Male saiga antelopes (Saiga tatarica) live in bachelor groups for most of the year, but during the mating season, they compete fiercely for females. The most successful males are those that can mate with the most females, and they often do this by preventing other males from mating.

One way that males prevent other males from mating is by guarding females. When a male finds a female that is in estrus, he will stay close to her and prevent other males from approaching her. He may also use his antlers to fight off other males.

Another way that males prevent other males from mating is by engaging in sibling sex. Sibling sex occurs when a male mates with his sister or half-sister. This behavior is thought to be evolutionarily advantageous because it helps to keep the male's genes within the family.

When a male mates with his sister, he is ensuring that his genes will be passed on to the next generation. This is because his sister is more likely to carry his genes than a female from another family.

Sibling sex also helps to strengthen the bond between males and females within a family group. When a male mates with his sister, he is creating a bond with her that will last for life. This bond can help to protect the male from being attacked by other males, and it can also help him to access food and resources.

The practice of sibling sex is not unique to saiga antelopes. It has also been observed in other species of mammals, such as lions, tigers, and bears. In these species, sibling sex is thought to serve the same purpose: to keep the male's genes within the family and to strengthen the bond between males and females within a family group.