Skepticon 5 Day Two – PZ Myers’ “Evolution: Let’s Do the Kinky Stuff!”

PZ Myers: the man, the legend. Author of one of the biggest science science blogs in the world, defeater of communion wafers, sacker of the City of God. For Skepticon 5 he has a talk on evolutionary pluralism. Random Mutation + Natural Selection (RM+NS) is the basis of all the diversity of species we see on the planet, he averred, stressing the importance of randomness in the evolutionary process.

He took us through four ways in which a mutation can become fixed in a community:

Selection

A mutation confers a discrete advantage on an individual, and that enables them to reproduce more, spreading the mutation through the population: “It’s spreading, just by virtue of its awesomeness.” Eventually, it will likely become fixed in the population – every member of the population will have it.

But random chance still plays a role. Through the process of Meiosis, half of a male’s sperm does not carry advantageous mutations. Since human beings don’t tend to have lots of children, chance therefore plays a significant role in the propagation of even highly beneficial mutations.

This is because, as PZ says, “Sex is really weird…I want to make an analogy between sex and Legos.” In Myers’ analogy, we all construct ourselves out of Legos, before smashing ourselves apart and mixing half our “pieces” with half of someone else’s pieces, then reconstructing a different people with all the mixed-up pieces. “That’s what we’re stuck with. That’s how we reproduce.”

Founder Effect

A new mutation is isolated from the main population in a smaller group, becoming a much larger percentage of that smaller population. That can quickly to fixation of the mutation. This has happened: among the Amish, who are descendants of only a few hundred German immigrants, there are “all kinds of strange genetic diseases at a higher frequency all because of the Founder Effect.”

Genetic Draft / Hitchhiking

A deleterious mutation can be “dragged to higher frequencies” by its proximity to a beneficial mutation. This means that some genes will increase their prevalence in a population despite being deleterious to the organism by “hitchhiking”.

Random Drift

Because chance plays a significant role in propagating even a highly beneficial mutation, random drift of mutations through a population will occur, sometimes leading to the expansion, contraction, and extinction of a new mutation. PZ stressed that “Just the fact that a gene has become frequent in a population doesn’t necessarily mean it confers an advantage on that population. It could be happening by chance.” Even without any selective pressures applied, this sort of genetic drift will occur – and it’s still evolution!

However, if you add selection pressures into your model of mutation drift, you can work out when selection is likely to be effective in changing a population. It turns out selection is most effective in large populations with low mutation rates. Small populations with a high mutation rate are dominated by chance.

And human beings are a relatively small population with a high mutation rate, and “our genetic makeup is dominated by chance events in our history!”

Selection still played a role, but odds are any randomly-selected gene from our gene-sequence is there due to chance mutation, not because it was selected due to its beneficial effects. This has some odd effects on our genetics, including the fact that, in %30 of our genome, humans are closer to gorillas to chimpanzees, even though humans and gorillas diverged earlier on the evolutionary tree. Contrary to the excitement of creationists when this discovery was announced, PZ averred that this is precisely what we would expect given our understanding of random drift.

I found the talk fascinating: PZ guided us through a series of complex mathematical ideas with humor and clarity, illuminating a part of evolutionary theory I had not considered before. I hadn’t been aware of the large effect of random drift on human genes, and to discover the effects of randomness on our genes was a revelation. PZ is a great communicator of science, and his talk was clearly appreciated by the assembled audience.

About James Croft

James Croft is the Leader in Training at the Ethical Culture Society of St. Louis - one of the largest Humanist congregations in the world. He is a graduate of the Universities of Cambridge and Harvard, and is currently writing his Doctoral dissertation as a student at the Harvard Graduate School of Education. He is an in-demand public speaker, an engaging teacher, and a passionate activist for human rights. James was raised on Shakespeare, Sagan and Star Trek, and is a proud, gay Humanist. His upcoming book "The Godless Congregation", co-authored with New York Times bestselling author Greg Epstein, is being published by Simon & Schuster.

  • Christenstain

    So human evolution is ultimately the result of chance.

    Despite Richard Dawkins trying to say it is not.

    Got it.


CLOSE | X

HIDE | X