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.
No, of course not.
But this discussion started when I offered, as a formulation of adaptive evolution by natural selection:
Heritable variance in reproductive success.
That works very well, as far as I can see, and avoids the artificial splitting of the existence of heritable variance from its correlation with reproductive success, while still leaving room for debate about the mechanisms of variance generation as well as the possibility that you can you have heritable variance without it being correlated with reproductive success.
The only drawback is that it it covers keiths’ scenario of infinite resources.
As do many other formulations of natural selection, including that of population genetics, and not, on my reading, even excluded by Darwin, although he didn’t quite think of it that way, being focussed on the argument that competition must be for resources, not merely for numerical dominance.
I’m sure that Darwin must have given some thought to why some species produce millions or billions of potential offspring. One explanation might be to ensure that a few survive in the competition against predators and in competition for resources.
But there must have been a stray thought that producing more offspring than your neighbor is analogous to running a bit faster when chased by a tiger.
I don’t see anyone arguing about facts; just people arguing about semantics.
Yeah.
Might I point out that reproductive rate is a favorite obsession of xenophobes?
I’ve lost count of the number of undesirable races and creeds that were going to out reproduce us good guys.
Well, facts (or data, sorry, Lizzie) can be a bit inconvenient when developing an argument. 🙂
Indeed. I’m still sceptical about drift. So where two absolutely neutral (to fitness in a static environment) alleles compete for a slot, in the complete absence of any selective bias, does neutral theory predict that one will eventually fix and the other eventually disappear?
petrushka,
Sure. The debate is (or was) over whether there is a canonical scientific definition of “natural selection”. There isn’t.
The debate is also about which definition is most useful in the current context.
No one has claimed that we are arguing over the mechanisms of evolution.
I’m all for clear definitions. I’m even more in favour of useful ones.
Alan,
Assuming just the two alleles, one of them will eventually fix purely by chance, though this is heavily dependent on the population size.
Consider an extreme case with only two “slots” in the population, each initially occupied by a distinct variant (call the variants A and B). You’ll quickly run into a situation, purely by chance, in which both slots are occupied by A’s or both by B’s. That’s fixation.
The only way to avoid fixation in this scenario is for each variant to get exactly one offspring into a slot, no more and no less, generation after generation after generation.
The odds get pretty slim as time goes on.
As the number of slots increases, the average time to fixation also increases.
keiths,
That seems to be definitional.
Alan,
Sure. So?
Most scientific questions depend on definitions, Alan.
Once you’ve chosen your definitions — assuming they’re precise enough — you can address the questions based on empirical evidence.
Because I think we have here the population-genetic definition, plus one other one, which alas is scientifically invalid.
There would be room for multiple scientifically-valid definitions, but we aren’t in that situation.
Joe,
Why do you think the other definition is “scientifically invalid”? Please be specific.
Lizzie,
In reading through the thread again, I came across a comment of yours that makes no sense to me. It was in response to a comment by William.
William:
Lizzie:
The second sentence is true, but the first and third sentences seem obviously false.
Alan Fox,
Absolutely. I think a spell with OM’s model, or coding one of your own, might help dispel your skepticism. There is nothing in this model except drift, and colours disappear one by one every single time. This would happen even if you started with a different colour for every starting individual.
Add a small amount of selection, and colours would still disappear one by one every single time. Sometimes, the one that disappears is the one that selection favours. It disappears through drift.
It’s because of sampling. Samples are (almost) always a distorted representation of the wider population from which they came. Iterated sampling amplifies distortions.
petrushka,
0% can be a frequency just like 0 can be a probability, I guess. Same for 100%
Yeah. It’s what we do! 😉
Which sounds like change in allele frequency!
The important thing is the combination of actual lineage change and the progress of that lineage thrugh the wider population. I like to think of an allele’s progress as describing an approximate cone within a cylinder in time. Cross sections through the cylinder are the wider population at a moment, the cone the amount of that population which has the allele. For any lineage within the cone, change occurred at the apex – that first ancestor. For any outside it, evolution has yet to occur. But for the population, it occurs microscopically with every birth and death.
Start one?
A Drift Thread?
petrushka,
If you like. We’ve had a couple, but it is a topic that doesn’t get much coverage in popular treatments. If nothing else, we could lay to rest the canard that it only applies to neutral alleles! (An error that I myself made for several yards of webinage before realising I was talking nonsense).
Elizabeth,
Indeed – the overriding competition, even at allele level, is for not-becoming-extinct! Alleles don’t compete for ‘resources’, they compete for finite loci. Which I suppose is a resource of sorts. Even when competing with equal strength, they are still competing.
I think it is a pedilogical mistake to reduce evolution to allele frequency change without following up with a discussion of how new alleles originate and how one determines neutral or not.
