Human Adaptation Can Be Rapid

How long does it take for humans to adapt to environmental changes?  Some recent papers investigated this question.

1. Paleface:  If it is assumed that humans started out medium or dark-skinned, how long did it take for Europeans to lose much of that original pigment?  An article in Science April 20 says maybe just 6,000 to 12,000 years.  “This contradicts a long-standing hypothesis that modern humans in Europe grew paler about 40,000 years ago, as soon as they migrated into northern latitudes,” the article states, reporting on a March meeting of the American Association of Physical Anthropologists.  Pale skin is said to have an adaptive value at high latitudes: “Under darker skies, pale skin absorbs more sunlight than dark skin, allowing ultraviolet rays to produce more vitamin D for bone growth and calcium absorption.”  The new date was based on genetic studies that suggested a “selective sweep occurred 5300 to 6000 years ago” or up to 12,000 years ago, “given the imprecision of method”.
2. High life:  Ann Gibbons in Science reported on another discussion item from the American Association of Physical Anthropologists: how Tibetan children can tolerate the high altitude.  “Researchers seldom see Darwinian natural selection happening in living people,” she began.  “So physical anthropologist Cynthia Beall was delighted in 2004 when she discovered a trait that boosts the survival of some Tibetan children, apparently by raising the level of oxygen in their mothers’ tissues–a crucial advantage during pregnancy 4 kilometers above sea level.”  Updated research has revealed a genetic change that allows women to boost their blood volume and deliver more oxygen to the tissues.  Beall measured the selective pressure at 1:0.44, stronger than the fitness ratio measured for the sickle-cell gene.  They said, “the adaptation represents some of the strongest natural selection yet measured in humans.”
       Surprisingly, this appears to be a different adaptation mechanism than that found in populations living in the Andes.  There, mothers are able to boost the amount of hemoglobin.  These correlations are uncertain, however; “it’s quite possible that the Tibetans have evolved more than one way to boost blood oxygen,” Beall cautioned.  Mark Gladwin threw in a Darwinian proverb: “Study the pregnant women, because that’s where you’ll see evolution in action.”
3. Got milk?  Another strong selection effect in humans is for lactose tolerance.  Current Biology (April 17) had an article on this phenomenon, which “might have meant the difference between life and death” to early dairy farmers, Greg Gibson (North Carolina State U) said.  The admittedly imperfect ability to tolerate lactose represents another selective sweep some 5,000 to 10,000 years ago, about the time humans began to domesticate cattle.  He remarked, “It is hard to refute that this is a lovely example of the coevolution of genes and culture.”
       Nevertheless, Gibson spent most of the article debunking the “thrifty genes” hypothesis of evolutionary selection.  This is a 45-year-old idea that the “high incidence of diabetes in modern humans is a result of positive selection for alleles that confer the ability to rapidly sequester rare caches of carbohydrates as fat that would tide us over during famine.”  This adaptation now works against us in our urbanized society, it is claimed: it tends us toward obesity.  So why does Gibson think this is a poor hypothesis?  “Unfortunately, these three preconditions for natural selection are all too often mistaken by adaptationists as both necessary and sufficient for evolution to occur,” he cautioned.  But we need to be more quantitative if sufficiency is to be proven.”  At the end, he was even more emphatic: “Those inclined toward Darwinian medicine like to explain disease as the price we pay for the beneficial effects of alleles that have accompanied human adaptation.  These cases of not-so-thrifty genes suggest though that we should not be so quick to jump on the bandwagon: the coevolution of genes and culture is tremendously more complex.”

Funny he should mention Darwinian medicine.  A paper on that very subject appeared in Public Library of Science: Biology this month.  Catriona J. MacCallum tried again to make the case that medical doctors need to study evolution to understand disease (cf. 01/13/2003.  Distressed that medical schools are not considering evolution essential to the curriculum (see 06/25/2003), MacCallum wrote,

It is curious that Charles Darwin, perhaps medicine’s most famous dropout, provided the impetus for a subject that figures so rarely in medical education.  Indeed, even the iconic textbook example of evolution—antibiotic resistance—is rarely described as “evolution” in relevant papers published in medical journals.  Despite potentially valid reasons for this oversight (e.g., that authors of papers in medical journals would regard the term as too general), it propagates into the popular press when those papers are reported on, feeding the wider perception of evolution’s irrelevance in general, and to medicine in particular.  Yet an understanding of how natural selection shapes vulnerability to disease can provide fundamental insights into medicine and health and is no less relevant than an understanding of physiology or biochemistry.

