London: Women who have twins tend to have single babies that are heavier at birth, according to a new study.
The study is based on a 40-year-dataset collected in Gambia, where seasonal food supply is variable.
Evolutionary biologist Ian Rickard from the University of Sheffield, UK, studied a long-term dataset from a rural Gambia, which included not only birth weights of about 1,900 babies born to around 700 mothers, but also the number of twins.
Analysing all 40 years, Dr Rickard explained that he and his Gambian and London-based colleagues saw that women who produced twins gave birth to heavier non-twin babies - around 100g (0.2lbs) heavier, in fact.
Intriguingly, the difference in birth weight between twin-producing mothers and singleton-mothers disappeared when food was scarce.
“We`ve known for quite a while that... if a [foetus] is exposed to a period of the year between about July and October during their third trimester they tend to have lower birth weight,” the BBC quoted Dr Rickard as saying.
Producing twins, said Dr Rickard, could be just a by-product of natural selection acting on birth weight.
Dr Rickard suspects that a hormone called IGF, which has long been linked to birth weight in humans could be responsible for this pattern.
The study has been published in the journal Biology Letters.