I've prepared a bunch of exam questions for my students and given them out two weeks before the exam. I promised them that I would post some of these questions on my blog to see how you would answer them. I'm hoping that you, dear readers, will show my students that there really is some controversy.Here's the second question.
Discuss the following statement by Daniel Dennett from his book Darwin’s Dangerous Idea (1995, p. 238). Do you agree or disagree? Pay particular attention to the kind of reasoning required in the field of molecular evolution.My students all have a copy of the Spandrels paper and they should be familiar with it. In case you're not (shame), it seems to me that Lewontin & Gould are advocating a pluralist approach to evolution. They criticize the adaptationist program and really would like to see it disappear. Is Dennett making a distinction between the adaptationist program and adaptationist reasoning? I don't think so because here's what he says on the same page as the quotation above.
Adaptationist reasoning is not optional, it is the heart and soul of evolutionary biology. Although it may be supplemented, and its flaws repaired, to think of displacing it from its cental position in biology is to imagine not just the downfall of Darwinism but the collapse of modern biochemistry and all the life sciences and medicine. So it is a bit surprising to discover that this is precisely the interpretation that many readers have placed on the most famous and influential critique of adaptationism, Stephen Jay Gould and Richard Lewontin’s oft-cited, oft-reprinted, but massively misread classic, “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Program” (1979).
The biologists' name for this style of reasoning is adaptationism. It is defined by one of its most eminent critics as the "growing tendency in evolutionary biology to reconstruct the evolutionary events by assuming that all characters are established in evolution by direct natural selection of the most adapted state, that is, the state that is an optimum solution to a problem posed by the environment" (Lewontin 1983). These critics claim that, although adaptationism plays some important role in biology, it is not really all that central or ubiquitous—and, indeed, we should try to balance it with other ways of thinking. I have been showing, however, that it plays a crucial role in the analysis of every biological event at every scale from the creation of the first self-replicating molecule on up. If we gave up adaptationist reasoning, for instance, we would have to give up the best textbook argument for the very occurrence of evolution (I quoted Mark Ridley's version of it on page 136): the widespread existence of homologies, those suspicious similarities of design that are not functionally necessary.Dennett is a philosopher so he might not be as familiar with modern biochemistry as his statement implies. Can anyone figure out why biochemistry would collapse if we stop attributing everything to adaptation? I wonder how adaptationist thinking helps us understand sequence-based phylogenetic trees and the molecular clock? At the other extreme, how crucial a role does adaptationism play in deciding whether birds are dinosaurs or punctuated equilibria are the dominant pattern in the fossil record?
I'm thinking that it might be a problem grading the answer to this question. Can a student defend Dennett's statement and still get a passing grade?
UPDATE: Dan Dennett Replies.
Let me close, for no particular reason, with a few quotations from one of my personal heroes, Betrand Russell.
A stupid man's report of what a clever man says can never be accurate, because he unconsciously translates what he hears into something he can understand.That last one is for John Wilkins.
I think we ought always to entertain our opinions with some measure of doubt. I shouldn't wish people dogmatically to believe any philosophy, not even mine.
If a man is offered a fact which goes against his instincts, he will scrutinize it closely, and unless the evidence is overwhelming, he will refuse to believe it. If, on the other hand, he is offered something which affords a reason for acting in accordance to his instincts, he will accept it even on the slightest evidence. The origin of myths is explained in this way.
In all affairs it's a healthy thing now and then to hang a question mark on the things you have long taken for granted.
It has been said that man is a rational animal. All my life I have been searching for evidence which could support this.
Passive acceptance of the teacher's wisdom is easy to most boys and girls. It involves no effort of independent thought, and seems rational because the teacher knows more than his pupils; it is moreover the way to win the favour of the teacher unless he is a very exceptional man. Yet the habit of passive acceptance is a disastrous one in later life. It causes man to seek and to accept a leader, and to accept as a leader whoever is established in that position.
