Investigating the arrival of first North Americans from Asia

Gerald Shields

In 1986, Dr. Gerald Shields began to gather DNA samples from indigenous groups of people on both sides of the Bering Strait and set about the task of determining how closely related they were. He knew it would take a while. In fact, he’s still at it. While 12 years may sound like a long time, consider that Shields’ research brings to the present events that may have occurred as early as 30,000 years ago.

Shields, an evolutionary geneticist, and UW zoology graduate student Jeff Simonson believe they have determined the point of origin of the migration of humans into the New World. “Is there a place in Northeast Asia to which the genetic diversity of these groups seems to coalesce? We believe it occurs in Northern Mongolia, not in Siberia as previously believed,” Shields said.

Although everyone has it, mitochondrial DNA is only passed on from mothers to daughters. The genetic material is present in the egg, not the sperm. A mutation in the sequence of one individual’s mitochondrial DNA can act like a fingerprint distinguishing that person from an individual with a different mutation. Individuals who share language, culture and ancestry, such as the 700 people of the 19 tribal groups in Shields’ study, tend to have similar genetic mutations.

By comparing mitochondrial DNA sequences of individuals from indigenous groups in Alaska, Siberia and Asia, Shields and colleagues found an ancestral link — a match between ancestors of New World indigenous groups and a Northern Mongolian indigenous group.

The key is knowing approximately how long it takes for mutations to occur in mitochondrial DNA sequences. In other words, scientists can estimate how long it has taken for the diversity of mitochondrial DNA sequence among all New World groups to develop from this Northern Mongolian group. How long? Over 30,000 years.

Shields will discuss this research, as well as how he and his team believe these early ancestors migrated to the New World, in a lecture on Oct. 23, from noon to 1 p.m. in room D-209, HSC. His lecture, “Peopling the Americas: Getting Our Berings Strait,” is the first in this year’s Science in Medicine Lecture Series, sponsored by the medical school’s Office ofResearch and Graduate Education. A professor of zoology and head of the Department of Biology and Wildlife at the University of Alaska Fairbanks, Shields is the 14^th lecturer in the Science in Medicine series from one of the other universities in the WWAMI Program, which includes Wyoming, Alaska, Montana and Idaho, as well as Washington.

“There have been a lot of archeological studies around the Bering Sea environment, but there is still a great deal of uncertainty about how humans entered the New World. Was it one continual migration or separate migrations?” Shields said.

Seeking answers to these questions has taken Shields from Alaska to Central Asia and Siberia and he has developed a collaboration with several Russian researchers, particularly Mikhail Voevoda, a human geneticist with the Institute of Internal Medicine in Novosibirsk, Siberia, and Miroslava Derenko of the Institute of Biological Problems of the North in Magadan, Russia.

Shields began working on these questions 14 years ago when he spent a research sabbatical in the Department of Biochemistry at the University of California-Berkeley with the late Allan C. Wilson, a renowned scientist in the field who developed the “mitochondrial African Eve hypothesis” in the mid 1980s.

Mitochondrial Eve, generally accepted today, is also based on evolutionary genetics; it suggests that modern humans arose about 300,000 to 400,000 years ago in Africa and replaced indigenous groups as they migrated into Europe and Asia.

When Shields returned to Alaska, he began applying the techniques he’d learned in Wilson’s lab to questions of how, when and from where humans entered the New World from Asia. In 1986, when he and his colleagues began their work, most investigators agreed that the New World was populated in three separate waves of migration from a fixed point in Siberia.

Developed by linguist Joel Greenberg, this “three-wave migration hypothesis” suggested that the first people to migrate, the Paleo-Indian language group, ancestors of modern Amerindians, came out of Siberia approximately 12,000 years ago; a second migration occurred when the NaDene language group, from whom many of the present Northwest coastal Indians descended, occurred about 9,000 years ago and a third migration, the Eskimo-Aleut migration, occurred approximately 4,000 years ago.

According to Shields, however, humans migrated from Northern Mongolia to Western Alaska more than 15,000 years ago. Amerindians, he said, may have moved south of glacial ice sheets before they coalesced. The evidence suggesting this movement is that the genetic diversity among Amerindians is about twice that of the combined diversity among the NaDene and Eskimo-Aleut peoples, who Shields said may have been blocked from southern expansion by ice sheets.

When climates eventually warmed again, the Eskimo-Aleuts expanded to the coastal regions of southwestern Alaska and across the high Arctic to Greenland, while the NaDene expanded south into coastal regions of the Pacific Northwest. Shields said he can find little or no genetic justification to separate the NaDene and Eskimo-Aleut groups, as linguists do.

Shields’ studies have been published in the American Journal of Human Genetics and elsewhere. He holds a Ph.D. in zoology from the University of Toronto and a master’s degree in biology from Central Washington State University. He has been a professor of zoology at the University of Alaska Fairbanks since 1975. ¶
Will Morton