Tuesday, May 6, 2008

Interview by student

I got these questions from a student, and decided to post them here.

> Hi, I'm currently doing a general research paper on evolutionary biology for my >writing class. I would really appreciate it if you could answer a few questions for >my paper. My main focus is on natural selection.
> 1. Besides natural selection, are there any other mechanisms observed in the evolution of a species?

Although natural selection is an important driving force in evolution, there are many other factors that influence the evolution of species, often in concert with natural selection. A primary consideration is genetic drift, which is related to the idea of "neutral evolution". In the field of population genetics, genetic drift is known to result from "sampling error", which is especially likely in very small populations. To understand what I mean by sampling error, first consider what we might expect if we were examining one gene in a population, and if we expect no evolution to happen to that gene in a population of individuals. Without evolution, we'd expect the different copies of a gene to stay at an equilibrium proportion. So, if we had two different types of a gene (types of a gene are called alleles), each occurring at 50% frequency, we'd expect the frequencies to stay the same over time without evolution. But if the population of individual organisms is very small, we might expect some "sampling bias". Sampling bias can occur in coin tosses. If we toss a fair coin 1000 times, we expect that pretty close to 50% of the time, the coin will land on heads. But if we toss the coin only 4 times, we wouldn't be too surprised to find that the coin landed on heads 100% of the time. The same can happen to alleles in small populations. Even though the alleles described above are equally prevalent, and we'd expect them to equally prevalent in offspring (without evolution), we could discover the result that the prevalence of alleles changes from 50% just by chance possibility. Just as we can obtain biased results in a few tosses of a fair coin, alleles can be passed on in a biased fashion by chance, especially in small populations. This is called genetic drift, and it is a mechanism for evolution other than natural selection.

Related to genetic drift is neutral evolution. Neutral evolution is the idea that some mutations in genes do not influence the phenotype of the organism. "Nearly neutral" means that some mutations have only a tiny effect on the phenotype of the organism. Neutral and nearly neutral mutations can enter into species in the absence of natural selection. Since the organismal phenotype is barely changed, there is very little cost to the organisms that maintain these mutations. Some have argued that major features of the genomes of species have been shaped by neutral and nearly neutral evolution. For example, genes can duplicate, and might be maintained in genomes simply because there is little cost to maintaining it.

Another mechanism that has a major influence on evolution, but has nothing to do with natural selection, is catastrophic events. For example, at several points in Earth's history, meteors have struck Earth, and are implicated in massive extinction of many species. Such massive extinction changes the interactions among species entirely, and has a profound effect on how evolution proceeds. Mass extinctions have little to do with how "fit" species are: most any species could be wiped out if a meteor drops on them.

A final consideration is constraints, which may channel or restrict the action of natural selection. Many traits are linked together genetically and/or developmentally. As such, changing one trait (perhaps by natural selection) can indirectly change other traits. Developmental evidence suggests that cavefish without eyes lost eyes through natural selection on increased jaw size. While selection changes jaw size, the direct arbiter of change in the eyes is thought to be the link with jaws. Selection may not have acted directly on eyes, but rather through a developmental constraint that ties jaw size and eye size together.

> 2. I’ve often heard that while natural selection is represented by the phrase “survival of the fittest,” it is not a correct way to describe the process. What are your thoughts on this statement?

The epitome "survival of the fittest" is in fact misleading. Instead, natural selection is better defined by some specific postulates. Namely, heritable variation exists, and there is differential survival of that heritable variation. So one thing missing in "survival of the fittest" is a mention of heritability.

> 3. Could you give an example of natural selection at work in the recent past?

There are many, many examples of recent natural selection. A textbook example is beak evolution in Galapagos finches, with examples based on decades of field work by Peter and Rosemary Grant and colleagues, which is chronicled in the Pulitzer Prize winning book The Beak of the Finch. As one specific example, they witnessed increased survival of larger beaked ground finches during times of drought because those birds could eat larger and harder seeds. The emergence of pesticide resistance and antibiotic resistance are two practically important examples of recent evolution by selection (although some may not consider these "natural", because humans have impacted the systems).

