Some female primates are promiscuous to prevent males from killing their offspring, scientists have said.

Previous research has found that infanticide by male mammals is common in species where the females live in social groups dominated by one or a few males.

When a rival male takes over those groups, they will kill infants to make sure they can produce their own offspring, researchers from the University of Cambridge said.

But a study found that females of some species − such as the mouse lemur − have developed a highly effective counter-strategy. By taking on as many mates as possible in a short amount of time, they confuse the paternity of the infants meaning any male committing infanticide risks killing his own offspring.

Females are more and more promiscuous to confuse paternity

In such species, the males must concentrate on producing larger quantities of sperm to ensure they can reproduce. In the male mouse lemur and some other species, this results in testicles which are up to 10 times larger than normal in breeding season.

Dieter Lukas, from the university’s department of zoology, said: “In species in which infanticide occurs, testis size increases over generations, suggesting that females are more and more promiscuous to confuse paternity.

“Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears − since males face the risk of killing their own offspring, and might not get the benefit of siring the next offspring.”

Closely related species that differ in infanticide and testes size include chimpanzees, where the males commit infanticide, versus bonobos, where males have not been observed to kill offspring.

Bonobos have testes that are roughly 15 per cent larger than those of chimpanzees.

Male Canadian townsend voles do not commit infanticide, and have 50 per cent larger testes compared to infanticidal males of close relatives the North American meadow voles, said Lukas.