Natural Selection and Adaptation

Cornelius Hunter seems very confused.

 …This brings us back to the UC Berkeley “Understanding Evolution” website. It abuses science in its utterly unfounded claim that “natural selection can produce amazing adaptations.”

In fact natural selection, even at its best, does not “produce” anything. Natural selection does not and cannot influence the construction of any adaptations, amazing or not. If a mutation occurs which improves differential reproduction, then it propagates into future generations. Natural selection is simply the name given to that process. It selects for survival that which already exists. Natural selection has no role in the mutation event. It does not induce mutations, helpful or otherwise, to occur. According to evolutionary theory every single mutation, leading to every single species, is a random event with respect to need.

He has forgotten what “adaptation” means.  Of course he is correct that “Natural selection is simply the name given to [differential reproduction]”.  And that (as far as we know), “every single mutation …is a random event with respect to need”.

And “adaptation” is the name we give to variants that are preferentially reproduced. So while he would be correct to say that “natural selection” is NOT the name we give to “mutation” (duh); it IS the name we give to the very process that SELECTS those mutations that promote reproduction.  i.e. the process that produces adaptation.

Cornelius should spend more time at the Understanding Evolution website.

ETA: CharlieM points out below that…

When CH says that natural selection does not produce adaptations he is talking about individual organisms. He is discussing mutations in individuals and adaptations in individuals. Natural selection has nothing to do with the first appearance of an adaptation in an individual.

 

And that of course is the confusion – I hadn’t seen just where Cornelius’s confusion lay.  Because, of course, the term “adaptation” is a population-level concept. At the level of the individual, the equivalent would be  “advantageous mutation”.  And that makes the Understanding Evolution website absolutely correct.

843 thoughts on “Natural Selection and Adaptation

  1. Alan Fox:
    Complaints about moderation should be made in “moderation issues”.

    There are no moderators here, only admins who abuse their powers. This is not a complaint about moderation. It’s just an observation.

    Are posts going to start getting moved to moderation now if they are about moderation? Or only if they are deemed to be a complaint?

    I think there are some entire threads then that need to be moved.

    Careful Gregory, Lizzie’s bulldogs are own the growl. They have their eyes on you.

  2. “So then comes Gregory, who either will not or cannot make a post on this site that does not contain personal remarks–generally digs but juvenile and stupid even when not digs.”

    Ok, even CANNOT?!

    This is walto’s shallow jealousy. I’ve made many comments that ‘do not contain personal remarks.’ Yet TAZ moderators condone his mudslinging lies. To me, walto is a bureaucrat, a bottom-dwelling wanna-be ‘philosopher’. Yet doesn’t he fit in just fine here at TAZ among atheists?

  3. Much as I hate to say this, having a thread all in my honor and such, I think it’s time for Noyau to go away.

    All of a sudden people think posts OUGHT to be in Noyau. A new moral code appears to be evolving right before our eyes.

  4. Gregory: Perhaps living in France (oops, did I just ‘out’ you?!) you’ve forgotten English grammar. ‘The environment’ is not an ‘AGENT’ capable of ‘designing’, Alan. You mistake your metaphors, just as Darwin did. (And no one here is the wise on kicking Darwin’s SSH credited Malthusianism out of the conversation.)

    I’ll call that a FAIL.

    Scientists use the word “agent” for many different things — chemical agent, mail transfer agent, etc.

    You need to try to follow the discussion before you criticize it.

  5. Gregory: Yet another example of walto antagonising and derailing. Maybe, just maybe, Alan Fox will say something to walto about it.

    No, Gregory derailed. Walto simply reported the derailing, though in colorful language.

  6. Neil, you’re saying walto was the first to whine? I just don’t believe that. The walto that I know and love is not a whiner.

  7. Get rid of all of this atheist bullshit.

    My simple question was to Joe F. Let him answer it. He only faked it so far.

    I quoted Darwin’s letter to Lyell regretting ‘natural selection’ in 1860. No one at TAZ has yet commented.

    I’m not interested in atheist insecurities here.

