Austin Hughes and Neutral Theory

Austin Hughes (1949 - 2015) died a few years ago. He was one of my favorite evolutionary biologists.

Chase Nelson has written a nice summary of Hughes' work at: Austin L. Hughes: The Neutral Theory of Evolution. It's worth reading the first few pages if you aren't clear on the concept. Here's an excerpt ...

When the technology enabling the study of molecular polymorphisms—variations in the sequences of genes and proteins—first arose, a great deal more variability was discovered in natural populations than most evolutionary biologists had expected under natural selection. The neutral theory made the bold claim that these polymorphisms become prevalent through chance alone. It sees polymorphism and long-term evolutionary change as two aspects of the same phenomenon: random changes in the frequencies of alleles. While the neutral theory does not deny that natural selection may be important in adaptive evolutionary change, it does claim that natural selection accounts for a very small fraction of genetic evolution.

A dramatic consequence now follows. Most evolutionary change at the genetic level is not adaptive.

It is difficult to imagine random changes accomplishing so much. But random genetic drift is now widely recognized as one of the most important mechanisms of evolution.

I don't think there's any doubt that this claim is correct as long as you stick to the proper definition of evolution. The vast majority of fixations of alleles are likely due to random genetic drift and not natural selection.

If you don't understand this then you don't understand evolution.

The only quibble I have with the essay is the reference to "Neutral Theory of Evolution" as the antithesis of "Darwinian Evolution" or evolution by natural selection. I think "Neutral Theory" should be restricted to the idea that many alleles are neutral or nearly neutral. These alleles can change in frequency in a population by random genetic drift. The key idea that's anti-Darwinian includes that fact plus two other important facts:

1. New beneficial alleles can be lost by drift before they ever become fixed. In fact, this is the fate of most new beneficial alleles. It's part of the drift-barrier hypothesis.
2. Detrimental alleles can occasionally become fixed in a population due to drift.

In both cases, the alleles are not neutral. The key to understanding the overall process is random genetic drift not the idea of neutral alleles—although that's also important.

Originally proposed by Motoo Kimura, Jack King, and Thomas Jukes, the neutral theory of molecular evolution is inherently non-Darwinian. Darwinism asserts that natural selection is the driving force of evolutionary change. It is the claim of the neutral theory, on the other hand, that the majority of evolutionary change is due to chance.

I would just add that it's Neutral Theory PLUS the other effects of random genetic drift that make evolution much more random than most people believe.

Austin Hughes was a skeptic and a creative thinker who often disagreed with the prevailing dogma in the field of evolutionary biology. He was also very religious, a fact I find very puzzling.

His scientific views were often correct, in my opinion.

In 2013, the ENCODE (Encyclopedia of DNA Elements) Project published results suggesting that eighty per cent of the human genome serves some function. This was considered a rebuttal to the widely held view that a large part of the genome was junk, debris collected over the course of evolution. Hughes sided with his friend Dan Graur in rejecting this point of view. Their argument was simple. Only ten per cent of the human genome shows signs of purifying selection, as opposed to neutrality.

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Denis Noble writes about junk DNA

I have read Dance to the Tune of Life. It's a very confusing book for several reasons. Denis Noble has a very different perspective on evolution and what evolutionary theory needs to accomplish. He thinks that life is characterized by something he calls "Biological Relativity." I don't disagree. He also thinks that evolutionary theory needs to incorporate everything that has ever happened in the history of life. That's where we part company.

I'm working slowly on a book about genomes and junk DNA so I was anxious to see how Noble deals with that subject. I tend to judge the quality of books and articles by the way they interpret the controversy over junk DNA. Here's the first mention of junk DNA from page 89. He begins by saying that it's difficult to explain development and the diversity of tissues in multicellular organisms. He continues with,

Debating philosophers: Epigenetics

Qiaoying Lu and Pierrick Bourrat are philosophers in Australia.¹ Their research interests include evolutionary theory and they have taken an interest in the current debate over extending evolutionary theory. That debate has been promoted by a small group of scientists who, by and large, are not experts in evolution. They claim that current evolutionary theory—which they define incorrectly as the 1960s version of the Modern Synthesis—needs to be overthrown or extended by including things like epigenetics, niche construction, developmental biology, and plasticity [New Trends in Evolutionary Biology: The Program].

