What is human uniqueness, and how did it contribute to what we could now call behavioral modernity? How did it develop? And what implications does it have for understanding our present and future? This past February the Origins Project that I direct at Arizona State University helped to convene an interesting meeting of paleontologists, anthropologists, primatologists, evolutionary biologists, geneticists, archaeologists and psychologists to attempt to address such questions, among others.

I began the meeting by pointing out that when some people heard about its subject, they had asked me what was so unique about humans? Surely all animals are unique in their own way, and although we have special traits, so do bees and giraffes. But as my A.S.U. colleague Kim Hill has put it, Even before the invention of agriculture, human communities may have eventually numbered around 70 million individuals... as Homo sapiens spread over the planet more broadly than any other large vertebrate. No creature on earth lives in cohesive social units that rival this complexity or biomass.

And spread over the planet we have. Several months ago in this column I commented on our species's capacity to breach, and sometimes tear down, the barriers that nature imposed on our evolution. More recently, a report by Kevin N. Laland of the University of St. Andrews in Scotland and his colleagues in Nature Reviews Genetics, building on an earlier proposal by Robert Boyd of the University of California, Los Angeles, and Peter J. Richerson of U.C. Davis, argued that human culture, defined as any learned behavior, including technology, has been the dominant natural selection force on modern humans.

Which brings me to the present. The vigorous, vehement and vexed reactions to any piece I have written that mentions climate change, combined with the power of greed on the one hand and the struggle for subsistence on the other, have convinced me there is no chance that governments will significantly reduce the output of industrial greenhouse gases in time to stave off considerable change to the planet's climate and to human habitats.

So it is perhaps time to think more about how we will respond to the range of possible environmental changes. Such planning should include the good, the bad and the ugly.

The good? Some regions of the planet that are not now conducive to agriculture surely one day will be. The bad? The possibilities here, it seems, vastly outweigh the good, with the worst case probably involving the displacement of several billion people from the poorest coastal regions of the world, with concomitant social, economic and political upheaval, possible starvation from regional losses in agriculture, and rises in international tensions, terrorism and political instability. The ugly will include the need, for example, to brace for the ever more jarring effects of extreme weather patterns, the extinction of a huge range of animal and plant species, and the invasion into new latitudes of predators and pests.

I don't think such effects will mean the end of humanity or even the end of civilization. I just see a changed world (although I would be very surprised if it were a better world) to which we will have to adapt. It will produce the ultimate example of gene-culture co-evolution: our technology will change the world, and it will dramatically affect natural selection, not just for a whole range of species but for humans as well. And it will reflect human uniqueness in the sense I described earlier: our evolutionary success may compete with that of microbes in our impact on the earth's environment.

Once again I am reminded of discussions during our Origins meeting in which Curtis W. Marean of A.S.U. described the evolution of hominids who lived near the southern tip of Africa for almost 100,000 years, during which dramatic sea-level rises and falls caused migrations, changes in hunting and dietary patterns, and developments of new technology. Those individuals, who may have been the ancestors of all of us, survived. I expect we will, too. What is new is that the environmental selection for hominids of the future will be induced by human culture and technology of today in ways we might have been able to alter rationally had we been rational enough.