1) Christ and a Bicycle by Andrew Brown. Apparently delivered as part of his advertising or publicity for his book Darwin Wars: The Scientific Battle for the Soul of Man.
2) Charles Darwin on Religion by John Hedley Brooke, an invited contribution to the website for The International Society for Science & Religion
3) Dawkins, R. 1997. Obscurantism to the rescue. The Quarterly Review of Biology 72(4):397-399. (pdf available)
4) portions of "Natural selection not inconsistent with natural theology", by Asa Grey, as published in the Atlantic Monthly in a series of articles for July, August, and October 1860.
Saturday, April 4, 2009
Friday, April 3, 2009
Blogging Mott Greene
Last night was historian Mott Greene's seminar in the public lecture series Introducing Darwin, which I've organized along with Maggie Osler, Tony Russell, and Jessica Theodor. Thanks to Shari and CJ for helping with the mikes and to CJ for taking some pictures.
Mott's talk was very good--first half some biographical remarks on "Darwin the man", then moving on to some very interesting remarks on "Darwin the myth", particularly the various ways in which Darwin has been enlisted by a wide range of people to support a wide range of ideas (he's been claimed as a justification for both unregulated capitalism and communism, for instance). As we've discussed, Darwin himself is notable for his insistence on getting his facts right and in his extreme reluctance to make inferences beyond what the facts will support. I'm sure this is why he was always very reticent about the implications (if any!) of his ideas for religion, economics, etc.
The point that will stick with me the most is Mott's remark that both religious conservatives and secular liberals today tend to resist Darwinian-style explanations for social phenomena. For instance, one can argue that the rise since the 1960s of feminism and gay liberation is not ultimately attributable to individuals making and responding to arguments about justice or equality. Rather, the ultimate drivers are economic pressures and reproductive imperatives. Appeals to justice and equality are at best the proximate mechanisms by which individuals happen to respond to those ultimate drivers of human behavior. The point is not that this explanation of the rise of feminism and gay rights is right or wrong, it's that people from across the liberal-conservative spectrum tend to dislike this kind of explanation, independent of any evidence.
One point Mott didn't make, which I got the chance to make briefly in response to a question from the audience afterwards, is that non-biologists who've developed "evolutionary" theories of economics or society (think of Hegel, Marx, Comte, and many others) tend to conflate Darwinian evolution with organismal development. That is, they tend to think of growth of an individual organism from child to adult as "evolutionary". It's not just famous thinkers like Comte who thought this way--the recent remarks from our own federal science minister indicate that he believes in "evolution" in the sense of individual development and change. To a biologist, this is a serious confusion. Darwinian evolution doesn't have a direction or goal or purpose (see Mayr's remarks in his introduction to the Origin). But the development of an individual organism does have a predetermined goal--to convert a fertilized egg into a functioning adult organism. If you claim that human societies are like developing organisms, that's a very different claim from the claim that human societies are like evolving populations.
This confusion between evolution and development has three obvious sources. One is that both involve "change over time", which is what "evolution" means in a colloquial sense. Second is that there are indeed directional trends in the history of life (e.g., increase in the average "complexity" of organisms since the origin of life), and it's natural (but incorrect) to think of such trends as analogous to the directional development of a newborn into an adult. Third is that it's very hard for non-specialists to grasp that the notion of "fitness" in Darwinian evolution is "relative fitness". All that matters in Darwinian evolution is your ability to survive and reproduce, relative to the other current members of the population. This notion of relative fitness does not imply that absolute fitness will increase over time (even in a constant environment), or that there is some "maximally fit" or "ideal" or "perfect" state toward which a population tends to evolve. I think this is the key Darwinian insight that even very smart non-biologists seem to find very difficult to fully absorb (though in fairness, evolutionary biologists don't help them by talking about evolution using engineering and hill-climbing metaphors that are fine in many respects but are subtly and importantly misleading in other respects). Evolution by natural selection is change over time that both lacks a goal or endpoint, but that is not simply random either (random evolution is genetic drift). Directional, non-random change--but the direction isn't "towards" anything. That's Darwinian evolution. As Mott noted, it's this kind of explanation that many people either misunderstand or find unpalatable.
Mott's talk was very good--first half some biographical remarks on "Darwin the man", then moving on to some very interesting remarks on "Darwin the myth", particularly the various ways in which Darwin has been enlisted by a wide range of people to support a wide range of ideas (he's been claimed as a justification for both unregulated capitalism and communism, for instance). As we've discussed, Darwin himself is notable for his insistence on getting his facts right and in his extreme reluctance to make inferences beyond what the facts will support. I'm sure this is why he was always very reticent about the implications (if any!) of his ideas for religion, economics, etc.
The point that will stick with me the most is Mott's remark that both religious conservatives and secular liberals today tend to resist Darwinian-style explanations for social phenomena. For instance, one can argue that the rise since the 1960s of feminism and gay liberation is not ultimately attributable to individuals making and responding to arguments about justice or equality. Rather, the ultimate drivers are economic pressures and reproductive imperatives. Appeals to justice and equality are at best the proximate mechanisms by which individuals happen to respond to those ultimate drivers of human behavior. The point is not that this explanation of the rise of feminism and gay rights is right or wrong, it's that people from across the liberal-conservative spectrum tend to dislike this kind of explanation, independent of any evidence.
One point Mott didn't make, which I got the chance to make briefly in response to a question from the audience afterwards, is that non-biologists who've developed "evolutionary" theories of economics or society (think of Hegel, Marx, Comte, and many others) tend to conflate Darwinian evolution with organismal development. That is, they tend to think of growth of an individual organism from child to adult as "evolutionary". It's not just famous thinkers like Comte who thought this way--the recent remarks from our own federal science minister indicate that he believes in "evolution" in the sense of individual development and change. To a biologist, this is a serious confusion. Darwinian evolution doesn't have a direction or goal or purpose (see Mayr's remarks in his introduction to the Origin). But the development of an individual organism does have a predetermined goal--to convert a fertilized egg into a functioning adult organism. If you claim that human societies are like developing organisms, that's a very different claim from the claim that human societies are like evolving populations.
