What does anisogamy mean?
Anisogamy is the form of sexual reproduction in which two fusing gametes differ markedly in size, most commonly a large, nutrient-rich, immotile egg and a small, highly motile sperm. Found across most animals and many plants and algae, it stands in contrast to isogamy, in which the mating gametes are similar in size and appearance. Because anisogamy implies unequal investment by the two parents in each offspring, it is central to evolutionary accounts of sex roles, sexual selection, and competition between gametes. The word derives from Greek roots meaning 'unequal' and 'marriage' or 'union', and appears almost exclusively in scientific and academic contexts rather than everyday speech. Its adjective counterpart, anisogamous, describes species or systems exhibiting this condition. Understanding anisogamy helps explain why distinct male and female sexes exist at all, making it a foundational concept in reproductive biology.
nounSexual reproduction involving the fusion of gametes that differ markedly in size or form, typically a large, immotile female gamete (egg) and a small, motile male gamete (sperm). It is the condition found in most animals and many plants, contrasted with isogamy.
- The biological condition in which sexual reproduction occurs through the fusion of dissimilar gametes differing in size (and often motility), as opposed to isogamy.
"In nearly all animals, anisogamy produces a striking asymmetry between the sexes: females invest in large eggs while males produce vast numbers of tiny sperm."
"Biologists trace the origin of male and female sexes to the evolution of anisogamy in early eukaryotes."
"Because anisogamy creates unequal parental investment in gametes, it underpins many theories of sexual selection."
Rarely pluralized in practice, since the term usually refers to a single biological condition rather than countable instances.
"Different lineages of algae exhibit distinct anisogamies, varying in the degree of size difference between their gametes."
Every egg-and-sperm pairing on Earth — from humans to sea urchins — is a product of anisogamy, the ancient evolutionary split that made 'male' and 'female' possible at all.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of anisogamy
Anisogamy comes from the Greek prefix 'an-' (meaning 'not' or 'without') combined with 'iso-' ('equal') and 'gamos' ('marriage' or 'union'), literally denoting an unequal union of gametes. The term was coined within nineteenth-century biology as scientists studied algal reproduction and began distinguishing species with equal-sized gametes from those with unequal ones. It shares its Greek root 'gamos' with related terms such as monogamy, polygamy, and bigamy, though these refer to marriage customs rather than gamete biology.
Related word forms
How anisogamy is actually used
A technical term used chiefly in biology, evolutionary theory, and related academic writing; rarely encountered in everyday conversation. The adjective form is 'anisogamous'.
Easily confused with anisogamy
Isogamy involves the fusion of gametes of similar size and form, whereas anisogamy involves gametes of distinctly different sizes.
Oogamy is the extreme form of anisogamy in which one gamete is a large, non-motile egg and the other a small, motile sperm.