Chapter 7 Univariate drift for 400 generations

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Figure 7.0a Genetic drift causes the phenotypic trait mean of a lineage to undergo a random walk. The lineage mean is shown in units of within-population phenotypic standard deviation. In this animation, 25 replicate lineages evolve independently from the same starting point (trait mean of 0) and with the same values for genetic variance (G=0.4) and effective population size (Ne=100). The theory of stochastic processes tells us to expect the means of replicate lineages to be normally-distributed at any given generation with a mean of 0 and a variance of tG/Ne, where t is number of elapsed generations. 99% confidence limits based on that theoretical expectation are shown as blue curves.

Figure 7.0b  Genetic drift causes the phenotypic trait mean of a lineage to undergo a random walk, showing the effect of genetic variance.  Same conventions and parameters as in Fig. 7.0a, but these animation runs contrast diversification when additive genetic variance is typical (0.4) and extraordinarily high (0.99).  Here as in Fig. 7.0a, within-population phenotypic variance is 1 (P=1), so heritability is equivalent to additive genetic variance (G).