Chance and Selection

Darwin’s conforming of his theory to the old vera causa ideal shows that the theory of natural selection is probabilistic not because it introduces a probabilistic law or principle, but because it invokes a probabilistic cause, natural selection, definable as nonfortuitous differential reproduction of hereditary variants.

Chance features twice in this causal process. The generation of hereditary variants may be a matter of chance; but their subsequent populational fate is not; for their physical property differences are sources of causal bias giving them different chances of survival and reproduction. This distinguishes selection from any process of drift through fortuitous differential reproduction in the accumulation of random or indiscriminate errors of sampling. To confirm the theory of natural selection empirically is to confirm that this probabilistic causal process exists, is competent, and has been responsible for evolution. Such hypotheses are both falsifiable and verifiable, in principle, if not in practice.

Natural selection has been accepted and developed by biologists with very diverse attitudes toward chance and chances. But the theory and its acceptance have always involved probabilistic causal judgments that cannot be reduced to correlational ones. So, the theory has contributed to a probabilistic shift within the development of causal science, not to any probabilistic rebellion in favor of science without causes.

– M.J.S. Hodge
– Natural Selection as a Causal, Empirical, and Probabilistic Theory
– The Probablistic Revolution: Volume 2
– p. 233

Thoughts?

130 Replies to “Chance and Selection”

  1. Mung Mung
    Ignored
    says:

    Is natural selection a probabilistic cause?

  2. Flint
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    says:

    Not clear to me exactly what you’re asking. I think differential reproduction rates is plausible. Kind of like weighted dice, it contributes to a pattern of results, but isn’t the only factor involved.

  3. keiths keiths
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    says:

    What do you think, Mung? Do you agree with Hodge?

  4. petrushka
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    says:

    Flint:
    Not clear to me exactly what you’re asking. I think differential reproduction rates is plausible. Kind of like weighted dice, it contributes to a pattern of results, but isn’t the only factor involved.

    You can make a lot of money with weighted dice, until you are dead.

  5. Joe Felsenstein Joe Felsenstein
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    says:

    Are the weightings on weighted dice a probabilistic cause?

    I’ve been asking things like this:

    1. Is the probability of winning when betting Red at roulette a constant (16/38) or is it probabilistic?

    2. If we have a Brownian Motion process plus gravity (acting on particles in suspension) is the gravity to be considered to be probabilistic?

    Mung has decided that it is not important to address these.

    In the quote in the OP, M.J.S. Hodge notes the difference between processes like mutation or genetic drift, and selection, saying that this “distinguishes selection from any process of drift through fortuitous differential reproduction in the accumulation of random or indiscriminate errors of sampling.” That Hodge then calls natural selection “probabilistic” is odd, but Hodge does clearly distinguish it from “chance fluctuation” and notes that this view is not “any probabilistic rebellion in favor of science without causes.”

  6. Rumraket Rumraket
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    says:

    Joe Felsenstein: That Hodge then calls natural selection “probabilistic” is odd, but Hodge does clearly distinguish it from “chance fluctuation” and notes that this view is not “any probabilistic rebellion in favor of science without causes.”

    It seems to me that Hodge implicitly considers “random” or “chance fluctuation” to represent a variable with multiple, equiprobable outcomes. And this is what sets selection apart from being merely random/chance, since selection constitutes a bias away from equiprobable outcomes.

    At least, that’s how I can make sense of what he says given he still considers selection to be probabilistic.

    I like that he also explicitly rejects interpretations of “chance/random” as uncaused change. As in something that happens (whether they be mutations or the deaths of carriers) without being caused by anything.

    In any case, I can understand why there are so much confusion and many misconceptions about what all these terms mean.

  7. Allan Miller
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    says:

    Until people stop going out of their way to equivocate on the term ‘random’, and its relation ‘chance’, I see yet another thread that will go nowhere at speed.

  8. Allan Miller
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    says:

    Biology is famed among the sciences for the variability of the things we might measure. There’s a lot of taking of summary statistics. We might for example take the heights of two cohorts of individuals. Height is a random variable – it has a distribution. But no-one is 2 inches tall, or 30 feet. It’s not random in the sense some people mean. But one is not helpless before the variability, as Creationists seem to wish to be rendered helpless by the concept of NS.

