That’s nice, but all animals have extensive and complex mechanisms to regulate all aspects of metabolism that have evolved over millions of years, including a specific mechanism to regulate appetite that has been mentioned in the thread. When a similar comment to yours was made upthread, I asked what plausible grounds there were to believe that the mutations necessary to evolve mechanisms to limit obesity would not have been available for natural selection to act on, if natural selection favored them? I received no answer. Do you have one?
In every thread about evolution, there always seem to be half a dozen posts where people trot out “common fallacies about evolution that I know because I read a Richard Dawkins book” without bothering to examine whether those fallacies are actually in evidence in any of the other posts in the thread, or whether they are relevant to what’s being discussed.
But the existence of people who are 1000+lbs in certain extreme environments does not refute the existence of any innate mechanism to regulate obesity in more “normal” environments. That would be like saying that if someone is stabbed and bleeds out, that refutes the existence of an innate blood clotting mechanism.
The fact that there are obviously a vast number of obese people in the modern world allows one of two possibilities:
(a) there was just no significant fitness advantage to the regulation of obesity at all in the ancestral environment, and we have no innate mechanism to limit obesity;
(b) we evolved some kind of obesity-limiting mechanism, but it was not “tight” regulation, and it clearly does not work well in the modern environment.
In one sense this is a distinction without a difference. Everything innate is environment-dependent. It is meaningless to say that an innate capacity exists if the environment in which the phenotype would be realized no longer exists.
However, there obviously is another important sense in which we should try to distinguish between the two possibilities. If it turns out that there’s something straightforward that we could change about the modern environment (some aspect of diet or exercise) that would “re-engage” an innate mechanism for obesity regulation, that could be very important.
Again, people keep repeating this from the hitlist of “evolutionary fallacies I have heard of” without making any plausible case for the fact that it is relevant here.
If you are so obese at the age of 25 that you cannot forage for food or defend yourself against competing humans or predators, natural selection will certainly take place. And people past child-bearing age are not irrelevant to evolution. If a grandparent is sufficiently fit and moblie to care for the grandchildren who bear their genes and help those grandchildren survive, that can be a significant fitness advantage.
I don’t know if natural selection did in fact favor the evolution of any obesity-limiting mechanism in the ancestral environment. But the trite manner in which people are dismissing the possibility is wrong. There are perfectly plausible reasons that such a mechanism could have evolved.
I am not claiming that it necessarily happened. I am simply pointing out that the reasons people have given for dismissing the possibility are inadequate. There are perfectly plausibly reasons for selection against obesity - at all ages - in the ancestral environment. You ignored the second part of my post. A non-obese grandparent who can effectively care for their grandchildren may have a significant fitness advantage.
Largely, but perhaps not entirely. There’s a whole “grandmother” hypothesis trying to explain why women go through menopause. There’s an obvious advantage to having grannies around to care for the grandbabies, and it may be enough of an advantage to impact evolution.
It only happens now with extreme rarity even though there are more humans on earth than ever before. That is pretty strong evidence that it never occurred in significant numbers that it might play an evolutionary role. Do you have any evidence at all to the contrary?
If one were to dismiss grandparents, why not dismiss all males at all ages past the point of insemination? Is limitation of Male Parental Investment though obesity irrelevant to fitness? Why not dismiss the physical capabilites of the mother after she has given birth?
The idea that natural selection would do no better than “get as fat as possible if enough food is available” seems implausible to me.
IF obesity was a significant evolutionary disadvantage AND there existed an environment in our past where obesity was commonplace AND our genes/mutation provided a mechanism to regulate our appetites when it occurred THAT DIDN’T have adverse evolutionary effects in more normal times I see no reason to believe it couldn’t occur. But I can say that about virtually any trait, no?
You’ve described the necessary conditions for any evolution by natural selection to take place, yes. So what? If you think one of those conditions was obviously not fulfilled in the ancestral environment, make your case. I don’t think anyone has made it in a convincing way.
Certainly the idea that mutations were not available (as you suggested early in the thread) as a substrate for natural selection is highly implausible. We have complex regulatory mechanisms for all aspects of metabolism. We do have a mechanism for the regulation of appetite. And the quantitative tweaking of existing regulatory mechanisms is one of the easiest things to evolve if natural selection favors it.
It’s also ridiculous to claim that there was no plausible selective advantage to not being obese in the ancestral enviroment. The advantage is obvious, at all ages, and all ages are relevant. It’s a question of how natural selection weighed the advantage of superior mobility & strength against a superior capacity to survive famine through stored fat.
I think the most plausible expectation (which fits the evidence of modern humans) is that we have some degree of regulation of obesity, but it was never tight regulation because frequent food shortage always mitigated against strict limitation, and what regulatory mechanisms we have are especially ineffective in the modern environment. But I certainly think it’s unlikely that the best evolution came up with was “accumulate fat without limit if enough food is available”.
Mothers nurse their babies, and men have been known to father children well into old age, so we have direct evolutionary pressure for women to stay alive at least until their youngest is weaned, and for men as long as they can still impregnate a woman. But what’s interesting about the grandmother hypothesis of menopause is that it posits that women lose reproductive capacity in order to care for their children’s children. If true, that’s a much stronger argument against the idea that evolution doesn’t care about you once you can no longer reproduce.
Yes, active selection for menopause is certainly interesting. But you’re talking about a much more sophisticated idea when people are dismissing the potential obesity and loss of physical mobility and capabilities of anyone who contributes to the survival of offspring as irrelevant to fitness.
And what do you think might explain that? A regulatory mechanism that limits obesity in 25-year-olds that evolved through natural selection against obese 25-year-olds in the ancestral environment, perhaps?
Yeah, I simply have to disagree. IMHO Occam’s Razor very clearly suggests that it just isn’t that plausible. To dismiss arguments that the widespread caloric excess and sedentary habit needed to have a serious evolutionary impact was very unlikely to be present that early in human or proto-human history is…hmmm…dismissive .
I think you’re being too stubborn on this one. Clearly no powerful inhibiting mechanism exists. And even the possibility that widespread excess calories at the population level necessary to inhibit successful reproduction of a large enough cohort of the population, at a young enough age to be meaningful, at an early enough stage of human evolutionary development, just seems wildly unlikely. I mean, like, incredibly unlikely.
Leave off the 25 year-old part, and consider instead any animal we evolved from might have developed such a mechanism in very different circumstances. But the lack of need by humans, and probably any other animal is still apparent.
I think Chronos’ concept of equilibrium is close to the mark. We probably have regulatory mechanisms whose purpose is to keep us in fit condition and not anywhere near a state of uncontrollable obesity under typical circumstances. Once weight overloads those mechanisms in improbable circumstances there’s not some emergency bypass system that will engage because that happens so rarely that none would have developed.
But to what extent does this happen in the wild? There are plenty of food surpluses in the wild, too.
Again, the fact that animals can get extremely obese under unusual artificial circumstances does not refute the possibility that they have regulatory mechanisms that operate under more “normal” conditions. It’s quite possible, for example, that an appetite regulation “module” depends on input from the way the body behaves under physical exertion, an input that is completely absent in many domestic pets, just as it is for most obese humans.
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