Rich Hillis, age 10, of Phoenix, Arizona, for his question

How big is a baby kangaroo?

The story of the baby kangaroo is downright remarkable and some¬what hard to believe. Chances are, his whopping mother stands more than five feet tall and tips the scales at about 175 pounds. You would expect such a large lady to bear a baby that weighs at least a few pounds. Not at all. A normal newborn kangaroo weighs much less than an ounce.

As we know, mammal animals give birth to live babies and nurse them on mother's milk. This, we are told, is the most advanced form of childbirth in the animal world. Baby birds develop inside eggs that may be stolen from the nest. Mammal babies have a better chance because they develop inside the mother's body. This pre birth growing stage is called the gestation period.

The gestation period varies in different mammal species. A lady lion gives birth to her furry cubs about 110 days after mating. A litter of helpless little mice is born after about two weeks and the gestation period for an elephant is 21 months.

Longer gestation periods give a baby animal a better chance to develop.

The early mammal of 60 million years or so ago, had very short gestation periods. Their newborn infants were tiny, blind and naked and completely helpless. In those days, we are told, many mammal mothers solved this problem with built in baby carriages. They were marsupial mammals with cozy pouches where their helpless little babes were nursed and protected.

Later, gestation for most mammals became longer and the newborn babes were stronger and not so helpless. In most parts of the world marsupial pouches went out of style. But not in Australia, home of the kangaroo.

The male great grey kangaroo is called Boomer. This bouncing beauty stands at least six feet tall and weighs about 200 pounds. The female is called Flier and though quite a bit smaller than the male, she also is a whopper. The baby kangaroo is born only four or five weeks after mating. And, as you would expect he is a helpless midget.

The blind and naked baby is about three quarters of an inch long. His body is no thicker than a pencil and its total weight is about one thirty fifth of an ounce. However, in three minutes he manages to scramble from his birth canal, through his mothers shaggy fur and. into the cozy fur lined pouch on her tummy.

There the amazing baby attaches his hungry mouth to one of her milk faucets and hangs on. Nobody hears a peep out of him for months. Meantime he grows and develops, opens his eyes and dons his fur coat. In Australia, this offspring of Boomer and Flier is called Joey. After eight months he weighs about ten pounds. Soon he ventures forth on short trips but for at least another six months he returns to the pouch for safety and feeding.