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The Human Nature Review Human Nature Review  2002 Volume 2: 340-342 ( 23 August )
URL of this document http://human-nature.com/nibbs/02/origins.html

Essay Review

Evolution and Human Origins

By Bruce Bridgeman*

Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution, edited by Frans B. M. de Waal. Cambridge, MA: Harvard University Press, 2001.

Evolution and the Human Mind: Modularity, Language, and Meta-cognition, edited by Peter Carruthers and Andrew Chamberlain. Cambridge, U.K.; New York: Cambridge University Press, 2000.

How can we understand ourselves, the bewildering variety of human emotions, motivations and experiences? Looking just at the surface features of human life has met with limited success, piecemeal observations spawning piecemeal theories; the integration, the big picture, seems just out of reach with this strategy.

In the past few decades science has begun to pursue a different tack, examining where we have been as a species for the past few million years to better understand what we are now. Using the methodological microscope that biology has developed for analyzing other species on the earth - their range, what they eat, what eats them, how they reproduce, everything about their lifestyles - science has turned the microscope back on ourselves. The results have been illuminating, sometimes uncomfortable, always fascinating.

The biological approach does not require a genetic determinism, for culture is older than humanity, so that genes and culture have been co-evolving for millions of years (Bridgeman in press, ch. 2). One of the most powerful ways of understanding both the biological and the cultural components, as well as their interactions, is to examine closely related primates who may have shared features with our common ancestors.

Several papers in Frans de Waal’s Tree of Origin attack the issue of cultural contributions to the human genetic legacy. Contrary to the conclusions from earlier more casual observation, several primate species show behaviors that can be interpreted as culturally transmitted. Most of the nine contributed chapters relate to culture in some way. In the most direct approach, William McGrew examines cultural traditions in several primate species. After a series of careful definitions, he gives a number of examples of behaviors that can only be described as cultural - distinct groups of animals of the same species who do similar things in different ways, eat some foods and ignore others, or treat each other differently. About 40 different populations of chimpanzees have been studied in the wild. Some use stone tools to crack nuts, while others are unable to exploit this food source. Nothing prevents those apes from nut-cracking except lack of cultural knowledge. All chimpanzees engage in grooming, but in only at Mahale do they groom with a characteristic scratch that other chimpanzees use only on themselves. Signs of cultural transmission are found in other primates as well, including gorillas and even baboons. One group of lowland gorillas, for instance, eats termites but not weaver ants, while another group is the other way around; both insects are common in both locations. Observation, imitation, experimentation - all are necessary to make this sort of cultural transmission work, limited though it is.

A lot can be gained by looking beyond the common chimpanzee to other primate species. Karen Strier devotes a chapter to comparative behavioral studies beyond the apes, while de Waal looks closely at bonobos, formerly called pygmy chimpanzees. In many aspects of their behavior and even their physiology, bonobos sit between common chimpanzees and humans. Female estrus is hidden by almost continuous sexual swellings, the groups use sex beyond reproduction to facilitate social interactions, and they are less violent than common chimpanzees. Like humans, chimpanzee groups generally practice female dispersal and male philopatry, as Anne Pusey points out in her introductory chapter, with the result, as de Waal notes, that males have less to lose from incest than do females. Here the science becomes productive, for we can predict from this that in both human and ape groups females should resist incest more strenuously than males. These are just a few examples of the rich additions that behavioral primatology can make to understanding the human condition.

What of a related approach, philosophers examining modularity, language and meta-cognition to gain insights into human evolution and from there into human life itself? Though it’s an attractive strategy in theory, the philosophical tradition falls short in practice. Philosophers are in some ways like very bright, well-read undergraduates, full of ideas but lacking the means to test them. They review the empirical results of others without contributing any of their own. Philosophers also share a distinct academic advantage with undergraduates, though, for they are not so invested in any particular empirical discipline that they cannot jump across numerous disciplinary boundaries. Philosopher Carruthers and biological anthropologist Chamberlain bring together in Evolution and the Human Mind anthropologists, linguists and even behavioral geneticists in their effort to understand the human mind through evolution. This gives their volume greater breadth but also less coherence than the de Waal volume, most of whose contributors can be described as primate behavioral ecologists.

The approaches of the two books can perhaps best be compared in chapters by Robin Dunbar, who contributed to both volumes. His chapter in the de Waal volume examines group sizes in extant primates and humans, interpolating to infer group sizes and mechanisms of managing groups in intermediate extinct species. There is a section on methods. Dunbar concludes that hominid group sizes began to exceed those that could be held together by grooming alone somewhere toward the end of the Homo erectus phase, implying that language had taken on part of the role of facilitating social cohesion by that time. A method section is lacking in the more speculative contribution to the Carruthers and Chamberlain volume, which concentrates more on the evolution of a theory of mind. Dunbar concludes from a series of arguments that since apes can manage second-order intentionality and humans fourth-order, Homo erectus with its intermediate group size would have been able to engage in third-order intentionality. The conclusions are backed up partly by the same figure reprinted in both volumes, Figure 7.2 in de Waal and 11.1 in Carruthers & Chamberlain, both adapted from an earlier article by Aiello and Dunbar.

The best way to learn about the role of human origins in consciousness? Read both books, but read de Waal first.


Bridgeman, B. (in press) Psychology and Evolution: The Origins of Mind. Thousand Oaks, Ca.: Sage Press.

Buy Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution from Amazon United States of America Amazon.com  Amazon United Kingdom Amazon.co.uk  Amazon France Amazon.fr  Amazon Deutschland Amazon.de  Amazon Japan Amazon.co.jp Amazon Canada Amazon.ca

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© Bruce Bridgeman.

* Bruce Bridgeman, Professor of Psychology and Psychobiology,  Psychology Department, 343 Social Sciences II, University of California, Santa Cruz, CA 95064, USA.


Bridgeman, B. (2002). Evolution and human origins. Human Nature Review. 2: 340-342.

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