Why do Marsupials have Pouches?

Marsupials like kangaroo and koala are pouched mammals. They give birth to babies which are at a very early stage of development, very small and helpless. The babies crawl to the pouch and continure to develop there safely, feeding on mother’s milk. Most of the mammals nourish their developing young ones by means of placenta in the mother’s womb. Marsupials do not have placenta and they have undeveloped babies. The baby kangaroo at the time of birth, is just grape sized with tiny, hardly developed legs. It crawls on its own, up to mother’s fur and then into her pouch. It hatches on to one of the mother’s nipples to suck milk. It stays there for six months and keeps visiting the pouch until it is an year old.