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?
If it does remain constant (close, sometimes, I suppose), doesn’t it remain a constant probability?
It’s really mostly semantics, of course, because the point is not whether or not it’s “probabilistic” or not, just whether or not it is “just luck.” Clearly not the latter, and I think one could consider NS a non-random bias (even if selective pressures are a bit of potluck itself), but it seems that one can’t deny that NS is a probabilistic process as another legitimate interpretation.
Glen Davidson
Quote of the week. We couldn’t agree more. So why is it the basis of your theory.?
Over-sensitivity to stupidity. He would apply for disability but that would requiring having contact with the government which would only exacerbate his condition.
Flog that straw man Joe. Flog it good. The question isn’t whether natural selection is random, it’s whether it is probabilistic and whether it is stochastic.
I have made this clear several times. Please try to do better.
Yes, I have plainly told Joe that I agree that natural selection introduces a bias, that some outcomes become more likely than others.
Will I roll a seven every time I roll the dice? No, but rolling a seven is more likely than rolling any other number.
So where have a claimed that Hodge has contradicted himself? Or are you reading chicken bones again.
Nice post.
That shit has some probability to happen.
Nope.
Nope. If it was “purely random,” then the one with 10% higher probability of surviving, would not have had that higher probability of surviving. It would have the very same probability of surviving as the other individual.
Think of a somewhat loaded dice. It has a higher probability of landing a 6, but it won’t always land a 6, sometimes the imbalanced weight will not be enough to guarantee the 6, but the 6 will come more often than expected by “pure randomness.”
Mung,
Cheers. Tell your friends!
I came to my viewpoint through taking what I now think was the wrong side in a lengthy series of threads on the old Richard Dawkins forums. Many were critical of their host’s insistence that NS is ‘non-random’. IIRC one such thread was entitled “Is there a definition of ‘random’ such that Drift is but NS is not?”. I spent a long time arguing that there was, but ended up conceding defeat. The ‘population resampling’ thing, with selection as a bias in the distribution; a shift of the mean, is due to Simon Gunkel, posting as ‘susu.exp’.
What does it mean to say that selection is probabilistic? Seems to me that is like equating selection to the whole process involving random variation, drift and also selection, in the sense Joe has been using it. Perhaps we’re just talking past each other here (while Mung, as always, tries hard not to understand)
I’m trying hard not to understand people talking past each other?
So what is impure randomness? Are you ok then with saying that natural selection is impurely random?
Natural selection is a random process in which not all outcomes are equiprobable. We call this kind of random process an impurely random process.
We good now?
J-Mac,
Someone needs to nail down what “remarkable adaption” means.
As one pair of authors put it, “by a stroke of good luck anthropoids were able to ‘win’ the sweepstakes.”
– Fleagle and Gilbert
dazz,
I think its more that drift and selection have a combined effect that renders the two effectively inseparable – we’re not including variation generation as well.
So where have I claimed that you have claimed, that Hodge contradicts himself? Or are you reading chicken bones again.
Don’t leave him alone then.
He says they’re random, and you think ‘random’ means “lucky accidents”. Since Mung has not given any indication that he disagrees with your definition of random, nonsensical as it is, one is entirely justified in inferring that Mung thinks both mutations and selection are “lucky accidents”.
Now if I’m wrong here then perhaps you and Mung could spend some time really fleshing out exactly what the words ‘random’, ‘stochastic’, ‘lucky’, and ‘accident’ means. It’s not at all clear that you understand those words to mean the same thing.
Good, I’m glad to see you agree with me that when phoodoo defines ‘random’ as “lucky accidents” that this doesn’t explain anything.
I will leave you two to duke this one out then.
Yeah phoodoo, why is the basis of the halluscination of evolution you think we are positing, based on a nonsensical term? Neither me nor Mung can make sense of it.
OK, but the point is that it’s the whole process (of allele fixation), involving selection and drift, that is stochastic. I don’t think saying that fitness is relative is the same thing as saying that selection is stochastic.
Not sure what the “relative” thing means.
I’ve been over this with Mung repeatedly, to no avail, so I will repeat myself. The whole process of selection+drift may be modeled as a stochastic process. That does not mean that the selection part should be regarded as “random” or “chance” or “probabilistic”.
Individual deaths may be modeled as random, and similarly individual redproduction. But the bias that favors one genotype over another is, in straightforward models, consistent. It is just like gambling in a casino where the odds are against you. You will lose your shirt more certainly the more times you gamble. If the casino owners find that the odds are actually “random” or “stochastic” they will be very upset and will close down the game. They depend on the odds being always biased in their favor. Straightforward models of natural selection and drift have a bias in favor of some genotypes. Mung has admitted that there is such a bias. Why Mung then insists on describing this bias as “random”, “stochastic” or “probabilistic” is a mystery.
