Contrary to what is believed if one bears in mind the interwoven unity of the mother and their offspring, the whales don’t form steady family groups.
Their system of mating is promiscuous, they form sexual groups that can be observed very well in the Valdés Peninsula, in which there is a female and several males. The males compete among them to fecundate the female.
This competition is the reason for the peculiar characteristic of this species: the size of the testicles of the male individuals. They are the biggest in relation to their corporal weight in the whole Animal Kingdom. It happens that, since several males compete in a sexual intercourse group, the one with more chances of fertilizing the only ovum of the female will be the male that produces a bigger quantity of sperm. It is a peculiar case of intrasexual competition called “spermatic competition”.