All vertebrate animals begin their lives as either newborns or hatchlings. Newborns emerge directly from a parent's body (usually, but not always, the mother's). The offspring of most mammals and some reptiles and fish are called newborns. Hatchlings emerge from eggs. The offspring of all birds and many species of reptiles, amphibians, and fish are called hatchlings.

Regardless of whether one climbs out of an egg or gets pushed through a birth canal, there are dramatic differences in the level of development among newborns and hatchlings of different species. Some creatures enter the world smaller than adults of their species but otherwise fully formed and able to care for themselves. Many reptiles, including the hatchling sea turtles pictured in this video and a small group of birds called megapodes, receive absolutely no parental care either before or after hatching. Parents of these animals lay their eggs and leave them to develop on their own. When the hatchlings emerge, they know instinctively how to find food and shelter and to otherwise care for themselves.

Most newborns and hatchlings, however, require at least some parental care. Ducklings, for example, need their parents to guide and protect them through their first weeks of life, even though the young birds are able to walk, swim, and feed themselves almost immediately after hatching. Similarly, many newborn deer, antelope, and farm animals like goats, sheep, and cattle are able to walk and even run just a few hours after birth. This allows them to stay with their mothers, who will be their chief source of food and guidance for months or even years.

Other newborns and hatchlings, including most mammals and birds, are born or hatch into the world blind, naked, and vulnerable. These animals require intensive parental care and are seldom separated for long from the warmth, food, and protection their parents provide. As the young animals grow and develop, they become less and less dependent upon their parents. However, some animals, especially mammals -- with the extreme case being humans -- take years to gain complete independence from their parents.