As we are talking of casinoes, does the analogy of a roulette wheel help? With equal slots acting as neutral selection and drift (all outcomes equiprobable), you can then widen some slots (representing beneficial alleles) and narrow others (deleterious) so outcomes are biased towards the wider slots but there is still an element of chance.
OK for one spin per individual, and modeling a whole generation by multiple spins. But where the analogy breaks down is that the mix of genotypes found does not then undergo random mating and reproduction, and does not become the starting point for the next generation, in the roulette analogy.
It’s a reference to this
I think I understand what you mean, and what Allan means, and I don’t see a problem between both positions to be honest.
dazz,
I wasn’t saying that “fitness is relative is the same thing as saying that selection is stochastic”, though!
When two alleles are segregating in a population at the same locus, relative fitness is the key. If their absolute fitnesses are equal, all is drift – it’s the neutral case. It’s just inevitable that turning one coefficient up will turn the other down, relatively speaking. But if one imagines doing this by the tiniest increment, one has hardly moved at all from the position where all is neutral. One hasn’t cranked a knob all the way to ‘selection’; there’s still loads of drift. One can imagine turning the knob by further such infinitesimal increments; drift incrementally goes down while selection goes up; there is nonetheless no point at which the randomness stops.
Of course we can separate them conceptually – if we couldn’t, I couldn’t make statements about the one or the other. But if, say, there are 1000 births to 999 in favour of one allele over the other, you can’t say for example that one of those births was due to selection, the rest to drift.
It’s like a biased dice. On a given roll, was it the bias that made it come up? Or is it not just probabilistic, with bias?
This confirms what I suspected about how the label “randomness” would be used.
Not really. 🙂
Maybe think of it in terms of colors rather than individual numbers At least in that scenario there is an unequal distribution and a clear bias. Red and black may have an equal chance of increasing or decreasing in the next generation but their chance is better than that of green. So it’s a clear bias against green, but it’s only a probability, not a certainty, that green will not increase.
I didn’t mean to misrepresent what you said, sorry about that
I think that’s the crux of the matter. Selection and drift are both intertwined in practice, but Joe is referring to selection conceptually, as a “parameter” in evolutionary models. That’s why I see no fundamental disagreement here
…the decomposition of an evolutionary process into its deterministic and stochastic components may seem rather contrived.
– Elliott Sober. The Nature of Selection. p. 115.
🙂
Joe Felsenstein,
A bet worthy of anyone’s bottom dollar.
dazz,
It’s true I think we are largely talking semantically. There is but one parameter though: selection coefficient. It can essentially take the value 0 (neutral; drift) or non-zero (beneficial/detrimental; selection+drift).
Do you think that, in population genetics, an allele that has lower fitness is certain not to increase?
No. It’s fate is probabilistic, not fatalistic. 🙂
Joe FelsensteinThis confirms what I suspected about how the label “randomness” would be used.
So, you agree that there is an inescapable element of randomness in natural selection, you just don’t like how it could or is being used?
Elsewhere Joe has argued that natural selection is deterministic, and this appears to be the reason that he thinks it cannot be probabilistic. Is there such a conflict though, in that both cannot be true?
Can a process be both probabilistic and deterministic?
I take back that thing about Mung trying hard to not understand. He doesn’t even need to try
If the theory of natural selection is a statistical theory, why is it wrong to say it is probabilistic?
Is the Theory of Natural Selection a Statistical Theory? (PDF)
meh
A statistical theory?
Hamilton in full:
Here’s a nice take on William Hamilton.
If the definition of lower fitness is alleles that are certain to not increase, than I believe an allele that has a lower fitness is certain to not increase.
I think what can happen however, is if an allele of lower fitness increases, it gets called an allele of greater fitness. Thus the paradox is solved.
I briefly forgot that the process is deterministic, in which case the allele would certainly be lost. Unless it wasn’t.
But because I don’t want dazz to think that we’re complete IDiots, if an allele does get fixed in spite of it’s lower fitness, we can always blame that on drift and thus save our theory from falsification. How convenient.
Don’t read that paper I linked to dazz. It might break something very fragile in your psyche and we would not want that.
Yes, I guess that is the definition of drift.
All of life’s problems can be solved through random definitions, that then become selected.
That’s me! Lying hard not to understand.
R.A. Fisher:
I have a distinct impression that Joe has a third option up his sleeve..Since he has recently become somewhat an expert in quantum mechanics, maybe he has cracked the secret code of the enigma of subatomic world?
What do you think of this?
https://www.inverse.com/article/12061-quantum-darwinism-is-where-natural-selection-meets-quantum-mechanics
The examples that Joe has provided of the fate of an allele appear to mitigate against his claim that natural selection is deterministic.
Perhaps I need to clarify. Perhaps Joe didn’t really say that natural selection is deterministic. Perhaps what he actually said is that in some models of natural selection, natural election is deterministic. In other models of natural selection, natural selection is not deterministic. So natural selection is deterministic, except when it isn’t.