    So we move on to fitness: the mean offspring numbers accruing to bearers of particular alleles of interest. Just like height above, it’s a summary statistic, with a distribution and a mean. But now, as usual, we get subjected to the spectacle of Creationists getting all giddy over a not-very-difficult notion.

    Try the substitution. “You can’t predict which one will have the most height!”. “The one with the most height is defined as the tallest!”. “Height is just random!”.

  9. J-Mac
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    says:

    Mung:
    Is natural selection a probabilistic cause?

    Out of 120 000 fertilized eggs of green frog only 2 individuals survive…
    Are we to conclude that they are the fittest and therefore selected by nature????
    Or natural selection is nothing more than blind mortality….

    take it away Joe…. fitness this and fitness that… fittest survival speculations….

  10. Corneel Corneel
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    says:

    J-Mac: Out of 120 000 fertilized eggs of green frog only 2 individuals survive…
    Are we to conclude that they are the fittest and therefore selected by nature????

    Why no, because as you have been explaining to us it is the genotypes of average viability that have the highest chance of surviving, right?

  11. newton
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    says:

    J-Mac: Out of 120 000 fertilized eggs of green frog only 2 individuals survive…
    Are we to conclude that they are the fittest and therefore selected by nature????
    Or natural selection is nothing more than blind mortality….

    How does the designer determine which will survive?

  12. Alan Fox Alan Fox
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    says:

    newton: How does the designer determine which will survive?

    Why does the designer design 120,000 eggs for only two to survive. Perhaps it a test to see which are the best designs? A way of improving on a design? Testing in the environment for survivability? Sort of reminds me of something…

  13. Entropy Entropy
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    says:

    The problem is that Mung doesn’t care about understanding, but about confusion.

    I keep wondering why it is so hard to find honest creationists. Does belief in an all-powerful god who knows your every thought, who knows everything you do, who therefore knows that you’re being dishonest, and who condemns such dishonesty, come together with the contradictory belief that dishonesty is the best way to protect and share the belief in that all-powerful god?

  14. GlenDavidson
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    says:

    Entropy:
    The problem is that Mung doesn’t care about understanding, but about confusion.

    I keep wondering why it is so hard to find honest creationists. Does belief in an all-powerful god who knows your every thought, who knows everything you do, who therefore knows that you’re being dishonest, and who condemns such dishonesty, come together with the contradictory belief that dishonesty is the best way to protect and share the belief in that all-powerful god?

    When you’re wedded to a false belief, any number of truths must go. I think that the most damaging effect of creationism/ID is that anyone and anything on the other side becomes in their minds the evil that deserves no decency or consideration. Mere opposition is what is required.

    In their minds they’re the ones who insist upon the truth. In actual fact, they’re at war with standards and epistemology. It’s amusing how UD opposes the anti-science stance of SJWs and the like in academia, when they’re really little different in their treatment of their opponents as “others” who must be opposed by any means.

    In war the first casualty is truth, and they (like SJWs) are at war with truth.

    Glen Davidson

  15. Joe Felsenstein Joe Felsenstein
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    says:

    J-Mac: Out of 120 000 fertilized eggs of green frog only 2 individuals survive…
    Are we to conclude that they are the fittest and therefore selected by nature????
    Or natural selection is nothing more than blind mortality….

    take it away Joe…. fitness this and fitness that… fittest survival speculations….

    No, the ones that survive among all those offspring aren’t precisely the fittest ones, but of different genotypes among them, the ones with higher fitness are proportionately more likely to survive and reproduce. That is what population genetics says, not that the fittest always survive. If two genotypes have fitnesses 1.0 and 1.1, then the second one is 10% more likely to be a survivor, if the selection is all on viability.

    So the requirement that the fittest of those offspring be precisely the survivors is bogus.

  16. Joe Felsenstein Joe Felsenstein
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    says:

    Allan Miller: Biology is famed among the sciences for the variability of the things we might measure.

    … because organisms are big and complicated, and live in complex environments. Another way of pointing this out is that Avogadro’s Number is very big, because one gram of stuff is an awful lot of atoms. Because any small weight big enough for us to notice is an awful lot of atoms. Because we are an awful lot of atoms.

  17. J-Mac
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    says:

    newton: How does the designer determine whichwill survive?

