Stuck in a Cul De Sac

[hobbes]

Have we stopped evolving?

[Toby Gymshorts]

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science has bad news: this is the best it is going to get.

I want a refund.

[evilC]

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There's one aspect in which I agree with the basic principle of some of that article's topic: Since we don't have the physical exertions that the majority of the populace were subject to, even as late as the industrial revolution, we are seeing a greater amount of obesity. That's not news, of course, but the basic fact is that it's a sign of a greater 'unfitness' and if - hypothetically - such an unfit population were plunged into some near-apocalyptic crisis, then alot of people simply wouldn't be cut out to survive.

So, yes - in that regard, at least, the driving factors that have influenced physical evolution are no longer in play.

A spell in the army - that's what we bloody need! Errr... hang on!

[Wyatt Earp]

Stuck in a Cul De Sac

Not sure about this. There are some quite sweeping statements being made here, which seem to ignore some complexities. For one thing, Western populations are far from genetically isolated. For another, it may be that choosing to have more children reflects, at least partly, inherited traits (naive optimism, for example); if so, then those traits are currently under selection pressure in Western populations (though they haven't been for long).

Finally, the relationship between the strength of a selection pressure and the pace of evolutionary change is complicated. If there's already plenty of inherited variation in the population, then fine: the stronger the selection pressure the faster the evolution. But if there isn't, then a strong selection pressure can work against rapid evolution, by making the environment especially unforgiving of mutation. So in the long term, a period of relaxed selection pressure might, for all we know, serve to accelerate human evolution.

I've noticed before that Jones is very scathing of people who get too speculative about human evolution, except when they're speculating along lines he likes.

[Wyatt Earp]

Stuck in a Cul De Sac

evilC wrote:

Since we don't have the physical exertions that the majority of the populace were subject to, even as late as the industrial revolution, we are seeing a greater amount of obesity.

That's an acquired trait, though, evilC. Or at least, if it reflects inherited traits, then those traits have only ever been expressed in the form of obesity under modern conditions. So in that case, it's likely that Western populations are now, for the first time, slowly evolving to be naturally slimmer--because now, for the first time, there may be an evolutionary edge in doing so.

If variation in obesity is wholly acquired (something Lyra vigorously, and I suspect rightly, denies) then the whole question's irrelevant anyway.

[Wyatt Earp]

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science has bad news: this is the best it is going to get.

What a fucking stupid thing to say.

Ben! Where's Ben?

[Third rate Leszno]

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I thought this was going to be the thread about Barrow-in-Furness being voted Working Class capital of Britain.

[evilC]

Stuck in a Cul De Sac

Wyatt Earp wrote:

evilC wrote:

Since we don't have the physical exertions that the majority of the populace were subject to, even as late as the industrial revolution, we are seeing a greater amount of obesity.

That's an acquired trait, though, evilC. Or at least, if it reflects inherited traits, then those traits have only ever been expressed in the form of obesity under modern conditions. So in that case, it's likely that Western populations are now, for the first time, slowly evolving to be naturally slimmer--because now, for the first time, there may be an evolutionary edge in doing so.

If variation in obesity is wholly acquired (something Lyra vigorously, and I suspect rightly, denies) then the whole question's irrelevant anyway.

Isn't it an acquired trait only in the first generation or so in which those traits are evident (as a reaction to prevalent conditions)? If - and I don't know how to phrase this without sounding 'dodgy' - a genetic propensity to quicker obesity under sedentary conditions gets spread throughout the population through breeding, then wouldn't the traits start to become genetically inherited?

On the whole, though, I have to agree that such assumptions as this article is implying after just a couple of generations of Western society becoming more 'desk-bound' would be an over-reaction.

[Guest]

Stuck in a Cul De Sac

Wyatt Earp wrote: So in that case, it's likely that Western populations are now, for the first time, slowly evolving to be naturally slimmer--because now, for the first time, there may be an evolutionary edge in doing so.

You sure about that, given the link between obesity and socio-economic status (particularly among women) and the increased incidence of larger families at lower socio-economic status. The poorer & fatter are more likely to have more children, who are more likely to live to an age to have their own children, than ever before. There doesn't appear to be significant selection operating in favour of slimness in the bulk (eh) of the population.

