TEMPE, Arizona—As a species of seeming feeble, naked apes, we humans are unlikely candidates for power in a natural world where dominant adaptations can boil down to speed, agility, jaws and claws. Why we rose to rule, while our hominin relatives died out, has long been a curiosity for scientists.

The study of our human nature encompasses a variety of fields ranging from anthropology, primatology, cognitive science and psychology to paleontology, archaeology, evolutionary biology and genetics.

Representatives of each of these disciplines gathered February 19-22 at a workshop, "Origins of Human Uniqueness and Behavioral Modernity," staged by Arizona State University's Origins Project to discuss recent advances in their respective fields.

Led by ASU professors anthropologist Kim Hill and paleoanthropologist Curtis Marean, co-organizers of the event, the panel of scientists agreed to adopt a working definition that human uniqueness is the "underlying capacity to produce complexity," and to think of behavioral modernity as "the expression" of those capacities.

The expression of capacities, Hill and Marean said, can be summed up, namely, as exceptional cognition, culture and cooperation. Each of the three C's was a topic of focus for the scientists. One of their goals at the conference was to pinpoint specific markers of these expressions, and then use them to identify the emergence of humans within the paleoanthropological record.

The beginning of human cognition, for example, is the result of the development of a larger brain, which can be represented by artifacts—stone tools, weapons—or productions that signify greater abilities for thinking and innovation, said archaeologist and paleoanthropologist John Shea of Stony Brook University.

In addition, although the adaptation of a larger brain may separate humans from their primate relatives, it also came at a cost of increased fuel requirements. A human brain uses at least 20 percent of an individual's resting metabolism, said Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Germany.

Evidence of early humans' use of fire could be used to mark how they overcame their energy needs, said primatologist and biological anthropologist Richard Wrangham of Harvard University. Heat helps free up energy by softening foods, denaturing their proteins and breaking down toxins, Wrangham proposed, which is why cooking may explain human brain size as well as small canine teeth and small guts in comparison to other primates.

By the same token, evidence of coastal adaptation can also mark human activity and a strategy for meeting the brain's growing energy needs. Archaeological excavations along the coastline of South Africa, Marean suggested, show that early humans obtained energy-dense foods by adopting a diet of shellfish, which afforded strong nutritional benefits for the brain.

Accordingly, the researchers discussed how an oversized brain led to culture, a product of thinking and social learning facilitated by language, creativity and innovation. The passing on of knowledge from generation to generation is metaphorically referred to as a cultural "ratchet effect," which creates greater complexity of culture over time.

In the wild, a lone human would not be able to survive without culture, explained evolutionary theorist Rob Boyd of University of California, Los Angeles. "Think about what is necessary to live in Alaska," he said. "You’d need a kayak, a harpoon, a float to not sink. Nobody invents a kayak. People learn the proper way to make a kayak from others."

Additionally, Boyd said culture gives humans a survival advantage that is beyond the capacity of other animals. "Typical apes live in a particular habitat. We can make the changes on timescales that are very fast," he said.

According to Shea, who specializes in ancient use of complex projectile weapons, "it's easy to imagine how complex projectile technology may have led humans to gain a broad and resilient human ecological niche."

Whether demonstrated by situations of hunting, foraging, child rearing or migrating, humans with culture, in pursuit of shared goals, had much to gain through cooperation. Cooperating humans would lead to greater survival, greater reproduction and colonization.

After all, other primates cooperate, said anthropologist Joan Silk of the University of California, Los Angeles, who specializes in reproductive strategies of old-world monkeys. Communal breeding, for example, reduces stress on bonnet macaques creating greater reproductive success.

Developmental psychologist Felix Warneken of Harvard University added that the social skills of human children include the capacity to look beyond shared intentionality (monkey see, monkey do) at an early age. They show an understanding of others' beliefs, exhibiting a "theory of mind,"which inspires cooperation.

Describing how field work with the !Kung people of southern Africa gave her insight into cooperation first hand, Polly Wiessner of University of Utah said hunter-gatherers used gifts as mnemonic devices across human groups and used personal adornment as an advertisement of marriage or social status.

Sequence of causal and timing factors
According to Hill, who has studied hunter-gatherers in South America for nearly 30 years, whether by shell beads, other kinds of gifts or through female transfer, the traits of cognition, culture and cooperation would eventually lead to specializations and government.

Stephen Shennan, a professor of archaeology at University College London, explained that as population size increases, culture increases exponentially: greater contact between human groups leads to much more copying of creative innovations.

Ultimately, the exponential cultural ratchet effect is demonstrated by humans' domination of the world today, said Hill and Marean, who collected proposals from the gathered researchers for a possible flowchart and eventual timeline. The proposals will be posted to a group Web site for further discussion.

In closing the workshop, Hill said, "Only by working together are we able to fully account for the emergence and timing of unique features of Homo sapiens and how humans, evolved through natural processes, resulted in a spectacular anomaly among living species."