WOMEN living in an isolated community in southwest Finland may have evolved a
tendency to bear twins, say researchers.
Using data from old church records, Virpi Lummaa and her colleagues from the
University of Turku found that 21.3 per cent of pregnant women on the Ã…land and
Ã…boland archipelago gave birth to twins compared with 14.9 per cent on the
mainland. Having twins seems to be an advantage only for women on the islands,
where mothers of fraternal twins produced more children in their lifetime than
mothers who had never had twins. On the mainland, mothers of fraternal twins had
fewer children (Nature, vol 394, p 533).
For centuries, food has been more consistently available on the islands than
on the mainland. The researchers say that when food is plentiful it makes good
evolutionary sense to produce as many offspring as possible. Selection for genes
which predispose mothers to produce fraternal twins could therefore explain the
high twin rates on the archipelago.