[Ginger Yellow]

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That's not news, of course, but the basic fact is that it's a sign of a greater 'unfitness' and if - hypothetically - such an unfit population were plunged into some near-apocalyptic crisis, then alot of people simply wouldn't be cut out to survive.

No, no, no. There's no such thing as generalised fitness. Fitness only has useful meaning in the context of a particular fitness "landscape" (basically environment+population, but I'll leave it to the professionals to give a better definition). What you're thinking about, arguably, is plasticity or flexibility - and on those grounds humans are surely very well placed. We have a greater geographic range than any other species (although obviously higher level groupings such as "bacteria" are more likely to survive a catastrophe.

Secondly, don't underestimate the role of luck in these things. SJ Gould:

Mass extinctions are not random in their impact on life. Some lineages succumb and others survive-as sensible outcomes based on presence or absence of evolved features. But especially if the triggering cause of extinction be sudden and catastrophic, the reasons for life or death may be random with respect to the original value of key features when first evolved in Darwinian struggles of normal times. This "different rules" model of mass extinction imparts a quirky and unpredictable character to life's pathway based on the evident claim that lineages cannot anticipate future contingencies of such magnitude and different operation.

To cite two examples from the impact- triggered Cretaceous-Tertiary extinction 65 million years ago: First, an important study published in 1986 noted that diatoms survived the extinction far better than other single-celled plankton (primarily coccoliths and radiolaria). This study found that many diatoms had evolved a strategy of dormancy by encystrnent, perhaps to survive through seasonal periods of unfavorable conditions (months of darkness in polar species as otherwise fatal to these photosynthesizing cells; sporadic availability of silica needed to construct their skeletons). Other planktonic cells had not evolved any mechanisms for dormancy. If the terminal Cretaceous impact produced a dust cloud that blocked light for several months or longer (one popular idea for a "killing scenario" in the extinction), then diatoms may have survived as a fortuitous result of dormancy mechanisms evolved for the entirely different function of weathering seasonal droughts in ordinary times. Diatoms are not superior to radiolaria or other plankton that succumbed in far greater numbers; they were simply fortunate to possess a favorable feature, evolved for other reasons, that fostered passage through the impact and its sequelae.

Second, we all know that dinosaurs perished in the end Cretaceous event and that mammals therefore rule the vertebrate world today. Most people assume that mammals prevailed in these tough times for some reason of general superiority over dinosaurs. But such a conclusion seems most unlikely. Mammals and dinosaurs had coexisted for 100 million years, and mammals had remained rat-sized or smaller, making no evolutionary "move" to oust dinosaurs. No good argument for mammalian prevalence by general superiority has ever been advanced, and fortuity seems far more likely. As one plausible argument, mammals may have survived partly as a result of their small size (with much larger, and therefore extinction- resistant, populations as a consequence, and less ecological specialization with more places to hide, so to speak). Small size may not have been a positive mammalian adaptation at all, but more a sign of inability ever to penetrate the dominant domain of dinosaurs. Yet this "negative" feature of normal times may be the key reason for mammalian survival and a prerequisite to my writing and your reading this article today.

[Ginger Yellow]

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If - and I don't know how to phrase this without sounding 'dodgy' - a genetic propensity to quicker obesity under sedentary conditions gets spread throughout the population through breeding, then wouldn't the traits start to become genetically inherited?

Why would it, though, except through genetic drift or as a side-effect of some other selected trait? What's the reproductive advantage to quicker obesity under sedentary conditions?

[Wyatt Earp]

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Raskolnikov wrote:

Wyatt Earp wrote: So in that case, it's likely that Western populations are now, for the first time, slowly evolving to be naturally slimmer--because now, for the first time, there may be an evolutionary edge in doing so.

You sure about that, given the link between obesity and socio-economic status (particularly among women) and the increased incidence of larger families at lower socio-economic status. The poorer & fatter are more likely to have more children, who are more likely to live to an age to have their own children, than ever before. There doesn't appear to be significant selection operating in favour of slimness in the bulk (eh) of the population.

But the causes of greater obesity among the poor are (presumably) environmental, meaning this component of the variation is invisible to evolution. Whereas all environmental factors being equal, if you stay slimmer you may be less likely to die young and more likely to get lots of shags. So the inherited component of the variation may be subject to a selection pressure away from obesity. That would be my guess, anyway.

