Skip to content


About the Authors

Dr. Dennis O'Rourke is the Interim Chair of the Anthropology Department at the University of Utah in Salt Lake City, Utah. He is also the Co-Chair of the International Review Board and Vice President of Research. Dr. O'Rourke received his BA (with Honors), MA and PhD in Anthropology  from the University of Kansas in 1973, 1976 and 1980. He then went on to his Post-Doctoral fellowship in the St. Louis School of Medicine at Washington University. There he focused on Psychiatry/Genetic Epidemiology.

As mentioned before in @rebeccaleon blog from week one of class;  Dr. O'Rourke work focuses on the sampling and analysis of ancient DNA,  quantitative methods, and population and evolutionary genetics. The areas and populations that he focuses on are native America, and the North American and Siberian Arctic.

Picture of Jake Enk cutting a Mammoth tooth.

Jake Enk is a Doctoral student at McMatser University in Hamilton, Ontario. He received his Masters at The University of Utah.

In reading this chapter of Human Biology (Chapter 4), the authors bring into focus the effects of genetics on human populations in reference to geography and how understanding these topics can be, at best, informative to the history of our species and, at worst, complicated or even convoluted. The equations aside (which are, admittedly,  of great importance in the derivation of these data), in this chapter we delve deeply into understanding the mechanics of mutation , the interplay between human migration and genetic information, and how these factors shape our, often debated, view of how human populations came into existence and continued to move around the globe.

The chapter begins with explanations of basic evolutionary factors, specifically how mutations come to prominence in populations and how not only natural selection, but population size directly affects how readily mutations take hold. In somewhat simpler terms, the smaller the population, the more readily the frequency of an advantageous allele will increase within that population (There’s a convenient figure on p.108 that lays it out for you). As interesting as data acquisition and these formulas are, the real meat of Chapter 4 lies within the application of these methods to understanding our species’ history and how this data can better serve that purpose.

To begin, we can challenge, disprove, or validate many earlier assumptions of this field through the use of genetics as evidence. One great example Chapter 4 illustrates is Hrdlička’s hypothesis of a replacement population in the Aleutian Islands roughly a thousand years ago. His 1945 work, based mainly on differences in cranial forms, hypothesized an existing Aleutian population being replaced by a wave of newcomers who would become the ancestors of modern Aleuts. While his assumptions weren’t definitive beyond a shadow of a doubt, modern genetic testing (after a few upsets with unfortunately small sample sizes) has proven his work correct, contributing even more validity to our understanding of human history.

Sometimes, however, this availability of new data can obscure what was previously seen as a clean-cut understanding of that history. The authors bring up the issue of the presence of Neanderthal genetic information in modern human and the debate as to how it got there, if it is Neanderthal DNA in the first place. Sequencing of Mitochondrial DNA from Neanderthals show incredible variation from modern humans and ancient anatomically modern humans (supporting that long-held belief that humans and Neanderthals never interbred), yet nuclear genome sequences suggest that one to four percent of our genome may be made up from Neanderthal DNA, possibly from admixture. So did early humans and Neanderthals mate, or could these traits be the result of latent genetic traits that we both received form an ancient ancestor? The answer: we don’t know. Maybe both. Perhaps you’ll be the ones to figure it out.

Finally, this chapter shows how even our understanding of genetic data in relation to prehistoric human events can be far more complicated than that data would initially suggest. In the example of the populating of Europe, differences in mitochondrial DNA and nuclear molecular DNA, which seem incompatible, illustrated a far richer story. In this case, the mitochondrial DNA suggests a movement of humans into Europe from the Middle East, roughly 10,000 years ago, coinciding with the advent of agriculture. The nuclear molecular DNA evidence, however, suggests something much different. Rather than 10,000 years ago, this evidence suggests a divergence in populations from 46,000 to 130,000 years ago. So which evidence is correct? Both. By comparing and combining these data, human biologist now surmise that while a clinal migration from the Middle East into Europe did take place around 10,000 years ago, Europe had already been populated by Homo Sapiens long before that event.

All in all, this chapter is helpful in illustrating the importance of genetic information and its contribution to our understanding of the human story. If you want to know the specifics of how DNA evidence is used to formulate new hypotheses and support or refute existing ones: this is the chapter for you... But don’t take our word for it! (Insert Reading Rainbow theme here)

1) What do you believe the current genetic distance is? Is this a good thing or bad thing?

2) What are some current examples of migration? And how have they influenced the current gene population?