Standard evolutionary theory of ageing predicts weaker purifying selection on genes critical to later life stages. Prolonged post reproductive lifespan (PPRLS), observed only in a few species like humans, is likely a result of disparate relaxation of purifying selection on survival and reproduction in late life stages. While the exact origin of PPRLS is under debate, many researchers agree on hypotheses like mother-care and grandmother-care, which ascribe PPRLS to investment into future generations---provision to one's descendants to enhance their overall reproductive success. Here we simulate an agent based model, which properly accounts for age-specific selection, to examine how different investment strategies affect the strength of purifying selection on survival and reproduction. We observed in the simulations that, investment strategies that allow a female individual to remain contributive to its own descendants at late life stages may lead to PPRLS. In sum, we showed that differential relaxation of selection on survival and reproduction, induced by appropriate investment strategies, can lead to adaptive evolution of PPRLS.