    All I’m saying there has to be, out of necessity, an inescapable element of randomness in natural selection…

  18. Joe Felsenstein Joe Felsenstein
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    says:

    J-Mac: All I’m saying there has to be, out of necessity, an inescapable element of randomness in natural selection…

    … which shows that you don’t correctly distinguish between natural selection and genetic drift. The randomness of survival is one source of genetic drift (random Mendelian segregation and the variability in offspring numbers being the other sources of genetic drift).

  19. Mung Mung
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    says:

    keiths: What do you think, Mung? Do you agree with Hodge?

    I agree with Hodge that natural selection is probabilistic. But I am not wedded to that false belief, as some people seem to think.

    Even Joe, in a moment of weakness, expresses agreement with Hodge:

    Joe Felsenstein: but of different genotypes among them, the ones with higher fitness are proportionately more likely to survive and reproduce.

  20. Mung Mung
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    says:

    Entropy: The problem is that Mung doesn’t care about understanding, but about confusion.

    But surely clearing up confusion is a path to understanding. And even if I am merely sowing confusion surely you and Glen are far too intelligent to become victims.

    Far be it from you though to say in what way I am confused. You, in all your great concern for honestly and clarity, left that part out. Go figure.

  21. Rumraket Rumraket
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    says:

    Mung: Far be it from you though to say in what way I am confused.

    I he didn’t say you were confused, he said you were trying to sow confusion. Those are two different things.

  22. Rumraket Rumraket
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    says:

    Mung: I agree with Hodge that natural selection is probabilistic. But I am not wedded to that false belief, as some people seem to think.

    You agree with Hodge on what you describe as a false belief? If it’s false, why do you believe it?

  23. Entropy Entropy
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    says:

    Mung: Far be it from you though to say in what way I am confused. You, in all your great concern for honestly and clarity, left that part out. Go figure.

    Nothing to figure. Since I have experienced, first hand, your preference for confusion over understanding, I already know the effect clarifications have on you: none whatsoever.

  24. J-Mac
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    says:

    Joe Felsenstein: … which shows that you don’t correctly distinguish between natural selection and genetic drift.The randomness of survival is one source of genetic drift (random Mendelian segregation and the variability in offspring numbers being the other sources of genetic drift).

    So, you do agree that offspring with average fitness survives…

  25. Mung Mung
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    says:

    This chapter aims to contribute to this most welcome trend. But it does not set out to do so directly. Rather the hope is to clarify the probabilistic character of the theory of natural selection, as it concerns biologists and philosophers alike, by beginning from a point of departure that lies within the discipline of neither party.

    – Hodge, p. 234

    Ah clarity. Who needs it. Who wants it. Sowing confusion by quoting an essay that seeks to clarify things. What mad genius!

  26. Mung Mung
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    says:

    Rumraket: You agree with Hodge on what you describe as a false belief? If it’s false, why do you believe it?

    Just sowin’ confusion! It’s what I do.

  27. Corneel Corneel
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    says:

    J-Mac: So, you do agree that offspring with average fitness survives…

    Yes, but it has to be exactly average, otherwise they start evolving and we can’t have that!

  28. phoodoo
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    says:

    Allan Miller:
    Until people stop going out of their way to equivocate on the term ‘random’, and its relation ‘chance’, I see yet another thread that will go nowhere at speed.

    I am with Allan, let’s stop equivocating on random!

    It means lucky accidents! Enough already!

  29. Mung Mung
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    says:

    phoodoo: I am with Allan, let’s stop equivocating on random!

    It’s unclear to me why he thinks Hodge is equivocating over the meaning of random.

  30. Joe Felsenstein Joe Felsenstein
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    says:

    J-Mac: So, you do agree that offspring with average fitness survives…

    I made that clear. If there are two individuals, and one has 10% greater viability than the other, then that one is 10% more likely to survive, which means that either, or both, could survive.

  31. Mung Mung
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    says:

    Joe Felsenstein: If there are two individuals, and one has 10% greater viability than the other, then that one is 10% more likely to survive, which means that either, or both, could survive.

    Could neither one survive?

    And that sure sounds probabilistic to me Joe. Doesn’t it sound probabilistic to you too? Do you really mean to convey that it is probabilistic or are you just trying to sow confusion?

  32. Joe Felsenstein Joe Felsenstein
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    says:

    Mung: Could neither one survive?

    And that sure sounds probabilistic to me Joe. Doesn’t it sound probabilistic to you too? Do you really mean to convey that it is probabilistic or are you just trying to sow confusion?

