Hummingbird mothers usually lay two tiny eggs, and the chicks hatch in a couple of weeks.

Across the animal kingdom, some of the most essential lessons -- and the most extreme challenges -- occur in the first moments of life.

In 1956, the Columbus Zoo in Ohio became the home of the first gorilla to be born and raised in captivity.

In the 1930s, a young Austrian scientist named Konrad Zacharias Lorenz formally documented the process of "imprinting" -- socially bonding to a parent figure.