An organism has a certain life span. Scientists have been trying to explain life and death and the riddle of longevity. Such studies are subdivided in two broad categories, physiological and evolutionary. Both the views hold that an individual has a limited amount of energy at its disposal to carry out its biological functions including reproduction. They agree that the motivation of an individual is to perpetuate itself by maintaining itself and by reproducing. Attaining reproductive success is the ultimate motive of an individual.
Physiological biologists hold that an individual maintains itself by investing its resources in maintenance and repair of its body. Evolutionary biologists point out that after the end of the reproductive phase of life there is no possibility of adding to reproductive success, so it would be pointless for nature to invest the maintenance and repair of the body. Therefore a living organism generally dies soon after its reproductive phase is over. Species that provide parental care, however, can escape the usual curtain call for a time because in them natural selection has a basis to favor genes that promote post-reproductive longevity – the so-called grandmother effect. ( cf. William Hamilton et al)
The intense phase of parental care is unusually protracted in the human species and has increased with time. Human child retains its dependence on parental care for survival even after weaning unlike other mammals. With advance in culture and technology the need of parental care became more intense and protracted. So the father is obliged to closely cooperate with the mother for quite long period to ensure the transmission and survival of his genes in the next generation. Thus protracted need of parental care laid the foundation of a man–woman–children family as we know it.
With the advent of agriculture arose division of labor and the bond between man, family and community. Even after their children reached adulthood those older people used to be tremendously important to the survival of not only their just their children but of their whole tribe. Especially in the days before writing, they acted as the carriers of essential knowledge. Dr. Ronald Lee says that parental care is of persistent importance. He says that it (parental care) should be factored in throughout the lifecycle. People start life as receivers but gradually switch over to being givers as they have children of their own.
Longevity of man gradually increased with our advances in culture,medicine and technology, though the relevance of old persons declined simultaneously as agrarian societies transformed to industry and technology based ones.In the process parenting and got delinked with longevity.
Obviously parenting and longevity do not appear to have cause-effect relationship.