This confusion between evolution and development has three obvious sources. One is that both involve "change over time", which is what "evolution" means in a colloquial sense. Second is that there are indeed directional trends in the history of life (e.g., increase in the average "complexity" of organisms since the origin of life), and it's natural (but incorrect) to think of such trends as analogous to the directional development of a newborn into an adult. Third is that it's very hard for non-specialists to grasp that the notion of "fitness" in Darwinian evolution is "relative fitness". All that matters in Darwinian evolution is your ability to survive and reproduce, relative to the other current members of the population. This notion of relative fitness does not imply that absolute fitness will increase over time (even in a constant environment), or that there is some "maximally fit" or "ideal" or "perfect" state toward which a population tends to evolve. I think this is the key Darwinian insight that even very smart non-biologists seem to find very difficult to fully absorb (though in fairness, evolutionary biologists don't help them by talking about evolution using engineering and hill-climbing metaphors that are fine in many respects but are subtly and importantly misleading in other respects). Evolution by natural selection is change over time that both lacks a goal or endpoint, but that is not simply random either (random evolution is genetic drift). Directional, non-random change--but the direction isn't "towards" anything. That's Darwinian evolution. As Mott noted, it's this kind of explanation that many people either misunderstand or find unpalatable.
Thursday, April 2, 2009
The Martyrdom of Man
I forgot to mention this yesterday in class: If anyone is interested in reading an application of selection theory on the development 'human tribes' and a 'natural' history of Western civilisation then take a look at Winwood Reade's Martyrdom of Man (1872). It is an account of the West's development that draws a great deal from social Darwinism and was a pinnacle work during the age of Empire. It was highly influential upon a great many British figures from Cecil Rhodes to Winston Churchill. Reade was a renowned atheist and tried to devise a secular conception of human destiny that also appears in a dialogue in Churchill's novel Savrola. The book is largely devoid of the racism that would dominate later Continental and American works, and focuses predominantly upon cultural selection. Obviously it has many of the typical biases of late Victorian writing, neverthless is an early and interesting exercise of parochial altruism and group selection, roughly along the lines of the Bowles article of last Wednesday. It is most interesting in its predictions for the distant future.
A copy is available at your friendly university library.
A copy is available at your friendly university library.
Wednesday, April 1, 2009
Further reading on group selection
I'm posting in advance of class today because I likely won't have time afterwards. Looking forward to today's discussion on group selection and altruism, as it raises a fascinating tangle of empirical and conceptual issues at the interface of biology, sociology, and philosophy.
Group selection and altruism is a topic on which my thinking has been very much shaped by reading a few key people. So if you're keen on reading more on this topic, I suggest you have a look at:
The work of young British philosophy hotshot Samir Okasha, especially his terrific 2006 book Evolution and the Levels of Selection. This book is already becoming the standard reference on the topic. Most of his papers can be downloaded from his website, so if you don't want to buy or read the book you can easily access individual papers to get snapshots of Okasha's views on key issues.
The work of philosopher Eliot Sober (Marc Ereshefsky's doctoral supervisor), especially his book Unto Others with evolutionary theoretician David Sloan Wilson. Sober basically invented contemporary philosophy of evolutionary biology (in his classic 1984 book The Nature of Selection), and David Sloan Wilson did as much as any biologist to revive group selection as a respectable idea.
The exchange of views between Eliot Sober and evolutionary biologist John Maynard Smith in The Latest on the Best (MIT Press, 1987) is a good non-technical introduction to certain key issues such as what counts as a "group" (yes, that's actually a non-trivial issue).
Richard Dawkins' The Selfish Gene. At the time it was published (1976), this was the final nail in the coffin of group selectionist thinking. Wonderfully clear and forcefully argued, even if some of the conclusions aren't widely held today (which isn't to say that today's group selectionist thinking bears more than a passing resemblance to the naive views that Dawkins was attacking).
Finally, I'll share a little anecdote. As a grad student (this was in the late '90s), I was fortunate enough to have the chance to discuss group selection with Dick Lewontin. Lewontin and Sober wrote a famous 1982 paper about group selection, which addressed the issue that one can often build mathematically-equivalent group-selectionist and individual-selectionist models of the same biological situation. That is, the models make the same predictions about future evolution, but do so by making different assumptions about the underlying causal processes driving evolution. The existence of such predictively-equivalent models could be taken to suggest that the distinction between group and individual selection is merely conventional, a matter of choosing one heuristic perspective over another. In contrast, Sober and Lewontin took a realist view and argued that, in the case of a specific example (heterozygote advantage), the group selectionist model "gets the causal facts right" while the individual selectionist model is simply a mathematical fiction that gives the right predictions for the wrong causal reasons. I'd read the paper and thought a lot about it, and so I was excited to ask Dick Lewontin himself if he still took the same view. He didn't. He'd changed his mind and decided that, at least in the case of the example of heterozygote advantage, that there were no "causal facts" that one could appeal to in order to motivate a choice of one model over the other. I don't know that Lewontin has ever published his revised view, so I don't know if it's widely known that he changed his mind.
Postscript: In Evolution and the Levels of Selection, Samir Okasha argues that Lewontin and Sober's example of heterozygote advantage has actually been misinterpreted by both sides in this realist/conventionalist debate. Okasha argues that Lewontin and Sober arrive at the right (realist) conclusion, but for the wrong reasons. This is a nice example of what I think is Okasha's greatest strength--he's very precise and analytical, and he's good at drawing distinctions that need to be drawn. Okasha's book convinced me that much of the debate and confusion in the group selection literature has arisen because of people failing to draw key distinctions.
Group selection and altruism is a topic on which my thinking has been very much shaped by reading a few key people. So if you're keen on reading more on this topic, I suggest you have a look at:
The work of young British philosophy hotshot Samir Okasha, especially his terrific 2006 book Evolution and the Levels of Selection. This book is already becoming the standard reference on the topic. Most of his papers can be downloaded from his website, so if you don't want to buy or read the book you can easily access individual papers to get snapshots of Okasha's views on key issues.
The work of philosopher Eliot Sober (Marc Ereshefsky's doctoral supervisor), especially his book Unto Others with evolutionary theoretician David Sloan Wilson. Sober basically invented contemporary philosophy of evolutionary biology (in his classic 1984 book The Nature of Selection), and David Sloan Wilson did as much as any biologist to revive group selection as a respectable idea.
The exchange of views between Eliot Sober and evolutionary biologist John Maynard Smith in The Latest on the Best (MIT Press, 1987) is a good non-technical introduction to certain key issues such as what counts as a "group" (yes, that's actually a non-trivial issue).
Richard Dawkins' The Selfish Gene. At the time it was published (1976), this was the final nail in the coffin of group selectionist thinking. Wonderfully clear and forcefully argued, even if some of the conclusions aren't widely held today (which isn't to say that today's group selectionist thinking bears more than a passing resemblance to the naive views that Dawkins was attacking).