  8. Gregory, your question about Darwin’s letter might have been interesting. But it was asked in your usual bellicose and self-aggrandizing manner.

    Let me ask you–Do you think that sort of behavior encourages or discourages civil conversation?

    And then let me ask you this: Why do you do this? Are you actually 12 and somebody kicked you on your way home?

  9. Mung:
    Neil, you’re saying walto was the first to whine? I just don’t believe that. The walto that I know and love is not a whiner.

    Thanks, but I can’t deny I’m a champion whiner. Much less mature than many here. As I often tell my family, “OK, I’m coming. But keep in mind, I’m not going if I can’t bitch.”

    Somehow, I’ve managed to avoid getting thrown out of the house. I think the rules here are similar to Lizzie’s. (I can’t actually understand either set of them too well, tbh, but I figure I’m a beneficiary of extreme latitude in both cases.)

  10. Gregory:
    Get rid of all of this atheist bullshit.

    My simple question was to Joe F. Let him answer it. He only faked it so far.

    I quoted Darwin’s letter to Lyell regretting ‘natural selection’ in 1860. No one at TAZ has yet commented.

    I’m not interested in atheist insecurities here.

    My insecurity came from not understanding Gregory’s question.

    I feel miserable as a result, evil and mean, and my life lacks meaning. Makes me feel like engaging in empty rhetorical posturing. If only he could answer my inquiry, my life would become meaningful again.

  11. Joe F, Math is not an agent. Equations do not cause anything to happen. Poor Darwin was no doubt well within Newton’s gravity well, still believing in causality.

    What breathes fire into your equations?

  12. “I feel miserable as a result, evil and mean, and my life lacks meaning.”

    Sarcasm noted. That may or may not be true (atheists often feel evil and mean). But I asked a very simple question to Joe F. after he mocked me for questioning the metaphorical character of ‘natural selection’ by citing his biology book.

    Will you finally answer the AGENCY question, Joe?

    It’s still simple and clear, asked to Joe F.: http://theskepticalzone.fr/natural-selection-and-adaptation/comment-page-13/#comment-75627

  13. Joe Felsenstein:
    4. Oh yes, and saying that natural selection “constructs” an adaptation is not standard terminology in the field.People may or may not use a term like that or say that natural selection “designs” a phenotype, but they are speaking informally, bot technically.

    I know many people have said the equivalent in this thread but I just wanted to try to explain what terminology the professionals in the field use.

    Thank you

  14. Joe F:

    Natural selection can be viewed either narrowly or broadly.
    Narrowly conceived, it is simply one class of violations of the assumptions of the Hardy-Weinberg Laws, namely the cases in which viability or fertility depends on genotype. Broadly conceived, it is the primary force which causes evolution to be adaptive, the creative and progressive element in the evolutionary process.

    Joe F:

    It is a central tenet of Darwinism that natural selection has an average tendency to increase adaptedness, and it is a nontrivial matter to investigate whether or not it act ually does so in simple model situations.

    By the way, I counted 28 instances of “natural selection ” in Chapter 2. Maybe one day if I have nothing better to do I’ll see whether Joe use the phrase only in the “pop gen” meaning of the term.

  15. Gregory:
    walto,

    Angry, angry condescending walto. Not a teacher. Just a bureaucrat angry atheist. (But hey, why not keep his posts, TAZ moderators and guano mine? They will support atheists and NEVER caution them.)

    Yeah, they’re gullible because you’re an atheist – it’s preferential treatment at TAZ.

    I’ve got an idea. You copy all the posts from this thread (or really any thread where you’ve “contributed”) and paste them on some lovely theistical board where you take the people to be nice, smart, and congenial. Then just ask them this: Who do you think is the most angry person at TSZ?

    I’ve got a C Note right here for you if THEY think it’s the atheists here who are the angry, obnoxious, and unhappy folks.

    FWIW, your religion seems to me to provide you no comfort whatever. But maybe you just act unhappy here. Hard to tell, obviously.