Patriots always talk of dying for their country but never of killing for their country.
So far as I can remember, there is not one word in the Gospels in praise of intelligence.
The universe may have a purpose, but nothing we know suggests that, if so, this purpose has any similarity to ours.
The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts.
This is one of those views which are so absolutely absurd that only very learned men could possibly adopt them.
This is patently absurd; but whoever wishes to become a philosopher must learn not to be frightened by absurdities.
When one admits that nothing is certain one must, I think, also admit that some things are much more nearly certain than others. It is much more nearly certain that we are assembled here tonight than it is that this or that political party is in the right. Certainly there are degrees of certainty, and one should be very careful to emphasize that fact, because otherwise one is landed in an utter skepticism, and complete skepticism would, of course, be totally barren and completely useless.
Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occurred to him to verify this statement by examining his wives' mouths.
The fact that an opinion has been widely held is no evidence whatever that it is not utterly absurd; indeed in view of the silliness of the majority of mankind, a widespread belief is more likely to be foolish than sensible.
It is undesirable to believe a proposition when there is no ground whatsoever for supposing it is true.
A process which led from the amoeba to man appeared to the philosophers to be obviously a progress though whether the amoeba would agree with this opinion is not known.
Advocates of capitalism are very apt to appeal to the sacred principles of liberty, which are embodied in one maxim: The fortunate must not be restrained in the exercise of tyranny over the unfortunate.
Almost everything that distinguishes the modern world from earlier centuries is attributable to science, which achieved its most spectacular triumphs in the seventeenth century.
I would never die for my beliefs because I might be wrong.
In America everybody is of the opinion that he has no social superiors, since all men are equal, but he does not admit that he has no social inferiors, for, from the time of Jefferson onward, the doctrine that all men are equal applies only upwards, not downwards.
It is possible that mankind is on the threshold of a golden age; but, if so, it will be necessary first to slay the dragon that guards the door, and this dragon is religion.
There is something feeble and a little contemptible about a man who cannot face the perils of life without the help of comfortable myths.
Men are born ignorant, not stupid. They are made stupid by education.
Religion is something left over from the infancy of our intelligence, it will fade away as we adopt reason and science as our guidelines.
Science is what you know, philosophy is what you don't know.
UPDATE: See Dan Dennett Replies
Does Dennett ever get arround to explaining how the Spandrels paper has been misread?
ReplyDeleteOne of the things that has steered me away from the adaptionist paradigm is the fact many organisms live in populations that are genetically structured into relatively small demes. This alone tells me that drift may play a large role in mediating the adaptive response to natural selection.
I'm not a biologist, so I can't comment on whether adaptationism "is the heart and soul of evolutionary biology." However, I do think that adaptation is overemphasized, and that biology would do better to pay more attention to the role of niche change.
ReplyDeleteI appreciate those Russell quotes.
Without quotes or citations:
ReplyDeleteAdaptation to change or environment is secondary while mutation is primary. It is
through many mutations (most of them failures) that a successful mutation then
appears to be a successful adaptation. Adaptation then is the description of a
successful mutation process. The tenacity of life to continue to reproduce is
such that a million failures is cost effective in finding a single successful
mutation. This is stated as if there is a goal or purpose when there in fact is
none. Life continues procreating and when faced with changing environments, those
more able to survive do. This appears to be adaptation but the mutations would
still occur if no change in environment were to happen and they would go unnoticed.
It is more pleasant to see this as life creating differently skilled competitors.
Some are bound to lose out. Adaptation then is merely looking at the herd after
the culling and assuming those still standing adapted to avoid being culled.
That's a little dramatic. Dennett is a philosopher masquerading as a biologist. I think he is an excellent philosopher of mind but a poor biologist. I doubt if he reads any of the primary literature.
ReplyDeleteI'm hoping that you, dear readers, will show my students that there really is some controversy.
