The evolutivo success of an individual does not only depend on its abilities of survival or reproduction, but also of the production of descendants who arrive at the adult life and if they reproduce. In the case of the Homo sort, as generally only one youngling for offspring was born, the parental investment if became basic for the success of the species. as then appeared paternal investment in the cares of the offspring? One of the factors that can be related is the loss of the pointers of rutting in the female. Thus, so that a male had paternity guarantees, and then he was advantageous to take care of of the youngling as a way to perpetuate its genes, it was necessary that he was always close to the female guaranteeing that none another one copulasse with it, and it did not take care of of the youngling of another one. But this did not happen of a so simple form. It was necessary that the male did not know when of the fertile period of the female and thus he was remained always close to it. In such a way, for natural election, the female was losing the characteristics that indicated its fertile period, as the swell in the vaginal lips and I smell it characteristic for the hormone release that attracted the male for cpula.
With this, the female was always ready for the sexual activity, guaranteeing the presence of the male and its aid in the care of the younglings. Moreover, as in diverse monogamous species, a sexual receptividade permanent on the part of the female, and not only during the fertile period, it favors the permanence of the male, since this has little information on reproductive periods. Exactly thus, amongst the mammals, the species human being is one of the few species where the male direct presents parental investment in the offspring.