[Wyatt Earp]

Stuck in a Cul De Sac

evilC wrote:

Isn't it an acquired trait only in the first generation or so in which those traits are evident (as a reaction to prevalent conditions)? If - and I don't know how to phrase this without sounding 'dodgy' - a genetic propensity to quicker obesity under sedentary conditions gets spread throughout the population through breeding, then wouldn't the traits start to become genetically inherited?

I don't follow you, sorry. Surely such a genetic propensity would spread more quickly when not selected against? That is, in the absence of sedentary conditions? Once the sedentary conditions get under way, that's when the genetic propensity starts having all these possibly deleterious effects on the phenotype. Before that, it can enter the population freely through drift, and may even be selected for (a propensity to put on fat might be handy in circumstances where famine is frequent).

[evilC]

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Ginger Yellow wrote:

If - and I don't know how to phrase this without sounding 'dodgy' - a genetic propensity to quicker obesity under sedentary conditions gets spread throughout the population through breeding, then wouldn't the traits start to become genetically inherited?

Why would it, though, except through genetic drift or as a side-effect of some other selected trait? What's the reproductive advantage to quicker obesity under sedentary conditions?

Ummm... that's what I'm saying: there isn't one. It's just happening! However, recent (last hundred years) conditions are protecting us from the kind of exertions that drove our physical evolution up to that point. As has been mentioned on threads passim prior to (moreorless) the 20th century, a measure of obesity was also 'proof' of a more wealthy lifestyle, since sedentary behaviour meant that one presumably wasn't working class. Of course, these days, that's been turned on its head and obesity seems to be seen as a working class thing and something that the middle and upper classes seem to want to avoid, spawning a business based on just that.

[Wyatt Earp]

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And, you know, what Ginger said.

[Wyatt Earp]

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evilC wrote:

Ummm... that's what I'm saying: there isn't one.

If there isn't a selective advantage, then we're not evolving in that direction, and that's pretty much that.

It's just happening!

Well, obesity is becoming more common, but not through changing gene frequencies. Firstly there hasn't been time, and secondly no-one's explained how this could possibly occur given that there's no obvious genetic advantage to being a lardarse.

[evilC]

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Wyatt Earp wrote:

evilC wrote:

Ummm... that's what I'm saying: there isn't one.

If there isn't a selective advantage, then we're not evolving in that direction, and that's pretty much that.

It's just happening!

Well, obesity is becoming more common, but not through changing gene frequencies. Firstly there hasn't been time, and secondly no-one's explained how this could possibly occur given that there's no obvious genetic advantage to being a lardarse.

Well, yeah - we seem to have come to a similar conclusion here (though apparently just through differing wording). However, when you say "If there isn't a selective advantage" I'm merely saying that there currently no longer has to be an advantage to it, due to our 'cushy' conditions.

I agree it's not genetic yet, but don't you think that it could become so if these current socio-economic conditions persisted for another three or four centuries or so? Of course, that is extremely unlikely to happen. (I happen to think - as stated on other threads - that Capitalism has pretty much peaked in the last 30 years and is now about to crash and burn.) Given that that would drastically change the socio-economic conditions, I don't think the changes we have seen in the last hundred years will get to become genetically 'popular'.

[Ginger Yellow]

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If there isn't a selective advantage, then we're not evolving in that direction, and that's pretty much that.

I don't think we can be so definitive, but it makes it much more unlikely. And certainly "in that direction" would be an inappropriate description.

evilC: you seem to be arguing something dangerously close to Lamarckism, which I'm not sure is your intent. On a more charitable reading, you could be arguing that, to the extent that genetics plays a part in obesity, the environment is more favourable to genetic drift that would increase it than in the past. Even if that is the case, it's a pretty weak claim and the timescales are all wrong.

[Ginger Yellow]

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On that latter point, there are some excellent simple demonstration videos on Youtube which show how long it takes to spread a trait through a population under different selection pressures (bear in mind we're not talking about genetic drift here, which is by definition neutral). In human generation terms, it would take much, much longer to spread even a strongly adaptive trait than a few centuries.

Edit: This guy produces some of the best videos of selection simulations, though he covers more than just evolution.

