Reverse evolution spawns ape-like people, researcher said
and World Science staff
An editor of a noted scientific journal said he has discovered a genetic defect that apparently sets back the clock on human evolution by more than a million years.
The disorder causes its human victims to walk on all fours, and to mouth an extremely primitive language, the scientist reported. The syndrome may literally undo eons of human evolution, he added, and thus reflect with some accuracy what our ape-like ancestors were like.
The researcher, Uner Tan of Cukurova University Medical School, Adana, Turkey, has posted an online videoclip of an affected woman walking on all fours.
The idea that evolution can run backward isn’t new; some scientists say there have been confirmed cases of it in animals. But it’s also a controversial subject, and considered hard to prove in any given case.
Tan, at any rate, is convinced that this could be a case of it. As such, he adds, the syndrome—known to run in a single family—could offer scientists an unprecedented glimpse into the makings of early man.
“This new syndrome may be used as a live model for human evolution,” wrote Tan in a research paper describing the condition. The paper appears the March issue of the International Journal of Neuroscience, where Tan sits on the editorial board. He also named the disorder after himself: Unertan syndrome.
The syndrome can be considered a “devolution” of the human, he wrote in another recent paper, in the journal Neuroquantology. It throws light, he added, onto the “transition from quadrupedality to bipedality”—the shift from four-legged to two-legged walking. Possibly more important, it may illuminate the evolution of the human mind, he added.
“The children exhibiting this syndrome originated from a family having 19 children,” he continued in the paper. Five of these, aged 14 to 32 years, “walked on two palms and two feet, with extended legs… They could stand up, but only for a short time, with flexed knees and heads.”
“The patients had a rather primitive language, i.e., they spoke to each other using their
own language, using only a few hundred words, which could be partly understand by mother
and father,” Tan wrote.
“They were mentally retarded; they could not count from one to ten. They were
not aware of time and space. For instance, they did not know where they live (which country,
which village, which city). They were unaware of year, season, day, and time. Otherwise, they
had quite strong legs and arms.”
“The sitting posture was rather similar to an ape,” Tan added. “They could not hold their
heads upright; the heads were flexed forward with their skulls. They could not raise their
heads to look forward. This head posture with flexed skull was rather similar to the head
posture of our closest relatives, like chimpanzees.”
Like most primates, Tan observed, victims of the disorder walk with a characteristic sequence of limb movements: after a foot touches the ground, the hand on the other side does. “They could walk fairly fast using their strong legs, without any imbalances.”
Tan’s report is reminiscent of a 2002 discovery that a mutation in one gene, called FoxP2, created severe speech and grammar difficulties. That finding has sparked intense research into what researchers think could be the first known “language gene.” FoxP2-mutated patients also have some coordination difficulties, prompting much discussion among scientists of possible links between language and coordination.
Those patients aren’t reported to have problems standing up, though.
Scientists generally consider the transition to upright walking as the most important event in human evolution, according to Tan. This freed the hands for skilled movements such as throwing and toolmaking, he added, and may have even made the experience of consciousness possible—though a growing number of scientists argue that consciousness may not be unique to humans.
Upright posture evolved by the age of Homo erectus, an extinct human ancestor believed to have evolved in Africa 1.6 million years ago. A later momentous event was the evolution of language, about 40,000 years ago, Tan noted, although Homo erectus likely possessed a primitive language.
Some biologists believe evolution takes place in sudden leaps rather than gradual, constant changes, a theory known as punctuated evolution. Unertan syndrome suggests this theory is correct, Tan argued, because it shows complex traits can be both lost and gained suddenly, probably because they involve just one gene or a group of related genes.
But the notion that reverse evolution can take place is controversial.
Evolution takes place when organisms with the worst genes for a given environment die out, leaving their fitter peers to survive and spread their better genes. This process, called natural selection, leads the species’ gene pool to slowly change, gradually producing major changes in the organisms themselves.
Reverse evolution would happen when organisms suddenly lose genes that their population gained earlier in evolution. Alternatively, it could occur when they regain an ability they had lost earlier, possibly because some genes that had fallen into disuse, but weren’t completely lost, became active again.
It has been shown to happen in some cases, wrote Megan Porter and Keith Crandall of Brigham Young University in Provo, Utah, in the Oct. 2003 issue of the research journal Trends in Ecology and Evolution.
For instance, fish that take up living in dark caves can mostly lose their eyes, since they don’t need them; but they can re-evolve them upon resuming life at the surface.
But it’s hard to prove reverse evolution in any given case, they noted. That’s because what seems to be a reversion to old traits, could simply be the evolution of new traits that look like the old. However, detailed studies can sometimes make a good case for reverse evolution, for instance, by showing that muscle and nerve patterns in both the old and the new structure correspond precisely.
Sometimes, reverse evolution may require a little human help.
In a new study published in the Feb. 21 issue of the journal Current Biology, researchers reported producing chickens with teeth. Birds don’t normally have teeth, but their dinosaur ancestors more than 70 million years ago did. Matthew P. Harris of the University of Wisconsin in Madison and colleagues said they made the toothy chickens by providing carefully chosen molecular signals to the beak region of developing embryos.
This suggests chickens still retain some ability to form teeth, they wrote, noting that the teeth in this case somewhat resembled those of modern birds’ closest living ancestor—alligators.
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