Sisyphean genotypes model of advantage of sexuality
The spreading of phenotype variability in sexually reproducing species allows generation amongst progeny of Sisyphean genotypes (genetic elite), i.e. individuals that are so well adapted to current conditions that they produce far more progeny during their lives than other individuals in the population. G.C. Williams introduced the term Sisyphean genotypes for them; the original name, genetic elite, was introduced by T. Dobzhansky. Williams’ name is probably more appropriate, as it primarily emphasizes the fact that the emerging genotype of these individuals appeared only because of segregation and recombination and thus has minimal heritability and must be formed anew in subsequent generations (Williams 1975). Both authors assumed that extraordinarily biologically fit individuals, whose direct or indirect descendants will subsequently constitute most of the individuals in the population, occur with very low frequency in very large populations of sexually reproducing species. s
It is very probable that this mechanism can work only for species with extremely high reproduction potential, i.e. where one individual produces so many embryos that its progeny could, in the ideal case, i.e. if all the embryos lived to maturity, maintain the existing population size even if the other members of the population did not reproduce at all. Williams introduced the term non-Markovian species for such species. While, in Markovian species, the number of individuals in the population depends on the number in the given population in the previous generation, this is not true in non-Markovian species, as the occurrence of only a single individual with optimum genotype (or with a good portion of luck) can supplement the size of the population from any random value to the maximum size, limited from above only by the relevant ecological regulation mechanisms (see IV.4.1). At the present time, only some species of wild fauna could fall in this category, possibly including fish, and also some endoparasites; however, in the past, the common ancestors of most of present-day Markovian species could have passed through this stage. Sexuality could be a trait that was advantageous in the past for non-Markovian species, as it allowed them to create Sisyphean genotypes; however this need not be advantageous from this viewpoint for modern species and could be preserved, for example, through the evolutionary trap mechanism (see XIII.3.3).
- more or less2240
- not at all1830