Editor's note: A podcast of the lecture is available at the UD Podcasts Web site.

8:50 a.m., Oct. 6, 2009----The fall series of the Year of Darwin Celebration at the University of Delaware kicked off on Friday, Oct. 2, with a lecture by Stephen O'Brien, chief of the Laboratory of Genomic Diversity at the National Cancer Institute.

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O'Brien provided a myriad of insights into the evolutionary history of mammals in his talk, “21st-Century Origins: Retracing Genomic Natural History Across Mammalian Radiations,” but the most captivating story he told focused on the domestication of the cat.

“Darwin gave us the concept of domestication as a major exercise by which civilizations captured outstanding adaptations over time for man's use,” O'Brien said. Most once-wild animals were valued and domesticated because they provided milk, meat, wool, or fur or because they performed servile labor. But the cat, still known in the 21st century for its independence, defied the rules.

“Cats don't take orders well,” he said. “So it's not surprising that they domesticated themselves.”

O'Brien explained that biologists had identified a number of species of small wildcats -- including Chinese, European, and African wildcats -- that seemed the likely ancestors of the small creatures that are now the most popular pets in the world, and DNA samples taken from thousands of domestic cats across the globe showed a mixing of genes, suggesting that domestication had occurred independently in multiple locations.

But O'Brien and his research team ultimately drew a different conclusion. “Domestication of the cat happened once and in just one place because a niche opened up for them,” he says. He and his colleagues narrowed the place and time to the Fertile Crescent about 10,000 years ago.

While the common belief previously was that cats were domesticated in Egypt some 3,600 years ago, O'Brien determined that they actually began to live with humans more than 6,000 years earlier. His theory is backed up by an archeological find in Cyprus -- a burial site containing the remains of a child and a cat. “This is the oldest evidence of the co-existence of cats and humans,” O'Brien said. “They obviously had a relationship.”

Archeology was just one of the tools used to solve the puzzle. “By combining phylogeny, dates, geography, geology, and paleontology, we were able to synthesize a scenario of how cats evolved and where they came to be,” O'Brien said.

He painted a vivid picture of formerly nomadic humans making a lifestyle change from hunter-gatherers to farmers. Agriculture brought rats and mice, attracted by grains stored in barn-like buildings.

Enter the always opportunistic cat.

“The mice played a role in attracting cats, who were always looking for something to do,” O'Brien explained. “Cats quickly figured out that they could get food this way, but they also had to learn not to eat the children. Those that learned this lesson quickly -- the ones that were cute and friendly -- were the ones that became domesticated.”

How does O'Brien explain the DNA evidence of wildcats mixing with domestic cats in parts of the world beyond the Fertile Crescent? That occurred afterwards as a result of migration and subsequent cross-breeding, he said.

O'Brien, who is recognized for a broad range of accomplishments in evolutionary biology, including leading the Feline Genome Project, talked about the tremendous influence Darwin had on the field. “He provided the platform by which we understand biology today, and his work changed biology forever,” O'Brien said. “The half-life of one of my papers is probably about seven days. For Darwin, it's about 500 years.”

While new techniques such as microsatellite genotyping and modern tools such as bioinformatics have enabled scientists to map the gene sequence of species like the domestic cat, O'Brien emphasized the critical role played by other branches of science in solving evolutionary puzzles.

For example, dinosaurs died off when a meteorite crashed into the Yucatan Peninsula about 65 million years ago, blocking the sun and blackening the earth. New species later evolved to fill the resulting vacant ecological niches.

Similarly, rises and falls in sea levels can effect evolutionary change by separating or joining bodies of land. For instance, when a drop in sea level caused the isthmus of Panama to form, carnivores migrated from North America to South America, eradicating the marsupials that had previously thrived there.

“Geologists have given us a view that enables us to interpret these facts and draw conclusions about the evolution of various species,” O'Brien said.

He also explained that genetic knowledge has enabled refinement of the concept of speciation, which was formerly predicated largely on morphology. For example, based on specimens collected from nearly a thousand elephants across Africa, O'Brien discovered that the African elephant, previously thought to be one species, is actually two -- one that lives in the forest and one that lives on the savanna. “Our conclusions, which were reported in Science in 2001, were all based on molecular data,” O'Brien said.

While O'Brien has published some 700 scientific papers, he has also done much to share the mysteries of evolution with the public. Known not only as a medical geneticist but also as a conservationist, he and his colleagues have written papers that have influenced decisions about the protection of endangered species and the preservation of biological diversity.

O'Brien is also the author of a book, Tears of the Cheetah and Other Tales from the Genetic Frontier, that has been referred to by Publishers Weekly as “14 firsthand evolutionary yarns [that] are the equivalent of genomic Aesop's fables.”

O'Brien trained in molecular and population genetics at Cornell University. He joined the National Cancer Institute as a postdoctoral researcher in 1971 and is now chief of the institute's Laboratory of Genomic Diversity, which he founded in the late 1980s. The laboratory has assembled more than 62,000 animal and 424,000 human tissue/DNA specimens, facilitating wide-ranging studies of disease gene associations, species adaptation, and natural history.

In 2008, the American Genetic Association presented the first annual Stephen J. O'Brien Award for the best student-authored article published in the 2007 volume of Journal of Heredity. O'Brien served as editor-in-chief of the journal from 1987-2007.

Article by Diane Kukich