All-powerful Selection to the rescue?
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and are not passed on to the offspring. Yet such “false selection” must still be paid for - requiring still more reproduction. We have still not started to pay for “real” selection! Real selection can take several forms - stabilizing selection, sexual selection, progressive selection, etc. Each form of selection has a reproductive cost. All reproductive costs are additive, and all costs must be paid for. Total reproductive costs must never exceed the actual reproductive potential of a species. Only if a species is sufficiently fertile, and there is sufficient surplus population to fund all other costs, does any type of selection become feasible. In other words, selection is only possible to the extent that there is residual excess population, after all other costs have first been paid. Selection is a little like discretionary spending for a family on a tight budget. The question always comes down to - “Can we afford it?” Fitness (due to phenotypic superiority) is actually the real trait that natural selection always acts upon, and this very fundamental trait is actually very poorly inherited. This runs counter to popular thinking. According to Kimura, fitness has low heritability - even as low as .004 (Kimura, 1983, p.30-31). The concept of heritability is dealt with in more detail in Chapter 6. For now it is sufficient to know that low heritability means that environmental factors are much more important than genetic factors, in determining who appears “superior”. For Kimura to say that general fitness has very poor heritability is an amazing acknowledgment!
It means that
even with intense selection pressure, nearly all of a population’s surplus ends up being “spent” to remove non-heritable variations, and thus most reproductive elimination is unproductive. In other words selection for general fitness has minimal impact on the makeup of the next generation. Kimura’s statement implies that only a small fraction of the surplus population is truly available