ReplyDeleteIn keeping with previous discussions here on this and related points, I took this statement to mean you are attempting to show your students that there are real controversies within science, including within evolutionary biology.
But Daniel Dennett does not, to my knowledge, describe himself as a scientist, nor does he describe his job as science or his day-to-day activities as science. I was under the impression he considers himself a philosopher.
So, how does this question illustrate the presence of a controversy in science? It looks like a disagreement between scientists and one particular philosopher, which is a different beast than disagreements about science between scientists.
I think it is possible for a student to get a passing grade on this question by defending Dennett's opinion. I hesitate to suggest exactly how this could happen, certainly it seems very difficult, but I am allowing for surprises here. Perhaps one of your students will come up with a previously unconsidered idea?
Will you be posting some of the more interesting student answers to these questions after the exam?
@TheBrummell,
ReplyDeleteThe Spandrels paper was not a criticism of Daniel Dennett. It was criticizing other scientists.
Z says,
ReplyDeleteLife continues procreating and when faced with changing environments, those
more able to survive do. This appears to be adaptation but the mutations would
still occur if no change in environment were to happen and they would go unnoticed.
You are presenting a (false) view of evolution that seems to require change in the environment. There are two serious problems with that viewpoint.
1. It focuses on adaptation as the mechanism of evolution ignoring random genetic drift. The assumption is that drift doesn't show up on your radar.
2. It carries the explicit assumption that most species are so well adapted to their present environment that they can't adapt any more. It's only when the environment changes that they can evolve.
Are you prepared to defend both of those assumptions?
Will you post your answers?
ReplyDeleteOK, I'll take the bait.
ReplyDeleteThe fundamental question of evolutionary biology has to be about adaptation:
"How do entities come to be able to persist and reproduce at all, and how have their descendants become able to survive and reproduce under the wide range of conditions experienced by different organisms?"
The answer to this question of course involves considering all the forces that act on the hereditary material, including the many non-selective forces that affect variation.
Larry, drift is constant (perhaps constantly sporadic) and adaptation to environment functions much like a PID controller where drift is continually adjusting one of the three controlling functions of the PID controller. I say like, not exact. Adaptation is a function of drift and environment. No species is perfectly adapted, or needs to be. They simply need to be adequately able to survive in their environment.
ReplyDeleteIf environment did not change, drift would still occur - selecting beneficial changes and depricate less useful features. Blind cave fish don't need to be blind to survive but they don't need to see with visible light either. The stable and dark environment let feature of sight be dropped.
Drift can assert many changes that are unnoticed until a change in environment selects for them or an additional mutation causes a previous mutation to become a useful feature (like the first blonde female for a crazy example). Clearly I did not speak well. Drift/mutation is the engine of change, adaptation is a resultant apparent process of it. Adaptation is not a response to change in the environment, but a result of it in the presence of drift/mutation.
A mutation could develop that killed off a species despite static environment. An environment can change so fast/widely that no amount of drift or mutation survives. The range of suitable environments (for survival of a species) is bounded by variety and drift within the species. If the changes are within the rate of drift we can see things like the arsenic life in Cali. and toxic fish in NY.
Summarized: adaptation is not a process but a fortunate side effect of drift/mutation.
"I'm thinking that it might be a problem grading the answer to this question. Can a student defend Dennett's statement and still get a passing grade?"
ReplyDeleteIf "environment" is read very broadly to include e.g. the sex ratios of an individual's species, its/prey species' grouping and migratory practices, etc., I don't see what is wrong with it.
Knowing little of biology, it seems to me implausible human intelligence developed in response to anything but politicking in social groups, and that the biology that produces a male for every female comes from evolving to the physical environment rather than for more direct sexual competition.
What does "environment" mean?
