Do Peoples Bodies Change Because of Where They Live?

In some cases, yes. The Indians of the Andes Mountains, on the west coast of South America, have developed bodies which are different from ours in order to survive where they live. At 17,000 feet above sea level, where these Indians live, we would find it very hard to breathe, but they do not.

The Indians' bodies have adapted in several ways. First, their lungs have grown bigger than ours, which means they can inhale and exhale more air with each breath. Then, too, they have about two quarts more blood in their systems than we do. They also have bigger red corpuscles to carry the oxygen. And their hearts are 20% bigger than ours.

The Indians also have shorter arms and legs to give the heart less distance to pump the blood, and smaller hands and feet, resulting in less of an area to be exposed to the cold.

What Decides If You Will Be a Boy or a Girl?

There were two special chromosomes in you when you were just beginning life as a fertilized egg. These are called sex chromosomes. Scientist have named them the X chromosome and Y chromosome.

A woman's egg cell contains only an X chromosome, while a man's sperm cell Y contains either an X or a Y. If the woman's egg cell is fertilized by a sperm cell with an X chromosome, the fertilized egg will have two X's and the baby will be a girl. But if the sperm cell has a Y chromosome, creating both an X and a Y in the fertilized egg, then the egg will develop into a boy.