Origin of sexuality

The primary cause of the emergence of sexuality, i.e. differentiation of individuals of a single species into males and females, was apparently morphological differentiation of gametes into two types, microgametes and macrogametes, i.e. the emergence of morphological anisogamy. This differentiation is a phenomenon that is very old in evolution; however, it was preceded by functional differentiation, i.e. functional anisogamy. The formation of two or more mating types of cells that cannot reproduce sexually within the group and can reproduce only with the members of another mating type occurs in organisms in which specialized sex cells, gametes, are not formed and where their function is fulfilled by a relatively unspecialized somatic cell. This situation is encountered, e.g., yeasts and ciliates.

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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