Human Social Evolution

Robert A. Foley’s “An Evolutionary and Chronological Framework for Human Social Behavior” examines the chronological framework and ecological basis for human social evolution. Foley argues that the combination of male kin-bonding and selection for energetically expensive offspring played a key role hominid social evolution and that this evolutionary path was not unitary or the consequence of a single event.

Foley maintains that although primatology, anthropology, and paleobiology have contributed behavioral and ecological theories to human social evolution, it is likely that “specific interactions between populations and their environment occurring cumulatively over millions of years”, rather than an inevitable evolutionary track, resulted in today’s observed human social behavior (96). Suggesting that the “particular times and … particular places [are] paramount”, Foley focuses on a chronological retelling of human social evolution. He suggests that human ‘sociality’ is a characteristic of anthropoid primates dating as far back as 35 mya and not a trait exclusive to humans (97). This is based on the argument that hormonal and biochemical mechanisms mediating behavior is similar across anthropoids.

The emergence of monogamy or instances of monogamy among anthropoids is associated with the inability for females to simultaneously have access to a resource base and a (undefined) “component of male contribution to infant survival” (99). According to Foley, monogamy is fairly unstable as if males are able to acquire more mates they will likely attempt to do so. Some primate groups have been shown to have various social states and are flexible within them. It is argues that this may have been the origin of social states which would have diverged with niche separation (99). In the development of hominids, however, an increase in infant dependency is likely to have affected the frequency of monogamy. Foley notes that an increase in infant dependency (as observed in chimpanzees) is typically dealt with by increased female kin-bonding which provides “allomothers”, lowering energetic costs for mothers. The lack of female kin-bonds in early hominid groups would have increased the importance of male-female bonds and food sharing.


This is supported by a distinct divergence between cercopithecoids and hominoids where the former show significant female kin-bonding and the later were likely characterized by “small social units made up of one male, one or more females, and young. It is suggested that the early diversification of Hominoidea between 25 to 20 mya was likely to have established the “small core units of homoid social life” of which gorillas, orangutangs and Gibbons are examples (100).

With the retreat of forests and the expansion of savannah grasslands, Foley argues that an increase in day range length, home range area and time for foraging was likely to have occurred due to the overall patchy dispersal of resources and increased seasonality. This is seen as a factor likely increasing the formation of small(er) social units and a strengthening of family bonds. (101-2). Although there have been disputes as to whether this was the ancestral condition (and that common chimpanzees departed from this model). The author proposes that it was likely an independent adaptation of the hominid lineage to open grasslands (102).

The increase in seasonality on the savannah is interpreted by Foley to have triggered an increased reliance on meat around 2 mya. This new reliance would further shift social relations and social structures such that this new behavior is different from australopithecine populations (102). The reason for this differentiation is not explained. This shift in diet is argued to have triggered an increase in encephalization , which consequentially would further alter human social behavior. Foley argues that for encephalization, being extremely costly, to occur and continue to develop there had to be positive selective pressures. The selective pressures for increased encephalization are argued to be “Greater meat-eating [as it] provided more energy, allowed for reduced energy expenditure, and acted as a selective pressure leading to greater levels of sociality” (102). This statement however relies on the assumption that during ecological changes gathering became insufficient and no longer provided the necessary calories and that hominids were skillful enough to hunt, kill, and butcher meat without expending more energy than attained (thus reducing energy expenditure). Also this suggests that encounter/success rates with prey were high enough to encourage increased meat consumption.

Foley further suggests that:

…during the period of 2.0 to 1.0 Mry the expected shift in social organization might well have been towards more intense and extensive male alliances…provided a premium in terms of foraging behavior under these new ecological conditions. Females associated with male groups that were numerically larger and effective at acquiring, and probably protecting resources (Foley 104).

This statement assumes that by 2-1 mya, males were the ones doing the hunting and that it was this male behavior that led to an increase in socially complex behavior. The notion that females would start to associate themselves with large male groups runs contrary to the small hominoid family unit previously argued by Foley. Also, this assumes that females were ineffective “at acquiring and probably protecting resources” and therefore had to rely on males (104). Changes in female behavior and therefore contribute to social complexity are ignored or are only discussed in relation or in response to male shifts in behavior.

Foley suggests that group size increased by 300,000 years BP to the point where grooming was no longer efficient for the maintenance of social relationships and therefore language emerged. The increase in brain size to 1000 grams during this time would have also prompted increased male competition and conflict between mating strategies as maturation of infants would have slowed and longer inter-birth periods would become characteristic (104-5).

The first 80,000 years of AMH is argued to not be characterized by social behavioral innovation but rather differences start to emerge around 40,000 BP and are not the founded in specific behavior but rather the propensity for dispersal which is argued to have come about as a result of increased hostility between males in male bonded kin-groups (106). As size increases, competition also increases and resulted in “demographic fission of communities” which would be composed of mainly kin-based groups (107). This is an interesting suggestion and would be consistent with fission of modern hunter-gatherers but the groups would have to maintain adequate genetic variability within the group or have a certain amount of inter-group exchange. The explanation of fission due to male hostility however seems incomplete and Foley ignores resource competition among other possible female conflicts (though it is not made clear if male hostility includes this).

Foley also claims that at about 30 kya, long-term evolutionary changes in behavior come to halt and are only reinstated with the beginnings of agriculture which require a “shift from small mobile hunter-gatherer groups to larger and more sedentary farming communities” and would have resulted in different social interactions and therefore a change in basic social structures (108).

The author maintains that the nature of social evolution must be considered similar to any other evolutionary process as one that is additive and that what we observe today is the product of individual elements. He argues that the “relationships between members of the same sex have remained more stable than relationship between the different sexes”. This is significant in that the author moves away from any type of biological determinism and suggests that male-female relations are flexible (and therefore existent unequal gender relations are not naturalized).

Finally, the author ends in summarizing the proposed “human revolution” theories of the Upper Paleolithic. These include language and symbolic thought. He stresses that “there is no clear anatomical boundary between archaic and modern” and “there is continual and regionally variable evolution in human cranial from 100-10kya” (113). Behavioral changes only become clear around 45 kya and this is restricted to Europe and the Mediterranean. This leads the author to suggest that symbolic expression was a regional phenomenon and not a reflection in change of “human global traits”. He claims that genetic diversification was not specific to the Upper Paleolithic but was present in both the Pleistocene and Holocene.

This paper presents a series of hypothesis for social evolution among early hominids and appropriately suggests that social evolution was not the result of a single event or drastic change. It is interesting that Foley suggests a regionally diverse hypothesis over a structural one. This paper was well argued though may have been more convincing if archaeological evidence was provided.

Works Cited

Foley, Robert A.
1996 An Evolutioanry and Chronological Framework for Human Social Behavior. In Evolution of Social Behavior Patterns in Primates and Man: A Joint Discussion Meeting of The Royal Society and The British Academy. W. Grunciman with John Maynard Smith and R.I.M. Dunbar, eds. Oxford: Oxford University Press.