for interpreting fossil hominin behavior and for ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1247 of 1365
1 the suitability of chimpanzees as a source of behavioral models of human ......
2 evolution......
3 If Pongo and Gorilla are as intelligent as Pan,itmay be that the ......
4 presence of coalitions maintain and even reinforce encephalization in Pan ......
5 and Homo but that other factors achieve the same end in other fossil and ......
6 living hominids. For Pongo and Gorilla it could be foraging challenges, ......
7 other social problems or, at least in the case of Pongo,very slow ......
8 reproductive turnover. All great apes appear to share fission-fusion ......
9 tendencies rendered more complex by the effects of large body size ......
10 (increased social leverage, less rigid dominance, enhanced social ......
11 tolerance), so complex social problems may simply manifest themselves in ......
12 other ways. It is also the case that Pan shares dietary complexities with the ......
13 other great apes associated with seasonal fruit scarcities, so shared ......
14 ecological pressures may be among the forces behind their ......
15 encephalization. Once achieved, encephalization is likely to be maintained ......
16 if social interactions remain important, although there is no reason a priori ......
17 to believe that only one mechanism is involved......
18 In summary, the evolution of hominoid intelligence can be best ......
19 studied by examining a combination of many types of data. The last ......
20 common ancestor of hominoids was likely the size of a large cercopithecid, ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1248 of 1365
1 perhaps a baboon, with a similar life history and frugivorous diet. The ......
2 hominid last common ancestor increased its brain size and body size, ......
3 extended periods of its life history, and altered its diet. It also may have ......
4 begun further restructuring its brain to improve cognitive function ......
5 internally, leading to the more complex cortical structure of extant great ......
c18rfa002 6 apes, both internally and externally (Adolphs 2003; McLeod this volume; ......
c18rfa065 7 Nimchinsky et al. 1999; Semendeferi & Damasio 2000). The increased ...... c18rfa092
8 ecological dominance resulting from large body mass resulted in social ......
9 interactions having increased relative roles in determining individual ......
10 reproductive success, resulting in selection for increased intelligence. This ......
11 process tapered off somewhat through the late Miocene and early hominin ......
12 evolution, when other constraints on cognitive abilities appear to have been ......
13 reached (see Potts and Begun & Kordos, this volume). The process of ......
14 encephalization later took off again in Homo......
......
A-Head 15 Conclusions ......
16 Complexities in brain-body size relations make predictions of brain size ......
17 from body size and assessment of cognitive capacities from brain/body size ......
18 ratio more complicated than once supposed. To track the evolution of ......
19 intelligence in the fossil record, one cannot simply calculate EQ and have ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1249 of 1365
1 the whole story. However, recognition of the interrelations between body ......
2 size, metabolism, ecological dominance, sociality, life history, diet, and ......
3 other factors help explain previously enigmatic aspects of brain size and ......
4 scaling relations within primates. With more complex models incorporating ......
5 these other adaptive links, we can better explain variations in brain size, ......
6 body size and cognitive abilities among extant animals. If we can identify ......
7 some of these other aspects of species’ biology in the fossil record, we can ......
8 then more accurately track changes in intelligence over evolutionary time......
9 Many of these factors have been identified as correlates of ......
10 intelligence. Here, we suggest that the concepts of ecological dominance ......
c18rfa005 11 and intraspecific arms races in cognitive capacities (Alexander 1989) are ......
12 important, yet hitherto unrecognized, phenomena. Ecological dominance ......
13 alters selective pressures in regard to predation and to sociality. Given ......
14 possible associations between body size, longevity, and diet on the one ......
15 hand, and ecological dominance on the other, increased selective pressure ......
16 for mental adaptations to a complex social and ecological environment ......
17 may result in increased brain size......
18 The recognition of the importance of social competition for ......
19 sophisticated cognitive capacities may explain some broad intertaxic ......
20 scaling patterns, such as why platyrrhines and catarrhines with similar ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1250 of 1365
1 social systems are not similarly encephalized. Social competition is ......
