The Science of Existence (127) Animals


Many invertebrates alternate between sexual and asexual generations; notably protozoa, jellyfish, and flatworms.

Alternation of generations for animals refers solely to reproductive mode: sexual (heterogamic) or asexual (parthenogenic) reproduction. Parthenogenesis may happen in nematodes, parasitic wasps, some bees, some scorpions, and a few vertebrates, including fish, amphibians, and reptiles.

In some species, switching between heterogamy and parthenogenesis may be triggered by the season (aphids, some gall wasps), by a lack of males, or by conditions that favor rapid population growth (e.g., rotifers and water fleas).

Asexual reproduction occurs either in summer (aphids), or as long as conditions are favorable. Asexual reproduction allows a successful genotype to spread quickly without the fuss of sex or wasting resources on males who can’t reproduce.

Animals are always diploid. As such, animal AoG has a limited context when contrasted against the genomic gyrations of plants.