TEMPE, Arizona—Based on our capacity for thought, social learning and cooperation, humans often hold our own species in high regard compared to all other living things.

It is certainly true that the human species is a statistical outlier along several dimensions, so scientists have recently been working out a sequence of the anatomical and behavioral adaptations that were necessary across evolutionary time for our ancestors to become fully human.

Emboldened by such developments, 25 experts from a range of disciplines gathered February 19-22 at a workshop, "Origins of Human Uniqueness and Behavioral Modernity," organized by Arizona State University’s Origins Project to identify the suite of traits that could be used to mark the starting point of humankind.

Participating scientists included paleontologists, anthropologists, archeologists, evolutionary ecologists and biologists, primatologists, developmental psychologists, geneticists and other specialists in cognition, cooperation, culture and social organization.

Theoretical physicist and cosmologist Lawrence Krauss, ASU professor and director of ASU's Origins Project, kicked off the workshop by saying it would help lay the foundation for the story of humanity's beginnings and open new avenues for future study.

"We are doing exactly what we had intended—bringing together the best minds from a wide variety of fields—to address a truly fundamental question about the nature of humanity," Krauss said. "What this ultimately means is that we want to understand what happened that led to 'us' and gave us Shakespeare."

The event's co-organizers, paleoanthropologist Curtis Marean of ASU, who directs archeological digs in South Africa aimed at understanding human origins, and anthropologist Kim Hill of ASU, whose focus is the emergence of human uniqueness from the vantage point of nearly 30 years of fieldwork with hunter-gatherer societies, recounted that during the Pleistocene epoch (between 1.8 million and 10,000 years ago) in Africa, a species of hominins walked along an evolutionary trail to "become something more than just bipedal apes," which led humans to persist, led hominins such as Neandertals not to persist, and gave humans the capability to eventually colonize the planet.

The question of how a seemingly feeble, naked ape could survive to become dominant is "one of those topics that always fascinate people," Marean said. He adds that a scientific consensus into "what comprises uniqueness" would also bolster research into human origins by helping to guide the development of identification markers—fossils and artifacts—that would help reveal human emergence in the paleoanthropological record.

The study of human uniqueness is fairly young and a cross-disciplinary approach is necessary, according to Hill. Having recently published research on the topic in the October 2009 issue of Evolutionary Anthropology, Hill said, "We are just now tackling the problem [of human uniqueness]. Most of the recent advances that I am aware of are covered in our review paper, but there are some areas that I know less well such as cognition and neuroscience."

What is meant by human uniqueness is also a point of confusion among scientists. Hill said that evolutionary scientists have historically been reluctant to pronounce humans as distinct. "What we mean by 'unique' is that humans show a combination of characteristics" that make humans a "statistical outlier in the living world" rather than unique "through processes that are unique to our species," he said. Whatever makes humans special, Hill added, it has led us to become biologically dominant—cycling the majority of all the nitrogen on the planet, technologically dominant and extremely complex.

Confronting the jigsaw puzzle of human uniqueness head on, as the organizers did, follows in the tradition of Charles Darwin, according to molecular biologist and geneticist Sean B. Carroll of the University of Wisconsin–Madison. Carroll said that Darwin himself would approach the topic of the workshop by saying, "What are the fresh facts? Let's put them on the table."

On Saturday and Sunday the fresh facts were indeed rolled out as each scientist gave a 20-minute presentation on findings in their field relevant to the question of human uniqueness, followed by five minutes of questions and discussion. On Monday morning Hill and Marean moderated a discussion of the sequence of events—including genetic, anatomical and behavioral adaptations—that led humans to where we are today.

The researchers plan to post the results to a Web site, but for now it will remain private, so the rest of us will have to wait a bit longer for a resolution to the question of what makes humans unique. However, more details from the conference will be reported at ScientificAmerican.com in the coming days, so stay tuned.