2 relative within a species, with individuals competing against conspecifics ......
3 and not against an external factor. If levels of intelligence are reached as a ......
4 consequence of social arms races, they are necessarily dependent on ......
5 lineage history and phylogenetic starting points. Most primates, ......
6 particularly haplorhines, are inherently social, and when ecological ......
7 dominance is increased by reducing predation, increasing dietary quality, ......
8 or changing other factors such as locomotion, social competition increases ......
9 in relative importance for individual reproductive success. This produces ......
10 within species arms races in social skills that will continue until capped by ......
11 other constraints, whether ecological, metabolic, or structural......
12 The evolution of body size in great apes influenced the evolution of ......
13 great ape intelligence. Size decreased metabolic constraints on ......
14 encephalization as it increased ecological dominance by reducing ......
15 predation risk. It also led to longer life histories, which in turn favored ......
16 increased cognitive capacities. All of these factors are interrelated, and ......
17 feed back on one another. It is in this context that we are in an improved ......
18 position to study how and why intelligence evolved in great apes......
......
......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1251 of 1365
A-Head 1 Acknowledgements ......
...... 2 Carol Ward and Mark Flinn would like to extend their gratitude to David ...... 3 Begun and Anne Russon for the invitation to contribute to this volume. We ...... 4 all thank Anne Russon for her many careful and useful comments on an ...... 5 earlier draft of this paper......
...... 6 References ...... c18rfa001 7 Aboitiz, F. (1996). Does bigger mean better? Evolutionary determinants of ......
8 brain size and structure. Brain, Behavior and Evolution, 47, 225–45......
...... c18rfa002 9 Adolphs, R. (2003). Cognitive neuroscience of human social behavior...... 10 Nature Reviews Neuroscience, 4, 165–78...... c18rfa003 11 Aiello, L. & Wheeler, P. (1995). The expensive tissue hypothesis. Current ......
12 Anthropology, 36, 199–211......
...... c18rfa004 13 Alexander, R. (1974). The evolution of social behavior. Annual Review of ...... 14 Ecology and Systematics, 5, 325–83...... c18rfa005 15 Alexander, R. (1989). The evolution of the human psyche. In The Human ......
16 Revolution: Behavioral and Biological Perspectives on the Origins of ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1252 of 1365
1 Modern Humans, ed. P. Mellars & C. Stringer, pp. 455–513. Princeton: ......
2 Princeton University Press......
...... c18rfa006 3 Alexander, R. (1990). How did humans evolve? Reflections on the uniquely ...... 4 unique species. University of Michigan Special Publication, 1, 1–38...... c18rfa007 5 Armstrong, E. (1985a). Relative brain size in monkeys and prosimians......
6 American Journal of Physical Anthropology, 66, 263–73......
...... c18rfa008 7 Armstrong, E. (1985b). Allometric considerations of the adult mammalian ...... 8 brain, with special emphasis on primates. In Size and Scaling in ...... 9 Primate Biology, ed. W. L. Jungers, pp. 115–46. New York: Plenum ...... 10 Press...... c18rfa009 11 Armstrong, E. (1990). Brains, bodies and metabolism. Brain, Behavior and ......
12 Evolution, 36, 166–76......
...... c18rfa010 13 Barton, R. (1996). Neocortex size and behavioural ecology in primates...... 14 Proceedings of the Royal Society of London B, 263, 173–7...... c18rfa011 15 Barton, R. (1999). The evolutionary ecology of the primate brain. In ......
16 Comparative Primate Socioecology, ed. P Lee, pp. 167–97......
......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1253 of 1365
1 Cambridge, UK: Cambridge University Press......
...... c18rfa012 2 Barton, R. & Dunbar, R. (1997). Evolution of the social brain. In ...... 3 Machiavellian Intelligence, ed. A. Whiten & R. W. Byrne, pp. 240–63...... 4 Cambridge, UK: Cambridge University Press...... c18rfa013 5 Barton, R. & Harvey, P. (2000). Mosaic evolution of brain structure in ......