To answer the question as posed, sure, you can give them a passing grade, if the defense recognizes the spirit in which the argument was made. First, it's probably not smart to bank on Dennett making arguments from a position of ignorance- the crux of his entire intellectual life seems to be centered around restoring empiricism and an appreciation for the state of the art to a central position in philosophical reasoning. Let's not succumb to an authority fallacy that simply because he does not spend his time elbows-deep in proteins that he has nothing worthwhile to say about how we approach *thinking* about said proteins- which is something he does examine.
ReplyDeletePart of why I have an affinity for Dennett (and part of why I think he, in his verbosity, is sometimes misunderstood) is that he wades into the midst of contentious parties, fond of leaping just past their data and into the land of declarative statements, and tries to clean out the accumulating cruft by asking human-scale questions- how is their use of language related or not to our deep understanding of a term? Are there instances where a scientific "team" really represents one set of intellectual tools with which to examine messy data sets, and is that the most useful toolkit for increased human understanding of the implications?
If we grant Dennett a little leeway for rhetorical enthusiasm (there aren't many places in the soup of biology where we should use words like "always" or "never") and see what he's trying to do, the position is pretty defensible. Evolution is a feedback loop between forces of contingency and forces of selection, and figuring out their respective contributions to a given feature is the crux of the science. Gould and Lewontin, in the Spandrels paper, looked around and realized that half of that loop had been forgotten- that evolutionary biology had become a hunt for Kiplingesque Just-So Stories, which is of course counterproductive, and said so. In the process, however, they established a camp that, in certain contexts and situations, *seems* to be in the business of spitting into the wind of the single most intellectually striking features of living organisms- that they are possessed of forms, and parts, and molecules that look to represent close approaches to optimums for accomplishing various tasks, and that said parts seem to have been built out of parts that did other things, or the same thing less effectively. While Gould was no "denialist" of the modern synthesis, I can attest that, reading Gould before receiving more training, there seemed to be instances where he seemed to be arguing that to attempt to uncover any more forces in evolution than "one damn mutation after another" was folly, and that's patently not true. If a frumious bandersnatch landed dead in a space capsule, and the biologists on the scene noted it had a very prominent frumiator, the questions that would accomplish the most intellectual heavy lifting and offer the most insight, at least at first, are "adaptationist" questions- what does it do? What ancestral component was it made from? Are there flowers in Wonderland with a similar shape? Do female bandersnatchi prefer colorful frumiators?
That's where I think Dennett is standing- reminding laypeople, and newcomers, and the contentious that "what does it do?" is still amongst the most potent questions we can ask when examining and organism- not the only question, not always even the appropriate question, but nevertheless a foundational one.
(Different Z)
The fundamental question of evolutionary biology has to be about adaptation:
ReplyDelete"How do entities come to be able to persist and reproduce at all, and how have their descendants become able to survive and reproduce under the wide range of conditions experienced by different organisms?"
Bu that one of the points that seems to be de-emphasized in the public discussion of evolutionary biology is that "entities come to be able to persist and reproduce"
often when there is no discernible
differential reproduction. This is in fact one of the major predictions of Neutral Theory, and observation of the fixation of neutral and slightly deleterious mutations confirms this.
The answer to this question of course involves considering all the forces that act on the hereditary material, including the many non-selective forces that affect variation.
Of course, it may not be helpful to view the constituent processes of evolution as "forces". If one ascribed some sort of ontological reality to the stochastic models of evolution, genetic drift and natural selection are not really two separate processes but two descriptors of the same process: population resampling.
Can anyone figure out why biochemistry would collapse if we stop attributing everything to adaptation?
ReplyDeleteYes. The probability-space of protein folding is so large that the overall evolution of functional proteins is necessarily primarily adaptive. To remove adaptation from a discussion of proteins is to remove the function of those proteins from the discussion as well.
Z says,
ReplyDeleteThat's where I think Dennett is standing- reminding laypeople, and newcomers, and the contentious that "what does it do?" is still amongst the most potent questions we can ask when examining and organism- not the only question, not always even the appropriate question, but nevertheless a foundational one.
