The Fish Within Us

What is most surprising is not that we once lived in the sea, but that we are still evolving. "Turning a fish into a human is like turning a Beetle into a hot rod," Shubin says. "As a species, we are actually kind of jury-rigged." In his new book, "Your Inner Fish," Shubin explains how a range of medical conditions, from hiccups to heart disease, are the byproducts of our clunky evolution. "The extraordinary disconnect between our past and our human present means that our bodies fall apart in certain predictable ways," he says. "Our circulatory systems are a good example. They were designed for activity, but we now have the lifestyles of spuds."

The good news is that natural selection may yet correct some of those inefficiencies. A study published in the December Proceedings of the National Academies of Sciences found that not only are humans still evolving, but we are doing so at a faster rate than ever before, with genes that affect our diets and brains leading the race. "If humans had always evolved this rapidly, the difference between us and chimps would be 160 times greater than it actually is," says the study's lead author.

The findings have turned some traditional assumptions on their heads. For decades, biologists believed that human evolution had ground to a halt about 10,000 years ago, when the dawn of agriculture and technology gave us unprecedented control over our environments and made us masters of our own destiny. But rather than slow evolution down, those advances, Harpending says, enabled humanity to hit the accelerator. With better technology, our ranks have swelled from millions to billions. This has driven us to colonize more and different regions of the globe.