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Evolution Continues

Bob Park begins his Friday the 13th "What's New" report with the following:

DARWIN: HOMO SAPIENS EVOLVED IN A SAVAGE WORLD. The oldest remains of Homo sapiens have been dated at about 160,000 years.  Hunter gatherers, they could talk, but we have no way of knowing what they said. It would be 150,000 years before the invention of writing. We have changed little from the earliest Homo sapiens and almost not at all since the birth of civilization; instead, we changed the world. That may explain why barely half the population believes we evolved over time as opposed to being created in our present form. 

One problem I see with claiming that homo sapiens have changed little in 160,000 years is that we really know only a little about our human predecessors who lived 160,000 years ago. We make a lot of assumptions about them, however. We assume that they lived similarly to hunter gatherers who lived about 150,000 years later in places like Africa, Australia, Brazil, and Papua New Guinea.

The idea that homo sapiens has hardly changed at all in the last 10,000 years is one that does not seem defensible any longer. Steven Pinker, for example, has written: "I've had to question the overall assumption that human evolution pretty much stopped by the time of the agricultural revolution."

New results from the labs of Jonathan Pritchard, Robert Moyzis, Pardis Sabeti, and others have suggested that thousands of genes, perhaps as much as ten percent of the human genome, have been under strong recent selection, and the selection may even have accelerated during the past several thousand years. The numbers are comparable to those for maize, which has been artificially selected beyond recognition during the past few millennia....

Humans might have evolutionary adaptations not just to the conditions that prevailed for hundreds of thousands of years, but also to some of the conditions that have prevailed only for millennia or even centuries.

Pinker assumes that length of time will trump the qualitative effectiveness of any recent environmental impact on human evolution, so there will probably be little need for evolutionary psychologists to revamp much of their current account of what drives human behavior. He also thinks that "human races and ethnic groups are psychologically highly similar, if not identical." Thus, evolutionary psychology is not likely to be greatly affected by discoveries of recent post-agricultural human evolution.

What kinds of traits are emerging from recent human evolution? John Hawks writes that "many of the selected genes are involved with pathogen defense....Some are apparently related to metabolism or even directly to diet, in terms of processing new food sources. Of course, lactase is an excellent example in this category." Researchers have found more than a dozen new genetic variants involved in fighting malaria that are spreading rapidly in Africa, Thailand, and New Guinea. 

One of the more curious evolutionary changes with our species happened between 6,000 and 10,000 years ago: "the first blue-eyed baby was born somewhere near the Black Sea."* Until then, everyone's eyes were brown. Imagine the reaction of the parents. Today, there are about half a billion people with blue eyes (about 13.5% of the world's population). It seems that that little modification gave some people a slight edge in the sexual selection game. (Don't ask me how they figured it out, but experts calculate that the blue-eyed descendents gained a 5% advantage over their brown-eyed competitors.*)

Milford Wolpoff, a paleoanthropologist at the University of Michigan says that the pace of evolution has been speeding up since our ancestors fanned out from Ethiopia to populate the globe more than 40,000 years ago. The pace has accelerated even more since the development of agriculture, primarily because of the growth of large societies that agriculture made possible. "When there's more people, there are more mutations," Wolpoff said. "And when there are more mutations, there's more selection."*

As John Hawks puts it: "It is quite simple; the rate of mutations in a population is a linear product of the rate per genome and the population size....Humans faced new selective pressures during the last 40,000 years, related to disease, agricultural diets, sedentism, city life, greater lifespan, and many other ecological changes. This created a need for selection."

So, is homo sapiens evolving? Yes, it seems so and thanks to the great size and rapid growth of our species, we are likely to continue to evolve. Are we changing the world? No doubt about it. What does this have to do with nearly half of all Americans not accepting evolution?

I have no idea, though Bob Park seems to think the two are connected. Maybe somebody can enlighten me.

Probably more interesting than Park's claim about our species not changing much in the past 10,000 years, is the claim by science writer Sharon Begley that there has been a development in evolutionary biology that "gives strict Darwinians heart palpitations, for it reeks of the discredited theory of Jean-Baptiste Lamarck." Lamarck is the one who is usually caricatured as "the guy who said giraffes have long necks because their parents lengthened their necks by stretching them to reach for higher vegetation." Begley's example is of a water flea:

Some water fleas sport a spiny helmet that deters predators; others, with identical DNA sequences, have bare heads. What differs between the two is not their genes but their mothers' experiences.

....something a parent experiences alters the DNA he or she passes on to children....

She thinks this is shocking and contrary to "Darwinian evolution" and supportive of "the new Lamarkism." PZ Myers has characterized Begley's assertions as "one big collection of misconceptions." The water flea's experiences do not alter its DNA (not that DNA in offspring can't be altered by radiation or chemicals affecting sperm or egg, for example). The mother flea's experience affects the expression of genes. PZ writes:

Stressed and unstressed [water flea] mothers switch on different genes in their offspring epigenetically, which lead to the expression of different morphology. It's very cool stuff, but evolutionary biologists are about as shocked by this as they are by the idea that malnourished mothers have underweight babies....

The population of water fleas have a genetic attribute that allows the formation of spines under one set of conditions, and suppresses them under others. This gene regulatory network did not pop into existence in a single generation! If it did, then Begley would have a big story, evolution would have experienced a serious blow, and we'd all be looking a little more carefully into this 'intelligent design' stuff.

Of course, Darwin had nothing to say about genetics, since that science was not developed until long after he was dead. It is unlikely. therefore, that he would be turning over in his grave on learning of the water flea's evolutionary development.

Begley's kind of writing about evolution, as PZ indicates, may well be one factor that fuels the active disbelief in what some have called "the greatest single idea ever," natural selection.

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