This never really made sense to me. If being extremely overweight is so unhealthy, why do our bodies store way more fat than what is helpful in regards to survival?
Oh boy, a question I’ve asked myself more than once.
My guess, if allowed in FQ, is that for hundreds of thousands of years of human and pre-human evolution the problem was getting enough food to eat, not eating too much. Natural selection favored those who were better equipped to hold onto fat in good months because they did better in lean months. There was absolutely no natural selection pressure for the body to develop a ‘fat governor’ system because chronic overeating was just not a problem until relatively recently in human history.
yes, that.
For millenias, the main problem was to find enough food. When you had the chance, you made grease for it was certain that would not last. Think of bears: they pull up 400 pounds of reserve before winter, and use it. Our ancestors were using the same trick. But in an abundance that last, that’s a trick that lead to health problems. May be we will evolve to adapt but that takes hundred of years…
As others have suggested, this may just be a false premise in the ancestral environment in which we evolved. Evolution is slow relative to the speed of the emergence and development of human civilization. We haven’t changed much since we developed agriculture.
But it’s not necessarily a false premise. It seems to me that there should have been some circumstances where a mechanism to limit obesity would have been favored, and it strikes me that it would have been quite easy to evolve such a mechanism - simple loss of appetite when we reach a certain weight. So another possibility is that we do have such an obesity-limiting mechanism, but our “appetite module” is dysfunctional because of our inactive modern lifestyle and the types of food we now eat.
Just a bit longer than that.
Evolution doesn’t work like that. Evolution works with the genes and mutations that are available, and with reproductive success. And it takes time.
There has been a little bit of adaptation in this direction. If you look at Polynesian people vs. Europeans, for example–a group with a long and recent history of facing food shortages, vs a group where food supplies have been much more stable for the last few thousand years, you’ll see that the Polynesians have a much stronger natural propensity toward obesity.
What do you mean by this? Why would mutations not have been available to allow the evolution of mechanisms to limit obesity?
It’s not that the mutations wouldn’t be available. It’s just that the conditions that make them reproductively advantageous wouldn’t occur naturally.
A mutation only becomes a trait when the conditions give the mutation a discernable situational advantage. So an anti-overweight mutation would only propoagate when the environment makes being overweight a recurring situation which puts the unaffected at a fitness advantage. Like, millennia of naturally-occuring calorie-dense junk food year-round, or an environmental condition that makes being overweight a reproduction-preventing condition (rapidly deadly before reproductive maturity, or directly affecting fertility).
The obesity-limiting mechanism was being too heavy and slow, for predators to catch prey and for prey to escape predators.
That’s not an obesity-limiting mechanism. That’s the definition of natural selection for a population to evolve an obesity-limiting mechanism. Which underlines OP’s question - why did such a mechanism apparently not evolve?
Well, that’s my point. Both things are required for a trait to evolve - a substrate of genetic variation for selection to act on, and the natural selection itself.
I was asking @Telemark why they thought insufficient variation was a factor. That does not seem likely to me - there is a wide variation in genetic susceptibility to obesity in modern humans, and there are many plausible and straightforward mechanisms for a weight-limiting trait if it’s favored by selection (such as simple loss of appetite).
Well at least for predators they went hungry until they dropped the flab. As for prey maybe increased need for exertion led to a homeostasis around the optimum weight?
As I said, it seems quite plausible to me that we do have an obesity-limiting mechanism, perhaps one that operates by reducing appetite, but that it’s just dysfunctional with the modern lifestyle. If the behavior of the body under exertion is an input into the “appetite module”, and we do not ever exert ourselves, we might expect it to be dysfunctional.
People who exercise regularly are much less likely to become obese. Obviously they are burning more calories - but it may also be that their appetite regulation is working as intended.
Evolutionary traits, however simple, don’t emerge unless they confer an advantage. The time period where humans have been able to overeat is a blink of an eye in evolutionary terms, so here was no reason that the ability to limit obesity would be favored. Quite the opposite in fact— if you had a gene that didn’t allow you to put on fat in months of abundance, you and your genes likely died off in the lean winter months.
Maybe we will eventually evolve in such a way that obesity is limited.
Of course not. And we have been describing exactly what that advantage would have been. You can’t operate effectively whether as predator, prey or forager if you are obese.
I don’t think you can take it for granted that this is true. There were almost certainly some situations in the ancestral environment where there was a temporary surplus of food for long enough to become obese, and you don’t want to store so much fat that you cannot move.
I think food surpluses have in the early years of human evolution been much more rare than food deficit. The ability to hold onto whatever extra calories one could scrounge and store it as a few lbs of fat was a net positive, not a negative.
It’s like asking “why haven’t we evolved to not get cancer?”. It’s because cancer is primarily an old person’s disease that occurs after child bearing and rearing years. There’s no selection pressure to evolve to not get cancer.
No, it’s not - because although storing calories as fat is beneficial, there is also clearly an advantage to not being so fat that you have such limited mobility that you cannot evade predators or defend yourself against other humans, or so that you die of a heart attack at age 30. And you cannot just assume that optimal fitness was achieved in the ancestral environment by storing calories without limit and ignoring those other factors.
Other animals in the wild certainly put on weight when calories are available. Are you suggesting that they do so without limit if food is abundant? Bears can get pretty fat if they have the opportunity, but do they ever become so fat that they cannot walk to their winter den?
I think it’s quite implausible that the we have NO innate mechanism to limit obesity at some level. It seems far more likely to me that whatever mechanisms that we do have are dysfunctional in modern humans because of our lifestyle and specific diet.
I think you’re the one making the shaky assumption— that our Paleolithic ancestors ever found themselves in a long-term food surplus situation to the point they may have been getting too chubby to go out and hunt for yet more food. The very effort to hunt and gather the food burned a lot of calories. The very fact that we haven’t revolved a fat limiting system I think points away from your argument.
They may simply not have occurred. Just because a mechanism is desirable or advantageous doesn’t mean that it has to appear.
Also i think you are greatly overstating how often an anti-obesity mechanism would have been iseful in human history. If it is that plausible you’d think it would have shown up in other species who have dramatic feast or famine cycles. Does it?