Lu and Bourrat have focused on epigenetics in their recent paper [Debating philosophers: The Lu and Bourrat paper]. They hope to reach an accommodation by re-defining the evolutionary gene as: "any physical structure that causes a heritable variation." Then they go on to say that, "we define the phenotype of an evolutionary gene as everything that the gene makes a difference to when compared to another gene."

By doing this, they claim that epigenetic changes (e.g. transient methylation) fall with the new definition. Therefore, epigenetics doesn't really represent a challenge to evolutionary theory. They explain it like this ....

Debating philosophers: The molecular gene

This is my fifth post on the Lu and Bourrat paper [Debating philosophers: The Lu and Bourrat paper]. The authors are attempting to justify the inclusion of epigenetics into current evolutionary theory by re-defining the concept of "gene," specifically the evolutionary gene concept. So far, I've discussed their understanding of current evolutionary theory and why I think it is flawed [Debating philosophers: The Modern Synthesis]. I described their view of "genes" and pointed out the confusion between "genes" and "alleles" and why I think "alleles" is the better term [Debating philosophers: The difference between genes and alleles]. In my last post I discussed their definition of the evolutionary gene and why it is too adaptationist to serve a useful function [Debating philosophers: The evolutionary gene].

Debating philosophers: The difference between genes and alleles

This is my third post on the Lu and Bourrat (2017) paper [Debating philosophers: The Lu and Bourrat paper]. Part of their argument is to establish that modern evolutionary theory is a gene-centric theory. They need to make this connection because they are about to re-define the word "gene" in order to accommodate epigenetics.

In my last post I referred to their defense of the Modern Synthesis and quoted them as saying that the major tenets of the Modern Synthesis (MS) are still the basis of modern evolutionary theory. They go on to say,

Debating philosophers: The Modern Synthesis

I'm discussing a paper by Lu and Bourrat (2017) [Debating philosophers: The Lu and Bourrat paper]. They begin by describing current evolutionary theory, known (to them) as the Modern Synthesis. The paper is about challenges to current evolutionary theory from those who advocate an extended evolutionary synthesis or from those who would replace, rather than extend, current evolutionary theory. It is reasonable to begin with a description of the theory that's being challenged.

Here's what Lu & Bourrat say,

Debating philosophers: The Lu and Bourrat paper

John Wilkins posted a link on Facebook to a recent paper by his colleagues in Australia. The authors are Qiaoying Lu of the Department of Philosophy at Macquarie University in Sidney Australia and Pierrick Bourat of the Department of Philosophy at The University of Sydney in Sidney Australia.

Lu, Q., and Bourrat, P. (2017) The evolutionary gene and the extended evolutionary synthesis. The British Journal for the Philosophy of Science, (advanced article) April 20, 2017. [doi: 10.1093/bjps/axw035] [PhilSci Archive]

Abstract: Advocates of an ‘extended evolutionary synthesis’ have claimed that standard evolutionary theory fails to accommodate epigenetic inheritance. The opponents of the extended synthesis argue that the evidence for epigenetic inheritance causing adaptive evolution in nature is insufficient. We suggest that the ambiguity surrounding the conception of the gene represents a background semantic issue in the debate. Starting from Haig’s gene-selectionist framework and Griffiths and Neumann-Held’s notion of the evolutionary gene, we define senses of ‘gene’, ‘environment’, and ‘phenotype’ in a way that makes them consistent with gene-centric evolutionary theory. We argue that the evolutionary gene, when being materialized, need not be restricted to nucleic acids but can encompass other heritable units such as epialleles. If the evolutionary gene is understood more broadly, and the notions of environment and phenotype are defined accordingly, current evolutionary theory does not require a major conceptual change in order to incorporate the mechanisms of epigenetic inheritance.

1 Introduction
2 The Gene-centric Evolutionary Theory and the ‘Evolutionary Gene’
      2.1 The evolutionary gene
      2.2 Genes, phenotypes, and environments
3 Epigenetic Inheritance and the Gene-Centred Framework
      3.1 Treating the gene as the sole heritable material?
      3.2 Epigenetics and phenotypic plasticity
4 Conclusion

The selfish gene vs the lucky allele

The Selfish Gene was published forty-one years ago (1976) and last year there was a bit of a celebration. I think we can all appreciate the impact that the book had at the time but I'm not sure it's as profound and lasting as most people believe ["The Selfish Gene" turns 40] [The "selfish gene" is not a good metaphor to describe evolution] [Die, selfish gene, die!].

