Dorothy Brian, age 13, of El Paso, Tex., for her question:

HOW DID LIFE DEVELOP ON A VOLCANIC ISLAND?

Volcanic and coral islands originally had no animals or plants living on them. These islands became inhabited at first by birds that flew across the sea. Then, scientists tell us, came animals that swam from other islands.

Some animals and insects may have arrived on logs and other debris. Plant seeds may have floated across the sea or perhaps were carried by birds or by the wind.

Often the animals and plants that live on an island are cut off from those elsewhere. Because of their isolation, they may gradually develop or evolve into species not found anywhere else. An example of this is the giant tortoise of the Galapagos Islands which evolved from ancestors that were much smaller.

Also, some sunflower plants that grow on the Galapagos Islands have developed into tall trees.