  16. Gregory:

    But I asked a very simple question to Joe F. after he mocked me for questioning the metaphorical character of ‘natural selection’ by citing his biology book.

    Gregory characterized discussions of natural selection as empty rhetorical posturing. I was pointing out that this “empty rhetoric” is a poor description of what I did in my mathematical discussion of the effects of natural selection. It seemed to reflect Gregory not understanding what such discussions actually consist of.

    Will you finally answer the AGENCY question, Joe?

    It’s still simple and clear, asked to Joe F.: http://theskepticalzone.fr/natural-selection-and-adaptation/comment-page-13/#comment-75627

    The issue is how many “agents” I refer to in my chapter. I was asking for clarification as what constituted invoking an “agent”. I will be happy to answer the question once I have some understanding of that. I asked about an example.

  17. I’ve got a simple idea, Joe. Call me crazy for asking. Just answer my question about AGENCY from your ‘biologist’ viewpoint.

    You want to put the burden on me to define ‘agent.’ No, speak straight your view because the metaphor of ‘selection’ is easy to doubt. It is directly relevant to this OP.

    “The issue is how many ‘agents’ I refer to in my chapter”

    No, Joe, not ‘how many’. The issue is: buckle up and tell us which ‘agents’ you refer to in your biology chapter. Name them. If there are none, then say openly “there are none.”

    Darwin himself spoke about the metaphor ‘natural selection,’ expressing regret. I doubt Joe will address this.

  18. “FWIW, your religion seems to me to provide you no comfort whatever. But maybe you just act unhappy here.”

    walto, your words are worth so little. Not even ‘seems to me.’ Your atheist worldview is both depressing and full of despair. Likewise, it is either amoral or morally relativistic. Iow, it is fanciful idiocy.

    Act ‘happy’ and be proud! 😉 We all know your atheist worldview is really both sad and empty. Only atheists will ‘support’ you in their co-despair.

    A better way is possible, if only you’d unplug your ears and stop antagonising. People around the world prefer inspiration and hope to despair.

    Maybe call it an intentional ‘adaptation’ on your part beyond determinism. But philosophistry apparently still drags you down, to disenchanted KN levels.

  19. Well, since Gregory won’t clarify what he means by discussion of “agents”, let me simply put here the opening two paragraphs of Chapter II. Is there discussion of “agency” in them? I can see a few places where Gregory may say that there is. But he can speak for himself.

    Natural selection can be viewed either narrowly or broadly. Narrowly conceived, it is simply one class of violations of the assumptions of the Hardy-Weinberg Laws, namely the cases in which viability or fertility depends on genotype. Broadly conceived, it is the primary force which causes evolution to be adaptive, the creative and progressive element in the evolutionary process. A comprehensive theory of evolution, one which does not yet exist, would integrate ecological processes (which determine the range of environments and the fitnesses of phenotypes), developmental processes (which determine
    the effect of genotype on phenotype), and population genetics (which tells us the changes in genetic composition of a population when the fitnesses of the genotypes are known). Lacking the other elements of this future theory, we concentrate here on the population genetics.

    We first examine the mathematics of gene frequency change, to see how much change of gene frequency is caused by a given pattern of differential viability and fertility, to see what the pattern of gene frequency change through time will be, and to see how selection acting on diploid genotypes affects gene frequencies. There are nontrivial evolutionary questions which are addressed by this part of the chapter. It is not obvious in advance how to quantitate fitness, nor how effective small differences in fitness can be. Diploidy is a major complication whose effects are also not obvious, and much of the effort in this part of the chapter is devoted to explaining its effects. The second part of the chapter discusses situations in which selection with constant fitnesses causes an equilibrium genetic composition to be maintained. The third part concerns the effect of natural selection on the mean fitness of individuals in the population. It is a central tenet of Darwinism that natural selection has an average tendency to increase adaptedness, and it is a nontrivial matter to investigate whether or not it actually does so in simple model situations.

    Gregory should be able to point out where we see “agency”.

  20. Kantian Naturalist:

    [Gregory sez:] The children laughing and playing in the sunshine outside of my window are much more interesting.