    The survival of the individual organisms can be modeled as probabilistic. But you weren’t referring to that but to their fitness values, the expectations of their viability. It’s the distinction between the expectation of a random variable and an individual value. Those are not the same.

  33. Mung Mung
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    says:

    Joe Felsenstein: The survival of the individual organisms can be modeled as probabilistic.

    Could neither one survive?

  34. Joe Felsenstein Joe Felsenstein
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    says:

    Mung: Could neither one survive?

    If you have (say) 20,000 newborns, only 2 of which will survive, then when we look at two particular newborns, most likely both will not survive. No surprise there. You have some problem with that?

    But if they are of different genotypes, one having 10% higher fitness than the other, then that one has a 10% higher chance of surviving.

  35. Allan Miller
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    says:

    phoodoo,

    I am with Allan, let’s stop equivocating on random!

    It means lucky accidents! Enough already!

    ‘Random’ has a good half dozen different meanings, none of which is usefully rendered as ‘lucky accidents’ in my view. But may your bovine repetition of your precious collection of slogans serve you well, anyway.

  36. Allan Miller
    Ignored
    says:

    Mung,

    It’s unclear to me why he thinks Hodge is equivocating over the meaning of random.

    It’s unclear to me why you think my reference was to Hodge, since I never mentioned him. It’s the likes of yourself, phoodoo and J-Mac at whom I was aiming. phoodoo merely makes my point. “Random means X”, he says. And yet, it doesn’t.

    For the record, I am in agreement that NS is a probabilistic process. For illustration, if one has a selection coefficient at the cusp of effective neutrality, and the population grows, we move from neutrality (all Drift), into actual selection simply by population growth alone. That growth simply shifts the distribution slightly from the neutral baseline, due to the effect of the Law of Large Numbers, a statistical effect due to sample size. Because of this, I don’t think there’s a sensible way to separate out drift from selection. You can turn down drift a notch, likewise you turn up selection, by infinitesimal degrees; all that changes is the value of your coefficient of selection, and/or its effectiveness.

    The basic process is one of population resampling, which has an inevitable result – fixation of one allele from any starting position. See the ‘M&M’ threads for a good illustration. So you get a kind of determinism: it is vanishingly improbable that alleles will remain indefinitely varied, in the absence of novel variation and any frequency dependence. That ‘determinism’ is actually a consequence of the probabilistic nature of the process: it is more likely that frequency will change than that it will stay the same, and probability of ultimate fixation = current frequency; these facts propel alleles towards fixation/extinction. The allele that succeeds is indeterminate; that one will succeed is not.

    So, that is the basic process, subject to a probability distribution. Selection is a bias in the distribution, not something separate from it. If one allele has a mean 1000 births to every 1001 accruing to the other in ‘ideal’ conditions, selection is in effect but there is no sensible way to separate out that 1 extra birth per 1000.

  37. Rumraket Rumraket
    Ignored
    says:

    Mung: Ah clarity. Who needs it. Who wants it. Sowing confusion by quoting an essay that seeks to clarify things. What mad genius!

    Don’t gimme this shit. Of course you didn’t quote it in order to clarify anything. As with all quotes you bring, you do it because you want to present some sort of gotcha with statements you can interpret to contradict each other. That’s what you do.

    We are the ones constantly left having to explain and clarify ourselves and even what the people you quote are actually saying.

  38. Rumraket Rumraket
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    says:

    phoodoo: I am with Allan, let’s stop equivocating on random!

    It means lucky accidents!Enough already!

    That doesn’t explain anything. Please define “lucky” and also “accident”.

  39. Rumraket Rumraket
    Ignored
    says:

    petrushka: You can make a lot of money with weighted dice, until you are dead.

    It works, except when it doesn’t.

    /Mung

  40. phoodoo
    Ignored
    says:

    Allan Miller: “Random means X”, he says. And yet, it doesn’t.

    Come on, stop equivocating !

    I thought we agreed we weren’t going to do that anymore.

    heck, Mung even gave a ling to the Evolution Institute that examples exactly how these lucky accidents happen. First a lucky light spot. More lucky lightspots, until you get a whole sheet of them, and then a lucky indentation accident. What’s so hard bout imagining that?

    Look in this day and age, when danger lurks around any corner, will it be long before the lucky spots happen upon someone’s left wrist? Then, you just slowly slip your left hand around the corner, look for terrorists, and if the left hand sees none, good to go, you have a much better chance of survival and reproducing. And even if you live in New Zealand, where its not very dangerous and you only have a slightly better chance of reproducing, that’s good enough. Could be 1/2 a percent. Over time, that adds up.

