A simple life cycle is one in which an organism goes through three stages: before birth, young, and adult. Birds and fowl, fishes, reptiles, and mammals have simple life cycles.

Birds and Fowl

The young of birds and fowl like chickens develop inside the parent animal in an egg. The egg contains everything needed by the embryo developing inside it. As the embryo grows, it is protected by a hard and brittle shell that keeps the egg from drying out.

The mother hen or bird sits on its eggs to keep them warm. When the embryo's development in an egg is completed within twenty-one-days, the shell breaks. A chick, or a little bird or fowl with very short feathers then breaks out of the shell.

In around four weeks, it will grow more feathers, a comb on its head, and a wattle under its beak. Within three months, the chick would have grown into an adult chicken. The females grow into hens and the males into roosters. The female chicken lays eggs and the cycle is repeated.