Finally, I'll share a little anecdote. As a grad student (this was in the late '90s), I was fortunate enough to have the chance to discuss group selection with Dick Lewontin. Lewontin and Sober wrote a famous 1982 paper about group selection, which addressed the issue that one can often build mathematically-equivalent group-selectionist and individual-selectionist models of the same biological situation. That is, the models make the same predictions about future evolution, but do so by making different assumptions about the underlying causal processes driving evolution. The existence of such predictively-equivalent models could be taken to suggest that the distinction between group and individual selection is merely conventional, a matter of choosing one heuristic perspective over another. In contrast, Sober and Lewontin took a realist view and argued that, in the case of a specific example (heterozygote advantage), the group selectionist model "gets the causal facts right" while the individual selectionist model is simply a mathematical fiction that gives the right predictions for the wrong causal reasons. I'd read the paper and thought a lot about it, and so I was excited to ask Dick Lewontin himself if he still took the same view. He didn't. He'd changed his mind and decided that, at least in the case of the example of heterozygote advantage, that there were no "causal facts" that one could appeal to in order to motivate a choice of one model over the other. I don't know that Lewontin has ever published his revised view, so I don't know if it's widely known that he changed his mind.
Postscript: In Evolution and the Levels of Selection, Samir Okasha argues that Lewontin and Sober's example of heterozygote advantage has actually been misinterpreted by both sides in this realist/conventionalist debate. Okasha argues that Lewontin and Sober arrive at the right (realist) conclusion, but for the wrong reasons. This is a nice example of what I think is Okasha's greatest strength--he's very precise and analytical, and he's good at drawing distinctions that need to be drawn. Okasha's book convinced me that much of the debate and confusion in the group selection literature has arisen because of people failing to draw key distinctions.
Tuesday, March 31, 2009
Evolution Obliterates Morality?
There was a quote put forth in Ruse in an effort to discern whether Darwin ever flirted seriously with the concept of group selection. It nevertheless carries other implications that caught my interest. I reproduce it here:
"It is extremely doubtful whether the offspring of the more sympathetic and benevolent parents, or of those which were the most faithful to their comrades, would be reared in greater number than the children of selfish and treacherous parents of the same tribe. He who was ready to sacrifice his life, as many a savage has been, rather than betray his comrades, would often leave no offspring to inherit his noble nature. The bravest men, who were always willing to come to the front in war, and who freely risked their lives for others, would on an average perish in large number than other men."
Does evolution obliterate morality? Are the noblest and greatest of service to the group destined to sacrifice themselves for the survival of those who indulge in a shallow life of self-preservation? Or is morality, a noble character, a learned rather than an evolutionary trait, and could the stuff of heroes spring from a brood of spoiled children and a bloodline of thoroughly spoiled adults?
"It is extremely doubtful whether the offspring of the more sympathetic and benevolent parents, or of those which were the most faithful to their comrades, would be reared in greater number than the children of selfish and treacherous parents of the same tribe. He who was ready to sacrifice his life, as many a savage has been, rather than betray his comrades, would often leave no offspring to inherit his noble nature. The bravest men, who were always willing to come to the front in war, and who freely risked their lives for others, would on an average perish in large number than other men."
Does evolution obliterate morality? Are the noblest and greatest of service to the group destined to sacrifice themselves for the survival of those who indulge in a shallow life of self-preservation? Or is morality, a noble character, a learned rather than an evolutionary trait, and could the stuff of heroes spring from a brood of spoiled children and a bloodline of thoroughly spoiled adults?
Wednesday, March 25, 2009
readings for april 1
Further thoughts on challenges to the Modern Synthesis
Very good papers this week. Rose and Oakley are actually much more knowledgeable about evolutionary biology sensu stricto than are many modern systems biologists and evo-devo folks who see their fields as challenging the Darwinian orthodoxy. Lots of interesting conceptual issues to chew on here, including:
1. If we want to say whether Darwinism, or the Modern Synthesis, or the possible Postmodern Synthesis, is a 'paradigm shift', we need to define what we mean by 'paradigm shift'. Infamously difficult, due in no small part to ambiguity in the writing of Thomas Kuhn, the physicist/historian/philosopher who came up with the idea of paradigm shifts. Kuhn used 'paradigm' in lots of very different ways, and philosophers have been arguing about his ideas ever since. I do think it's pretty clear that some senses in which Kuhn used the term don't really apply to Darwinism or the Modern Synthesis. As Mike indicated, there was no failure of communication between Darwin and his opponents, or between the developers of the Modern Synthesis and their opponents. People weren't talking past one another. They mostly agreed on what the questions were and simply disagreed about the answers. That means those paradigm shifts, if that's what they were, weren't like 'gestalt switches', contrary to some of Kuhn's claims. (A gestalt switch is like when you look at an ambiguous drawing such as the famous one that can look like either a rabbit or a duck, and switch from seeing it one way to seeing it the other way. The two different perspectives are just that--different. Neither is incompatible with the other, and so the choice between them isn't rational but rather is merely a matter of preference).
2. The distinction between proximate and ultimate explanations, and the relationship between them, seems to me to absolutely indispensable for understanding the relationship between evolutionary biology and molecular biology/genetics/biochemistry. This distinction is, or should be, familiar to biologists. Ethologist Niko Tinbergen wrote a classic 1963 paper on four kinds of questions in ethology, which basically draws this distinction. Unfortunately, a lot of unproductive argument and attempts at synthesis in science basically boil down to arguments over which of these kinds of questions is "best".
3. Following on from 2, it's very interesting to think about how proximate and ultimate explanations relate to one another, both in general and in specific cases. Simple reduction of ultimate to proximate explanations generally isn't possible or desirable. This is in part because of supervenience--properties like "fitness" are not physical properties like "mass" or "charge". So statements about fitness cannot be translated into, and thereby reduced to, statements about physical properties, although an organism's physical properties obviously affect its fitness. This kind of "translation problem" crops up in other fields. It's the basis of the mind-brain problem the prevents psychology from being reduced to neuroscience. States of mind (e.g., "happy", "sad") can be correlated with states of the brain (patterns of neuron firing), but that doesn't mean the mind "is nothing but" the brain.
