London, Nov 28 : A new hypothesis has suggested that the Neanderthals may have gone extinct because their cells couldn't cope with climate change.
The extinction of Neanderthals, close relatives of modern humans, some 25,000 years ago, remains unexplained.
One theory holds that they were physically outcompeted by modern humans , another that they were economically eclipsed by us. Yet another theory suggests that Neanderthals couldn't adapt to climate change.
According to a report in New Scientist, Patrick Chinnery, a molecular biologist at Newcastle University, UK, and colleague Gavin Hudson identified potentially harmful mutations in the newly sequenced Neanderthal mitochondrial genome, which supports the climate-change idea, with a twist.
In particular, the researchers found genes that are associated with neurodegenerative diseases and deafness.
"If they were found in modern humans they would be bad news," Chinnery said.
Chinnery and Hudson suggest that mutations in mitochondria helped Neanderthals cope with the cold weather, but that when the climate started fluctuating between warm and cold periods, they were at a disadvantage.
In all cells, from yeast to human, a mitochondrion's main job is to produce the energy that powers cells. This takes the form of a chemical called ATP.
In the case of modern humans, the mitochondria do this quite efficiently under ideal conditions, making 36 ATP molecules with the energy stored in a single molecule of glucose sugar.
Mutations that sap this efficiency would generate heat instead, which is a potentially useful trick for Neanderthals who are known to have had adaptations to cold weather, according to Chinnery.
However, a warmer and less climatically stable habitat could have spelled trouble for Neanderthals with such mutations.
Perhaps the Neanderthals' mitochondrial DNA adapted them to the cold, and they couldn't cope when the climate started to change, hypothesized Chinnery.
However, with only a single Neanderthal DNA sequence decoded so far, that hypothesis remains provisional.
"This 'n of 1' experiment raises a question which needs to be tested on a large number of cases," said Chinnery.
They might not have to wait long.
According to Edward Green, a researcher at Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, "We hope to be able to provide (Neanderthal) subjects for doing that kind of analysis really soon."