Li introduced the field of molecular phylogenyBy Sharon Parmet
Medical Center Public Affairs
Molecular phylogenya way to classify life forms and assign them places on the evolutionary tree based on gene similaritiesemerged in the 1960s. But the first textbook on the subject, Molecular Evolution, would not be written until 1997.
The author, evolutionist Wen-Hsuing Li, revolutionized the young field of molecular phylogeny with his mathematical and theoretical work and joined the University in December 1998 as the George Beadle Professor in Ecology & Evolution.
Li is the premier evolutionist in the world today, said Chung-I Wu, Chairman of Ecology & Evolution. E&E caught a big fish by recruiting Li.
Lis equations and computer programs allow scientists to compare genes that have the same function in different species to determine how closely related they are to one another. The final result is an evolutionary tree with a branching pattern and length of limbs that shows species relatedness.
Before molecular phylogeny, evolutionary trees were based on morphology, which grouped together animals with similar forms. But many of these trees have been thrown into question when molecular phylogeny was applied. For example, in 1991 Li published a paper in the journal Nature titled Is the Guinea Pig a Rodent? The paper, which received attention from evolutionary biologists and geneticists around the world, described how molecular phylogeny shows that the guinea pig is not as closely related to other rodents, such as the rat and mouse, as previously thought. Today, Li believes the guinea pig is indeed a rodent, but its genetic fingerprint shows it holds a more distant place on the evolutionary tree.
However, in general, Li is more interested in showing how similar species are to one another. We used to think that we were so different from apes, but were really much more closely related than we thought. If you compare human and chimpanzee DNA, there is only a 1.5 percent difference, Li explained.
Molecular data have lots of important social implications, said Li.
Currently, Li is working to determine the similarities in human DNA by gathering and testing samples from around the world. So far he has sequenced a large DNA region in 70 samples and estimates that human DNA differs by only about 0.1 percent, though in terms of skin pigmentation, people from different geographic locations may look rather different.
Scientists think skin pigmentation is directly related to the latitude at which a particular group of humans evolved, said Li. People who have lived closer to the equator for a long time are darker skinned to protect them from harmful UV rays and to prevent the overproduction of vitamin D, which is made when the skin is exposed to the sun. Too much vitamin D can be toxic, said Li.
Groups that evolved in the northern or southern latitudes where the sun is weaker need to be sure they can produce enough vitamin D, so their skin is lighter. Too little vitamin D can cause the disease rickets.
The data Li gathers will also allow him to study the migration of early human populations.
Li is also interested in the study of co-evolution of the human growth hormone and its receptor and the evolution of color vision.
Li, who came to Chicago from the University of Texas, Houston, where he was the Betty Trotter professor in medical sciences, earned his B.E. in civil engineering from the Chung-Yuang College of Science and Engineering in Taiwan in 1965; his M.S. in geophysics in 1968 from National Central University in Taiwan; and his Ph.D. in applied mathematics and genetics from Brown University in 1972.