Useammansikiöinen

Useammansikiöinen is a Finnish term that translates to "viviparous" or "live-bearing" in English. It describes a mode of reproduction in which the offspring develop inside the body of the parent and are born live, rather than hatching from an egg laid externally. This developmental strategy is found across a wide range of animal groups, including certain fish, reptiles, amphibians, and mammals.

In viviparous organisms, the embryo receives nourishment and protection within the mother's reproductive tract. The extent of maternal provisioning can vary greatly, from simple yolk reserves to complex placental structures that facilitate nutrient and gas exchange between mother and fetus. This internal development allows for a more controlled environment for the developing offspring, often leading to higher survival rates compared to oviparous (egg-laying) species.

Mammals are perhaps the most well-known group exhibiting viviparity, with the vast majority giving birth to live young. However, the phenomenon is not exclusive to them. Certain sharks, some species of snakes and lizards, a few amphibians, and even some invertebrates employ this reproductive strategy. The evolution of viviparity is thought to be an adaptation to various environmental pressures, such as providing offspring with greater protection or enabling reproduction in environments where external egg development would be difficult.