Where does Dennett say that such a question may not be the appropriate question?
What do you think about the question, "Does this thing actually do anything?" Is that a "foundational" question?
What about the question, "Did this evolve by random genetic drift?" Is that a "foundational" question?
Is you answer "yes" to those questions then you are admitting that there are many different "foundational" questions besides the adaptationist ones. That would make you a pluralist.
If that's the case, why would you agree with Dennett that adaptationist reasoning occupies the "central position in biology." Why is it any more central that other kinds of reasoning about evolution?
Let me ask you a specific question. Let's say you are a biochemist studying glyceraldehyde 3-phosphate dehydrogenase. You have sequenced the genes from two related bacterial species and discovered that the amino acid sequences of the two enzymes are not the same.
How would you go about constructing an explanation for these differences? Would you begin with "What does it do?" and then try and develop an explanation based on adaptationist reasoning? Is that the best way to address this question?
anonymous says,
ReplyDeleteTo remove adaptation from a discussion of proteins is to remove the function of those proteins from the discussion as well.
That is correct. We agree that adaptation is a very important part of evolution and to ignore it completely would be ridiculous.
Now could you please answer my question?
anonymous says,
ReplyDeleteThe probability-space of protein folding is so large that the overall evolution of functional proteins is necessarily primarily adaptive.
I believe that the modern enzymes we see today are primary a result of accident and happenstance coupled with selection for residues at the active site. (Let's ignore regulatory sites for now.)
The fact that we see so many examples of completely different proteins carrying out the same biochemical reaction suggests to me that what we are looking at is usually a frozen accident.
I believe that 99% of the differences between homologous proteins in different species are due to fixation of neutral alleles by random genetic drift. These differences—which can account for 75% of the sequence—have almost no significant effect on how the protein folds or how it functions.
I believe that proteins can change functions—some enzymes can become lens crystals and others can become regulatory proteins—and that contingency and accident are better primary explanations for such events than adaptation. Adaptation is secondary.
Why do you think that your adaptationist view of evolution is superior to my pluralist view?
Why do you think that your adaptationist view of evolution is superior to my pluralist view?
ReplyDeleteIf the driving for for protein evolution is accident and happenstance rather than adaptation, then there should be a lot of genes that express non-functional proteins as intermediate steps on the route to new function, but this is not what we observe. Instead we see protein coding sequences that lose functionality are rapidly degraded by mutation. This suggests that it is primarily adaptation actively holding the protein-coding portion of the genome together. Not to dismiss the pluralist view, but give adaptation the proper credit it deserves.
You used the words "I believe" twice. Would be nice if you could also cite some references in support of your belief. Is there data to show that the differences you are talking about are caused by fixation of neutral alleles by random drift? Thanks.
ReplyDelete@anonymous,
ReplyDeleteI'm not denying that modern functional proteins are under negative selection to preserve their functionality. (This doesn't qualify as adaptation.)
I though we were addressing the origin of those proteins.
Aspirin asks,
ReplyDeleteYou used the words "I believe" twice. Would be nice if you could also cite some references in support of your belief. Is there data to show that the differences you are talking about are caused by fixation of neutral alleles by random drift?
What's the alternative? The vast majority of difference between homologous proteins are conservative amino acid substitutions on the surfaces of the proteins. When they are tested they don't affect function. It's possible to swap these genes between species without obvious effects.
To the best of our knowledge, these differences are neutral. That means they must have become fixed by random genetic drift.
Furthermore, when you construct phylogenetic trees using these sequences you find that change in each lineage is relatively constant and looks a lot like it's occurring at the mutation rate (μ). That's what population genetics predicts for fixation of nearly neutral alleles by random genetic drift and it's very hard to construct explanations where natrual selection is playing a major role.
This is all covered in most introductory genetics and evolution textbooks.