The main criticisms fall into two categories: (1) the primary unit of selection is the individual organism, not the gene, and (2) the book placed too much emphasis on adaptation (Darwinism). I think modern evolutionary theory is based on 21st century population genetics and that view puts a great deal of emphasis on the power of random genetic drift. The evolution of a population involves the survival of individuals within the population and that, in turn, depends on the variation that exists in the population. Thus, evolution is characterized by changes in the frequencies of alleles in a population.

Darwin Day 2017

Today is Darwin Day but I'm too busy with other things to write a new post in his honor. So here's a post from 2007 (slightly updated) to help you enjoy the day.

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Today is the birthday of the greatest scientist who ever lived. When you visit Darwin's home (Down House) you get a sense of what he must have been like. One of the things that's obvious is the number of bedrooms for the children. The house must have been alive with the activities of young children. It's no wonder that Darwin needed some peace and quiet from time to time.

Gwen Raverat was Darwin's granddaughter (daughter of George Darwin). She described Down House as she knew it in the years shortly after Darwin died.

Of all places at Down, the Sandwalk seemed most to belong to my grandfather. It was a path running round a little wood which he had planted himself; and it always seemed to be a very long way from the house. You went right to the furthest end of the kitchen garden, and then through a wooden door in the high hedge, which quite cut you off from human society. Here a fenced path ran along between two great lonely meadows, till you came to the wood. The path ran straight down the outside of the wood--the Light Side--till it came to a summer-house at the far end; it was very lonely there; to this day you cannot see a single building anywhere, only woods and valleys.

I became interested in Darwin's children about fifteen years ago when I first began to appreciate the influence they had on his life. We all know the story of Annie's death when she was ten years old and how this led to Darwin's rejection of religion. There were other tragedies but Charles and Emma turned out to be very good parents.

Here's a short biography of each of Darwin's children from AboutDarwin.com

William Erasmus Darwin
The first of Darwin's children was born on December 27, 1839. He was a graduate of Christ’s College at Cambridge University, and was a banker in Southampton. He married Sara Ashburner from New York, but they had no children. William died in 1914.

Anne Elizabeth Darwin
Born on March 2 1841, and died at the age of ten of tuberculosis on April 22, 1851. It was the death of Annie that radically altered Darwin’s belief in Christianity.

Mary Eleanor Darwin
Born on September 23, 1842 but died a few weeks later on October 16th.

Henrietta Emma Darwin ("Etty")
Born on September 25, 1843 and married Richard Buckley Litchfield in August of 1871. She lived 86 years and edited Emma's (her mother) personal letters and had them published in 1904. She had no children.

George Howard Darwin
Born on July 9, 1845. He was an astronomer and mathematician, and became a Fellow of the Royal Society ... in 1879. In 1883 he became the Plumian Professor of Astronomy and Experimental Philosophy at Cambridge University, and was a Barrister-at-Law. He studied the evolution and origins of the solar system. George married Martha (Maud) du Puy from Philadelphia. They had two sons, and two daughters. He died in 1912.

Elizabeth Darwin
Born on July 8, 1847 and died in 1926. She never married and had no children.

Francis Darwin
Born on August 16, 1848. He became a botanist specializing in plant physiology. He helped his father with his experiments on plants and was of great influence in Darwin's writing of "The Power of Movement in Plants" (1880). He was made a Fellow of the Royal Society in 1879, and taught at Cambridge University from 1884, as a Professor of Botany, until 1904. He edited many of Darwin's correspondence and published "Life and Letters of Charles Darwin" in 1887, and "More Letters of Charles Darwin" in 1903. He also edited and published Darwin’s Autobiography. He married Amy Ruck but she died when their first child, Bernard, was born in September of 1876. He then married Ellen Crofts in September of 1883, and they had one daughter, Frances in 1886. Francis was knighted in 1913, and died in 1925.

Leonard Darwin
Born on January 15, 1850. He became a soldier in the Royal Engineers in 1871, and was a Major from 1890 onwards. He taught at the School of Military Engineering at Chatham from 1877 to 1882, and served in the Ministry of War, Intelligence Division, from 1885-90. He later became a liberal-unionist MP for the town of Lichfield in Staffordshire 1892-95, and was president of the Royal Geological Society 1908-11. Leonard married Elizabeth Fraser in July of 1882. He married a second time, but had no children and died in 1943.

