Two Sexes in One
Two Sexes in One
This chapter defines hermaphroditism, and contrasts male with female in diverse organisms. A hermaphrodite is a dual-sex organism that has the capacity to reproduce as both male and female during its lifetime. Hermaphroditism is relatively rare in vertebrates, but extremely common in plants and invertebrate animals. Anisogamy refers to the bimodal distribution of gametic sizes that characterizes all multicellular sexual species; by definition, male gametes are relatively small, and female gametes are relatively large. It arose early in the history of multicellular life, probably through a combination of evolutionary factors, including disruptive selection on gametic size, selection against sexual diseases housed in the cell cytoplasm, and the resolution of potential evolutionary conflicts between nuclear and cytoplasmic genomes. It implies that males have an inherent capacity to produce large numbers of small and energetically cheap gametes, whereas females can produce far fewer and individually more expensive gametes.
Keywords: hermaphroditism, hermaphrodite, male, female, anisogamy, gametes, sexual diseases
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