Cloning genes from extinct animals may give researchers insights on evolution
Cloning genetic material from extinct species may ultimately shed new light on the tempo and nature of the evolutionary process. That is the hope of Allan C. Wilson, director of the laboratory at the University of California, Berkeley, where the use of genetic engineering techniques to recover and clone fragments of DNA from the tissue of extinct animals has been developed.
This week a member of Professor Wilson's staff, Russell Higuchi, reported the successful cloning of bits and pieces of the genetic material of the quagga, a creature that looked half-horse and half-zebra and was hunted to extinction in Africa a century ago.
The purpose of this effort is not to revive an extinct species - this is decades beyond the capabilities of today's genetic engineering - but to resolve a long-standing zoological controversy: Was this creature more closely related to the horse or the zebra?
Beyond this, the new technique could be the key to unlocking some of the basic secrets of evolution itself.
''While I am interested in the question of the quagga, I am really involved because I hope it may prove possible to test the molecular evolutionary clock hypothesis,'' Dr. Wilson says.
He is one of the foremost proponents of this theory, which holds that evolution is the result of a steady, clocklike accumulation of genetic mutations at the molecular level. Most of the these mutations have no significant effect on the organism as a whole. Only a small percentage affect an animal's viability and so are subject to the force of natural selection.
The evidence for such a steady rate of change in genetic makeup comes from comparing the DNA of pairs of existing species with common ancestors, like sheep and goats. Dividing the number of microscopic differences in their genetic material by the best estimate of the amount of time that has passed since the two species diverged results in a mutation rate that is remarkably constant for a large number of species, the biochemist explains.
Despite this, the proposal is controversial. Darwinian anatomists have assumed evolution proceeds at different rates in different species and at different times because this is what they have seen in the fossil record.
Also, the theory predicts that the split between ape and man came only 5 million years ago. Many paleoanthropologists place the date somewhere between 10 million to 30 million years.
''If prehistoric DNA exists, and we can analyze it, then this could provide a direct test,'' Wilson explains.
Going from successfully recovering and cloning genetic material from a centuries-old sample to samples millions of years old requires a certain leap of faith, the scientist acknowledges.
But if DNA is quickly dehydrated, kept relatively cool, and not exposed to acidic conditions, it preserves fairly well, he explains.
Before working on the quagga, Dr. Higuchi and his coworkers spent considerable time on a sample from a 40,000-year-old mammoth discovered in Siberia. They were able to extract mammalian DNA from this sample, but it was too deteriorated and contaminated with bacterial genes to be of much use. Still, it suggests DNA may be recovered from much older tissues if they have been properly preserved and handled, the biochemist argues.
Wilson isn't sure what to work on next. ''There are so many possible avenues that I'm not sure what the right thing to do is,'' he explains. He has only two or three people free to work on this, and his is the only laboratory in the world doing research along these lines.
To answer the quagga question, the DNA they have cloned must be thoroughly analyzed and compared with that of the horse and zebra. Shortly, the lab will be getting tissue from a well-preserved prehistoric bison found recently in Alaska. They have tried the technique on animal skins and gotten some positive and some negative results so are not sure how useful analysis of the skins of animals like the California grizzly or the Dodo will be. They have also collected 26 million-year-old fruit flies trapped in sap which turned to amber, but have not determined whether they retain any genetic material.