I actually think there are a lot of really cool scientific questions that are inspired by our new genetic knowledge. But those questions seem to me to fall within the conceptual framework of the Modern Synthesis. For instance, much of the mathematical theory of quantitative genetics developed by Fisher, Haldane, and Wright assumes that a quantitative phenotype of an organism(e.g., its weight or length) is determined in part by its genotype at each of infinitely many loci, each of which has a very small, additive effect on phenotype. This assumption is mathematically convenient, because it turns out to predict that phenotypic variation will be normally distributed (i.e. follow a bell curve), and normal distributions are easy to work with mathematically. This assumption is also empirically supported, in that we do indeed observe that phenotypic variation of quantitative traits like height often is normally distributed, even when all individuals are grown in a shared, controlled environment. But recently, modern molecular biology has falsified the genetic assumptions on which the mathematical theory is based. We can now identify most of the genetic loci that affect, say, height, and we can estimate the additive effect of each genotype at each locus. And it turns out that genetic variation in quantitative traits is mostly due to variation at only a few loci, each of which has a big rather than a small effect on phenotype. But this doesn't mean we should just chuck quantitative genetic theory and start over, since (again) it's a matter of empirical fact that phenotypic variation is normally distributed. So quantitative genetics gives the right answer for the wrong reasons, and it's a very interesting question to try to work out how that's possible. We now know the genome isn't at all like we thought--so how can it be that false assumptions about the genome nevertheless give the right answer?
4. Closely related to ideas about proximate vs. ultimate explanations and supervenience is the idea of "screening off". This is the idea that, if A (an event or state of affairs) causes B and B causes C, B "screens off" C from A. That is, in order to predict C, I only need to know B. Knowing A doesn't help predict C, because A only affects C indirectly, via B. But that doesn't mean one never wants to know anything about A. For instance, once I've explained C by appeal to B, it's natural to ask "What explains B?", which leads me to work backwards along the causal chain. I leave it to you to think about how this idea relates to the ideas discussed in class today.
5. We didn't talk about Gould today, but I hope it's clear that objections to Darwinism as wrong or incomplete tend to run to type. The claim that development imparts some kind of directionality to adaptive evolution (or so strongly constrains it that the constraint is really the main story) resonates with much earlier ideas about orthogenesis and the "bauplan".
6. Objections to Darwinism and the Modern Synthesis also run to type in caricaturing Darwinians as believing that natural selection is all powerful and entirely unconstrained. My experience is that evolutionary biologists focus so much on natural selection not because they think it can produce any adaptation, but because they think it's the only thing that can produce what adaptations exist. And so if you're interested in explaining adaptation, you have no choice but to be interested in natural selection--it's the only game in town. That doesn't mean you don't care about constraints on adaptation. But those constraints aren't interesting in and of themselves, they're only interesting by virtue of their effects on adaptive evolution. Of course, scientists prefer to argue about objective empirical claims rather than subjective claims about what's "interesting". So if you want to argue against the Modern Synthesis, you can't accuse its proponents of making uninteresting claims, you have to accuse them of making false claims.
1. If we want to say whether Darwinism, or the Modern Synthesis, or the possible Postmodern Synthesis, is a 'paradigm shift', we need to define what we mean by 'paradigm shift'. Infamously difficult, due in no small part to ambiguity in the writing of Thomas Kuhn, the physicist/historian/philosopher who came up with the idea of paradigm shifts. Kuhn used 'paradigm' in lots of very different ways, and philosophers have been arguing about his ideas ever since. I do think it's pretty clear that some senses in which Kuhn used the term don't really apply to Darwinism or the Modern Synthesis. As Mike indicated, there was no failure of communication between Darwin and his opponents, or between the developers of the Modern Synthesis and their opponents. People weren't talking past one another. They mostly agreed on what the questions were and simply disagreed about the answers. That means those paradigm shifts, if that's what they were, weren't like 'gestalt switches', contrary to some of Kuhn's claims. (A gestalt switch is like when you look at an ambiguous drawing such as the famous one that can look like either a rabbit or a duck, and switch from seeing it one way to seeing it the other way. The two different perspectives are just that--different. Neither is incompatible with the other, and so the choice between them isn't rational but rather is merely a matter of preference).
2. The distinction between proximate and ultimate explanations, and the relationship between them, seems to me to absolutely indispensable for understanding the relationship between evolutionary biology and molecular biology/genetics/biochemistry. This distinction is, or should be, familiar to biologists. Ethologist Niko Tinbergen wrote a classic 1963 paper on four kinds of questions in ethology, which basically draws this distinction. Unfortunately, a lot of unproductive argument and attempts at synthesis in science basically boil down to arguments over which of these kinds of questions is "best".
3. Following on from 2, it's very interesting to think about how proximate and ultimate explanations relate to one another, both in general and in specific cases. Simple reduction of ultimate to proximate explanations generally isn't possible or desirable. This is in part because of supervenience--properties like "fitness" are not physical properties like "mass" or "charge". So statements about fitness cannot be translated into, and thereby reduced to, statements about physical properties, although an organism's physical properties obviously affect its fitness. This kind of "translation problem" crops up in other fields. It's the basis of the mind-brain problem the prevents psychology from being reduced to neuroscience. States of mind (e.g., "happy", "sad") can be correlated with states of the brain (patterns of neuron firing), but that doesn't mean the mind "is nothing but" the brain.
I actually think there are a lot of really cool scientific questions that are inspired by our new genetic knowledge. But those questions seem to me to fall within the conceptual framework of the Modern Synthesis. For instance, much of the mathematical theory of quantitative genetics developed by Fisher, Haldane, and Wright assumes that a quantitative phenotype of an organism(e.g., its weight or length) is determined in part by its genotype at each of infinitely many loci, each of which has a very small, additive effect on phenotype. This assumption is mathematically convenient, because it turns out to predict that phenotypic variation will be normally distributed (i.e. follow a bell curve), and normal distributions are easy to work with mathematically. This assumption is also empirically supported, in that we do indeed observe that phenotypic variation of quantitative traits like height often is normally distributed, even when all individuals are grown in a shared, controlled environment. But recently, modern molecular biology has falsified the genetic assumptions on which the mathematical theory is based. We can now identify most of the genetic loci that affect, say, height, and we can estimate the additive effect of each genotype at each locus. And it turns out that genetic variation in quantitative traits is mostly due to variation at only a few loci, each of which has a big rather than a small effect on phenotype. But this doesn't mean we should just chuck quantitative genetic theory and start over, since (again) it's a matter of empirical fact that phenotypic variation is normally distributed. So quantitative genetics gives the right answer for the wrong reasons, and it's a very interesting question to try to work out how that's possible. We now know the genome isn't at all like we thought--so how can it be that false assumptions about the genome nevertheless give the right answer?
