help the female and caring for the young resulting in biparental care biparental care often goes hand in hand with monogamy since investing in a single mate means the male can expend the energy he would have spent searching for more mates into caring for the young instead biparental care is seen in the vast majority of bird species possibly because they are highly altricial young require a great amount of care from both parents to survive although monogamy initially evolved among the solitary amphidonts as a response to low population densities it also provided the opportunity for the males to assist in parental care so biparental care will be an ancestral trait for the amphidonts but the species that evolve sociality will have the opportunity to employ an even more effective strategy there are other ways for an organism to pass on its genes than simply producing offspring in a species that reproduces sexually an individual inherits half of its genes from each of its parents and will therefore also share half its genes with its direct offspring statistically it will also share on average half of its genes with each of its four siblings a quarter with half siblings and eighth with first cousins and so on this means that when an individual reproduces it's not only propagating its own genes but also those of its relatives and thereby acting to increase their fitness as well as its own this concept is called inclusive fitness and provides a way for altruism to still result in a net reproductive benefit the conditions under which altruistic behaviors will be selected for are described by hamilton's rule which takes into account this proportion of shared genes or relatedness as well as the cost to the initiator of the altruistic act and the benefit to the recipient hamilton's rule predicts that the more closely related two individuals are the more likely they are to behave altruistically towards each other since the greater the proportion of their shared genes they're helping to propagate and the greater inclusive fitness they gain because of this most social species usually have a relatively high degree of relatedness between group members meaning they all gain inclusive fitness from one another's reproduction to maximize this benefit some social species especially monogamous ones exhibit cooperative breeding in which young receive care not only from their parents but also from other members of the social group usually called helpers in this context if the clans of these amphidonts have a suitably high degree of relatedness then they may seek to increase their inclusive fitness by sharing the duties of parental care among the entire clan all the clans young will be kept together in a communal nest site and the adults will take turns guarding them while the others are off hunting giving these amphidonts which we'll call xenopsids a very high rate of juvenile survival but if the right ecological factors are in place some clades may evolve to take cooperative breeding one step further one of the osteopod clades that's most reliant on parental care are the trepanocyrants as their highly altricial young or grubs are completely unable to fend for themselves until they develop bones and functioning eyes in the semel paris species the female can afford to expend all of her energy into caring for the young since she inevitably dies once they're developed enough to leave her protection but species that can't afford such extreme parental investment may rely on another form of cooperative breeding once again the higher the relatedness between the individuals the greater the inclusive fitness an organism will gain
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