Discover magazine has interviewed Smithsonian paleoanthropologist Rick Potts, featured in a special "evolution" issue "How We Won the Hominid Wars, and All the Others Died Out". Potts is well-known for his emphasis on past environments and climate variability in forcing human evolutionary adaptations. The interview goes over these topics and spends some time considering why humans are the "only survivor" of a past diversity of hominin species. A sample:
In one of your essays, you ask the question “Are we it?”—are we the final blossom of the human flower? What is your answer?
Actually, my answer to “Are we it?” is to turn the assumption on its head. Considering that we are the only survivor of a diverse family tree—that is, an evolutionary tree characterized by lots of extinction—the notion that our twig is the final blossom of evolution is incredibly outdated. It’s incorrect no matter how ingrained it is in our thinking. Our amazing adaptability has allowed us to shape the environment to our own needs. This transformation has taken place in a remarkable period of climate stability, over the past 8,000 years or so. One deeply ironic result is that we have now narrowed our own options at a time when climate fluctuation appears to be increasing. Of an estimated 15,000 species of mammals and birds, fewer than 14 account for 90 percent of what we eat. Of more than 10,000 edible plants, three crops—wheat, rice, and corn—provide half the world’s calories. And through greenhouse gases released by burning fossil fuels, we’re pulling on the strings of the earth’s unstable climate.
I had to face that issue of "only survivors" recently in a review. Clearly that means something very different now that we know people have a diversity of ancestors among Neandertals, Denisovans, and other archaic populations in Africa.