4. Closely related to ideas about proximate vs. ultimate explanations and supervenience is the idea of "screening off". This is the idea that, if A (an event or state of affairs) causes B and B causes C, B "screens off" C from A. That is, in order to predict C, I only need to know B. Knowing A doesn't help predict C, because A only affects C indirectly, via B. But that doesn't mean one never wants to know anything about A. For instance, once I've explained C by appeal to B, it's natural to ask "What explains B?", which leads me to work backwards along the causal chain. I leave it to you to think about how this idea relates to the ideas discussed in class today.
5. We didn't talk about Gould today, but I hope it's clear that objections to Darwinism as wrong or incomplete tend to run to type. The claim that development imparts some kind of directionality to adaptive evolution (or so strongly constrains it that the constraint is really the main story) resonates with much earlier ideas about orthogenesis and the "bauplan".
6. Objections to Darwinism and the Modern Synthesis also run to type in caricaturing Darwinians as believing that natural selection is all powerful and entirely unconstrained. My experience is that evolutionary biologists focus so much on natural selection not because they think it can produce any adaptation, but because they think it's the only thing that can produce what adaptations exist. And so if you're interested in explaining adaptation, you have no choice but to be interested in natural selection--it's the only game in town. That doesn't mean you don't care about constraints on adaptation. But those constraints aren't interesting in and of themselves, they're only interesting by virtue of their effects on adaptive evolution. Of course, scientists prefer to argue about objective empirical claims rather than subjective claims about what's "interesting". So if you want to argue against the Modern Synthesis, you can't accuse its proponents of making uninteresting claims, you have to accuse them of making false claims.
Monday, March 23, 2009
Sunday, March 22, 2009
primary reading for march 25
1) Rose, M. R. and T. H. Oakley. 2007. The new biology: beyond the Modern Synthesis. Biology Direct 2:30. (pdf available)
2) Huxley, J. 1942, 1963. Evolution: The Modern Synthesis. Chapter 1 of First Edition, excerpts from the Introduction of Second Edition.
2) Huxley, J. 1942, 1963. Evolution: The Modern Synthesis. Chapter 1 of First Edition, excerpts from the Introduction of Second Edition.
Monday, March 9, 2009
Further thoughts on Chapters XIII-XIV
A few--okay, many--further thoughts on the last two chapters. May try to post with further thoughts on the Origin as a whole at some point, but I'll probably wait until around the time of the last class (but don't let that stop you from posting your own lookback on the whole "long argument").
1. The idea that classification was based on evolutionary principles without actually realizing it has intriguing implications. For instance, does that comprise evidence for those evolutionary principles? I'm reminded of the argument (discussed in one of Gould's essays, I believe) that biological species, as classified by taxonomists, are "real" entities because hunter-gatherer tribes classify organisms in the same way (i.e. they recognize each biological species as a distinct kind of organism and give it its own name). Or maybe that thought doesn't stand up to the scrutiny you all will surely apply to it next week as part of your discussion of Darwin's species concept. ;-)
2. I love the final passages of the Origin (from the bottom of p. 480 on) more than I can say. It's so satisfying to see Darwin rising to the occasion and finishing with a flourish. All the caveats and doubts drop away as he drives home the argument and its enormous implications. And it's beautifully written, it just sweeps you along. My highlights (warning: long list!):
(a) p. 481: "But the chief cause of our natural unwillingness to admit that one species has given birth to other and distinct species, is that we are always slow in admitting any great change of which we do not see the intermediate steps." Yup (although I don't know that this is true of today's evangelical creationists; their unwillingness has other sources).
(b) p. 481: "Although I am fully convinced of the truth of the views given in this volume...I by no means expect to convince experienced naturalists whose minds are stocked with a multitude of facts all viewed, during a long course of years, from a point of view directly opposite mine. It is so easy to hide our ignorance under such expressions as the 'plan of creation,' 'unity of design,' &c., and to think that we give explanation when we only restate a fact. Any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject my theory...but I look with confidence to the future, to young and rising naturalists, who will be able to view both sides of the questions with impartiality." Oh no he didn't! This is stunningly direct. He might as well have written "The close-minded old farts who dominate the field are so blind they can't even see that their so-called 'explanations' are empty. I can't hope to change their minds because science advances one death at a time. But history will show that I'm right and they're wrong." I'm sure this would read as arrogant--except that history did indeed prove Darwin right. As Reggie Jackson once said in a different context, "It ain't braggin' if you can do it."
(c) p. 483, the rhetorical attack on the emptiness of special creationist 'explanations': "These authors seem no more startled at a miraculous act of creation than at an ordinary birth. But do they really believe that at innumerable periods in the earth's history certain elemental atoms have been commanded suddenly to flash into living tissues? Do they believe that at each supposed act of creation one individual or many were produced?...and in the case of mammals, were they created bearing the false marks of nourishment from the mother's womb? Although naturalists very properly demand a full explanation of every difficulty from those who believe in the mutability of species, on their own side they ignore the whole subject of the first appearance of species in what they consider reverent silence." Wow. One gets the sense here that deep down Darwin is quite frustrated and even angry with special creationism. I imagine that, if one is an open-minded fact hound like Darwin, if one is absolutely determined to get things right, then one is likely to be very impatient with those who aren't equally open-minded and determined. And one is likely to be especially impatient with those who aren't even sufficiently open-minded to recognize and engage with questions so big as to demand an answer. Clearly Darwin took seriously the mottoes from Whewell and Bacon with which he chose to preface his book.
(d) p. 484: "[P]robably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed." Talk about following the evidence wherever it leads. At the time, it would've seemed like a very good question to ask just how far Darwin's argument goes. One might well have wondered, why couldn't there have been several or even quite numerous events of special creation (say, one per family), with evolution by natural selection merely driving subsequent within-family diversification? But there's no evidence for this, and so Darwin calls it like he sees it: the Tree of Life has one root. When I started reading the Origin, I was most impressed with Darwin's insight regarding the mechanism of adaptive evolution. But this passage really convinces me that his insight regarding the fact of evolution was equally impressive. Not only is there an evolutionary Tree of Life--it has one root! No pun intended here but--my God! I wish I could forget what I know about evolution and read that as it would've read to a Victorian. Because in all likelihood I'll never have the chance to be told something that astonishing about the world--something that runs so counter to my whole picture of how the world works. I'll never get to have my world turned upside down. Then again, if I was told something that would turn my world upside down, I'd probably dismiss it as wrong, if not crazy. I'd have to hope I had the insight of Thomas Henry Huxley, who wrote upon reading the Origin, "How extremely stupid not to have thought of that."
