Expert: Florence M Rollwagen - 6/26/2009

Question
Hello,

I'm an undergraduate working towards a degree in Ecology and Evolutionary Biology.  Through my pleasure reading I've started learning how the idea of using proteins as molecular clocks works.  The method seems to hinge on the assumption that mutations in the measured protein sequences occur at a fairly constant rate.  Why would it be constant?  I'm also curious to know how this method has been refined over the decades and how accurate it is today.

Any knowledge you can give me or related sources you can point me to will be much appreciated.  Thank you.

Answer
Hi Tom:  Thanks for your question.

It's true, the use of molecular clocks as evolutionary tools has become more refined over the years.  It is still subject to some controversy, however, since, as you pointed out, why do we expect proteins to change at a constant rate?

In fact, different proteins change at different rates, and to correlate them with evolutionary changes requires some assumptions.

Here is some additional reading.


http://www.nature.com/scitable/topicpage/The-Molecular-Clock-and-Estimating-Spec...

http://focus.aps.org/story/v20/st9

This is a good review at Panda's Thumb (a little anti-creationism, but still scientifically valid)
http://pandasthumb.org/archives/2006/12/molecular-clock.html

A little harder to read, but still relevant:
http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0040151

This is a complex and somewhat controversial theory, it has worked for some divergences among species, but requires additional testing and corroboration with other timelines.

Hope this helps, write back if you have more questions.

FM Rollwagen, PhD