Uncited bibitem 6 mammals. Nature, 405, 1055–7......
...... c18rfa014 7 Bauchot, R. & Stephan, H. (1966). Donn´es nouvelles sur l’enc´ephalisation ...... 8 des insectivores et des prosimiens. Mammalia, 30, 160–96...... c18rfa015 9 Bauchot, R. & Stephan, H. (1969). Enc´ephalisation et niveauevolutif ´ chez ......
10 les simians. Mammalia, 33, 225–75......
...... c18rfa016 11 Begun, D. R. (2002). European hominoids. In The Primate Fossil Record, ...... 12 ed. W. Hartwig, pp. 221–40. Cambridge, UK: Cambridge University ...... 13 Press...... c18rfa017 14 Begun, D. R., Ward, C. & Rose, M. (ed.) (1997). Function, Phylogeny and ......
15 Fossils: Miocene Hominoid Evolution and Adaptations.New York: ......
16 Plenum Press......
......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1254 of 1365 c18rfa018 1 Clark, D., Mitra, P. & Wang, S-H. (2001). Scalable architecture in ......
2 mammalian brains. Nature, 411, 189–93......
...... c18rfa019 3 Clutton-Brock, T. & Harvey, P. (1977). Species differences in feeding and ...... 4 ranging behaviour in primates. In Primate Ecology, ed. T. H...... 5 Clutton-Brock, pp. 557–79. London: Academic Press...... c18rfa020 6 Clutton-Brock, T. & Harvey, P. (1980). Primates, brains and ecology......
Uncited bibitem 7 Journal of the Zoological Society of London, 190, 309–23......
...... c18rfa021 8 de Waal, F. & Tyack, P. (ed.) (2003). Animal Social Complexity: ...... 9 Intelligence, Culture and Individualized Societies. Cambridge, MA: ...... 10 Harvard University Press...... c18rfa022 11 de Winter, W. & Oxnard, C. (2001). Evolutionary radiations and ......
12 convergences in the structural organization of mammalian brains......
13 Nature, 409, 710–4......
...... c18rfa023 14 Delson, E., Terranova, C., Jungers, W., Sargis, E., Jablonski, N. & Dechow, ...... 15 P. (2000). Body mass in Cercopithecidae (Primates, Mammalia): ...... 16 estimation and scaling inexteinct and extant taxa. American Museum of ...... 17 Natural History, Anthropological Papers, 83, 1–159......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1255 of 1365 c18rfa024 1 Dobzhansky, T. (1962). Mankind Evolving: The Evolution of the Human ......
2 Species.New Haven: Yale University Press......
...... c18rfa025 3 Dunbar, R. (1992). Neocortex size as a constraing on group size in primats...... 4 Journal of Human Evolution, 20, 469–93...... c18rfa026 5 Dunbar, R. (1993). Coevolution of neocortical size, group and language in ......
6 humans. Behavioral and Brain Sciences, 16, 681–735......
...... c18rfa027 7 Dunbar, R. (1996). Grooming, Gossip and the Evolution of Language...... 8 Cambridge, MA: Harvard University Press...... c18rfa028 9 Dunbar, R. & Bever, J. (1998). Neocortex size predicts group size in ......
10 carnivores and some insectivores. Ethology, 104, 695–708......
...... c18rfa029 11 Elgar, M. A. & Harvey, P. H. (1987). Basal metabolic rates in mammals: ...... 12 allometry, phylogeny and ecology. Functional Ecology, 1, 25–36...... c18rfa030 13 Finlay, B. & Darlington, R. (1995). Linked regularities in the development ......
14 and evolution of mammalian brains. Science, 268, 1578–84......
...... c18rfa031 15 Finlay, B., Darlington, R., & Nicastro, N. (2001). Developmental structure ...... 16 in brain evolution. Brain and Behavioral Sciences, 24, 263–278......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1256 of 1365 c18rfa032 1 Fleagle, J. (1999). Primate Evolution and Adaptations.New York: ......