    Everyone knows that atheists never laugh and play in the sunshine.

    Oh so right. I spent my free afternoon playing inside 100-meter-long storm conduits. Not exactly sunshine.

    Laughing, though. 🙂

  21. keiths:

    Your argument would a bit more convincing if it were an actual argument, Joe. “It’s silly and it’s invalid” is mere assertion, not an argument.

    If it’s scientifically legitimate to disentangle sexual selection from natural selection — and it clearly is — then why can’t differential fecundity be similarly disentangled?

    Please be specific.

    And:

    You don’t like the idea of separating pure fecundity from selection, but Mayr is okay with that, preferring to limit “natural selection” to cases in which the systematic elimination of unfavorable variation is taking place.

    How is his definition any less scientific than yours?

    Joe:

    I have explained this before, but let me explain this again:

    If we have three genotypes AA, Aa, and aa that have equal viabilities, your position (and Mayr’s) says that there is no natural selection. If their fertilities differ, then their fitnesses will differ, and this will tend to drive change of gene frequencies. Isn’t that too natural selection?

    If keiths wants to call the fertility selection something else, I can’t stop him. But I know of no population geneticist who would use that convention.

    You didn’t answer my question. You merely told us that you don’t like Mayr’s definition, which we already knew, and that population geneticists don’t use Mayr’s definition, which we already knew.

    “Joe doesn’t like it” is not equivalent to “it’s unscientific”. “Population geneticists don’t use it” is not equivalent to “it’s unscientific”.

    Why do you think Mayr’s definition is unscientific, Joe?

    If it’s scientifically legitimate to disentangle sexual selection from natural selection — and it clearly is — then why can’t differential fecundity be similarly disentangled?

    Please be specific.

  22. keiths,

    I think you’re getting too hung up on Mayr (Joe G is a big fan too! 😉 ).

    When it comes to ‘the appropriate definition for the thread’, the aim is presumably one that makes all adaptive change due to that set of causal factors, and any causal factor that does not cause adaptive change to be outside it.

    So if Natural Selection is ‘the thing that causes adaptation’, then it incorporates sexual selection, environmental selection and fertility selection, provided one is happy to call the products of those processes ‘adaptations’!

    Male-expressed peacock genes adapt to the tastes of their mates (which themselves may adapt to correlates), and fertility-optimising genes adapt to the constraints provided by having suboptimal offspring numbers or rates.

    Malaria parasites in a body can adapt by replicating faster. They are adapting to the fact that they can only get out by dominating the population prior to being sampled by a mosquito. This may not look like an adaptation – it’s not a peacock’s tail or sharp teeth – but it is one. Birds can adapt by laying more or fewer eggs. They suffer costs if there are too few and if there are too many. It is a tunable parameter.

    This one could run and run. But I don’t see it getting anywhere (Red Queen!).

  23. “Gregory should be able to point out where we see ‘agency’.”

    The question is which agents? Are you suggesting that ‘natural selection’ is an ‘agent,’ Joe? And who is the ‘we’ that you say ‘sees agency’? I don’t see ‘agency’ in those 2 paragraphs. So you must have some ‘special’ view of ‘agency’ in your biologist’s vocabulary.

  24. Gregory

    The questions to you, nevertheless remain. Agents, Joe, agents in biology? Your ‘kind’ (of ‘scientist/scholar’) spew empty rhetorical talk quite often, apparently trying to be ‘important’ socially. We’ve been studying your communication! 😉

    In the paragraphs I posted, you found no discussion of “agents in biology”. The rest of the chapter, which is about mathematical analysis of natural selection, talks about the results of different patterns of fitness, supporting the argument with lots of equations showing how gene frequency changes.

    I am presuming, therefore, that you would find no discussion of “agents in biology” there, and no identifying of those “agents”. So saying that natural selection “selects for” higher fitness does not constitute invoking an agent or identifying the agent, by your definitions.