    Couple of lucky pupils and irises, you are pretty much done. And think of the business opportunities for wrist glasses!

  41. Allan Miller
    Ignored
    says:

    phoodoo,

    Come on, stop equivocating !

    ‘Equivocate’ is evidently one of those words Creationists have their own private definition of – I see it misused all the time in their gibberings. Which is kind of ironic.

    The rest of your post I didn’t read; you are as boring as hell.

  42. phoodoo
    Ignored
    says:

    Allan Miller,

    What does ‘Eq… mean?

    I didn’t read the rest.

  43. Rumraket Rumraket
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    says:

    Looks like something’s got phoodoo all riled up today. Oh well…

  44. Joe Felsenstein Joe Felsenstein
    Ignored
    says:

    It’s extremely clear why creationists and design advocates are so insistent on labeling natural selection as “random” or “chance” or “lucky accidents”. So that they can then argue that it is just random wandering, unrelated to the direction of changes that would improve adaptation.

    These folks are terribly insistent on Clarity, but when the creationist debaters get up and start arguing that evolutionary biology has a theory that explains remarkable adaptations as purely accidental, as occurring by pure random wandering, somehow you won’t hear any of these advocates of Clarity standing up and correcting the creationist debaters.

  45. Joe Felsenstein Joe Felsenstein
    Ignored
    says:

    Allan Miller: For the record, I am in agreement that NS is a probabilistic process. For illustration, if one has a selection coefficient at the cusp of effective neutrality, and the population grows, we move from neutrality (all Drift), into actual selection simply by population growth alone

    For the record, I disagree. I think that this phenomenon involves the interaction of natural selection with genetic drift, and that it does not involve a change in the natural selection, which remains constant even as genetic drift overwhelms it.

  46. phoodoo
    Ignored
    says:

    Joe Felsenstein: It’s extremely clear why creationists and design advocates are so insistent on labeling natural selection as “random” or “chance” or “lucky accidents”. So that they can then argue that it is just random wandering, unrelated to the direction of changes that would improve adaptation.

    Joe, Joe, how many times do we need to repeat this: It is the “changes”, the mutations that we are insisting on reminding of the random component. I could care less frankly, what you want to call the selection part, it is the “creation” part of the process, not the keeping part, which is what the neo-Darwinian view of evolution is built upon.

    We have stated this to you many times, I am wondering why you are willfully ignoring that we have said this?

    Mutations, new creations, random. The selection, natural selection, you can call this guided if it helps you.

  47. Joe Felsenstein Joe Felsenstein
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    says:

    phoodoo: Mutations, new creations, random. The selection, natural selection, you can call this guided if it helps you.

    Good, then Mung disagrees with you.

  48. phoodoo
    Ignored
    says:

    Joe Felsenstein: Good, then Mung disagrees with you.

    I don’t think Mung ever labeled selection as lucky accidents. You are making up that part.

    Though I will say, I believe the reason most reproductions happen is pure luck. But there is no method for measuring these percentages.

  49. Allan Miller
    Ignored
    says:

    Joe Felsenstein,

    I’m still not sure how those processes are really separable. If two competing alleles have equal selection coefficients, we have drift alone. Then if we add a tiny increment to the one, such that the other goes down relative to it, I don’t see that we have materially changed what’s going on, other than that we have introduced a bias, a directional arrow, to the neutral fixation probability and rate (I realise that’s a slight variation on my original ‘near-neutral’ case). We’ve shifted the mean of the distribution.

    I know that there is some reluctance to concede randomness because of the hay Creationists inevitably make of this. But they make hay of anything they can lay their hands on, so let ’em.

    If we see the process as one of generational resampling, a probabilistic process with varying degrees of bias, I don’t see that this is a fundamentally wrong way of looking at it.

  50. J-Mac
    Ignored
    says:

    Joe Felsenstein: I made that clear.If there are two individuals, and one has 10% greater viability than the other, then that one is 10% more likely to survive, which means that either, or both, could survive.

    So, if out of the 2 individuals the one with 10% greater viability doesn’t survive and the “inferior” one does, what are we to conclude?
    Did natural selection eliminate the more fit or viable individual?
    Or, was it just pure random process?

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