I would not classify the first iPhone as a change in iPhone frequency.
I also think it is unfortunate to say that neutral alleles are not subject to natural selection. Purifying selection is still selection. Neutral alleles are a small percentage of possible variations to functional sequences.
Anyway, an educational thread might be a welcome change from flat earthism.
petrushka,
Purifying selection doesn’t affect neutral alleles! Not directly, anyway.
Purifying selection affects the frequency of alleles by eliminating nonviable ones. The problem with terminology arises when you try to communicate with some outside the loop.
petrushka,
Hmmm. So if a nonviable allele arises at a locus, the existing alleles (momentarily) stop being neutral? Kind of!
If zero is a frequency, then fatal mutations are subject to selection. Also, non-fatal mutations that prevent reproduction.
I guess I’m a bit opposed to saying drift is outside selection. A selection coefficient of zero is still selection. All neutral alleles having been sieved by purifying selection.
This is consistent with the claim that most sequence changes are not adaptations. I suppose drift proponents are reacting to claims that every feature is an adaptation and is the result of competition.
Mung,
She seems to have gotten back on track after that, although it would have been nice if she had acknowledged her mistake.
Doesn’t really matter — one flask for each allele, or one flask for each organism. Either way, you can choose to treat the entire ensemble as a population.
I see the point of your argument. Bacterial species are pretty much arbitrary to start with, and there’s no clear dividing line between ecological interspecies competition and natural selection for them. Nevertheless, I’ve never seen anyone use a term other than “selection” for the within-species case (and the issue here seems to be entirely linguistic). There are words for other causes of allele frequency change — genetic drift, meiotic drive — but nothing that would apply here except selection. One thing that is different (sort of) between the within-species case is that the evolutionary trajectory of the species depends on the relative success of the two alleles: beneficial mutations are more likely to occur in the larger subpopulation.
We are in agreement that simply doubling fecundity within a bounded population does impose selection. You can treat that as caused by increased culling of the less fecund allele, even though it hasn’t changed at all in its biological capabilities; there are just more of the more fecund strain. Try these two scenarios to explore the situation: 1) A single population, constrained by food supply, new mutation for increased fecundity. Survival rate of old allele drops. Selection occurs. 2) Same population, but now the new mutation doesn’t change anything. But add a second population that sends a stream of migrants into the first population, all carrying the new mutation. Survival of the old allele again decreases, for the same reason as in (1), but no selection has occurred. Does that seem like the correct description?
Let’s take the case where three genotypes AA, Aa, and aa have viabilties 1, 1, and 0.9. Should we say that they show natural selection favoring the A allele? If they also have fertilities 1, 1, and 1.2 then their fitnesses are 1, 1, and 1.08. So allele a is expected to win out. I don’t see the sense of just judging by the viabilities. Nor, if the vaibilities were all equal, would it make sense to say there is no natural selection, if fertilities differed.
I was looking for biologists commenting on the specific question: whether selection still occurs in the absence of competition (or in the absence of death). That was what I couldn’t find. None of your quotations suggest that the authors have even considered the problem. We’re not talking just about a thought experiment or about population genetics theory, either. As I mentioned earlier, your flask example is not that different from a virus replicating in the early stages of an infection, during exponential increase and before effective immune response. We can and do look for mutations that increase in frequency during that expansion, and we refer to such an increase as being due to selection. (Most of us aren’t population geneticists, either.) What would your authors call that process?
Steve:
keiths:
Steve:
My point is that you were talking about a two-flask case, but Allan and I were talking about a one-flask case versus a many-flask case. I wanted to make sure we were on the same page before continuing. It sounds like you now agree that there is no two-flask case, correct? (Except for a brief moment at the beginning of the many-flask case, of course.)
And if you hold that there is selection in both the one-flask and many-flask scenarios, then what was the point of writing the following to Allan? How was it relevant?
Steve, You’re a biologist/geneticist, so I don’t expect you to concede any ground to non-biologist/geneticists. But ‘selection’ is a ‘stolen’ metaphor from Malthus’ humanitarian population argument. You biologists just spew empty, rhetorical talk without it.
A.R. Wallace at least acknowledged this, see his paper on “Human Selection” (1890). The attempt to make ‘nature/Nature’ an ‘agent’ by ideological naturalists has largely failed, even if biologists (& a significant # of others) are blind to it. But you likely won’t ask for help from people who study actual ‘selection’ the way most people mean/intend it.