    Is there some reason why, in order to discuss natural selection and its effects, I have to discuss and name “agents”? Maybe call it “Arthur”?

    I understand that your main concern with discussions of selection is to point out misuses of the concept of natural selection when it is applied to human society. And yes, much of that usage is “empty rhetorical talk”. I just don’t see how biologists using the concept of natural selection to discuss biological evolution qualifies as “empty rhetorical talk”.

  25. keiths:

    “Population geneticists don’t use it” is not equivalent to “it’s unscientific”.

    How can you tell is a term is “unscientific” except by its consensus usage by the scientists who work in the relevant field of study? Is there a necessary/sufficient type purely logical definition for “scientific usage” which can be applied from the outside somehow?

    I recently read Gravity’s Ghost: Scientific Discovery in the Twenty-first Century. The author is a sociologist working closely with the community of scientists trying to detect gravitational waves. That whole community meeting in conference at one point could not come to agreement on how to interpret a piece of evidence. So they took a vote on it.

    Now you might think that taking votes is not the way science should proceed, even when such voting is limited to the recognized experts in the field. I mean, isn’t about interpreting the evidence objectively? But before you can answer the how should it?, you need to understand how does it?. Then factor that understanding into why you think an answer to a how should it is correct.

    ETA: For clarity, taking votes is not the way the community normally decided issues. They had an algorithm with different task forces applying different analysis techniques followed by discussion on how to interpret the results. But in this exceptional case, that did not lead to a consensus decision.

  26. Bruce,

    How can you tell is a term is “unscientific” except by its consensus usage by the scientists who work in the relevant field of study?

    As written, your question doesn’t make sense. Are you trying to say

    a) that any definition that isn’t the consensus definition among the practitioners in a particular field is unscientific, or

    b) that any definition that is regarded by consensus as unscientific is unscientific, or

    c) something else?

  27. keiths:
    Bruce,

    As written, your question doesn’t make sense.Are you trying to say

    I am trying to ask you how you can tell if a term is “unscientific” as you used the word in the phrase I quoted. What did you have in mind for the meaning of that word?

  28. Bruce,

    I am trying to ask you how you can tell if a term is “unscientific” as you used the word in the phrase I quoted. What did you have in mind for the meaning of that word?

    The relevant question is “What does Joe have in mind when he dismisses Mayr et al’s definition as unscientific?” It’s his claim, after all. My point is simply that “Joe doesn’t like it” and “population geneticists use a different definition” are poor reasons for labeling a definition as “unscientific”, “silly”, or “invalid”.

  29. keiths:
    Bruce,

    The relevant question is “What does Joe have in mind when he dismisses Mayr et al’s definition as unscientific?”It’s his claim, after all. My point is simply that “Joe doesn’t like it” and “population geneticists use a different definition” are poor reasons for labeling a definition as “unscientific”, “silly”, or “invalid”.

    OK, thanks for your thoughts.

  30. Bruce,

    Two more things that you may have missed in the thread:

    1) The pop gen definition of “natural selection” is not binding on the rest of evolutionary biology; and

    2) the pop gen definition is not a scientific consensus.

  31. hotshoe_: Everyone knows that atheists never laugh and play in the sunshine.

    Oh so right.I spent my free afternoon playing inside 100-meter-long storm conduits.Not exactly sunshine.

    Laughing, though.:)

    He’s also indicated, to petrushka, that he thinks we should be guided in our views about the world by the views of toddlers and others under 11. My take from that is he’s never had any kids.

    Someone should start an OP about what the world would be like if toddlers were right about everything. Even about anything.

    One of my favorite confabs with my first daughter (this was back in the age of video tapes, and as she was our first we taped her A LOT.) She was four and kind of precocious. She went on for about an hour about how horses live longer than people. And was keen to elaborate on how important that was to world harmony.

  32. keiths:
    Bruce,

    Two more things that you may have missed in the thread:

    OK, but I’m not interested in the definition of NS per se, but rather in the History, Sociology, & Philosophy of Science issue of what “scientific usage” and “correct scientific usage” mean. I suppose that is somewhat off topic, so I will stop now.