2 Academic Press......
...... c18rfa033 3 Flinn, M., Ward, C., & Geary, D. (in prep) The social competition model of ...... 4 human evolution...... c18rfa034 5 Fox, J. & Wilczynski, W. (1986). Allometry of major CNS divisions: ......
6 towards a reevaluation of somatic brain-body scaling. Brain, Behavior ......
7 and Evolution, 28, 157–69......
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12 brain size in relationship to cognition. In Evolutionary Anatomy of the ......
13 Primate Cerebral Cortex, ed. D. Falk & K. Gibson, pp. 79–97......
14 Cambridge, UK: Cambridge University Press......
...... c18rfa037 15 Harrison, T. & Rook, L. (1997). Enigmatic anthpoid or misunderstood ape? ...... 16 The phylogenetic status of Oreopithecus bambolii reconsidered. In ...... 17 Function, Phylogeny and Fossils: Miocene Hominoid Evolution and ......
XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1257 of 1365
1 Adaptations, ed. D.R Begun, C. Ward & M. Rose, pp. 327–62. New ......
2 York: Plenum Press......
...... c18rfa038 3 Hallowell, A. I. (1963). The protocultural foundations of human ...... 4 adaptation. In Social Life of Early Man, ed. S. L. Washburn, ...... 5 pp. 236–255. Chicago: Aldine...... c18rfa039 6 Harvey, P. & Clutton-Brock, T. (1985). Life history variation in primates......
Uncited bibitem 7 Evolution, 39, 559–81......
...... c18rfa040 8 Harvey, P. & Krebs, J. (1990). Comparing Brains. Science, 249, 140–5...... c18rfa041 9 Hofman, M. (1982). Encephalization in mammals in relation to the size of ......
10 the cerebral cortex. Brain, Behavior and Evolution, 20, 84–96......
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15 Academic Press......
...... c18rfa044 16 Joffe, T. (1997). Social pressures have selected for an extended juvenile ......
XML Typescript c Cambridge University Press – Generated by TechBooks. Body Size and Intelligence in Hominoid Evolution Page 1258 of 1365
1 period in primates. Journal of Human Evolution, 32(6), 593–605......
...... c18rfa045 2 Kaas, J. (2000). Why brain size is so important: design problems and ...... 3 solutions as neocortex gets bigger or smaller. Brain and Mind, 1, 7–23...... c18rfa046 4 Kay, R. (1984). On the use of anatomical features to infer foraging ......
5 behaviour in extinct primates. In Adaptations for Foraging in Primates, ......
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XML Typescript c Cambridge University Press – Generated by TechBooks. The Evolution of Thought Page 1269 of 1365 c18tab001 Table 18.1. Ballpark body mass estimates (kg) for fossil hominoids discussed in this ......
chapter ......
...... Males Females Evidence ......
...... Proconsul heseloni ?10Dental, cranial & postcranial
Proconsul nyanzae 35 15 Dental, palatal & postcranial ......
Micropithecus clarki ? 3.5 Dental and palatal ......
Afropithecus 35 ? Dental, facial & postcranial ......
Morotopithecus 54 ? Dental, facial & postcranial ......
Dryopithecus laietanus 35 20 Dental, cranial and postcranial ......
Dryopithecus brancoi 40 25 Dental, cranial and postcranial ......
Sivapithecus punjabicus 40 20 Dental, cranial and postcranial ...... Sivapithecus parvada 60 ? Dental, postcranial ...... Oreopithecus 30 15 Dental, cranial and postcranial ...... Australopithecus∗ 70 31 Postcranial ......
∗ Australopithecus afarensis. Based on estimates from Fleagle (1999), Gebo et al. (1997), c18rfa032......
Harrison (1989), Jungers (1987), Leakey & Walker (1997), McHenry (1988), Ruff et al...... (1989), Walker et al. (1993) and personal observations (which authors)......
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