Horace Darwin
Born on May 13, 1851. He was a graduate of Trinity College, Cambridge, and became an engineer and a builder of scientific instruments. In 1885 he founded the Cambridge Scientific Instrument Company. He was the Mayor of Cambridge from 1896-97, and was made a Fellow of the Royal Society in 1903. Horace married Emma Farrer in January of 1880 and they had three children. He died in 1928.

Charles Waring Darwin
Born on December 6, 1856 but died on June 28 1858.

This is something I wrote about my visit to Westminster Abby 17 years ago.

Eventually we wind around the Monastery and finally enter the Nave. Ignoring the monument to Winston Churchill (1874-1965) and hardly bothering to look up and admire the high ceiling, I head for the front of the church where I can see the statue of Isaac Newton (1643-1727). This is the same statue that plays such an important role in the Da Vinci Code but today I’m not interested in Newton or his orb. I takes me only a few seconds to find the marked stone on the floor. I’m standing on the grave of Charles Robert Darwin.

I can picture the scene on Wednesday, April 26, 1882—a grand funeral attended by all of London’s high society and the leading intellectuals of the most powerful nation in the world. Darwin would not have been pleased. He wanted to be buried quietly in the Downe cemetery with his brother Erasmus and two of his children. Darwin's family was persuaded by his friends Galton, Hooker, Huxley and the President of the Royal Society, William Spottiswoode, that, for the sake of England, Darwin should be laid to rest in Westminster Abbey. As Janet Browne writes in her biography of Charles Darwin, "Dying was the most political thing Darwin could have done."

Looking around I can see the tomb of Joseph Hooker and a memorial to Alfred Wallace, two of the scientists who were Darwin’s pallbearers. (Another pallbearer, Thomas Henry Huxley, is buried elsewhere.) Nearby are the final resting places of a host of famous scientists; Kelvin, Joule, Clerk-Maxwell, Faraday, Herschell, and Sir Charles Lyell. Lyell was Darwin’s hero and mentor. We are told that Darwin’s wife Emma wished he were buried closer to Lyell.

I am not overly sentimental but this visit has a powerful effect. I think Charles Darwin is the greatest scientist who ever lived—yes, even greater than Sir Isaac Newton whose huge statue overshadows Darwin’s humble marker in the floor. Natural selection is one of the greatest scientific ideas of all time. Darwin discovered it and he deserves most of the credit. But Charles Darwin died on April 19 in 1882 and that was a long time ago.

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A philosopher tells us how to think clearly about evolutionary causes ... avoid adaptationism

I think philosophy has lost its way. The discipline gives credence to religious philosophers who write about god(s) and to other philosophers who reject determinism and think the mind-body problem is still an open question. Philosophers still debate the validity of the ontological argument. Philosophers of science have not even settled the question of what is science, let alone come up with a valid answer of how to do it. There are few other disciplines that are still respected after several hundred years of trying, and failing, to answer the most fundamental questions in their field. Many academic philosophy department are hotbeds of political correctness and just plain politics.

Why does the human population carry an allele that increases the risk of Alzheimer's?

The human apolipoprotein E gene (ApoE) has several alleles segregating in the human population. One of them, E4, is associated with increased risk of Alzheimer's. Ed Yong, writing for The Atlantic, asks "Why Do Humans Still Have a Gene That Increases the Risk of Alzheimer's?

I can think of several answers off the top of my head. The most important one is that Alzheimer's has very little effect on your ability to have children. The disease may not even have developed in most of our ancestors who tended to die younger. In order to be subject to negative selection the allele has to affect adults before they reproduce.

The second reason is that the slight deleterious effect, if there is one from an evolution perspective, may not have been significant enough in small populations. I know, and I hope my students know, that neutral and deleterious alleles can reach significant frequency in a population by chance. The general public doesn't know this.

Check out Ed Yong's article to see his explanation.

“It doesn’t make sense,” says Ben Trumble, from Arizona State University. “You’d have thought that natural selection would have weeded out ApoE4 a long time ago. The fact that we have it at all is a little bizarre.”

