Evolutionary theorists have had a difficult time reconciling the demographic transition within an adaptive life history model. Why does increased socioeconomic development result in a failure to increase reproductive success? A failure to identify an adaptive cause is a major problem since its universality suggests that these trends can only be explained in deeper evolutionary terms. Proposed explanations have included maladaptation to contraceptive technologies, fragmentation of kin networks, emerging roles of social prestige in labour market, and rising investment costs in producing socially and economically competitive offspring. The best life history framework is definitely provided by the idea that industrialization
makes it increasingly energetically costly to invest valuable time and energy in current reproduction. However, this framework cannot address the relatively new phenomenon of adults en masse opting not to reproduce. Arguably, delaying biological reproduction completely and effectively removing oneself from reproductive gene pool is a novel behavioural phenomenon for an individual organism with reproductive capability. This makes modern societies life history trajectory increasingly bizarre and difficult to explain when conceptualized within a traditional life history framework.