‘Natural selection’ is a faulty metaphor for natural science, though ‘non-agential’ quasi-selection of course occurs; about that there is no debate. As Darwin himself corrected, ‘natural preservation’ (http://www.darwinproject.ac.uk/letter/entry-2931) rather than ‘natural selection’ would have been preferred. (Nobody has yet acknowledged Darwin’s words in this thread; Lizzie only diverted to ask if I’d read Darwin’s work, then didn’t follow-up.) With such a linguistic reform, there would need be no debate about the Malthusianism in Darwinian evolutionary theory, which, in case you only read English and ‘western’ ideas of ‘evolution’, you might know next to nothing about.
Nevertheless, just as ‘Intelligent Design’ is a deceptive metaphor, so is ‘Natural Selection.’ One is not innocent while the other is dirty guilty; they are both deceptive. You atheist-naturalists (is this Steve Schaffner practically?) dance deceptively together with theist-IDists in your common English language equivocation. Why not finally own up to this at TSZ? Or is this a site where being ‘skeptical’ of atheism is only real for a small few?
Steve:
Take another look at the Mayr quote:
No competition and no death means no elimination. No elimination means no selection, according to Mayr.
You and Joe are simply wrong to claim that all evolutionary biologists agree with your definition and that it is the One True Scientific Definition of natural selection.
Steve Schaffner,
No, and this is interesting when you look at the sexual/asexual boundary. Asexual offshoots of a sexual population are much like individual bacteria. I think a fundamental error was committed by some pretty big names in the field in treating sex as just another allele, and adding asexuals to ‘the population’.
The ‘twofold cost of sex’ is essentially a selective argument via fecundity (fecundity being measured in the currency of grandchildren in that case). The expectation, for years, has been that a twofold selective benefit is required in order for sex to earn its keep. But I think the entire argument is wrongly formulated. A doubling of potential fecundity in asexual offshoots should not be treated as if it were a simple locus within a species, but it often is. Is there a ‘cost’ to not becoming a different species? I don’t see how.
I’m not sure what the point of this thought experiment might be. If a population of bacteria experienced no death and no limitations of resources, it would exceed the mass of the universe in a very short time.
Attempting to model it would quickly overwhelm any computer system.
Steve, to Allan:
Relative fecundity. The faster-reproducing strain B comes to dominate the population not because the environment favors B’s over A’s, but simply because strain B produces more offspring in a given period. It is more fecund.
No organisms are eliminated, so by Mayr’s definition there is no selection. B’s population advantage comes entirely from relative fecundity.
petrushka,
I introduced it to show why I disagreed with Lizzie’s statement:
My on-line (free) textbook Theoretical Evolutionary Genetics has a Chapter II on “Natural Selection”. It has 161 equations, and is followed by 17 exercises and 23 Problems.
If this chapter were “spew[ing] empty rhetorical talk” isn’t that an awful lot of trouble for me to go to?
How can a faster reproducing allele dominate a population in which all alleles reproduce without limit?
Is this a Cantor thing?
It doesn’t seem to be too much trouble for Gregory.
How many ‘agents’ do you reference in that chapter, Joe? If any, please name them one by one. I’m not going to read your genetics textbook (free or not). Nor will 99.8+% of human beings who are not ‘geneticists.’
I’m not faulting you for ‘doing biology,’ Joe, as a specialisation. But your metaphors have their limits too (don’t they?). And I and too many other will not allow such a fiasco as Wilson’s demolished ‘sociobiology’ again any foothold these days.
Don’t think that (the possibilities and limits of) biologists’ language cannot be taken into account and challenged by non-biologists. You will simply lose.
Joe,
As I keep saying, I am not advocating a change in population genetics terminology. Please continue to use your current definition of natural selection when doing pop gen.
My argument is that contra you and Steve, there is no One True Scientific Definition of natural selection. The Mayr quote alone demonstrates this, because Mayr is considered one of the greatest evolutionary biologists of the last century and there is nothing unscientific about his definition.
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?
Hey, Lizzie!! Why can’t the atheists be gentle and non-aggressive like the kind. helpful, and always professional Gregory here? Jeez, Lizzie, TSZ needs to take a stand against the hostile atheists who just want to throw stones, and refuse to enter into calm, rational discussions!
petrushka,
It's a percentage thing. The faster-reproducing allele occupies a larger and larger percentage of the total population.
Lizzie, Joe, Steve, et al want to call this "natural selection". I don't begrudge them their definition, but I think the Darwin, Mayr, et al definition is more appropriate in this situation.
So it is a Cantor-like thing. One infinity is greater than another infinity, although this sounds more like JoeG math than JoeF math.
When you come back to earth and have limited resources, the allele that produces greater fecundity has an advantage, and it is a selection advantage.
IMHO, it’s a quibble-dee-dibble-dee-dum.
Gregory,
Cheers! Hic! Spot-the-misuse-of-‘equivocation’ – a great drinking game, but I’m permanently legless.