Past sexual partners determine the size of your baby
Scientists show that children can resemble the mother's previous sexual partnerReuters

Just when you thought you will never have anything to do with that "ex" you never want to see again, he comes back in miniature form to haunt you for the rest of your life.

For the first time, scientists have discovered a new form on non-genetic inheritance, wherein the child can resemble the mother's previous sexual partners.

University of New South Wales Australia scientists Dr Angela Crean, Professor Russell Bonduriansky and Dr Anna Kopps, after studying male flies and their offspring, came to the conclusion that the size of the youngling is determined by that of the first man the mother had sex with, rather than the man that sired the offspring.

This confronting idea, known as telegony, had originated with the Greek philosopher Aristotle, but was discredited in the early 20th Century with the advent of genetics.

Lead author of the study and evolutionary ecologist Dr Crean told the Sunday Morning Herald that the team was shocked when their experiments revealed they had discovered a new form of non-genetic inheritance. They even conducted a lot of follow-up studies to confirm the results, she said.

"Our discovery complicates our entire view of how variation is transmitted across generations, but also opens up exciting new possibilities and avenues of research. Just as we think we have things figured out, nature throws us a curve ball and shows us how much we still have to learn," says Dr Crean in UNSW newsroom.

The team produced large and small male flies by feeding them larvae that were high or low in nutrients as required and then mated the immature females with either a large or a small male. Once the females matured, they were mated again with either a big or a small male, and their offspring were studied.

The study, "Revisiting telegony: Offspring inherit an acquired characteristic of their mother's previous mate", which has been published in Ecology Letters revealed that while the offspring's body is positively related to maternal body size, it is not influenced by the body size of the male that fathers it, at least in the case of the flies on which the experiment was conducted.

"We know that features that run in families are not just influenced by the genes that are passed down from parents to their children. Various non-genetic inheritance mechanisms make it possible for maternal or paternal environmental factors to influence characteristics of a child... Our new findings take this to a whole new level – showing a male can also transmit some of his acquired features to offspring sired by other males," says Dr Crean.

It is still unknown whether this theory can be applied to other species.