(e) p. 485: "When we no longer look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate every complex structure and instinct as the summing up of many contrivances, each useful to the possessor, nearly in the same way as when we look at any great mechanical invention as the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting, I speak from experience, will the study of natural history become!" Great analogy. And a great summary of the modern scientific mind. To a scientist, things become more wonderful, not less, the more we learn about them.
(f) p. 488: "Light will be thrown on the origin of man and his history." Perhaps the most famous understatement of all time.
(g) p. 489. God love him, Darwin saves the best for last. Maybe for some people, the beauty of some famous passages of literature is dulled by familiarity. But for me, the final paragraph of the Origin, with which I was familiar before the term started, will never get old. Indeed, I used to regard it as merely a nice passage. But having read the book I now see it as it was intended, as a summary of everything that came before. And so now this passage impresses and thrills me more than I can say. I am not a religious person, and like many such people if you asked me, "So what do you believe in?" I would struggle to articulate a satisfying answer, by which I mean a spiritually (rather than intellectually) satisfying answer. But although I would struggle to speak for myself, I'm happy to let this passage speak for me. This is the best thing I've ever read:
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing in the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the direct and indirect action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling according to the fixed law of gravity, from so simple a beginning endless forms most beautiful have been, and are being, evolved.
1. The idea that classification was based on evolutionary principles without actually realizing it has intriguing implications. For instance, does that comprise evidence for those evolutionary principles? I'm reminded of the argument (discussed in one of Gould's essays, I believe) that biological species, as classified by taxonomists, are "real" entities because hunter-gatherer tribes classify organisms in the same way (i.e. they recognize each biological species as a distinct kind of organism and give it its own name). Or maybe that thought doesn't stand up to the scrutiny you all will surely apply to it next week as part of your discussion of Darwin's species concept. ;-)
2. I love the final passages of the Origin (from the bottom of p. 480 on) more than I can say. It's so satisfying to see Darwin rising to the occasion and finishing with a flourish. All the caveats and doubts drop away as he drives home the argument and its enormous implications. And it's beautifully written, it just sweeps you along. My highlights (warning: long list!):
(a) p. 481: "But the chief cause of our natural unwillingness to admit that one species has given birth to other and distinct species, is that we are always slow in admitting any great change of which we do not see the intermediate steps." Yup (although I don't know that this is true of today's evangelical creationists; their unwillingness has other sources).
(b) p. 481: "Although I am fully convinced of the truth of the views given in this volume...I by no means expect to convince experienced naturalists whose minds are stocked with a multitude of facts all viewed, during a long course of years, from a point of view directly opposite mine. It is so easy to hide our ignorance under such expressions as the 'plan of creation,' 'unity of design,' &c., and to think that we give explanation when we only restate a fact. Any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject my theory...but I look with confidence to the future, to young and rising naturalists, who will be able to view both sides of the questions with impartiality." Oh no he didn't! This is stunningly direct. He might as well have written "The close-minded old farts who dominate the field are so blind they can't even see that their so-called 'explanations' are empty. I can't hope to change their minds because science advances one death at a time. But history will show that I'm right and they're wrong." I'm sure this would read as arrogant--except that history did indeed prove Darwin right. As Reggie Jackson once said in a different context, "It ain't braggin' if you can do it."
(c) p. 483, the rhetorical attack on the emptiness of special creationist 'explanations': "These authors seem no more startled at a miraculous act of creation than at an ordinary birth. But do they really believe that at innumerable periods in the earth's history certain elemental atoms have been commanded suddenly to flash into living tissues? Do they believe that at each supposed act of creation one individual or many were produced?...and in the case of mammals, were they created bearing the false marks of nourishment from the mother's womb? Although naturalists very properly demand a full explanation of every difficulty from those who believe in the mutability of species, on their own side they ignore the whole subject of the first appearance of species in what they consider reverent silence." Wow. One gets the sense here that deep down Darwin is quite frustrated and even angry with special creationism. I imagine that, if one is an open-minded fact hound like Darwin, if one is absolutely determined to get things right, then one is likely to be very impatient with those who aren't equally open-minded and determined. And one is likely to be especially impatient with those who aren't even sufficiently open-minded to recognize and engage with questions so big as to demand an answer. Clearly Darwin took seriously the mottoes from Whewell and Bacon with which he chose to preface his book.
(d) p. 484: "[P]robably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed." Talk about following the evidence wherever it leads. At the time, it would've seemed like a very good question to ask just how far Darwin's argument goes. One might well have wondered, why couldn't there have been several or even quite numerous events of special creation (say, one per family), with evolution by natural selection merely driving subsequent within-family diversification? But there's no evidence for this, and so Darwin calls it like he sees it: the Tree of Life has one root. When I started reading the Origin, I was most impressed with Darwin's insight regarding the mechanism of adaptive evolution. But this passage really convinces me that his insight regarding the fact of evolution was equally impressive. Not only is there an evolutionary Tree of Life--it has one root! No pun intended here but--my God! I wish I could forget what I know about evolution and read that as it would've read to a Victorian. Because in all likelihood I'll never have the chance to be told something that astonishing about the world--something that runs so counter to my whole picture of how the world works. I'll never get to have my world turned upside down. Then again, if I was told something that would turn my world upside down, I'd probably dismiss it as wrong, if not crazy. I'd have to hope I had the insight of Thomas Henry Huxley, who wrote upon reading the Origin, "How extremely stupid not to have thought of that."
(e) p. 485: "When we no longer look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate every complex structure and instinct as the summing up of many contrivances, each useful to the possessor, nearly in the same way as when we look at any great mechanical invention as the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting, I speak from experience, will the study of natural history become!" Great analogy. And a great summary of the modern scientific mind. To a scientist, things become more wonderful, not less, the more we learn about them.
(f) p. 488: "Light will be thrown on the origin of man and his history." Perhaps the most famous understatement of all time.
