Bob Zelenka, age 14, of Dallas, Texas, for his question:

Do snakes and whales have traces of legs?

The ancestors of snakes and whales were four‑footed animals. The snake ancestors were cold‑blooded lizards, for the modern snake is really a legless lizard. The whale ancestors were warm‑blooded land. animals. So far no fossil remains of the whale ancestors have been found. But we know they must have been land animals to become warm‑blooded.

Both the ancient snake and the ancient whale changed their way of living. When there is a good reason for this, Mother Nature goes along with an animal and helps him adjust to a new way of life. The process of changing the form of an animal, however, is a slow one. It takes millions of years to complete. Even so, taletell. signs may remain.

Inside the body of the modern sea‑going whale are bony traces of the hind limbs he once had. Inside the body of a snake there may be bony traces of the hip and hind legs his ancestors once had. These remains are in very small bones and the leg bones are never more than little spurs. What's more, they are not present in every snake and no signs of the front limbs remain at all.

Both these animals took their time in changing their ways of life. What happens in such a change is this. The features needed in the now life become stronger, better developed and move useful in the new environment. But Nature soon discards what is not being used and features not used in the new life tend to disappear.

The ancient whale had become warm‑blooded, had grown fur and had learned to bear live babies. He was a mammal. Most likely he was a fisherman. As time went by, he spent more and more time in the sea. He grew fat on his favorite food and, because water supports weight better than the dry land, he was more comfortable in the sea ,

In time he spent all his time in the year. He practiced swimming, diving and holding breath. and nature helped him. His lungs grew big to hold long breaths, his long breaths, his front legs became flippers for swimming, but he lost his fur, all but a few bristles, and he lost his back legs which he no longer used. The whale has been a well adjusted sea animal for 50 million years or more;

The first lizard became a snaky about 100 million years ago, or so we believer Ho was originally a squat, four‑logged fellow with a long tail. For some reason he chose to live in a burrow. He preferred to wiggle along, perhaps because he could move faster that way.

In this new way of life, legs were of little use to him. They became smaller and smaller, and finally disappeared. It is believed that several different lizards took up a burrowing life and became snakes. The 3,000 or so modern snakes, then, must have descended from different ancestors.