Scientists have discovered a new form of non-genetic inheritance, showing Greek philosopher Aristotle's hypothesis that offspring can resemble a mother's previous sexual partner has some merit.
The idea of telegony - the once-held theory that a male can leave a mark on his mate's body that influences her offspring with a different male - dates back to ancient Greek times and was popular as a scientific theory in the 1800s.
Although the theory was discredited in the early 1900s with the advent of genetics and is classed as superstition, researchers have now shown for the first time that the hypothesis has merit - in flies.
To test the idea of telegony, Australian scientists at the University of New South Wales manipulated the size of male flies and studied their offspring.
They discovered that the size of the young was determined by the size of the first male the mother mated with, rather than the second male that sired the offspring.
Dr Angela Crean, who led the study, 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."
The researchers suggested that the effect is due to molecules in the seminal fluid of the first mate being absorbed by the female's immature eggs, and then influencing the growth of offspring of a subsequent mate.
The team produced large and small male flies by feeding them larvae that were high or low in nutrients. They then mated the immature females with either a large or a small male.
Once the females had matured, they were mated again with either a big or a small male, and their offspring were studied.
"We found that even though the second male sired the offspring, offspring size was determined by what the mother's previous mating partner ate as a maggot," said Crean.
Despite major advances in genetics, many questions remain about how some traits are inherited.
"We know that features that run in families are not just influenced by the genes that are passed down from parents to their children," said Crean. "Various non-genetic inheritance mechanisms make it possible for maternal or paternal environmental factors to influence characteristics of a child."
In the flies, for example, it has been shown that males that are well-fed as larvae go on to produce big offspring.
"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," she explained. "But we don't know yet whether this applies to other species."
The study is published in the journal Ecology Letters.