Times of plenty mean more twins, say researchers

TWINS ARE nature's way of ensuring that human reproduction takes the greatest advantage of times of plenty, according to a study of the area with the highest frequency of twins in Europe.

People whose ancestors lived in regions with rich and stable supplies of food would have inherited a stronger predisposition to produce twins, the research suggests.

Scientists believe the research shows there is an evolutionary explanation for why some regions in the world have a significantly greater incidence of twins than others, a phenomenon that has until now evaded plausible explanation.

Although the chance of a mother producing twins has a genetic component - it tends to run in families - the scientists believe it is also influenced over many thousands of years by the environment in which the women and their ancestors have been brought up.

The study compared two areas of Finland, the archipelago of Aland in the south-west, where frequency of twins is higher than anywhere in Europe, and the adjacent mainland areas where twins are born at about the average rate.

The scientists believe their research, using birth records dating back to 1752, before Finland became industrialised, shows that the difference in twin frequencies between the archipelago and the mainland is not due to chance but to the forces of natural selection, which ensure the survival of the fittest.

An explanation for why twins should be more common on the archipelago, the researchers say, is that the amount of food available to the people living there has been traditionally relatively high and stable because crop failures are rare and fishing has always provided an alternative source of sustenance.

``In poor mainland areas, on the other hand, crop failures and subsequent famines have been common throughout the centuries,'' said Virpi Lummaa, of the University of Turku.

Steve Jones, professor of genetics at University College London, said the research presented an interesting hypothesis, but it is unlikely to be the whole explanation for twins. ``The genetic component for twinning is very small so it would need strong natural selection for it to be significant in human evolution,'' he said.