Gestation: growing before birth
Biology · Key Stage 2 · The School
Growing before birth
Before a baby mammal is born, it grows inside its mother. This time of growing has a name: GESTATION. It ends when the baby is born. Every mammal goes through gestation. But not every mammal takes the same length of time. The differences between animals can be huge.
Different lengths for different animals
A mouse is born after about three weeks. A human baby grows inside its mother for about nine months. An elephant grows inside its mother for almost two years. That is longer than any other land mammal. Scientists have measured these times carefully, species by species. The pattern holds true across hundreds of different mammals.
Why the length is different
A bigger baby, born more ready for the world, usually needs more time to grow. An elephant calf can stand up within hours of being born. It can even walk that same day. Growing that ready takes a very long time. A tiny mouse pup needs far less. It is born blind and helpless, and does not need to be ready to walk right away.
A mouse pup is born blind and helpless. It has only had about three weeks to grow. A human baby is born after about nine months. It still needs constant care. An elephant calf is born after almost two years. It can already stand and walk that same day. A longer gestation usually means a more ready baby at birth. The elephant's long wait gives it a calf that can keep up with the herd almost straight away.