MacCallum agreed that the “thrifty gene” concept has fallen into disfavor.  Some other evolutionary ideas are also simplistic: “The relationship between changing environment, diet, and susceptibility to disease, however, is also far from clear.”  Attempts to recreate a Stone-Age Diet “can be misleading,” she said.  Still, she promoted the idea that evolutionary concepts can help medical practice.  Granted, a mechanic may not need to understand the history of technology to fix a car, but an understanding of the evolutionary principles can help prepare for outbreaks of infectious disease, like bird flu, she argued.
    Why the resistance to evolutionary teaching in medical schools?  In some cases, it’s the students who rebel:

Although Paul O’Higgins thought a comparison of the brachial plexus to the pentadactyl limb was helpful, not all his students agreed—complaints were lodged that he was forcing evolution on them.  That lack of support was also reflected in the participation of only three medical students at the York meeting (albeit enthusiastic ones), despite being widely publicized.  It is not clear whether this is because medical students are more overburdened than most or because of a more deep-rooted resistance to the subject, reflecting wider political and religious prejudice against evolution.

So what’s the solution?  “But evolutionary medicine isn’t and shouldn’t be controversial, and the best way to challenge prejudice is through education.”  She took refuge in the famous Dobzhansky quote, “Nothing in biology makes sense except in the light of evolution.”  As an experiment, let’s consider the three cases listed above.  It isn’t very controversial that survivors of lactose, decreased sunlight and oxygen will predominate in those environments, but aren’t they all still human?  Is this really the kind of evolution that Darwin meant?
    MacCallum was undaunted by such questions.  “The time has clearly come for medicine to explicitly integrate evolutionary biology into its theoretical and practical underpinnings,” she ended with rhetorical flair.  “The medical students of Charles Darwin’s day did not have the advantage of such a powerful framework to inform their thinking; we shouldn’t deprive today’s budding medical talent of the potential insights to be gained at the intersection of these two great disciplines.”  Convincing the medical students of this may be the hard part.

You do NOT want an evolutionary biologist in the room when you need TLC at the hospital.  Lying in bed with pain and weakness, you are not going to look like a fit individual who deserves to survive.
    MacCallum again exhibited the shallowness and uselessness of evolutionary thinking.  Notice also the elitist snobbery: anyone who doesn’t agree with the Darwin Party Framework is prejudiced by definition, and must be sent to the re-education camp (cf. 12/21/2005).
    Despite the pleas to pul-lease teach Darwin in medical school, medicine is doing fine without the help of Dropout Darwin.  Medicine has a multi-thousand year history that was advanced largely by Christians.  The examples she cited, including the “iconic textbook example” of evolution – antibiotic resistance (dealt a blow by Jonathan Wells in his book Icons of Evolution; see also the Darwinist confession from 09/12/2004) – are all just microevolutionary changes.  The three examples reported above are all microevolutionary changes.  Natural selection at the micro level is not the issue.  Even young-earth creationists accept that.
    Such evidence has nothing to do with Darwin’s colossal simplistic generality, the Mystical Tree of Life (02/01/2007).  It has nothing to do with proving that humans have bacteria ancestors, and most medical students and professors know it.  You can almost hear the snickers of students in the classroom when the Prof tells his little fable about how the brachial plexus resembles the pentadactyl limb.  “Right, Teach.  Will that be on the test?  Can I take a pill and call you in the morning?”  Maybe the only way to get a higher turnout than three students at the next well-publicized “Medicine and Evolution” meeting is to award extra credit, provided the students are allowed to bring cots and pillows.
    Despite the Dobzhansky rallying cry, things make perfect sense without evolution.  In none of the three cases listed above is Darwin vindicated or needed.  All the humans in those societies are still one species with the rest of humanity, capable of intermarrying and raising children.  What’s more, the adaptive changes observed did not take hundreds of thousands of years.  To the consternation of earlier Darwinists whose ideas are now discredited, the changes fit easily within a Biblical framework of human history.  What is Darwin’s score?  Even MacCallum admits that previous evolutionary ideas like “thrifty genes” have been discarded.  Is anything left that is not controversial and subject to overthrow?  We don’t need Darwin.  We don’t want Darwin.  We want to make sense in the light of the evidence, and help the weak in the process.