Posted by: drew | March 7, 2006

Evidence of Backward Evolution?

This story really grabbed my attention today: The UPI News wire ran this story today about a family of quadrupedals who walk on all fours.

Walking patterns of victims of Uner Tan syndrome.LONDON, March 7 (UPI) — Five members of a Kurdish family in Turkey, who can only walk naturally on all fours, are being hailed as a unique insight into human evolution.

Scientists told the Times of London the family might provide invaluable information on how humans evolved from four-legged hominids, developing the ability to walk on two feet more than 3 million years ago.

Two daughters and a son have only walked using two palms and two feet, with their extended legs, while another daughter and son occasionally manage a form of two-footed walking, the Times reported, noting all five can stand upright, but only for a short time.

Last year’s discovery of the family in rural southern Turkey has produced a scientific debate: Some researchers believe genetic faults caused the siblings to regress in a form of “backward evolution,” while other scientists claim genes triggered brain damage.

Interesting theory, but is it provable? Some scientists say no, some say yes.

The “no crowd”:

Several researchers disputed the idea that the syndrome might represent reversion or backward evolution. The claim is “untestable,” wrote Henrique Teotónio, an evolutionary geneticist at the Gulbenkian Science Institute in Oneiras, Portugal, in an email.

It’s “impossible to judge it,” because scientists don’t know which genes underlay human evolution, added Teotónio, who has studied reverse evolution in flies.

He and others also said a key implication of Tan’s theory is doubtful: that just one or a few genes could produce a complex trait such as upright walking—although new studies have surprised scientists with how much one gene can do, such as orchestrating elaborate courtship rituals in flies.

Tan conceded his theory is debatable.

The “yes crowd”:

Keith Crandall of Brigham Young University in Provo, Utah, said the idea is nothing extraordinary, calling it a “nice and testable hypothesis.”
….
Scientific doubts on reverse evolution, Crandall wrote, have nothing to do with a popular misconception that evolution “has no direction.” It does to some extent, he argued—species tend to become better suited to their environment—and that may be irrelevant anyway, since a return to ancestral genes can occur whether or not one thinks of evolution as directed.

“I don’t know of any evolutionary biologists who would subscribe to the notion that reverse evolution is impossible,” Crandall wrote. “It doesn’t take long in evolutionary biology to figure out that nothing is impossible!” An affected patient tries to stand.

There’s a short clip of a woman walking on all fours here. It isn’t particularly interesting as it just looks like a person walking on all fours. It is interesting when you consider that this person has always done so and can only stand upright for very short periods.

Also of interest to me is that these folks are apparently retarded, cannot count to 10, and speak only a few hundred words or so. Very strange in the context of a “backward evolution” idea. This article discusses it:


“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 syndrome walk with a characteristic sequence of 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.”

Also, from this article:

“The local villagers laugh at and tease” the victims, they added. “Because of this, the females tend to stay close to the house, but the male sometimes wanders for several kilometres. He helps raise money for his family by collecting cans and bottles, which he carries home in a pouch made from his shirt, held by his teeth. He is remarkably agile.”

The British group portrayed the victims’ language abilities more generously than did Tan, who wrote that they speak a “primitive” language of a few hundred words.

“They can all speak and understand Kurdish well enough to communicate within their own family, and three of them also speak some Turkish,” Humphrey’s group wrote. “But their articulation is poor, and it seems they have a restricted vocabulary” and problems with word arrangement. However, “They interacted with us as visitors in a friendly and courteous way.”

Although they can walk on two legs briefly, the team noted, they prefer to go on all fours.

Based on brain scans, the scientists ascribed the condition to a type of disorder called an ataxia, tied to underdevelopment of the cerebellum, a brain structure. Yet this can’t be the whole explanation, they added; it could be “a combination of unusual factors—genetic, physiological, psychological and social.”

The topic of evolution and genetic mutation is always interesting to me. I’m no geneticist or biologist, so I shouldn’t speak to whether this could in fact represent “reverse evolution”. I will say that their movement and mental capacity don’t seem too far from what you might expect from an early human.

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