In the book The 10,000 Year Explosion: How Civilization Accelerated Human Evolution, authors Gregory Cochran and Henry Harpending use this insect and others endemic to the creosote bush to demonstrate that evolution can happen on scales that correspond to recorded history. About the time that humans began farming in the Middle East, members of a species of American walkingstick already present began to prowl the newly-invasive creosote bushes for prey. While people were learning to live with agriculture, and developing it over and over again around the world, these insects evolved better and better camouflage, and habits better suited to the way the plant's twigs move in the wind, so that they are now unable to live elsewhere.
The aim of these authors is not, however, to provide a catalog of rapidly-evolving insects, but to set a few of them, and other creatures including birds and mammals—all of which show evidence of rapid evolution—alongside humans, to indicate that we, also, can evolve on such time scales.
Accepted dogma among most scientists has been that humans stopped evolving when they developed civilization. Civilization is thought to protect humans from the selective pressures that drive evolutionary changes. People who once would have died from many causes now live because of better sanitation, medical care, and a richer food supply. For me at least, long ago, a moment's thought was sufficient for me to realize that this just changed the style of selective pressure we experience. I concluded that in the past several thousand years, humans have most likely been evolving in a direction more dependent on such systems of care than before. These authors reach the same conclusion.
When I was young, the early humans just prior to the modern era were called Cro-Magnon, and I got the impression that if you put one is a suit or dress, it would be hard to distinguish that person from anyone else. Cro-Magnon humans are now called "Early Modern Humans" (EMH's), which encompasses a wider array of fossils than those that were known in the late 1800's through the early 1900's, when the textbooks I read were published. I have since learned that the average EMH was stronger than 99.9% of us (even the women were stronger than most modern men!), with heavier bones, thicker skulls, and a brain about 10% larger than the modern average. They had slightly larger jaws, with teeth of very similar size to ours, so they would not have had problems with wisdom teeth, as so many of us have. (FYI: I had no trouble with wisdom teeth, but more than half of my classmates in high school had to have theirs removed).
We have been taught that it takes a few hundred thousand, or millions of years, for significant evolution to take place. But some scientists, including one of my favorite science authors, Stephen Jay Gould, promoted "punctuated evolution": as long as the environment is comparatively stable, the species that live within it don't change, but when environment changes, such as at the beginning or end of an ice age, species then evolve rapidly so that new species develop which are better adapted to the new situation. I read almost everything by Gould, and I don't recall that he put a time frame on "rapid". The authors of this book come closer to doing so, contending that measurable changes in various human groups have taken place in "a few" thousand years, probably less than 5,000.
What could drive evolution at a more rapid pace? How could new and favorable mutations be gathered at a rate that would allow a group of humans to adapt to something new and different, in just 50-100 generations, and perhaps much less in some cases? One key factor that these authors stress repeatedly is the great expansion of population that resulted from agriculture. A larger number of people means that the little, random mutations that happen in every one of us are equally larger in number. Apparently, this is not too hard.
Consider lactose tolerance. The default condition is that adults and adolescents don't drink milk, so they don't need to digest lactose. Thus the enzymes needed to do so aren't produced in most adults and teens. But the domestication of cattle by various groups of people made quantities of cow milk available, and other animals' milk, such as horse or goat, were also available among other groups. At least four times, in different places, a mutation or two occurred that allowed the continued production of enzymes that carry out digestion of lactose throughout life. All occurred within the past 10,000 years.
Think about it. A herder might gather some milk to nourish an orphaned calf or kid. He might taste it himself; it would be a little sweet and taste good. But he would usually suffer discomfort or indigestion soon after, and would not try that again. But maybe not. Initially, scattered families here or there would be able to digest milk. This added source of nutrition would result in larger families for such folks. Over time, such a favorable genetic trait would become widespread and could even dominate a population. However, populations that never developed ranching or herding have very few members who can digest lactose. All of my relatives are milk drinkers. My wife is Japanese, and she and her family also drink milk. Most Japanese don't, and they can't without discomfort. My wife's family must have ancestors that were herders. The primary milk used in Japanese households is soy milk, and most people of the generation that is now in their 60's and older know how to make it. Younger folks buy it at the store because they are too busy earning a salary to learn traditional skills.
Lactose tolerance is one of many examples of recent evolutionary changes in many human populations. And this matter brings up a wider view: If a large cohort of people look distinctive, there is a genetic reason for it. Although the human species is one species, and there are no "breeding barriers" between any human groups, the concept of "race" is really an oversimplification of a blatant reality. Any cohesive group ("Tribe" is a common term) that doesn't outbreed with other groups will become a distinctive group (better adapted to a different environment, perhaps), and it isn't hard for people in "Tribe A" to recognize people of "Tribe B" on sight alone, even if all cultural accouterments and accessories are removed.
The last chapter touches on a sensitive subject: can there be a "Tribe" of humans that are smarter than average? Consider the controversy that erupted over The Bell Curve, by Herrnstein and Murray. This is a very non-PC subject! But, face it, folks, facts are facts and truth is truth. There does happen to be a group of people whose average IQ is 12-15 points above the average for all people. Though they number only about 11 million worldwide, about 1/7th of a percent of the human race, their members have earned more than 20% of all Nobel Prizes. Of course, an average implies a range of values. There are dumber ones also, just not as many of them. The proportion of them that are smarter than average is larger than that proportion in humanity generally.
Who are these people? The Ashkenazi Jews, usually just called "European Jews". They comprise 3/4 of the total Jewish population of the world. Einstein was one. So was Stephen Jay Gould.
The authors present the case for a history that could have produced such a result. One key element is almost total in-group marriage; they strongly discourage marriage to non-Jews. They experienced nearly a thousand years of persecution in Europe. For much of that time they were forbidden from engaging in most trades. They were allowed to have certain "professional" occupations, and money-lending was but one. Those who were most adept at managerial and accounting skills prospered and had larger families. Both the Jews and their neighbors favored large families, but a more prosperous family will raise more children to adulthood than a poor one, even if the number born is the same. This factor alone could result in a "smartening" of the European Jews over those centuries.
There is another factor that the authors don't touch (maybe they avoided it purposely): the Holocaust under Nazism. Many, many Jews left Nazi-controlled, areas, or countries they were soon to control, before the end of the 1930's. I reckon they tended to be the smarter, better-educated ones. Of those left behind, half or more were murdered by the Nazis and left no descendants. This probably boosted the average IQ even more.
Whether or not such processes were the deciding factors, the fact remains that worldwide IQ testing has shown that average IQ and the spread of IQ scores are practically universal, with the glaring exception being the Ashkenazi Jews. (Just by the way, the letters n-a-z-i "Ashkenazi" are in no way related to "Nazi", which is an acronym formed from German words meaning National Socialism.)
For those who think there is no evolution anyway, don't sweat it. I'd be surprised if you read this far anyway. But for those who accept evolution as "the way biology works", this book helps us understand that humans haven't been somehow extracted from Nature, but still form a part of it. The environments that we have built for ourselves haven't made us "not natural", just natural in a different way. We continue to evolve, and it would be interesting to be able to look forward another 10,000 years, to see what directions have been taken by the various tribes of mankind.
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