> 4. Can you point out some results of natural selection in our own natural areas around the UCSB campus?

Natural selection has influenced the evolution of every living thing on earth, including every living thing on the UCSB campus, in natural areas or otherwise.

> 5. What are your views concerning evolution versus creation?

I am very embarrassed and concerned by recent polls showing that the US is second only to Turkey in the proportion of citizens who reject the science of evolution. This reflects a general lack of critical thinking among a large portion of Americans, which is dangerous to our way of life, to American values and freedoms, and to the success of our country in economics and as global citizens. Much of this lack of critical thinking among Americans is rooted in fundamentalist Christian anti-evolutionism. Large institutes (e.g. Discovery Institute) have formed a strategy to impose their religious beliefs on the people of the US through a plan called the "wedge strategy". They see evolution as the easiest target for anti-intellectualism. Once the wedge pierces evolution, the plan is to proceed to other fields of science, until their religious perspective dominates how Americans learn science. This is a fundamentally unconstitutional, and anti-American.

Despite the tired nature of anti-evolution arguments, like Intelligent Design, that were refuted already in Darwin's time, many Americans reject evolution. This is despite the fact that evolutionary biology has thrived as a predictive, and well-established science for 150 years, amassing huge amounts of supportive and consistent evidence supporting the fact that evolution is the causal agent of the diversity of life we see on Earth.

Some people have a less fundamentalist view of religion, and accept the established science of evolution within their faith.

My own personal view is that I have no doubt that evolutionary processes have created all of the diversity of life on Earth. It is also quite clear to me that documents like the Bible are internally inconsistent, and contain many claims that have been disproved - I therefore see little reason to put much stock in such documents. I also believe that religion can be dangerous because it is often co-opted as a means to control the masses, especially by promoting a lack of critical thinking. I do believe that religion can be beneficial to some people, for example by establishing a sense of tradition, connection, and community in some people.

After all that, I still haven't addressed my views on the "creation" question, which is whether I think some sort of creative force is responsible for setting up the universe. I just don't see how anyone could know that - one way or the other - so I call myself an agnostic. And except when someone tries to impose their religious views upon me (for example the Discovery Institute wedge strategy), I don't see any reason why it matters whether there is some creative force or not. Evolution does just fine in explaining where humans came from and when, and evolution does not impinge negatively upon morality or eithics. Humans are an inherent part of nature - I spiritually do not need to know any more than that.

> 6. How does human activity interfere with natural selection among other species?

First, I found interesting your use of the word "interfere" in the question, which sometimes has a connotation of hampering or hindering. I would say that nothing humans could ever do will hinder natural selection, in general. But there is no doubt that human activities impact the course of natural selection. Some examples I already mentioned (the evolution antibiotic resistance in bacteria, and pesticide resistance in insects). Humans are also causing a mass extinction event that is changing the specific interactions among species. Finally, global climate change, and other environmental impacts are influencing how natural selection will act in different species.


author@ptgbook.org said...

In a recent discussion I saw posted on a blog, there seemed to be disagreement between evolutionists over whether the term "evolution" as it is taught in public schools includes the meaning that species arose through natural causes only, or if evolution as taught in the classroom leaves the cause of genetic change undetermined and therefore allows for the possibility that there was supernatural intervention to produce genetic change. My position seemed similar to yours on this issue, that though a number of mechanisms for genetic change may be suggested, all of them are natural causes, and supernatural causes are not considered to be a part of evolution as it is taught. Is that your view?

Todd Oakley said...

Any evolutionist would only consider the possibility that natural causes produce genetic changes. The causes of mutation are well established, and mainly include errors in copying DNA. Whether these mutations are subsequently fixed in populations brings us to the evolutionary mechanisms of drift and selection.

So, yes, I would agree that supernatural causes of mutation and fixation are not scientific, and therefore not part of the field of evolution.

Mike said...

This is a great post. Thank you.
I especially like phrasing "differential survival of heritable variation". This is really more accurate, neutral, and harder for anti-evolutionists to pervert into social Darwinism.