eggbearing

Eggbearing refers to a reproductive mode in which embryos develop inside eggs laid by the parent, with development often occurring outside the body. The term is closely related to oviparity and describes many animals that produce eggs, though some groups lay eggs but exhibit complex patterns of incubation and care. Eggbearing is contrasted with viviparity (live birth) and ovoviviparity (embryos hatch from eggs inside the mother).

Eggs may be shelled or unshelled. In amniotes—birds, reptiles, and monotreme mammals—theeggs typically have protective membranes and a outer shell, enabling reproduction on land. Many fish and amphibians lay eggs in water or moist environments, usually without hard shells. Invertebrates such as insects, mollusks, and crustaceans also reproduce by laying eggs, with a wide range of developmental strategies and parental care.

Monotremes, a small and primitive group of mammals including the platypus and echidnas, are notable for laying eggs. After laying, the eggs are incubated externally in nests or pouches, and the young are nourished afterward by milk produced by the mother.

Ecology and evolution of eggbearing reflect its versatility. Egg development protects embryos and allows life cycles to exploit diverse habitats, from aquatic to terrestrial. Parental care varies widely—from guarded nests and incubation to unguarded eggs that rely on environmental conditions. The broad distribution of eggbearing strategies across vertebrates and invertebrates highlights its central role in the reproductive diversity of life.