Caring for parents: an evolutionary rationale

Abstract

BackgroundThe evolutionary roots of human moral behavior are a key precondition to understanding human nature. Investigations usually start with a social dilemma and end up with a norm that can provide some insight into the origin of morality. We take the opposite direction by investigating whether the cultural norm that promotes helping parents and which is respected in different variants across cultures and is codified in several religions can spread through Darwinian competition.ResultsWe show with a novel demographic model that the biological rule “During your reproductive period, give some of your resources to your post-fertile parents” will spread even if the cost of support given to post-fertile grandmothers considerably decreases the demographic parameters of fertile parents but radically increases the survival rate of grandchildren. The teaching of vital cultural content is likely to have been critical in making grandparental service valuable. We name this the Fifth Rule, after the Fifth Commandment that codifies such behaviors in Christianity.ConclusionsSelection for such behavior may have produced an innate moral tendency to honor parents even in situations, such as those experienced today, when the quantitative conditions would not necessarily favor the maintenance of this trait.Electronic supplementary materialThe online version of this article (10.1186/s12915-018-0519-2) contains supplementary material, which is available to authorized users.

To save or not to save your family member’s life? Evolutionary stability of self-sacrificing life history strategy in monogamous sexual populations

“…It was shown that honest begging results in decreased variance of collected food among siblings, which leads to a higher mean number of surviving offspring. Furthermore, in Garay et al [28] the evolutionary roots of human morality were studied. It was found that the biological version of the Fifth commandment, called the Fifth rule (“ During your reproductive period, give away from your resources to your post-fertile parents ”) can spread by means of natural selection, by increasing the survival rates of the family members.…”

“…We use the term “offspring gratitude” to emphasize the difference from other kinds of gratitude as e.g. “upstream reciprocity” [52, 53], and the Fifth rule [28]. Now we can make precise what we understand under “ self-sacrificing life history strategy ”: an individual having this phenotype is altruistic and grateful in juvenile age, and is a provider parent during adult age.…”

An evolutionary perspective on kin care directed up the generations

“…Older women are likely to be post-menopausal and therefore unable to directly reproduce, making the possible indirect fitness gains minimal; and fathers of adults may physiologically be able to reproduce in old age, but their fertility will be constrained by mate availability, as it is likely these older men will be partnered with women of a similar age who are post-menopausal making reproduction unlikely 21 . Despite the apparent limited inclusive fitness gains to be had from the behaviour, caring for elderly parents is a cross-cultural norm.At present, we are only aware of one model attempting to address elder care from a fitness maximising framework 22 . Here, in a demographic model it is proposed that upwards intergenerational care would be selected for due to the possible reciprocal benefits of the behaviour.…”

“…At present, we are only aware of one model attempting to address elder care from a fitness maximising framework 22 . Here, in a demographic model it is proposed that upwards intergenerational care would be selected for due to the possible reciprocal benefits of the behaviour.…”

“…Though the elderly would already have an incentive to invest in younger kin as it is the only route to increase their inclusive fitness, it is thought that receiving care from adult relatives makes the elderly more able to offer direct care towards younger relatives. This additional support from the elderly then allows fertile adults to allocate their energy into other activities, such as increasing their direct fitness through reproduction (which would not be possible for the elderly to do) resulting in each individual doing the task they are 'best' at 22 . However, within this model, it is assumed that the adults directing care towards the elderly are fecund and therefore physiologically able to increase their fitness directly.…”