Why humans have no fur

Washington, June 12 (ANI): Atmospheric heat might explain why humans lost their fur and developed an upright and slim posture.

A theory suggests that if our ancestors lived somewhere really hot, it would have made sense for us to lose body hair, start sweating more, become slender and even walk upright- to create distance between our bodies and the hot ground.

And a new study supports the theory that heat helped drive human evolution, by showing that a key cradle of human evolution in East Africa has indeed been really hot for at least 4 million years.

"That's something that's been hard to get at. It's nice to say that these things would be advantageous to living in hot, open environments. But was it actually hot and open?" Discovery News quoted Ben Passey, a geochemist at Johns Hopkins University in Baltimore, as saying.

Thus, researchers analysed dated soil samples from the Turkana Basin, a well-studied region in Kenya and Ethiopia that contains lots of fossils from our human and pre-human ancestors.

They particularly looked at weighted carbon and oxygen atoms, called isotopes.

As temperatures drop, a rare isotope of carbon called carbon-13 tends to clump together with a rare isotope of oxygen called oxygen-18 within soil.

Through a fairly simple relationship, the more clumping the scientists see between these isotopes, the colder they are able to say a sample is.

The results showed that dirt in the Turkana Basin has remained above about 85 degrees Fahrenheit with spikes above 95 degrees F over the past 4 million years.

Since soil absorbs heat from the air, it means that the region has been really hot for a really long time.

Currently, air temperatures in the Basin regularly exceed 100 degrees Fahrenheit, Passey said, with nighttime temperatures in the 70s.

Temperatures average in the mid-80s all year-round.

The landscape is sparse with grasses, shrubs and bushes.

"The heat is sort of unrelenting. You think, God, it could not have been as hot when humans were evolving here. It must have been much a nicer, lush place. Our results say no, it was still hot," said Passey.

He added that as the researchers could look only at soil temperature, it is possible that the air was even warmer millions of years ago than it is today, but with more vegetation and more shade that could have cooled the soil a little bit.

The study was published in the Proceedings of the National Academy of Sciences. (ANI)