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An Evolution Revolution

An Evolution Revolution

Summary

Laura Poling unfazed by the sudden attention on the controversy around an article published in the February 12, 1999 issue of the journal Science, which challenges the fossil record by concluding that turtles, not birds, are the closest living relatives of crocodiles.

What started as an undergraduate research project has brought a young scientist into the limelight and into the midst of scientific debate. But 23-year-old Laura Poling seems unfazed by the sudden attention. "In science, there's bound to be controversy," she said. "New things are found all the time and things previously thought to be true are constantly being replaced. That's kind of the beauty of science." The controversy centers around an article published in the February 12, 1999 issue of the journal Science, which challenges the fossil record by concluding that turtles, not birds, are the closest living relatives of crocodiles.

Now a graduate student earning her Master's degree in genetics, Poling was a senior at Pennsylvania State University when she started this research. A grant from the Howard Hughes Medical Institute's Undergraduate Biological Sciences Education Program, which funds programs that support students' summer and academic year laboratory training to prepare them for research careers, enabled her to pursue her work in the laboratory of S. Blair Hedges.

Poling and Hedges startled the world of evolutionary biology with a genetic study that indicates that turtles, not birds, are the closest relatives of crocodiles, and that turtles are much younger, evolutionarily speaking, than most scientists believe. The work challenges long-held assumptions, based on decades of anatomical and fossil research, which place birds as the reptile group most closely related to crocodilians. Another important conclusion reached by the genetic study flaunts scientific convention: According to Poling and Hedges, genetic evidence shows that lizards are not closely related to tuataras, a group of spiny reptiles that seem to resemble lizards and have long been considered their closest living relatives.

As a college student, Poling wanted to gain laboratory experience and interviewed with Hedges, an evolutionary biologist. After deciding to investigate turtles' place in the reptile family, Poling spent the summer of 1998 working with Hedges, who places a high value on undergraduate research. "Many graduate students who come to my lab from other institutions have 4.0 grade point averages but no research experience as undergraduates," he said. As a result, many students "are unfocused and may leave after a year because they didn't understand what research is like," he said. His undergraduate students, on the other hand, learn early on what it means to collect and manage data and are better prepared to stick with a Ph.D. program. While he views grades as important, he also believes scientists need two qualities to succeed: curiosity and an ability to work independently.

In conducting her investigation, Poling demonstrated the ability to tackle a tough problem and stay with it. She sequenced the same gene in five reptile species and analyzed them, together with another gene in a tuatara, in order to compare them with other known reptile sequences. After she found strong statistical evidence that turtles belonged with crocodiles, Poling said she delved into databases, collected gene sequences from all the representative reptiles she could find, and built trees for all of them as well. Ultimately, these new sequences were added to 340 available protein and DNA sequences representing 33 genes.

When she started her research, Poling said she was not fully aware of the importance of the work. "Once I learned more about the subject and did a literature search and talked to people, I found it was an important evolutionary question," she said. "Based on morphology, turtles are considered one of the older and more basal lineages. So that's where the controversy arises, with morphologists and paleontologists holding one view. But molecular data do point to turtles being one of the youngest lineages and grouping with crocodilians."

Poling and Hedges were so convinced by the data that they wrote a manuscript and fired it off to Science. The rest is history. After receiving what Hedges called "an incredibly quick response from Science," the story was published, and an article describing their results also appeared in the February 12 issue of The New York Times. "Twenty three is rather young to have a cover story in Science," Poling acknowledged. "I don't know how many people who have been in the field for a long time have accomplished that. I'm really happy I've accomplished this so far even if I'm just beginning."

After completing her Master's degree, Poling expects to earn a Ph.D. in human genetics and pursue genetic research into the causes of disease. Poling said her research experience in the Hedges laboratory has given her a strong background in evolutionary biology and may ultimately help her in understanding human disease and what makes people vulnerable to disease.