Yes, we are still evolving

kw: book reviews, nonfiction, anthropology, paleoanthropology, evolution, human evolution

The history of life is incredibly more complex than we ever thought. Just the history of this little cluster of twigs on the tree of life that we can call "humans, hominins, and their close kin" is incredibly complex. I truly enjoy reading essays by someone who knows these things deeply and tells us our stories with grace and wit. Close Encounters With Humankind: A Paleoanthropologist Investigates Our Evolving Species, by Sang-Hee Lee with Shin-Young Yoon, is just such a book. Dr. Lee is an anthropologist and department dean at U.C. Riverside. Mr. Yoon worked with her to prepare essays for the popular press in Korea and the U.S., and for this book.

One root question people have is this, "Are Neanderthals our ancestors, our cousins, or something else?" Simply put, they were "kissing cousins" when the species we call "modern humans" was being formed. Neanderthals are one of at least two ancestral species, and we are hybrids!

The book doesn't start there. The first chapter is titled, "Are We Cannibals?" I would put it this way: We cannot include human meat as a major part of our diet because that's too much like a perpetual motion machine. However, some human cultures have included small amounts of carnivory for primarily ritual purposes. Read the chapter for the gory details.

Dr. Lee doesn't sidestep controversies. Chapter 3 asks, "Who Were the first Human Ancestors?" We could thus ask which species represents the first Hominin. A Hominin (note the final "n") is a member of a species characterized by upright walking, a larger brain than a Hominid (note the "d") of similar size, and sophisticated tool use; probably also complex language. The Hominids are the great apes—Gorillas, Orangutans, Chimpanzees, Bonobos, Gibbons, and Humans—and all their ancestors back to the first great ape that split from the lesser apes and monkeys. The recognized Hominin genera are Homo, Australopithecus, Ardipithecus, and Paranthropus. Species in the genus Homo are H. sapiens (ourselves), H. neanderthalensis, H. habilis ("handy man"), possibly H. rudolfensis, and H. erectus. Homo erectus, "upright man" is probably the first, but various scientists argue for other possibilities, and the chief ones are discussed in this chapter.

Along the way to tracking down our Neanderthal (and other) roots, matters are discussed such as the incredibly painful birth experience, because of a combination of large brains in newborns and narrow hips due to upright walking (waddling is wasteful of energy); when different skin colors arose (I was surprised to find it was primarily 5,000 years ago); the biggest of the apes, the half-ton Gigantopithecus; and why we still have sore backs.

Once we get to the time period from 100,000 to 40,000 years ago, we find that our twig of the tree of life is actually braided, or networked. Perhaps half a million years ago some people left Africa for Europe and Asia. At present it seems two groups followed similar but distinct evolutionary tracks to become the Neanderthals in the west and Denisovans in the east. Later, some time before 70,000 years ago, another group left Africa. They are called by various names; the most neutral is "early modern humans" or EMH. They are considered early members of H. sapiens, and they must have had better teamwork and better tools, and perhaps a different breeding schedule with close spacing of offspring, because they multiplied until they outnumbered their cousins who already lived there.

Now that a genetic sequence has been produced for both Neanderthals and Denisovans, it is clear that they interbred with the EMH people. Whether the N's and the D's were wiped out or subsumed into the larger group is not known. What is known is that European DNA includes about 4% Neanderthal DNA and a lesser amount of Denisovan DNA, while for Asians it is the reverse, and Australians may have 6% Denisovan DNA.

At this point I wonder, was there perhaps yet another species out there, not yet discovered, that contributed to the modern gene pool? And I find another matter even more interesting: All three of these types of humans were more robust, and had a little larger brains (5%-8%) than modern humans. We don't know enough about the Denisovans to be sure how strong they were. An average Neanderthal was twice as strong as an EMH, and the average EMH was at least twice as strong as modern humans.

Not all of that is because so many of us have sedentary lifestyles (Most people living outside the West have more active lives). I live near a large population of Amish. They work hard and are all very strong. A typical EMH would be even stronger. They were genetically prepared to become stronger.

The last chapter asks, "Are Humans Still Evolving?". The answer is, "Of course!" Just because we invented culture and science and technology with all their conveniences, doesn't mean there are still no selective pressures for natural selection to work on. Remember, 2/3 of the world has only a fraction of the conveniences and medical infrastructure that an American or European would consider normal. I certainly hope that we are evolving toward having less lower back pain! But considering that it has been with us for about two million years, I suppose it will be a good while yet. I point out wisdom teeth, and our shrinking jawbones, as evidence of continuing evolution. Dr. Lee thinks we have removed that matter from selective pressure because of low-cost dental surgery. However, there are still large numbers (the 2/3 mentioned above) who have little or no dental care, but whose jaws are also shrinking as food sources change. In whatever measure infected impacted wisdom teeth reduce reproductive potential, there will be benefit to having a mutation that reduces or eliminates them.

There is reason to believe that the great increase in human population that followed the agricultural revolution about 10,000 years ago has led to an increased rate of evolution among us. This is just touched on in this book, but we are referred to another, The 10,000 Year Explosion, by Gregory Cochran and Henry Harpending. I got a copy right away. Stay tuned!

This review just skates on the surface of Dr. Lee's offerings. What a joy to read!