LONG WINDED VERSION AT UD:
Darwin’s Delusion vs. Death of the Fittest
CONCISE VERSION AT TSZ
From Kimura and Mayurama’s paper The Mutational Load (eqn 1.4), Nachman and Crowell’s paper Esitmate of the Mutation Rate per Nucleotide in Humans (last paragraph), Eyre-Walker and Keightley’s paper High Genomic Deleterious Mutation rates in Homonids (2nd paragraph) we see that by using the Poisson distribution, it can be deduced that the probability P(0,U) of a child not getting a novel mutation is reasonably approximated as:
where 0 corresponds to the “no mutation” outcome, and U is the mutation rate expressed in mutations per individual per generation.
If the rate of slightly dysfunctional or slightly deleterious mutations is 6 per individual per generation (i.e. U=6), the above result suggests each generation is less “fit” than its parents’ generation since there is a 99.75% probability each offspring is slightly defective. Thus, “death of the fittest” could be a better description of how evolution works in the wild for species with relatively low reproductive rates such as humans.