(g) p. 489. God love him, Darwin saves the best for last. Maybe for some people, the beauty of some famous passages of literature is dulled by familiarity. But for me, the final paragraph of the Origin, with which I was familiar before the term started, will never get old. Indeed, I used to regard it as merely a nice passage. But having read the book I now see it as it was intended, as a summary of everything that came before. And so now this passage impresses and thrills me more than I can say. I am not a religious person, and like many such people if you asked me, "So what do you believe in?" I would struggle to articulate a satisfying answer, by which I mean a spiritually (rather than intellectually) satisfying answer. But although I would struggle to speak for myself, I'm happy to let this passage speak for me. This is the best thing I've ever read:
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing in the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the direct and indirect action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling according to the fixed law of gravity, from so simple a beginning endless forms most beautiful have been, and are being, evolved.
Today's Supplementary
The line of demarcation between natural and artificial selection seems to become blurred if one views intelligence as a product of the mind which in turn was developed by natural selection. This point in itself is highly debatable and no doubt some of you will disagree entirely. Nevertheless, let us venture down Dennett's rabbit hole. Cutting to the chase, it does open the door for everything cultural, political, and economic to be explained in the framework of the "Darwinian Algorithm". The 19th century politician did it for national competition in the West and imperialism in the Third World, the 19th century historian did it for cultural transmission, and Margaret Thatcher did it for economics. The algorithm can be applied anywhere because of its unique and ingenious construction allows it to explain anything, (although this does not necessarily mean the explanation is correct, and Dennett even allows for an imaginary super-algorithm being produced someday that does the task even more efficiently.) The point is, it can potentially be applied anywhere. But the question is where it is most usefully applied.
Now I do hope I was not misunderstood in this "ought question". I was not raising an ethical question. That would have been very dull of me. More useful is the question of where the framework is of most use. If every nook and cranny of the living world can be explained along the lines of natural selection, that is all and well. However, an all encompassing theory has a tendency to get a little stale. If the theory potentially explains everything social scientists can all retire, unless they'd like to devote their careers to filling in the details. If so, I eagerly anticipate the doctoral thesis on how does Darwinian theory guides the ability of Midwestern American housewives to make chocolate chip cookies. However, one suspects it is rather inefficient to spend our lives explaining everything. Rather, it is worthwhile to focus on things that need to be explained. In the face of an all-encompassing theory, the fact seems self evident. Therefore, a more pragmatic question seems to be, how does it aid us in pursuing our respective topics? Is, for instance, the transmission of language and culture any better understood by cramming what we now into a Darwinian framework? To a significant degree that would justify a dissertation on the subject? (which, sadly, has already been written more than once) How is any particular topic more greatly elucidated by viewing it through such a lens? That is the question we must ask ourselves. We must selfishly ask whether thinking about it that way profits us and enhances our perspective, in the same way historians today consider the usages of a 'Gender lens' or a 'Marxist lens' when writing their histories. All these algorithms or frameworks belong to what is commonly called the 'methodological toolbox' from which they draw a perspective when it is found useful to the purpose.
Where is the 'Darwinian tool' most useful and best suited? The immediate answer seems to be the obvious one - the study of the evolution of species. Alternately, in the study of human activity from Capitalism and Freedom to Mein Kampf, social and economic theory has been written taking from quasi 'Darwinist' perspectives. Yet these writings deal with topics vastly different from those with which Darwin was concerned. Nor would Darwin have necessarily agreed with how his theory was applied. Not to dismiss the many ideas in the social sciences that could not have been generated without Darwin, many of these explanations of culture seem to be an intellectual exercise at best, and at the worst, a blatant subversion of Darwin's principles. There are many ways Darwin has influenced the social sciences, but his algorithm seems to have made tangible progress seems to have been made in the realm of biology. I cannot even begin to imagine how long that list may be. A lot of quasi-social darwinist prattlings, on the other hand, have turned out to be a highly decorative waste of time. I say this as delicately as I can, with many notable exceptions in mind, as well as bearing in mind the army of scholars who would take offence to such a sweeping remark and seek hang me from a lampost. Nevertheless, if a line of demarcation cannot be clearly made because Darwin's algorithm can be deployed everywhere, to explain even the products of the human mind, perhaps a line of demarcation can at least be drawn pragmatically and opportunistically, like a tool drawn from a toolbox, it is best suited to tackling certain kinds of jobs.
Now I do hope I was not misunderstood in this "ought question". I was not raising an ethical question. That would have been very dull of me. More useful is the question of where the framework is of most use. If every nook and cranny of the living world can be explained along the lines of natural selection, that is all and well. However, an all encompassing theory has a tendency to get a little stale. If the theory potentially explains everything social scientists can all retire, unless they'd like to devote their careers to filling in the details. If so, I eagerly anticipate the doctoral thesis on how does Darwinian theory guides the ability of Midwestern American housewives to make chocolate chip cookies. However, one suspects it is rather inefficient to spend our lives explaining everything. Rather, it is worthwhile to focus on things that need to be explained. In the face of an all-encompassing theory, the fact seems self evident. Therefore, a more pragmatic question seems to be, how does it aid us in pursuing our respective topics? Is, for instance, the transmission of language and culture any better understood by cramming what we now into a Darwinian framework? To a significant degree that would justify a dissertation on the subject? (which, sadly, has already been written more than once) How is any particular topic more greatly elucidated by viewing it through such a lens? That is the question we must ask ourselves. We must selfishly ask whether thinking about it that way profits us and enhances our perspective, in the same way historians today consider the usages of a 'Gender lens' or a 'Marxist lens' when writing their histories. All these algorithms or frameworks belong to what is commonly called the 'methodological toolbox' from which they draw a perspective when it is found useful to the purpose.
Where is the 'Darwinian tool' most useful and best suited? The immediate answer seems to be the obvious one - the study of the evolution of species. Alternately, in the study of human activity from Capitalism and Freedom to Mein Kampf, social and economic theory has been written taking from quasi 'Darwinist' perspectives. Yet these writings deal with topics vastly different from those with which Darwin was concerned. Nor would Darwin have necessarily agreed with how his theory was applied. Not to dismiss the many ideas in the social sciences that could not have been generated without Darwin, many of these explanations of culture seem to be an intellectual exercise at best, and at the worst, a blatant subversion of Darwin's principles. There are many ways Darwin has influenced the social sciences, but his algorithm seems to have made tangible progress seems to have been made in the realm of biology. I cannot even begin to imagine how long that list may be. A lot of quasi-social darwinist prattlings, on the other hand, have turned out to be a highly decorative waste of time. I say this as delicately as I can, with many notable exceptions in mind, as well as bearing in mind the army of scholars who would take offence to such a sweeping remark and seek hang me from a lampost. Nevertheless, if a line of demarcation cannot be clearly made because Darwin's algorithm can be deployed everywhere, to explain even the products of the human mind, perhaps a line of demarcation can at least be drawn pragmatically and opportunistically, like a tool drawn from a toolbox, it is best suited to tackling certain kinds of jobs.
