Promiscuity breeds better babies, study shows

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AntechinusThere is ancient lore to the effect that learning to make love without orgasm is protective of health. Here's some research showing that too much fertilization-driven sex can suppress the immune system. Males of the species Antechinus stuartii are "overtly preoccupied with copulation and die abruptly at the conclusion of the mating season."

1 Autopsies of males revealed a variety of disease states, all associated with suppression of immune and inflammatory responses. However, inhibition (or removal) of androgens allows the animal to mount an effective immune response. Could learning to make love without orgasm also balance androgen levels? The ancient Chinese noted that this practice actually decreased sexual frustration.2

Australian researchers have found that a mouse sized marsupial with a promiscuous sex life breeds much healthier babies than her monogamous sisters. A team of scientists based at the school of botany and zoology (BoZo) at the Australian National University (ANU) in Canberra, has spent the past two years studying the sex life of the brown antechinus. The brown antechinus is a small carnivorous marsupial, about the size of a mouse, which belongs to the same family as the Tasmanian devil and the quoll. The research team, led by Dr Diana Fisher, found that promiscuous females of the species were more likely to give birth to healthier offspring than those which had mated with only one male. "Scientists have developed many theories to explain why some female animals have multiple sex partners, whether it's trading sex for food and protection, dealing with infertile males or avoiding the negative effects of inbreeding in species that can't recognise their relatives," Dr Fisher said. "Another theory is that mating with multiple males would result in sperm competition. "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." The Brown Antechinus, which is found in forest in south-eastern Australia, usually has a short and intense single mating season. When the males are about 11-months-old they begin a two-week breeding frenzy in order to father as many young as possible. Each male will mate for about six hours at a time with as many females as it can then die of sheer exhaustion at the end of the mating season. The stress of their vigorous mating and aggressive encounters with other males with which they compete for the females, usually results in their death. The females have a much better chance of survival and usually live to breed for a second or third year. The researchers studied a group of the marsupials in captivity - one where the females were only allowed to mate with one male and the other where the females were allowed multiple partners. "In one year we released families back into the wild when the babies were still in the mother's pouch," Dr Fisher said. "The result was that survival of babies with promiscuous mothers was almost three times as high as those in the monogamous group. "The next year we kept families in captivity until the babies were almost weaned. "Again babies of promiscuous mothers did much better. "Paternity tests showed that the sperm of some males were far more successful than others and ... that babies fathered by these males were twice as likely to survive." The researchers concluded that the females who had the most partners were more likely to have healthier offspring because they increased their chances of mating with males who had the strongest sperm. The findings of the study will be published in the latest edition of Nature magazine. (Nature, vol 44, p 89).