'Junk' DNA linked to evolution of human hands and feet

Human hands and feet may owe their existence to so-called "junk" DNA that was once assumed to have no purpose, a study has shown.

Scientists believe mutations in the DNA might have "humanised" the limbs of our ape ancestors.

As a result, humans developed hands that could manipulate tools and weapons and feet that allowed them to stand upright.

"Our study identifies a potential genetic contributor to fundamental morphological differences between humans and apes," said study leader Dr James Noonan, from Yale University School of Medicine in New Haven, Connecticut, US.

In the past decade scientists have discovered that non-coding DNA sequences previously dismissed as "junk" can regulate gene activity.

Unlike genes, they do not provide instructions for building proteins. But some of these non-coding stretches of DNA determine whether particular genes are switched on or off.

Their biological importance is highlighted by the fact that many have been "conserved" in species as distantly related as chickens and humans.

The new study involved searching vast non-coding regions of the human genome to identify regulatory sequences whose function may have changed since humans evolved from apes.

One sequence, given the name HACNS1, was found to have evolved rapidly in humans compared with chimpanzees and macaque monkeys.

By creating mouse embryos with the HACNS1 sequence, the scientists were able to observe how it affected limb development.

The biggest impact was at the base of the primordial thumb in the fore limb, and the great toe in the hind limb.

The results, published yesterday in the journal Science, provide tantalising evidence that functional changes in HACNS1 may have contributed to adaptations in the human ankle, foot, thumb and wrist.

However, it is still unclear which gene or genes have their activity affected by the sequence.