Jeff Hecht
28 February 2009
New Scientist
44
volume 201; issue 2697
(c) 2009, New Scientist, Reed Business Information UK, a division of Reed Elsevier, Inc. All Rights Reserved.
How to Build a Dinosaur: Extinction doesn't have to be forever
Jack Horner and James Gorman
Dutton
$25.95
JACK HORNER wants to raise the dead by growing a dinosaur from a chicken embryo. The publisher calls his idea "astonishing new science that trumps science fiction". Has palaeontologist Horner's stint as a consultant on the Jurassic Park films infected him with some science-fictional virus? Is chickenosaurus his bid to create a new monster-movie franchise?
Fortunately, it's "no" to both questions. In How to Build a Dinosaur Horner is at his best: provocative yet firmly grounded in science. I doubt he'd mind hitting the bestseller list, but his goal is to make people think about how evolution works, and by extension, about our own origins.
Science holds out some hope for cloning ancient DNA and resurrecting the victims of recent extinctions, from dodos and moas to mammoths and woolly rhinos. But for dinosaurs, it doesn't look promising. Horner's former student Mary Schweitzer, for example, has extracted traces of protein and possibly soft tissue from the extremely well-preserved leg bone of a Tyrannosaurus rex that died more than 65 million years ago. DNA is far less stable than protein, so if the protein was scarce, Horner sees no chance that enough DNA survives to clone the extinct giants. So much for Jurassic Park.
Happily, Horner thinks there's a different way to build dinosaurs, and it doesn't involve finding any fossil DNA. He wants to alter the embryological development of chickens, which are living descendants of dinosaurs. His idea comes from the fertile field of "evo-devo", which focuses on how evolution affects the way animals develop from fertilised eggs. Look closely at a developing embryo and you can see some ancestral forms briefly appear. Birds, for example, start to develop tails, then convert the would-be-tail into a pygostyle, a bony lump at the base of the spine which holds the tail feathers.
Careful study of this process reveals that two sets of genes are involved, one controlling the expression of the other. There are the genes to build tail bones plus additional genes to transform the tail bone into other structures. Crucially, evolution most often affects the latter "control" genes. That led Horner to propose altering the chicken embryo so that it would grow a long tail, like those seen in dinosaurs or in Archaeopteryx , the earliest known bird, as well as other ancestral traits such as claws and teeth.
With Horner's encouragement, Hans Larsson of McGill University in Montreal, Canada, thought he might be able to grow a dinosaurian tail on a chick by splicing the fast-growing tail tip from a young embryo onto the tail of an older embryo before it turned into a stunted pygostyle. The experiment didn't work, a failure that points to the tremendous complexity of the development process. We don't yet know how to coax out a chicken's inner dinosaur, but for Horner, it's a worthwhile quest.
Horner's dream is to walk on stage on The Oprah Winfrey Show with chickenosaurus following him on a leash, but he wants more than fame. A dino-chicken, he writes, "would be shockingly vivid evidence of the reality of evolution... The creature would be its own sound and vision-bite". It wouldn't be the first experiment in evolution - we live among uncontrolled examples including microbial response to antibiotics and insect resistance to pesticides - but it would be the first rewinding of evolution, the first time we could watch it happening in reverse.
Linking the most charismatic of fossils with the humble barnyard chicken would make a great scientific story. It would show how molecular changes bring about the large-scale differences in form seen throughout the fossil record. It would teach us about birds, dinosaurs and evolution.
Co-authored by James Gorman, deputy science editor of The New York Times , this book makes for a good read, whether or not a chickenosaurus ever hatches.
Jeff Hecht is a regular contributor to New Scientist.
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