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Free loving mums have healthier babies

Mothers who practised free love dramatically increased the survival rate of their offspring. Image: Andras Keszei/ANU

SYDNEY: Promiscuous females are more likely to give birth to fitter offspring than their monogamous sisters, an Australian study shows.

Researchers at the Australian National University in Canberra said they had proven for the first time that female promiscuity increases the survival rate of offspring in an animal species. Their findings are published this week in the British journal Nature.

“Scientists have developed many theories to explain why some female animals have multiple sex partners," said team leader Diana Fisher.

These have included theories that females trade sex for food and protection, safeguard against infertile males, or avoid the negative effects of inbreeding in species that can’t recognise their relatives.

“Another theory is that mating with multiple males would result in sperm competition," said Fisher. "This means that males with the strongest sperm are more likely to become sires and father better quality offspring. Until now, this theory hasn’t been demonstrated convincingly.”

Fisher’s team has found the first compelling evidence for this sperm competition theory among brown antechinuses – mouse-sized, insect-eating, nocturnal marsupials that are common in the forests of south-eastern Australia.

The team brought male and female antechinuses into captivity for the mating seasons in two successive years. Some females were only allowed one mate, while others had three.

Groups of three males were mated - one at a time - with three different promiscuous females, so that paternity tests could reveal their success at sperm competition.

In the first year, families were released back into the wild when the babies were still in their mother’s pouch. The result was that babies with promiscuous mothers were almost three times as likely to survive as those in the monogamous group.

The second year, families were kept in captivity until the babies were almost weaned. Again, babies of promiscuous mothers showed higher survival rates.

Paternity tests showed that the sperm of some males was far more successful than others, and most importantly, that babies fathered by these males were twice as likely to survive, said Fisher.

Despite the advantages to the species from free love, males usually died due to exhaustion and aggressive encounters with other males after a single, torrid mating season.

Females fared much better, usually living to breed for a second or third year.

Do we live in an artificial society. The reproductive make up of the regular Homo sapien suggests to me that we should be as promiscuous as the small marsupials in this story. Are we truly designed for the monogamous life? What about survival of the fittest, does that still apply to our modern society? I think not!