[Wyatt Earp]

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As ever, I think Gould is a little sloppy there. I like, and have always liked, his central point, that apocalyptic catastrophes are so different from normal times that what's "fit" in normal circumstances tells us nothing about what traits will help with survival when the meteor hits or we get runaway climate change or whatever.

However, a few things. First, he seems to be rather assuming that the "large body size" niches that the mammals failed to radiate into when the dinosaurs were around were in some sense "desirable" or "best", as opposed to simply being "already taken". Secondly, it presumably wouldn't have mattered if the mammals had colonised those niches, as long as they hadn't at the same time abandoned the "small body size" ones--which they never have, so presumably wouldn't have.

Finally (and I've always thought this): isn't his emphasis on the role of catastrophic chance in competition between lineages at odds with his idea that "higher level species sorting" can be a constructive process in evolution? You can't construct anything if meteors keep breaking it.

[Wyatt Earp]

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I agree it's not genetic yet, but don't you think that it could become so if these current socio-economic conditions persisted for another three or four centuries or so?

I'm still not following you. How would this happen? Through drift?

Are you saying, in effect, that a tendency to obesity used to be selected against, but now isn't, so can enter the population through drift? If so, how was it selected against in the past? How could it have been, when people weren't able to become obese in the first place?

How do you answer my point that if a tendency to run to fat has ever been selected against, this can only have been when this tendency has been able to be widely expressed as a physical trait: that is, recently?

[evilC]

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Ginger Yellow wrote:

evilC: you seem to be arguing something dangerously close to Lamarckism, which I'm not sure is your intent. On a more charitable reading, you could be arguing that, to the extent that genetics plays a part in obesity, the environment is more favourable to genetic drift that would increase it than in the past. Even if that is the case, it's a pretty weak claim and the timescales are all wrong.

Yes, that's it - the last point. (I don't even know what Lamarckism is! I'll go and look it up, though.) However, as you say, the timescales are way too short for real evolutionary forces to kick in. I didn't realise that a few centuries wouldn't be long enough for tendencies to begin to show, though! After all, height has increased so rapidly over the last few centuries. By the way - what is the driving force behind that change?

It's interesting, by contrast, how humans have managed to seriously change the appearance of dogs and cats in just a couple of centuries, using selective breeding. (What is lesser known is that genetic make-up of dogs within breeds varies wildly, so that totally different breeds can have more in common that two dogs within the same breed. But that's another topic entirely.)

[Ginger Yellow]

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However, a few things. First, he seems to be rather assuming that the "large body size" niches that the mammals failed to radiate into when the dinosaurs were around were in some sense "desirable" or "best", as opposed to simply being "already taken". Secondly, it presumably wouldn't have mattered if the mammals had colonised those niches, as long as they hadn't at the same time abandoned the "small body size" ones--which they never have, so presumably wouldn't have.

I don't think he is assuming that at all. He's just counteracting the argument that mammals won out because they were objectively superior. And as for your second point, again, I'm not sure that you disagree with him. He's just saying that mammals happened to occupy those "small size" niches, while dinosaurs occupied the "large size" ones, and things in the "small size" niches survived the extinction event better.

That said, studies of island populations seems to suggest there is an optimum body size absent predators, which is larger than Cretaceous mammals tended to be.

[Bruno]

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How do you answer my point that if a tendency to run to fat has ever been selected against, this can only have been when this tendency has been able to be widely expressed as a physical trait: that is, recently?

Could not the tendency to become fatter (i.e. relatively) have been selected against, which wouldn't have required anyone ultimately running to fat?

[Ginger Yellow]

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Yes, that's it - the last point. (I don't even know what Lamarckism is! I'll go and look it up, though.) However, as you say, the timescales are way too short for real evolutionary forces to kick in. I didn't realise that a few centuries wouldn't be long enough for tendencies to begin to show, though! After all, height has increased so rapidly over the last few centuries. By the way - what is the driving force behind that change?

I haven't really looked at the evidence on that, so I'll leave it to others. But there are pretty obvious reproductive advantages to height (so long as the body can support it), which means we're not talking about genetic drift. Also, natural selection can have a strong effect on single variables in relatively short timescales (the classic example being beak size in Galapagos finches).

As Wyatt says, if anything a tendency toward obesity is probably much more strongly selected against now than it ever was before, for both cultural and phenotypic expression reasons.