Classic theories talk about the sex war, in which males must bang everything they catch, while females must choose the best to have the best offspring. But a new research presented at the Zoological Society of London, and carried on the African topi antelopes (Damaliscus lunatus) (a close relative of the more known wildebeest) points to the fact that males too can play hard to get; they can even reject advances from aggressive females they have already copulated so that they spread their semen in more female partners.

"When biologists talk about the 'battle of the sexes' they often tacitly assume that the battle is between persistent males who always want to mate and females who don't", said author Jakob Bro-Jørgensen, a biologist at Stirling University, UK. who has been studying these antelopes for 10 years.

Previous observations found female gorillas disturbing copulation in the competition for receiving the attention of the dominant silverback male. Topi too act similarly. Bro-Jørgensen studied topi antelopes in Masai Mara National Park (Kenya), where they form herds of thousands of individuals.

About 10-20 dominant males defend small areas, each with a diameter of 30 m (100 ft), and called leks, located in the best aras of the herd's territory. Males combat to defend their leks, that's why weaker males get leks at the edge of the leks' area, more exposed to predators. Females choose the high quality males, as these carry the best genes, passing from one lek to another.

Bro-Jørgensen investigated the mating behavior of 98 cows. In these antelopes, the estrus takes place for just one day annually, an extremely short period in which females want their calves to be fathered by the best males. "On average, the females mate with 4 males 11 times during this day. This is possible because the actual sexual act takes only a few seconds", said Bro-Jørgensen.

Fertile females were observed to attack with their horns mating couples, if they found the male attractive, forcing the bull to mate with them. But this does not happen always: if he has already had sex with the attacker, there's a high chance that the male will chase her away.

Such a choosy male behavior is explained by the fact that the male wants to spread as much as possible his semen during the brief estrus period. The author observed one case of a topi bull which had 36 sex intercourses in a day, remaining "totally exhausted", and perhaps spermless for a while. "For so long we have assumed that sperm is in unlimited supply. That old dogma is falling by the wayside.", comments Paul Verrell at Washington State University in Pullman, US.