The 'adaptationist' caricatured in the (over-rated and rather mediocre) 'spandrels' paper is one of the largest and flimsiest straw men ever erected. The nearest approach I know to a full-blooded adaptationist credo came, surprisingly enough, from R C Lewontin himself, in 1967: "That is the one point which I think all evolutionists are agreed upon, that it is virtually impossible to do a better job than an organism is doing in its own environment" (cited in The Extended Phenotype, the chapter called 'Constraints on Perfection').
ReplyDeleteI am commonly quoted as an arch adaptationist,
yet I have no trouble at all in accepting that the majority of evolutionary change at the molecular level is neutral or nearly neutral. This is entirely compatible with saying that adaptationism is the heart and soul of evolutionary biology at the organismal level, the level at which many of us work, and the level at which Lewontin was apparently speaking. They are compatible because neutral mutations do not manifest themselves at the level of phenotype.
Daniel Dennett is not 'masquerading' as a biologist. He is indeed a brilliant philosopher, but he also knows a great deal more of the evolutionary biology literature than almost all biologists.
Richard Dawkins
Richard Dawkins says,
ReplyDeleteI am commonly quoted as an arch adaptationist, yet I have no trouble at all in accepting that the majority of evolutionary change at the molecular level is neutral or nearly neutral. This is entirely compatible with saying that adaptationism is the heart and soul of evolutionary biology at the organismal level, the level at which many of us work, and the level at which Lewontin was apparently speaking. They are compatible because neutral mutations do not manifest themselves at the level of phenotype.
How do you know that neutral mutations do not manifest themselves at the level of phenotype? That sounds like adaptationist reasoning to me.
In any case, Dan did not say that adaptationism was only at the heart and soul of organismal biology. In fact, he specifically mentions biochemistry. That's the field in which an awful lot of people work, including me.
One of the questions for my student is about you, Richard. It addresses statements in your latest book and raises the issue of whether accepting Neutral Theory is the same as understanding that random genetic drift can be a common way of fixing alleles in a population. Neutral Theory is about mutations and drift is about mechanisms.
The majority of beneficial alleles are lost by drift before they ever become fixed in a population and that has nothing to do with Neutral Theory.
I'll post that question tomorrow and you can respond.
"How do you know that neutral mutations do not manifest themselves at the level of phenotype?"
ReplyDeletePardon my ignorance, but isn't that how they're defined as neutral? Not that proofs by definition tell us about our world, since they're true in every world, this would just put the question back to how one might know most mutations are neutral.
I have noticed a lot of the argument between pluralists and adaptationists is based on semantics. It seems to me that both sides recognize the importance of the other side, and follow it with a big "But...".
ReplyDeleteAt this point I am more interested in why it is that people care so much about which side is right? What is so important about proving one side over the other? We are here the same either way.
Genetic drift is important...Natural selection is important...The ranking system between which is more important, in my opinion, isn't important.
Brian asks,
ReplyDeletePardon my ignorance, but isn't that how they're defined as neutral? Not that proofs by definition tell us about our world, since they're true in every world, this would just put the question back to how one might know most mutations are neutral.
Neutral, and nearly neutral, mutations are defined as mutations that are not under significant selection in a population. In technical terms this means that in a given population the selective coefficient associated with that allele is too small to play any role in its fixation.
Neutral mutations can easily have a visible phenotype. Just look around you at all the people you see. Much of their appearance has a genetic basis—that's why children resemble their parents. If you live in a place with a lot of diversity you will see an enormous range of appearances ranging from the shape of a nose and an earlobe to the size of ones feet and ankles.
There's no evidence to suggest that all of these genetically determined features are in any way adaptive. They appear to be neutral and their eventual fixation or loss is determined by random genetic drift.
Adaptationists have trouble with this concept, as I'm sure you are about to see in the comments that follow.
But then, they also (usually) have trouble with the concept of junk DNA as well. That's why they are adaptationists.
anonymous asks,
ReplyDeleteAt this point I am more interested in why it is that people care so much about which side is right?
