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No. 35: Sep-Oct 1984

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Getting The Pouch Right

When we think of kangaroos hopping about Australia (which isn't very often), we know that all baby kangaroos are safely "buckled in" their mothers' pouches -- nature's own vehicle restraint system. How fortunate it is that kangaroo pouches open at the top; otherwise, little kangaroos would be falling out all over the place. While some marsupials have pouches opening "up" or "forward" in quite a few others evolution got the directions for pouch manufacture reversed. The koala, the wombat, the thylacine, and the marsupial mole all have backward-opening pouches. Obviously, a forward-opening pouch on the mole would act like a dirt scoop, to the great inconvenience of any occupants. On the other quadrupeds, the backwardopening pouch may protect the young from branches and vegetation.

(Marshall, Jeremy H.; "Directional Pouches," Nature, 309:300, 1984.)

Comment. This is an example of the socalled Problem of Perfection, where life seems marvelously attuned to its environment; that is, "fittest." Somewhere among the millions of species alive today, there must be one out-and-out failure. Of course, if full-scale nuclear war breaks out, we will know that evolution did make at least one mistake!

Nature's cartoon of a kangaroo with a wrong-way pouch. Evolution gone wrong! Nature's cartoon of a kangaroo with a wrong-way pouch.

From Science Frontiers #35, SEP-OCT 1984. 1984-2000 William R. Corliss