IV.9 The effectiveness of individual selection is crucially limited in sexually reproducing organisms, as the individual’s genotype (or even its phenotype) is not inherited from generation to generation.

One of the five basic preconditions for the functioning of Darwinist evolution is the existence of heritability of the properties of organisms (I.9).Over time, organisms can develop complicated adaptive structures and patterns of behaviour only if randomly formed mutations and phenotype manifestations of these mutations and their consequences for the biological fitness of the individual are transferred from the parent organisms to their progeny.This precondition is fulfilled for organisms reproducing asexually – an individual with a certain mutation produces progeny whose genome contains copies of the same mutation and, if further mutation does not occur in the progeny that would somehow change the manifestations of the original mutation, the phenotype manifestations of this mutation and their impact on the biological fitness of the individuals will be the same as for the parent organism. However, a very different situation occurs in organisms with sexual reproduction.In these organisms, the progeny do not receive a copy of the genome of their parents, but rather their zygote is formed with a unique genome through combination of the genes derived half from the mother and half from the father.Although the newly formed mutations are also transferred (with a probability of 50%) from the parents to the progeny, their impact on the phenotype and thus on the biological fitness of the individual is usually fundamentally different than for the parent organism.Compared to asexually reproducing organisms, sexually reproducing organisms have substantially limited heredity of phenotype properties as, because of epistatic interactions between the individual genes, the same allele in the context of various genomes can cause the formation of completely different phenotype traits.Similarly, they have substantially limited heritability of biological fitness as, in the context of certain phenotype traits, a single trait can increase the biological fitness of its bearers, while it can reduce it in the context of other traits.This means that a great many mutations cannot become fixed in the population because, while they can contribute to increasing the biological fitness in the genomes of some individuals, and are thus preferred by natural selection here, in the genomes of the progeny of these individuals they can, on the other hand, reduce their fitness and their frequency is then reduced by natural selection.The degree to which the heritability of properties in sexually reproducing organisms only reduces the effectiveness of the functioning of Darwinist evolution and the degree to which it prevents its functioning is a question that has not yet been resolved.

            Attempts to come to terms with the problem of the apparent existence of biological evolution under the conditions of low heritability of traits and biological fitness in sexually reproducing organisms are exemplified in the theory of the selfish gene (Dawkins 1976)and thetheory of frozen plasticity (Flegr 1998).

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.