This case may explain some issues in our own evolution

Nov 16, 2006 11:06 GMT  ·  By

Scientists believe that early humans began walking on two legs more than three million years ago.

Now, an odd case found in a rural family from a remote zone in Kurdish southern Turkey could bring some evolutionary explanations about this.

Five adult siblings, three brothers and two sisters, out of 19 of a cousins couple, walk on all fours.

These brothers, with an age between 18 and 34, were born with a genetic mutation affecting brain's cerebellum.

The two sisters and one brother have walked only on all fours their entire lives, while two other brothers can walk in two legs for short distances.

Scientists investigating the case found it is not a hoax.

It is known the abnormalities suffered by some children are more likely caused by recessive traits displayed because of inbreeding, when the parents are cousins.

German geneticists at the Max Planck Institute showed that the siblings carry a mutation that eliminated the gene responsible for bipedalism in humans.

MRI (magnetic resonance imaging) technique revealed a form of cerebellar ataxia (reduction) associated with balance and muscle coordination.

On the other hand, the case is not just as simple as that: how these children were carried played its role.

In fact, children with no cerebellum at all can walk and ride a bicycle, as the brain's cortex can take over cerebellum's functions.

"Having a damaged cerebellum doesn't explain why these kids ended up walking on all fours." said British evolutionary psychologist Nicholas Humphrey.

"The mother says all of her children, when they were infants, ran around on all fours before they learnt to walk. Not just ordinary crawling, either-these kids ran around like monkeys on their feet and hands."

As the brain-damage would have provoked problems for standing up, "there's actually quite a good chance that they would make the best of a bad job and remain on all fours," Humphrey said.

In a Western family, "everything would be done to persuade and cajole the children to stand upright" he continued, but the handwalkers have never had the benefit of physical therapy.

In an isolated and very poor environment, the family didn't regard the handicap as something that needed to be corrected and accepted and tolerated it.

To see the case is not a bogus, "You only have to look at the calluses on the hands of the young man to see he's been on his hands for a very long time." said Humphrey.

"Here we've got a living example of how it might be for a member of our species to walk on four legs," he said.

Scientists have long assumed that the four-legged ancestors of humans walked like gorillas and chimpanzees but the Turkish siblings walk on their wrists, with their fingers kept out of the ground.

This posture saves the fingers from damage; so the sisters, for instance, can embroider or crochet.

Apes, however, use their whole hands and fingers for walking.

"Chimpanzees basically wreck their fingers by walking on them," Humphrey said.

"I think this new evidence, suggesting that [early-human ancestors] walked on their wrists, is much more plausible and interesting," Humphrey said.

Photo credit: Uner Tan.