PMC Journal List A – Nat Rev Genet. Wright’s attempted solution to this problem involved his shifting balance theory” of evolution 41 – 43 Briefly, Wright maintained that species find and ascend global peaks because evolution involves two additional processes: genetic drift (random change in allele frequency in finite populations) and inter-demic selection (wherein some local populations perform better, and so presumably produce more migrants, than do others).
PMC Journal List A – Approach
(The approach takes advantage of the fact that beneficial mutations that change an amino acid will contribute to the number of diverged amino acid sites between two species but not to the number of amino acid polymorphisms segregating within species: beneficial mutations generally sweep through species too rapidly to contribute to within-species standing genetic variation.) This inference represents one of the most elegant and profound in recent population genetics.
Turning to empirical issues, we confront a large and diffuse literature and can hope to do no more than highlight important parts of it. Experimental studies of fitness generally take one of three approaches: i) measuring fitness differences among genotypes that currently segregate in a population; ii) inferring past increases in fitness from DNA sequence data; or iii) watching fitness evolve in real time.
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Indeed these various cases constitute a considerable part of the classical population genetic literature 11 , 15 Although we have considered species that have discrete generations, population geneticists have also generalized measures of fitness and have derived selection equations for the case in which populations or genotypes grow continuously through time (see Box 2 ).
PMC Journal List A – Conclusion
But the approaches required for resolution are reasonably clear: except for the problem of the fitnesses of genotypes in natural populations, most can be settled by labor-intensive but straightforward microbial experimental evolution studies or by the (similarly labor-intensive) genetic mapping and characterization of alleles underlying derived, adaptive phenotypes.