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Why are most biologists adaptationists?

I enjoyed listening to Michael Lynch's talk on Friday. Much of what he said has been covered in Sandwalk over the past few years. His main point was that nothing in biology makes sense except in the light of population genetics. He laments the fact that most biologists, and even most evolutionary biologists, don't have a firm grasp of population genetics and the importance of random genetic drift.

I asked him why he thought this was true. He said he didn't know why. I think he was being polite. If you read his book, "The Origins of Genome Architecture," you'll see that he attributes this phenomeon to ignorance of modern evolutionary theory.

The dynamic duo tell us about five problems with evolution

Here's a link to a remarkable radio interview with Stephen Meyer and Doug Axe. The subject is the Royal Society meeting last November on New trends in evolutionary biology: biological, philosophical and social science perspectives. The theme is not Intelligent Design Creationism, instead it's all about so-called problems with evolutionary theory. That's really what ID is all about in spite of what the IDiots may claim. [see A Royal Pain: Stephen Meyer and Douglas Axe on Five Problems for Evolution.]

Here are the five problems according to IDiots.

1. Fossil record (Cambrian explosion)
2. The origin of information (no known natural source of information)
3. The necessity of early mutations (you can't mutate regulatory genes that act early in development because all mutations in those genes are lethal)
4. Epigenetic information (you can't evolve new body plans by mutating DNA because development is controlled by non-DNA epigenetic information)
5. The universal design intuition that we all have (everybody thinks that people are created by a god-like designer, even atheists, so it must be true)

You MUST read this paper if you are interested in evolution

A reader alerted me to a paper that was just published in BMC Biology.¹ The author is Eugene Koonin. He makes the case for neutral evolution (random genetic drift) and against adaptationism. You may not agree with his take on evolutionary theory but you better be aware of it if you claim to be knowledgeable about evolution.

Koonin, E.V. (2016) Splendor and misery of adaptation, or the importance of neutral null for understanding evolution. BMC biology, 14:114. [doi: 10.1186/s12915-016-0338-2]

The study of any biological features, including genomic sequences, typically revolves around the question: what is this for? However, population genetic theory, combined with the data of comparative genomics, clearly indicates that such a “pan-adaptationist” approach is a fallacy. The proper question is: how has this sequence evolved? And the proper null hypothesis posits that it is a result of neutral evolution: that is, it survives by sheer chance provided that it is not deleterious enough to be efficiently purged by purifying selection. To claim adaptation, the neutral null has to be falsified. The adaptationist fallacy can be costly, inducing biologists to relentlessly seek function where there is none.

Is the high frequency of blood type O in native Americans due to random genetic drift?

The frequency of blood type O is very high in some populations of native Americans. In many North American tribes, for example, the frequency is over 90% and often approaches 100%. A majority of individuals in those populations have blood type O (homozygous for the O allele). [see Theme: ABO Blood Types]

Since there's no solid evidence that blood types are adaptive,¹ the standard explanation is random genetic drift.

Jerry Coyne explains it in Why Evolution Is True.

One example of evolution by drift may be the unusual frequencies of blood types (as in the ABO system) in the Old Order Amish and Dunker religious communities in America. These are small, isolated, religious groups whose members intermarry—just the right circumstances for rapid evolution by genetic drift.

Accidents of sampling can also happen when a population is founded by just a few immigrants, as occurs when individuals colonize an island or a new area. The almost complete absence of genes producing the B blood type in Native American populations, for example, may reflect the loss of this gene in a small population of humans that colonized North America from Asia around twelve thousand years ago.

Restarting the function wars (The Function Wars Part V)

The term "function wars" refers to debates over the meaning of the word "function" in biology. It refers specifically to the discussion about junk DNA because junk DNA is defined as DNA that does not have a biological function. The wars were (re-)started when the ENCODE Consortium decided to use a stupid definition of function in order to prove that most of our genome was functional. This prompted a number of papers attempting to create a more meaningful definition.

None of them succeeded, in my opinion, because biology is messy and doesn't lend itself to precise definitions. Look how difficult it is to define a "gene," for example. Or "evolution."

Nevertheless, some progress was made. Dan Graur has recently posted a summary of the two most important definitions of function [What does “function” mean in the context of evolution & what absurd situations may arise by using the wrong definition?]. The two definitions are "selected-effect" and "causal-role" (there are synonyms).

