A Gene Map for the Cute Side of the Family

When scientists announced last week that they had deciphered the complete genetic playbook for the duck-billed platypus, the public reacted with considerably more enthusiasm than it had accorded similar bulletins about the sequencing of, say, the mustard plant, the mosquito or the wild chicken. A "fantastic response," said Jennifer Marshall Graves of the Australian National University in Canberra, a principal author on the report. "More than I expected."

One reason for the glowing reviews is that people love platypuses the way they love penguins and panda bears, as adorable, clumsy and nonthreatening creatures that remind them of kids playing dress-up. But the platypus trumps its plush-toy costars by adding a kind of Dada prankishness to the equation, what with its bill that looks like a Charlie Chaplin shoe, the leathery, thumb-sized eggs it insists on laying, the Daffy Duck webfeet outfitted with venomous spurs and the milk that dribbles down its unnippled chest. That the genetic code of the platypus proved to be as bizarrely pastiched as its anatomy enhanced the popular appeal of the report, published in the journal Nature.

Yet for researchers in the burgeoning field of comparative genomics, the real beauty of having spelled out all 2.2 billion chemical letters of the platypus's genetic blueprint lies not with the freak-show charm of the animal but rather with its sublime ordinariness, positioned as almost a platonic abstraction of a mammal, yet one with enough specifically derived features to remind us that it is just an animal trying to make its way in the world. It is archaic and post-modern, primitive and refined. By studying the platypus and its close relatives, scientists hope to better understand the genesis and evolution of the entire mammalian family tree.

"Modern mammalian diversity is enormous," said Zhe-Xi Luo, curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh, "but our view of that diversity has been heavily influenced by our focus on two of the three groups of mammals, the placentals and the marsupials."

That fixation isn't surprising, he said, given their numbers. Placental mammals that gestate their young internally, as do we and most of the pelts we know, account for 95 percent of the world's 5,600 species of mammals, and marsupials like the kangaroo, koala and our very own opossum, whose young are born at a grublike stage and do most of their developing externally, often in a pouch, constitute nearly all the rest.

The third group of mammals, the monotremes, claims a measly three distinct animals, and all are indigenous to Australia and New Guinea: the duckbilled platypus and the long-beaked and short-beaked echidnas, also known as spiny anteaters. Yet this small club goes very deep, and with the sequencing of the platypus genome, Dr. Luo said, "the total scope of mammalian diversity" can now be explored.

The monotremes are considered the most ancient mammalian group, dating back to the Jurassic period, which began roughly 200 million years ago. They are not our direct ancestors, but rather split off from the rodenty line that gave rise to us and marsupials some 180 million years ago, with marsupials breaking away maybe 40 million years later.

However ancient the rupture, the last common ancestor between us and monotremes was clearly mammalian, for we all sport mammalian traits, some of us more luxuriously than others. The duckbilled platypus, for example, is jacketed in two layers of fine, dense fur, the better to keep it warm in its semi-aquatic existence, and "it's the softest fur you can imagine," said a co-author of the platypus paper, Wesley Warren of Washington University School of Medicine. ...

•	A Gene Map for the Cute Side of the Family Basics The New York Times, Tuesday, May 13, 2008 Byline: Natalie Angier