MadSci Network: Evolution |
I have two hypotheses as explanations. 1) having fewer children is not necessarily maladaptive. Parents have limited investments (not simply in a financial sense, but in all that a parent can give) to make in their children, and human babies are particularly expensive. Fewer children at the start may result in more children surviving to maturity and successfully finding high-quality mates. Although you are right that the genotype that grows the faster will be the one to predominate, the genotype which is the fastest growing *in the long term* is not necessarily one that favors maximizing the number of offspring. Indeed, one can assist in propagating one's own genotype without having children at all-- by being available to assist in the rearing of one's relative's children. Thus, other "decisions" about whether to reproduce or not are not necessarily maladptive. 2) married couples "deciding" to have fewer children is maladptive, and the reason this behavior has not been selected out of the population is that the phenomenon is incredibly new in the timeframe that evolution operates on. To differentiate between these hypothesis, one could run an analysis of the number of great-great-grandchildren, great-great-nieces and nephews, etc-- any relatives-- of people deciding today not to have many children, and those deciding otherwise. But without such data, be wary of pronouncing something maladaptive. Science is empirical, and what works and what doesn't work in an evolutionary sense can be very surprising.
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