  33. The seven assumptions underlying Hardy–Weinberg equilibrium are as follows:

    organisms are diploid
    only sexual reproduction occurs
    generations are non overlapping
    mating is random
    population size is infinitely large
    allele frequencies are equal in the sexes
    there is no migration, mutation or selection

    And this is the foundation required for natural selection to be scientific?

  34. Mung: And this is the foundation required for natural selection to be scientific?

    No. They are idealizations used in the mathematical model that was considered.

  35. Mung: And this is the foundation required for natural selection to be scientific?

    As Neil noted, no. We start with this ideal model, where it is easy to derive formulas for what happens. Then we relax some of the assumptions, one by one, in each case seeking situations where we can do the math. In my Theoretical Evolutionary Genetics text (which you can download free) I relax most of those assumptions in various chapters. In particular, the infinite population size assumption, which you highlight, is relaxed in Chapters 6 and 7.

    People do the same thing in physics texts. You might as well complain about them assuming an ideal gas or a perfectly spherical and homogeneous Earth.

  36. keiths,
    I’m afraid I haven’t been able to keep up with entire discussion. Under your preferred definition of natural selection, does a mutation that does nothing but increase fecundity in a resource-limited population, and that therefore increases in frequency, undergo natural selection or not? (And likewise for a mutation that decreases fecundity.)

  37. Steve,

    I’m afraid I haven’t been able to keep up with entire discussion.

    I’m in the middle of a short-term coding project, so I’ve been neglecting the thread too.

    Under your preferred definition of natural selection, does a mutation that does nothing but increase fecundity in a resource-limited population, and that therefore increases in frequency, undergo natural selection or not? (And likewise for a mutation that decreases fecundity.)

    If the mutations truly affect fecundity and nothing else (which is pretty unlikely in real life, especially in a resource-limited scenario) — meaning that individual mutants are no more and no less likely to survive and reproduce than the “wild type” — then I would say that the mutants are not undergoing natural selection due to their fecundity-influencing mutations, but that they may still be undergoing natural selection due to alleles at other loci.

    That’s one of the reasons I stipulated unlimited resources and no death in my thought experiment. It keeps things clean because differential fecundity is then the only factor influencing relative reproductive success.

  38. Mung: And this is the foundation required for natural selection to be scientific?

    Why don’t you check those biology textbooks you claim to own?

  39. keiths:
    Steve,

    I’m in the middle of a short-term coding project, so I’ve been neglecting the thread too.

    If the mutations truly affect fecundity and nothing else (which is pretty unlikely in real life, especially in a resource-limited scenario) — meaning that individual mutants are no more and no less likely to survive and reproduce than the “wild type”— then I would say that the mutants are not undergoing natural selection due to their fecundity-influencing mutations, but that they may still be undergoing natural selection due to alleles at other loci.

    That’s one of the reasons I stipulated unlimited resources and no death in my thought experiment.It keeps things clean because differential fecundity is then the only factor influencing relative reproductive success.

    I understand your motivation for the limiting case, but I’m trying to understand the application of your definition to real biology. (More precisely, I’m trying to understand whether biologists actually employ “selection” in the way defined by you.) We can make all of the organisms genetically identical except for this one mutation, if you like. The population size is limited by resources. When the mutation occurs, those who have it have higher fitness (in the pop gen sense) and those who do not have lower fitness than they did before. The new increases increases in frequency while the old decreases, but not because of selection (by your definition) — right?

    Would you say this locus is evolving neutrally? Would you call the new mutation beneficial?

    Suppose the new mutation decreases fecundity instead of increasing it, and therefore fails to propagate for long. This, presumably, is not the result of purifying selection, since no selection is operating. How would you describe this process? The reduction in genetic diversity in constrained sites is usually (in my experience) ascribed to purifying selection. What would you say causes it? Indeed, is it appropriate to call them constrained sites, since in many cases they’re not being constrained by selection — and what else is there?

    How about an embryonic lethal mutation, one that is independent of the details of the environment — can its loss be ascribed to natural selection?

