Thanks to genetic differences, an average Neanderthalwoman could have whupped Arnold Schwarzenegger athis muscular peak in an arm-wrestling match.
Modern Homo sapiensis still evolving. Despite the long-held view that natural selectionhas ceased to affect humans because almost everybody now lives longenough to have children, a new study of a contemporary Massachusettspopulation offers evidence of evolution still in action.
A team of scientists led by Yale Universityevolutionary biologist Stephen Stearns suggests that if the naturalselection of fitter traits is no longer driven by survival, perhaps itowes to differences in women’s fertility. “Variations in reproductive successstill exist among humans, and therefore some traits related tofertility continue to be shaped by natural selection,” Stearns says.That is, women who have more children are more likely to pass oncertain traits to their progeny.
Stearns’ team examined the vital statistics of 2,238 postmenopausal women participating in the Framingham Heart Study, which has tracked the medical historiesof some 14,000 residents of Framingham, Mass., since 1948.Investigators searched for correlations between women’s physicalcharacteristics – including height, weight, blood pressure and cholesterol levels- and the number of offspring they produced. According to theirfindings, it was stout, slightly plump (but not obese) women who tendedto have more children – “Women with very low body fat don’t ovulate,”Stearns explains – as did women with lower blood pressureand cholesterol levels. Using a sophisticated statistical analysis thatcontrolled for any social or cultural factors that could impactchildbearing, researchers determined that these characteristics werepassed on genetically from mothers to daughters and granddaughters.
If these trends were to continue with no cultural changes in the town for the next 10 generations, by 2409 the average Framinghamwoman would be 2 cm (0.8 in) shorter, 1 kg (2.2 lb.) heavier, have ahealthier heart, have her first child five months earlier and entermenopause 10 months later than a woman today, the study found. “Thatrate of evolution is slow but pretty similar to what we see in otherplants and animals. Humans don’t seem to be any exception,” Stearnssays.
Douglas Ewbank, a demographer at the University of Pennsylvania who undertook the statistical analysis for the study, which was published Oct. 21 in the Proceedings of the National Academy of Sciences (PNAS),says that because cultural factors tend to have a much more prominentimpact than natural selection in the shaping of future generations,people tend to write off the effect of evolution. “Those changes wepredict for 2409 could be wiped out by something as simple as a newschool-lunch program. But whatever happens, it’s likely that in 2409,Framingham women will be 2 cm shorter and 1 kg heavier than they wouldhave been without natural selection. Evolution is a very slow process.We don’t see it if we look at our grandparents, but it’s there.”
Other recent genetic research has backed up that notion. One study, published in PNAS in 2007 and led by John Hawks, an anthropologist at the University of Wisconsin at Madison,found that some 1,800 human gene variations had become widespread inrecent generations because of their modern-day evolutionary benefits.Among those genetic changes, discovered by examining more than 3million DNA variants in 269 individuals: mutations that allow people todigest milk or resist malaria and others that govern brain development.
But not all evolutionary changes make inherent sense. Since the Industrial Revolution,modern humans have grown taller and stronger, so it’s easy to assumethat evolution is making humans fitter. But according to anthropologistPeter McAllister, author of Manthropology: the Science of Inadequate Modern Man, the contemporary male has evolved, at least physically, into “the sorriest cohort of masculine Homo sapiens to ever walk the planet.” Thanks to genetic differences, an average Neanderthalwoman, McAllister notes, could have whupped Arnold Schwarzenegger athis muscular peak in an arm-wrestling match. And prehistoric AustralianAborigines, who typically built up great strength in their joints andmuscles through childhood and adolescence, could have easily beat UsainBolt in a 100-m dash.
Steve Jones, an evolutionary biologist at University College London who has previously held that human evolutionwas nearing its end, says the Framingham study is indeed an importantexample of how natural selection still operates through inheriteddifferences in reproductive ability. But Jones argues that variation infemale fertility – as measured in the Framingham study – is a much lessimportant factor in human evolution than differences in male fertility.Sperm hold a much higher chance of carrying an error or mutation thanan egg, especially among older men. “While it used to be that men hadmany children in older age to many different women, now men tend tohave only a few children at a younger age with one wife. The drop inthe number of older fathers has had a major effect on the rate ofmutation and has at least reduced the amount of new diversity – the rawmaterial of evolution. Darwin’s machine has not stopped, but it surelyhas slowed greatly,” Jones says.
Despiteevidence that human evolution still functions, biologists concede thatit’s anyone’s guess where it will take us from here. Artificial selection in the form of genetic medicine could push natural selection into obsolescence, but a lethal pandemicor other cataclysm could suddenly make natural selection central to thefuture of the species. Whatever happens, Jones says, it is worthremembering that Darwin’s beautiful theory has suffered a long historyof abuse. The bastard science of eugenics(1), he says, will haunt humanityas long as people are tempted to confuse evolution with improvement.”Uniquely in the living world, what makes humans what we are is in ourminds, in our society, and not in our evolution,” he says.
(1) Eugenics was practiced around the world and was promoted bygovernments, and influential individuals and institutions. Itsadvocates regarded it as a social philosophy for the improvement of humanhereditarytraits through the promotion of higher reproduction of certain peopleand traits, and the reduction of reproduction of certain people andtraits.
However, developments in genetic, genomic, and reproductivetechnologies at the end of the 20th century have raised many newquestions and concerns about what exactly constitutes the meaning of eugenics and what its ethical and moral status is in the modern era.