Because there's a right way and a wrong way to do science.
Imagine that you are seeking a scientific explanation for a given character or phenomenon.
The wrong way to go about it is to dismiss out of hand a whole range of possibilities (non-adaptive evolution) and jump right to your favorite type of explanation (adaptation).
The right way is to keep all of these possibilities in mind until you can prove that a character is truly adaptive.
Want a specific example of adaptionationism gone wrong? Try Naked Adaptationism and Dennett on Adaptationism.
"There's no evidence to suggest that all of these genetically determined features are in any way adaptive. They appear to be neutral and their eventual fixation or loss is determined by random genetic drift."
ReplyDeleteDoesn't everyone agree that you could take a specific member of a species and some of its genes have effects that are not operated on by selection? Is the disagreement about how many genes can be classified like this, how many parts of an individual can be classified like this, both or neither?
I have wide feet; one must have feet to have wide feet, and having feet one must have feet in the range of narrow to wide. Assuming foot width depends partly on genes, and assuming it gives no advantage, it still seems a bit strong to say it's not dependent on adaptation if having feet is so dependent.
Do the different scientific camps have different expectations for what traits/genes a newly discovered species/ecosystem has given partial information about it?
Suppose we find a gene that makes all shells of a certain turtle species purple, and we catch some and paint some purple and others orange. Knowing nothing else about the turtle species, are there (non-even, obviously) odds at which "non-adaptationists" will bet on the well-being of the orange painted ones while "adaptationists" are willing to bet on the demise of the orange painted ones (and if the purple painted ones die, no one pays out)? If not, the debate seems like so much noise...I propose scientific testing of the scientists' beliefs, not being content with polite letters!
Larry Said
ReplyDeleteBecause there's a right way and a wrong way to do science.
Me:
So the reason you care that it become proven that the pluralist view is more correct than the adaptationist view is simply because you view adaptationism as faulty science?
Interesting...if you pick a null hypothesis of evolution to be random genetic drift, and, using some method prove that null hypothesis statistically unlikely, you would accept your alternative hypothesis of adaptation. correct?
But, if you flipped the script, and viewed some given trait as the result of natural selection as your null hypothesis, you would view this as bad science?
But, if your pluralist view suggests that these two mechanisms should be considered equally, why can you discriminate between which is the null and which isn't?
Simply because it's easier to prove random genetic drift wrong as a null hypothesis, in my opinion, is not a good enough reason. In fact, I would argue that picking a hypothesis based on the ease in which it is proven is bad science - not the other way around.
That is all beside the point though. Here is an example of an answer I was looking for when I asked "why it is that people care so much about which side is right" earlier.
In the late 1700's/early 1800's there was an argument between Neptunism(age of earth same as bible...6000 yrs-ish...was the prevailing theory b/c conformed with bible etc.) and Uniformitarianism (age of earth much older than bible). Big debate...Yada Yada Yada, Uniformitarianism won, and we now date the Earth 4.65 bya.
Question: Why is it that people cared so much about which side is right?
Answer: Because knowing the age of the earth is important because...[insert a bunch of reasons here...one being it opened the door for Darwin to explain things over vast amounts of time].
Now that you have an idea of the type of answer I was looking for, I challenge you once more:
why it is that people care so much about which side is right? (re:adaptationists vs pluralists)
"why it is that people care so much about which side is right? (re:adaptationists vs pluralists)"
ReplyDeleteI'm not convinced that there even are sides. Do adaptationists and pluralists make different predictions, ever? Or is there only one scientific theory, for which we need a linguist and historian of science to help us figure out the best name.
Brain asks,
ReplyDeleteI'm not convinced that there even are sides. Do adaptationists and pluralists make different predictions, ever?
Imagine that you have just discovered that genes make up only a small percentage of our genome and most of it doesn't have a known function.