  40. Steve,

    We can make all of the organisms genetically identical except for this one mutation, if you like. The population size is limited by resources. When the mutation occurs, those who have it have higher fitness (in the pop gen sense)…

    They have higher fitness in my sense, too. It’s just that fitness is a function of fecundity as well as natural selection.

    …and those who do not have lower fitness than they did before. The new increases increases in frequency while the old decreases, but not because of selection (by your definition) — right?

    No, I still regard it as selection — but it’s fecundity selection, not natural selection.

    Would you say this locus is evolving neutrally? Would you call the new mutation beneficial?

    No and yes.

    I understand your motivation for the limiting case, but I’m trying to understand the application of your definition to real biology. (More precisely, I’m trying to understand whether biologists actually employ “selection” in the way defined by you.)

    They do. For example:

    However, while the fitness components mediated by natural (survival) and sexual (mating success) selection have extensively been debated from most possible perspectives, fecundity selection remains considerably less studied.

    And:

    Three major mechanisms are responsible for the fitness dynamics that determine the trajectory of evolutionary change through differences in lifetime reproductive success (Darwin, 1859, 1871; Bell, 2008). Among these, natural and sexual selection explain how inter-individual differences in the exploitation of ecological resources and access to mates, respectively, regulates the genetic basis of phenotypic adaptations (Andersson, 1994; Schluter, 2000; Charlesworth & Charlesworth, 2010). Both mechanisms of selection form the central structure of current evolutionary theory, and have extensively been studied from a variety of conceptual and empirical perspectives (Williams, 1992; Andersson, 1994; Schluter, 2000; Gavrilets, 2004; Rice, 2004). The third mechanism, fecundity selection, traditionally describes the fitness advantages resulting from the selection for traits that increase fecundity (i.e., number of offspring; see section II) per reproductive episode (Roff, 2002).

  41. So why, for the purposes of this thread, do I prefer a narrower definition of natural selection that excludes differential fecundity?

    Recall that William was defending the claim that natural selection does not “produce” or “build” complex features. He asked Lizzie to consider two scenarios: in the first, there was no mutation; in the selection, there was no selection, and no organisms ever died. The latter was similar to my thought experiment except that William allowed mutation to continue forever, whereas in mine it (implicitly) stopped after the initial mutation. We were only interested in the population changes that were due to that single mutation.

    Anyway, William correctly pointed out that his “no selection” scenario, as described, would quickly produce complex features, while his “no mutation” scenario would not. He concluded that it is mutation, and not natural selection, that builds complex features.

    His conclusion was incorrect, but William was right that mutation by itself could quickly produce complex features if there were no death. Lizzie kept disagreeing with that — I’m not sure why — but William was correct.

    As part of her counterargument, Lizzie pointed out that you can have differential reproductive success even if no organisms die. She argued that this meant that natural selection was happening even in William’s “no selection” scenario, since according to her, “Natural selection IS heritable differential reproduction.”

    Her statement is correct if you choose the pop gen definition of natural selection, but doing so clouds the issue, because it isn’t natural selection that is producing the complex features in William’s scenario. It’s better to choose the narrower definition and confront William’s scenario head-on.

    Then you can freely acknowledge that yes, mutation by itself could produce complex features in a no-natural-selection, no-death scenario — but in realistic scenarios that include death and finite populations, mutation is not enough. You need natural selection to help you build complex features like the chameleon chromatophores that Cornelius mentioned.

    Under the pop gen definition of natural selection, there is selection going on in both of William’s scenarios, so the argument is more confusing. You have to say that yes, selection is going on even in the no-death situation, but that there’s a crucial difference from “real life” — natural selection doesn’t build the complex features that arise in the no-death scenario.

    Far simpler to say something like this:

    With infinite population “slots” available, complex features can be produced even in the absence of natural selection. With a realistic and finite number of slots, you won’t see complex features unless you “turn on” natural selection.

    But to say that requires us to define natural selection in a way that excludes differential fecundity.

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