Cruel world scenario

The essence of the cruel-world scenario is that natural selection is continually pursuing an elusive optimum that the population is being pushed away from. The result is genetic variance in fitness and positive correlations among fitness components, that is, the existence of an f factor. 

In summary, there is good evidence that both optimal-world and cruel-world scenarios supply variation in fitness components, but the quantitative balance between the two is unclear. 

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