LIZARDS GET A LEG UP IN EVOLUTION EXPERIMENT.

Byline: Scott Allen The Boston Globe

Filling a major gap in the evidence for evolution, researchers have documented what appears to be a striking example of the process at work: Lizards that developed shorter legs, better suited to their new environment, in the years after their ancestors were released on islands in the Bahamas.

The real-life experiment goes a long way toward answering complaints that science has not been able to show a species actually evolving toward a new form in an observable time frame, researchers said.

Jonathan B. Losos of Washington University in St. Louis, the lead researcher, said descendants of one group of the common lizards, called Anolis sagrei, had shorter hind legs within 14 years - less than 20 generations - after they were put on islands with smaller trees than those in their original home. Shorter hind legs help the lizards to balance on smaller branches, he said.

The findings, published Thursday in the journal Nature, may provide a well-documented microcosm of the immense evolutionary changes that scientists say occurred over millions of years in the battle for survival of the fittest. Until now, with rare exceptions, evolutionary biologists have relied on lab experiments to demonstrate how plants and animals physically adapt to new environments.

``We were able to document changes that occurred rapidly'' in response to a new environment, said Kenneth I. Warheit of the Washington Department of Fish and Wildlife, who wrote the paper with Losos. ``The environment . . . was having a major say as to what these creatures were going to look like.''

The time problem

Evolutionary biologists have identified numerous species that have apparently evolved to adapt to their environment, such as the 12 species of finches Darwin found in the Galapagos Islands, each with different beaks or other characteristics depending on where they lived and what they ate.

The trouble is that evolution occurs on such a vast time scale that no researcher can typically observe it. Recently, however, field research has increasingly suggested that rapid evolution can occur following big environmental changes.

The descendants of guppies in Trinidad were reaching sexual maturity at a later age within 11 years after the guppies were moved to an area with fewer predators. Researcher David Reznick of the University of California, Riverside suggested that once the threat of predators was reduced, later-breeding guppies were able to survive long enough to pass on their genes.

But biologist Ted J. Case of the University of California, San Diego, said the lizard study stands out because the leg changes were so marked and were noted on so many different islands. The rapid, clear-cut change in Anolis sagrei on tiny islands ``mirrors in miniature some elements of the larger-scale'' evolution of Caribbean lizards into different species, Case wrote in an accompanying article in Nature.

Defenders of the theory of evolution cheered the new study, pointing out that creationists who believe God created the world as it is today are making inroads against teaching evolution in schools. Alabama biology textbooks, for example, now carry a pasted-in disclaimer calling evolution a controversial theory, not a fact.

``The public really does need to know how much evidence there is that evolution takes place,'' said Eugenie Scott, director of the National Center for Science Education in Berkeley. ``You can look at these lizards and see that in a relatively short period of time, you can see really substantial changes.''

A creationist's rebuttal 

But supporters of creationism said Losos' findings do nothing to upset their views, since a short-legged lizard is still a lizard. Creationists believe there is genetic variation within a species of animals, but reject the idea that, for example, humans evolved from apes.

``Is there any evidence in the fossil record of one species turning into another? The answer is no,'' said Frank Sherwin of the Institute for Creation Research in El Cajon.

However, Harvard University paleontologist Stephen Jay Gould, a leading critic of creationism, said he has long since given up trying to persuade his opponents that evolution is a fact. ``Nothing is going to persuade them. This is a political debate, not a scientific debate,'' he said.

The Bahamas lizard study began in 1977 when Thomas W. Schoener, an ecologist at the University of California, Davis, took small groups of Anolis sagrei from Staniel Cay in the Exuma chain of the Bahamas to 14 smaller islands with no lizards. While Staniel had many trees, including large ones, the small islands had few trees, since periodic hurricanes wiped out plants and animals alike.

Schoener expected the lizards to die, but they thrived on most of the islands, multiplying from 10 or fewer individuals to as many as 700. Losos, an evolutionary biologist, convinced Schoener to turn the lizard study into a test of evolution.

Evolutionary theory predicts that when plants and animals colonize new territory, the specimens best adapted to the new conditions as a result of random genetic variation thrive, so their offspring eventually diverge in form from the parent population. Losos predicted that among the lizards' descendants, shorter legs would predominate, because they offer a survival advantage - helping lizards balance on the narrow branches of the small shrub and bushes in the new environment.

Tiny differences mean a lot

A computer analysis found that not only did the relocated lizards' hind legs become shorter in succeeding generations, but they were shortest on islands that had the smallest branches for lizards to perch on.

Though the differences are tiny - imperceptible to a layperson - the researchers found that the lizards were changing physically at a pace rivaled only by the Trinidad guppies. Losos suggested that the pace may reflect the lack of competing lizards and the fact that Anolis sagrei is highly adaptive, with 400 different species in its genus.

Now, Losos is trying to determine whether the changes in the lizards are simply physiological, achieved the way a weight lifter gains muscle mass, or the result of genetic inheritance. He said lizards now being raised at the St. Louis Zoo could provide an answer in a matter of months.

If shorter legs are being inherited, it would be a graphic demonstration of the law of natural selection, which posits that the organisms best adapted to their environments are most likely to survive and pass on genes to the next generation.

Even if the shorter legs are a physical adaptation - explained by a phenomenon called phenotypic plasticity - Losos believes they herald genetic changes to come. If shorter-legged lizards thrive, eventually lizards genetically inclined to shorter legs will come to dominate the colony, Losos argued.