Bear ye one another’s genetic burdens: the price of diversity and complexity

Genetic variability and diversity are the result of a mutation-selection balance that acts permanently within and between species. The presence of deleterious mutations is a necessary consequence of this process and thus “the price paid by a species for its capacity for further evolution” (Haldane 1937, Am Nat 71:337–349). Recent estimations of mutation rate in the human lineage has revived the debate as to whether the high number of deleterious mutations poses a severe problem for the future of mankind. Theoretical considerations allow a scenario in which the survival of the human race is maintained by truncation selection of deleterious mutations that removes as many mutations as appear anew in every generation. In this case our genetic burden is carried by those individuals that suffer a genetic death resulting from random distribution of deleterious alleles. Nevertheless, one has to ask whether the mutation rate may set absolute limits on the complexity of a species.