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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Putting a Face on the Past
13 December 2004 (All day)
Natural selection is a force to be reckoned with in the biological world, but it may not explain the diversity of facial features found in our recent ancestors. A new analysis suggests that around the time our Homo ancestors took up tools, random genetic changes overtook adaptive evolution as the major influence on their facial features.
About 2.7 million years ago, two lineages arose from our bipedal ancestors: the robust australopiths, distinguished by their big heads and teeth, and the more petite-skulled Homo line. Although australopiths ultimately petered out, the Homo lineage diversified into several species, including eventually Homo sapiens. Scientists often invoke adaptations to a changing climate and environment to explain morphological changes such as bone size and shape in hominids. But some scientists argued that random processes such as "genetic drift" could play a role as well.
So Rebecca Ackermann of the University of Cape Town, South Africa, and James Cheverud of Washington University Medical School in St. Louis, Missouri, decided to take a new look at the forces shaping our old relatives. The scientists measured certain facial landmarks of seven fossil skulls of hominids and took similar measurements of adult humans, gorillas, and chimpanzees. Rather than assume that adaptation shaped morphology as previous studies had done, the researchers assessed the pattern of variation both within and between the groups.
Their analyses suggest that natural selection probably crafted australopith features such as big bones and a crested skull that may have anchored strong cheek muscles for chewing. But the scattershot pattern of variation among facial features within the genus Homo suggests that genetic drift played more of a role than natural selection, they report online this week in the Proceedings of the National Academy of Sciences.
Technological advances such as chopping and cooking may have lessened selection pressure on the face, says Cheverud. That makes sense to anthropological geneticist Charles Rosemann of Stanford University. At one time, he says, facial features such as the condition of the teeth would have played a large role in determining an individual's overall vigor. But that may have changed with the advent of tools--which happened roughly when the genus Homo arose. "If you are preprocessing food with stone tools, some features may become functionally unimportant," he says.