What does it mean to be human was one of the panel discussions at the 2008 World Science Festival in New York City. Anthropology.net had a post some time back reviewing that discussion. The panel pundits were a collection of eminent psychologists, geneticists, anthropologists and neuroscientists among many other fields. Each expert gave an opinion of what makes humans unique, in the sense of possessing a unique biological property. Most of the answers focused on various aspects of our cognitive abilities and for good reason since we seem to differ qualitatively in our ways of thinking and communication from other animals. Almost all the answers were rejected by the blog author, who gave examples of similar traits being present in various species of apes and birds. The post is worth reading. I was left thinking, so okay just what is it that makes us different? Maybe the difficulty arises because of the insistence of the term unique. That carries the burden of showing that we posses something that absolutely does not exist anywhere in the animal kingdom. This approach will likely fail, since our characters are ultimately derived from an ancestral condition and echoes of human-like properties are bound to exist in related groups. Besides evolution can be strongly convergent. Evolution comes up with similar solutions to deal with similar problems. Even in groups such as birds which are only distantly related to us, cognitive properties similar to our own, such as anticipation and deception have been shown to exist, a result not due to shared ancestry but due to convergence.
I am trying to think of what evolutionary trigger could have lead to the considerable differences in cognition that have accumulated between humans and our closest relatives. If I was to thrown my opinion in the ring I would go for neoteny , which is the retention of juvenile features in adults due to a slowing down or delay in development. The main consequence in humans of developmental delay has been a prolongation of helplessness in infants and an extended childhood. Some say we, especially the men, never really grow up, but there is a deeper evolutionary reason for it! Having helpless infants and inquisitive children in early human groups would have had radical consequences on group dynamics and given rise to different selection pressures on different sex and age groups. Sexual selection for intelligence in harsh habitats is one of the favoured explanations for the rapid rise of our cognitive abilities but that is consistent with a children centric scenario. Women may have selected men more capable of acquiring food and with more tolerant temperaments , ones likely to stick around and help out with the kids, giving rise to the now familiar system of pair-bonding. Another consequence would be an increase in group size, these social changes setting up evolutionary pressures for more complex forms of communications and signalling. As tool use became an intergral part of human life, children too would have come under selective pressures for skills and abilities to use tools and communicate what they have learned. As we grapple with the problems of economic growth, "knowledge economy" has become something of a buzzword. But humans have always been experimenters and innovators and evolution of a distinct life-history characterized by a long period of learning most likely played a big role in fuelling selection for and reinforcing these cognitive traits. In this sense we have always been knowledge based societies with a high premium placed on innovation, communication and information sharing. Neoteny is again not unique to humans. Within primates, apes in general are the most neotenous. Within mammals, primates in general are the most neotenous, and mammals tend to be more neotenous among terrestrial animals. This is not a rejection of neoteny being a special feature in our evolution, merely an acknowledgment that evolution works by remolding, re sculpting, exaggerating and recombining pre-existing traits. Evolution is descent with modification and not descent with "poof, where did that come from?".
In trying to make a list of what make us unique, I felt too much attention of the panel was on the what is now unique/very very different and not on how we got there. I accept the panel's agenda might have been restricted to the here and now but maybe it does make sense to take a longer view. What I mean is that all humans share an evolutionary history and uniqueness lies in the particulars of the evolutionary pathway taken by the human species, a trajectory followed only once in the 4 billion years or so of life on earth. Whatever our differences, genetic and cultural, what we do share is a history, one that is not shared with any other species, and that it is this history that we can use to differenciate ourselves from other species. And that applies equally to all other creatures as well. And so just what could be the particular shared history, the longer view that I referred to? Competition and adaptation take place in an ecological context and I like Jonathan Kingdon's explanation of what makes humans so different. He calls us "niche thieves", who through superior use of technology have gradually expanded out of habitats that we were originally biologically adapted to. Throughout our evolutionary history human populations have progressively encroached upon the habitats of competing species, driving many including other hominid species to extinction. Our biological evolution since the advent of complex tool use more than 2 million years ago has been keeping pace with and sometimes falling behind new cultural practices and our tool driven expansion into evolutionarily unfamiliar habitats. I like this definition because it is a constant reminder that we are an invasive species, one that has appropriated resources with total impunity. But it is also a reminder that with command and control comes the responsibility of managing these resources in a sustainable way. Our abilities to displace other species and take over resources has deep evolutionary roots. But evolution has also given us the mental make up to override these impulses and fix past wrongs. Maybe that's what makes us unique.