Thursday, March 5, 2009
supplementary reading for march 9
Dennett, D. C. 1995. Darwin's dangerous idea. Sciences 35 (3):34-40 (pdf available to EBSCOhost subscribers here)
Wednesday, March 4, 2009
Further thoughts on chapters XI-XII
A few further musings on the biogeography chapters:
1. After today's discussion, I now want to go and read Mayr (which I've never actually done, embarrassingly), and decide for myself just how firm are the empirical (as opposed to theoretical) foundations of the 'conventional wisdom' that allopatric speciation is the rule.
2. Darwin's own theory of speciation is (in)famously hard to decipher. As was correctly pointed out in class today, much of the biogeography material sounds like it was written by a man who believes in allopatric speciation as the dominant mode of speciation. But the earlier chapters don't read that way. Darwin clearly understood that what we would now call gene flow can prevent lineages from splitting. But his theory of speciation also relies a lot on the 'principle of divergence of character' (see chapter IV). Briefly, this is the idea that the 'fittest' types of organism will be those that produce the most divergent offspring, so that collectively those offspring can occupy a greater number of niches in the economy of nature, thereby allowing more of the offspring to survive than if they were all suited only for a single niche. This principle has several logical and empirical problems with it, although something like it is the basis for one hypothesis to explain the evolution of sexual reproduction (which produces more variable offspring than asexual reproduction).
I wonder if Darwin was drawn to the principle of divergence of character in part because he was afraid that otherwise his theory would predict a world populated only by a very few 'superspecies' rather than the polyglot diversity that we see. There are other ideas that Darwin might have hit on (or emphasized more strongly) to explain why we don't just have a few superspecies, such as the fact that selection pressures vary geographically. But taking that view seriously would've required him to find another way to explain why some species have larger geographical ranges than others besides the simple claim that the wide-ranging species are the 'fittest'. In general, Darwin isn't as sensitive as I expected to the notion that fitness is typically very context-dependent. He talks about the fittest type replacing all other types in its own lineage, and then spreading widely to replace other similar lineages, as if any one type could possibly be the 'best' in very different contexts. Then, to ensure continued maintenance and production of diversity, he appeals to the principle of divergence of character, which introduces an element of self-contradiction. Your offspring can't fill the gaps in the economy of nature (thereby avoiding competition with other species), and at the same time outcompete other species for already-occupied places in that same economy. Your offspring either compete with other species, or they don't.
But Darwin had such a head full of ideas, it's hard to fault him too much if those ideas didn't all quite fit together.
3. A rare instance of Darwin just getting it wrong: Darwin refers at multiple points to species failing to evolve in response to climate change because they all shift their ranges as a group, so that each continues to live with its coevolved fellows. There are a number of problems with this view, starting with the fact that it's false. Empirical research has now shown that, while species do generally migrate north (and up mountain slopes) in warming periods, and the reverse in cooling periods, they do so at very different rates. Many ancient ecosystems therefore were comprised of combinations of species that don't currently exist. But in fairness, Darwin's suggestion is a perfectly reasonable one given the evidence available to him at the time.
1. After today's discussion, I now want to go and read Mayr (which I've never actually done, embarrassingly), and decide for myself just how firm are the empirical (as opposed to theoretical) foundations of the 'conventional wisdom' that allopatric speciation is the rule.
2. Darwin's own theory of speciation is (in)famously hard to decipher. As was correctly pointed out in class today, much of the biogeography material sounds like it was written by a man who believes in allopatric speciation as the dominant mode of speciation. But the earlier chapters don't read that way. Darwin clearly understood that what we would now call gene flow can prevent lineages from splitting. But his theory of speciation also relies a lot on the 'principle of divergence of character' (see chapter IV). Briefly, this is the idea that the 'fittest' types of organism will be those that produce the most divergent offspring, so that collectively those offspring can occupy a greater number of niches in the economy of nature, thereby allowing more of the offspring to survive than if they were all suited only for a single niche. This principle has several logical and empirical problems with it, although something like it is the basis for one hypothesis to explain the evolution of sexual reproduction (which produces more variable offspring than asexual reproduction).
I wonder if Darwin was drawn to the principle of divergence of character in part because he was afraid that otherwise his theory would predict a world populated only by a very few 'superspecies' rather than the polyglot diversity that we see. There are other ideas that Darwin might have hit on (or emphasized more strongly) to explain why we don't just have a few superspecies, such as the fact that selection pressures vary geographically. But taking that view seriously would've required him to find another way to explain why some species have larger geographical ranges than others besides the simple claim that the wide-ranging species are the 'fittest'. In general, Darwin isn't as sensitive as I expected to the notion that fitness is typically very context-dependent. He talks about the fittest type replacing all other types in its own lineage, and then spreading widely to replace other similar lineages, as if any one type could possibly be the 'best' in very different contexts. Then, to ensure continued maintenance and production of diversity, he appeals to the principle of divergence of character, which introduces an element of self-contradiction. Your offspring can't fill the gaps in the economy of nature (thereby avoiding competition with other species), and at the same time outcompete other species for already-occupied places in that same economy. Your offspring either compete with other species, or they don't.
But Darwin had such a head full of ideas, it's hard to fault him too much if those ideas didn't all quite fit together.
3. A rare instance of Darwin just getting it wrong: Darwin refers at multiple points to species failing to evolve in response to climate change because they all shift their ranges as a group, so that each continues to live with its coevolved fellows. There are a number of problems with this view, starting with the fact that it's false. Empirical research has now shown that, while species do generally migrate north (and up mountain slopes) in warming periods, and the reverse in cooling periods, they do so at very different rates. Many ancient ecosystems therefore were comprised of combinations of species that don't currently exist. But in fairness, Darwin's suggestion is a perfectly reasonable one given the evidence available to him at the time.
Darwin and art
I continue to be proven wrong in my claim early in the term that Darwin had little or no influence on art. This week's Nature contains a review of an exhibition on the response of artists to Darwin's ideas. Darwin: Art and the Search for Origins is running at the Shirn Kunsthalle in Frankfurt, Germany. Above is Monkey Before a Skeleton by Gabriel von Max (1840-1915), one of the artists featured in the exhibition. von Max was a convinced Darwinist and a prolific zoological collector.
I hate it when Nature runs reviews of things that I can't go to see. Sigh. I miss living in London...
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