Platypus unlocks evolution's secrets.

• Position: Genome Sequencing

By any account, the platypus is an odd creature. It has a broad, rubbery bill that brings to mind a duck, but it swims mere like a beaver; yet, it lays eggs and can inject poisonous venom like a reptile. No wonder it is considered an elaborate hoax by scientists who examined the first specimen pelt shipped to England from the colony of New South Wales in 1799.

A consortium of scientists, including Cold Spring Harbor (N.Y.) Laboratory's Gregory J. Harmon, published results of an international effort to sequence the platypus genome. It reveals evolutionary secrets that go far beyond the obvious fact that the creature, found exclusively in eastern and southern Australia--including on the island-state of Tasmania--neither is a typical mammal nor reptile. In fact, the platypus is a member of a mammalian species called the menotremes, which includes only four other subspecies (those being echidnas, varieties of spiny anteaters). The monotremes diverged from other primitive mammals about 166,000,000 years ago, in the late Jurassic period--a fact corroborated indirectly in the newly sequenced genome.

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The platypus has a distinct mode of rearing its offspring. All mammals, in addition to being warm-blooded, can be grouped according to their modes of gestation. Marsupials like the kangaroo rear profoundly immature young in external pouches for extended periods of time. Eutherian mammals like mice and humans protect their progeny for lengthy...