Accelerated Human Evolution: Models and Data

I've prepared a bunch of exam questions for students in my molecular evolution course. I gave them out two weeks before the exam and I promised them that I would post some of these questions on my blog to see how you would answer them. I'm hoping that you, dear readers, will show my students that there really is some controversy.

Here's the fifth question.

In their 2007 paper Hawks et al. conclude,

The rate of adaptive evolution in human populations has indeed accelerated within the past 80,000 years. The results above demonstrate the extent of acceleration: the recent rate must be one or two orders of magnitude higher that the long-term rate to explain the genomewide pattern.

If the actual results demonstrate that human evolution has accelerated then why are there still scientists who dispute the conclusion?

The point of the question is the conflict between how scientists deal with data that conflicts with their model. In this case, it's scientists (like me) who are uncomfortable with the conclusions of Hawks et al. (2007). If the data they published is valid then this should be a situation where all scientists abandon their former models it light of a "nasty little fact."

But that never happens. Why?

I'd also like to discuss another topic. How many people who read the Hawks et al. paper are actually capable of evaluating the data to see if it supports the conclusions? Are we in a new age of biology where the complexity of the databases and the sophistication of the computer algorithms make it impossible for the average scientist to judge the quality of the experiments? How about reviewers, can they evaluate the methods and results?


Note: The issues get bound up with the adaptationist/pluralist debate because two of the authors on the paper published a book to promote their views. You can read some examples of the adaptationist views of Cochran and Harpending at: Examples of Accelerated Human Evolution. I don't think John Hawks supports such an adaptationist position but I'm hoping he will chime and tell us. (John is a really smart guy—on more than one occasion he has demonstrated that my arguments are full of holes. It's embarrassing.)

Another Note: Here are some blogs that you might enjoy reading if this question interests you.

Signals of recent positive selection in a worldwide sample of human populations…maybe

Signals of Positive Selection in Humans?

Overstating the obvious

SEED Reviews The 10,000 Year Explosion

Did biologists really think that human evolution stopped?

Are Humans Still Evolving?

John Hawks doesn't like random genetic drift

Genetic differences between human populations: more drift than selection?

Is Evolution Linked to Environmental Change?

Accelerated Human Evolution

Human evolution has accelerated

Are humans evolving faster?

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Hawks, J., Wang, E.T., Cochran, G.M., Harpending, H.C., and Moyzis, R.K. (2007) Recent acceleration of human adaptive evolution. Proc. Natl. Acad. Sci. (USA) 104:20753-20758. Epub 2007 [PubMed] [DOI:10.1073/pnas.0707650104]

Hofer, T., Ray, N., Wegmann, D., and Excoffier, L. (2009) Large allele frequency differences between human continental groups are more likely to have occurred by drift during range expansions than by selection Annals of Human Genetics 73:95-108 [doi: 10.1111/j.1469-1809.2008.00489.x]

Pickrell, J.K., Coop, G., Novembre, J., Kudaravalli, S., Li, J.Z., Absher, D., Srinivasan, B.S., Barsh, G.S., Myers, R.M., Feldman, M.W., and Pritchard, J.K. (2009) Signals of recent positive selection in a worldwide sample of human populations. Genome Research 23 published in advance March 23, 2009 [DOI: 10.1101/gr.087577.108]