Pluralists are likely to predict that this extra DNA is junk with no function while adapationists are likely to predict that we will eventullay find a function for most of it.
Imagine that you have just discovered that humans have lost the ability to make several amino acids even though they are essential for survival. What kind of evolutionary scenario explains this fact? Your preference will indicat whether you think like an adapationist or a pluralist.
Imagine that you are interested in speciation—specifically, the step where true reproductive isolation evolves so that two separate populations can no longer interbreed.
How does this happen? Your answer identifies you as a pluralist or an adaptationist.
Let's say I ask you to predict whether the changing climate will speed up evolution among flowering plants in the temperate zones of the world. How would you answer?
Do you know about the MN blood types? The frequency of the M allele is 90% among Eskimos/Inuit while it is only 18% among native Australians. How did these two populations evolve such different frequencies from a common ancestral population that left Africa only 100,000 years ago?
Your prediction will be different depending on whether you are a pluralist or not.
In reverse order of strength.
ReplyDelete"...humans have lost the ability to make several amino acids...What kind of evolutionary scenario explains this fact?"
An explanation after the fact is not a prediction. Creationists can explain things after the fact.
"Imagine that you are interested in speciation..."
The world is comprised of leptons etc. at most, not species. Species are leaky generalizations, not ontologically basic units of reality, and I am skeptical of anything that hangs on them. You realize this and somewhat ameliorated this problem by asking about "true reproductive isolation" rather than "speciation".
Yet even so...when a spider is blown to an island by a gale, has it achieved "true" reproductive isolation? When large and small varieties cannot mate, but would be able to would they reconverge in size from evolutionary pressures, are they isolated?
One must make actual predictions, e.g. say that a male island spider put into a featureless jar with a female land spider will be x% likely to reproduce, given that land spiders mate y% of the time and island spiders mate z% of the time when put in similar conditions, with x a function of time isolated etc.
I am not looking for apparently different answers to "how does this happen" since those can arise despite agreement on what has happened, particularly since apparent difference could be caused merely by different emphasis at a non-technical level.
Phenomenon x is explained by sub-phenomena y and z. Were y different, x would look much as it does, were z different, x would be unrecognizable. Al thinks 10% of a lesson should be spent understanding y, with 90% spent on z. Bob thinks 45% should be spent on y, 55% on z.
Since mutation is the fuel for evolution and selection the engine...I need to see actual differing predictions to be convinced that fuel-emphasizers and engine-emphasizers disagree at the technical level.
"The frequency of the M allele...
Humans are not good at intuiting the value of explanatory models based on their interface with known facts, which is why we require predictions.
A good heuristic for recognizing a prediction is that one could bet on it.
All scientists' models would be perfectly compatible with those allele frequencies...like creationists'.
Tell me what each side predicts about other alleles or other groups and where predictions of the unknown differ.
"...genes make up only a small percentage of our genome and most of it doesn't have a known function.
Pluralists are likely to predict that this extra DNA is junk with no function while adapationists are likely to predict that we will eventullay find a function for most of it"
Those predictions are not symmetrical. They are not about the same phenomenon. It should read something like: "Pluralists are likely to predict that no prediction-producing models will be found that depend on the non-gene genome being as it is because there is no function to it. Adaptationists are likely to predict prediction-producing models will be found that depend on the non-gene genome being as it is because there is function to it."
Problems with this prediction include that it is a prediction about a rate of discovery in a field prone to irregular rates of progress and that it depends on assessing other predictions (models produced) and so is hard to interpret.
"...predict whether the changing climate will speed up evolution among flowering plants in the temperate zones of the world."
YES! Assuming the current rate is quantifiable such that saying "more" or "less" about the future is testable, then this is an actual prediction, and different predictions about the unknown is the sign of differing models of how the world works. Differing models of how the world works, not mere differing preferences about how to describe a single model that everyone shares.
The factions predict this differently?