Suzan Mazur doesn't like Carl Zimmer

There weren't many science writers are the Royal Society meeting in London (UK) [New trends in evolutionary biology: biological, philosophical and social science perspectives]. Carl Zimmer was there and so was Suzan Mazur. Carl was there to learn and do some research. Suzan was there to promote herself as the main publicist of the paradigm shifters.

Carl Zimmer wrote a news article about the meeting for Quanta: Scientists Seek to Update Evolution. The subtitle was "Recent discoveries have led some researchers to argue that the modern evolutionary synthesis needs to be amended." It was a pretty fair article and pretty good reporting on what went on at the meeting. I would have been a bit more harsh about the success of the so-called "paradigm shifters" but Carl did a good job of conveying the skepticism exhibited by many at the meeting. [See Kevin Laland's new view of evolution for my take on these "revolutionaries."]

Kevin Laland's new view of evolution

The recent meeting at the Royal Society in London was organized by The Royal Society (UK) and The British Academy. The theme of the meeting was, "New trends in evolutionary biology: biological, philosophical and social science perspectives." The main organizers were Denis Noble, Nancy Cartwright, Patrick Bateson, John Dupré, and Kevin Laland. The point of the meeting was to discuss new evolutionary theory.

It's difficult to describe everything that went on at the meeting because so much of it was details about individual research results. These scientific talks were often presented as an alternative to modern ways of thinking about evolution. The general theme was that the Modern Synthesis was out-of-date and needed revision or, perhaps, replacement. There was very little discussion of evolutionary theory and how best to interpret those results. The data was supposed to speak for itself.

The only serious objections came from scientists who claimed the Modern Synthesis had already incorporated the ideas of niche construction, plasticity, epigenetics etc. This message was promoted mainly by Douglas Futuyma and Russell Lande. They weren't very successful.

Learning about modern evolutionary theory: the drift-barrier hypothesis

Many evolutionary biologists are engaged in research that focuses on large organisms that are (presumably) adapting to a local environment. These "field biologists" are mostly concerned with rapid evolutionary changes. Those kind of changes are almost always due to natural selection. Many of these biologists are not interested in molecular evolution and not interested in any process other than natural selection.

Unfortunately, this promotes an adaptationist mentality where all of evolution is viewed through the filter of natural selection. This is the view criticized by Stephen Jay Gould and Richard Lewontin back in 1978 when they presented the Spandrels paper at a Royal Society meeting in London (UK).

Gould, S. J. and Lewontin, R.C. (1979) The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme. Proc. R. Soc. Lond. B 205:581-598. [doi: 10.1098/rspb.1979.0086

I believe there was a substantive change in our view of evolution back in the late 1960s and early 1970s. That's when the results of evolution at the molecular level were first being published. It lead to the development of Neutral Theory, Nearly-Neutral Theory and a growing appreciation of the importance of random genetic drift. Modern population genetics was able to cope easily with this new view of evolution.

Extending evolutionary theory? - Melinda Zeder

I will be attending the Royal Society Meeting on New trends in evolutionary biology: biological, philosophical and social science perspectives. I'll post each of the abstracts and ask for your help in deciding what question to pose to the speakers. Here's the abstract for Melinda Zeder's talk on Domestication: a model system for evolutionary biology.

In his book The Variation of Animals and Plants under Domestication Darwin used domestication as a model system to explore his theories about the role of natural selection in evolution. Gregor Mendel used peas to trace the rules of heredity that formed the basis of the science of genetics, and that, when combined with Darwinian evolution, formed the basis of the Modern Synthesis. It seems only appropriate for domestication to serve once again as a model system for assessing how recent insights into the role of multiple shaping processes and forms of inheritance can be incorporated into an extended understanding of evolution. This presentation explores the value of domestication in evaluating core assumptions that differentiate the classical Modern Synthesis and the Extended Evolutionary Synthesis including: 1. reciprocal causation, 2. developmental processes as drivers of evolutionary change, 3. inclusive inheritance, and 4. the tempo and rate of evolutionary change.

Melinda Zeder works at the National Museum of Natural History, Smithsonian Institution (USA). I think I'll ask her what domestication teaches us about the fixation of deleterious alleles by random genetic drift and how that fits into Darwin's ideas and her view of the Modern Synthesis.

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