



DNA twist puts evolution on speed


Deborah Smith

SYDNEY scientists have added a new twist to the theory of evolution.

They have demonstrated for the first time that physical characteristics can be inherited and become more common in a population, without any underlying genetic mutation as the cause.

The research could help explain rapid changes in populations, such as the present obesity epidemic.

Jennifer Cropley, of the Victor Chang Cardiac Research Institute, said Darwin knew nothing about DNA, but it is now accepted that his idea of evolution through natural selection occurs when a random genetic mutation arises in an individual.

"If it is advantageous, it will be passed on through generations and eventually populations," she said.

This is a very slow process, however, taking tens of thousands of years for a new trait to become common.

Recently scientists have suggested another more rapid mechanism – epigenetics – might also play a role in evolution.

"But there has never been any evidence of it up until now," Dr Cropley said.

Epigenetics refers to chemical modifications to DNA that do not alter the actual DNA code, but which switch genes on or off.

A Sydney team, led by Cath Suter, studied mice that are genetically identical, but which look very different depending on their environment, due to an epigenetic change.

Those fed a special diet which switches off a gene are brown and lean, while the ones with the gene still active are obese and yellow.

The researchers found that when the diet was continued in lean mice over five generations, these epigenetic effects were inherited.

The proportion of lean, brown mice in each subsequent generation increased, despite no alteration of their genetic code.

Dr Suter said the effect was reversed when the diet was withdrawn.

"This kind of reversibility could be very advantageous if a change in environment was only temporary. Populations could revert to the way they were before fairly rapidly, if need be, because a genetic change hasn't occurred."

People do not have the same gene as the fat or lean mice.

But it is possible epigenetics could play a role in rapid changes in the human population, including the obesity epidemic, she said.

In this scenario, a mother's diet during pregnancy could influence the child's, and even the grandchild's propensity to developing metabolic syndrome, which increases the risk of cardiovascular disease and diabetes, irrespective of what the child or grandchild eats.

"But there is no hard evidence yet," Dr Suter said.

What would Darwin make of the proposed new mechanism for evolution?

"I think he would think it makes perfect sense," she said.

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