Melissa Ann Oliva, age 12, of Berlin Center, Ohio, for her question:

WHY DO BEAVERS BUILD DAMS?

Judging from his remarkable dams and waterways, the busy beaver seems to be an architectural genius. However, recent observers tell us that, though usually a smart fellow, he does not have a super IQ. It seems that he is by nature a born builder and his talents work as a sort of instinct that drives him to build build build.

No doubt the beaver's story began in the dim distant past, when his rather slow, roly poly .ancestors lived in woodsy regions beset by famished foes. Those that survived long enough to bear baby beavers escaped by swimming in and under the water of a pond or stream. For added protection they dug burrows and raised their families in muddy banks.

The beaver kits with webbed toes and strong digging claws on their fingers had a better chance of surviving. So did those with nose valves to close during long swims under water.  Their rodent teeth grew constantly and constant gnawing kept them comfortably worn down. Since children resemble their parents, more and more beavers inherited these useful family features.

Through countless generations, they also inherited a fantastic group of behavior patterns. For safety's sake, they protected their range with ever present supplies of water. To accomplish this amazing feat they cut down trees to dam up streams, creating ponds where they built elaborate houses with underwater doors.

Beaver parents mate for life and the family unit includes teen agers plus a new brood of two to eight kits. No doubt the teen agers learn a great deal about constructing waterways during their two years at home. But this is not the whole story.

We know now young beavers separated from their parents repeat the family building skills. Captive beavers use whatever building material is handy, even when no safety structures are needed. For these reasons it seems obvious that a beaver builds because he feels he must.

Basically the elaborate dams and waterways make it possible for the beavers to survive in hostile territory. But they do not figure this out. They inherited not only certain useful physical features, but a whole group of inborn talents that impel them to build and build and build. The busy beaver just does what comes naturally.