In the wild there are other factors that limit nutrition. When prey species are abundant, predators’ reproductive efficiency increases. Increase in the predator population then leads to a decrease in the prey population.
Disease also plays a role in the wild. When raccoon population goes up, the increased raccoon density leads to more disease transmission (such as rabies).
Well, consider prey species. Antelope, for example. Any antelope that gets fat and loses the ability to run fast would immediately be caught and eaten. One could hardly imagine stronger natural selection, so although I don’t know the technical physiological details it’s obvious that antelope must have tight regulatory mechanisms that limit the amount of body fat they will accumulate, even when food is abundant.
So it’s hardly as though such mechanisms are always implausible or difficult to evolve. For an antelope it’s abundantly clear that the fitness advantage from mobility vastly outweighs any advantage to be gained through fat storage to survive famine. For other animals the fitness tradeoff between “superior mobility” vs “famine survival” will be less clear-cut.
But again, for any species I’m highly skeptical that the best evolution can do is “continue eating and accumulate fat without limit if there is a food surplus”. I think for some species optimum fitness might be a lot of body fat, but I doubt that it is completely unregulated.
There are many environmental factors which would limit weight gain of a primitive person regardless of how much they wanted to eat. If they have to climb, walk, run, etc. to get food, putting on too much weight will limit how much food they can acquire because those activities get more difficult. Plus, they burn calories, and burn more calories the heavier they are, so the activity itself would help to counteract putting on excessive fat. If someone wanted to eat an unlimited amount, that would likely mean they’d have to move constantly. Most people want to sit around and relax rather than scour the land for food, so just from a behavioral standpoint primitive people likely wouldn’t make the effort to eat unlimited amounts of food.
Not a great example. Antelope are herbivores. They eat fairly constantly, but their diet is not nutrient dense. They’ve evolved the ability to digest grasses, but the only way they could over consume would be if there was a complete lack of predation.
Prehistoric peoples created art depicting obese women, so that morphology was not unknown to them. Anthropologists are unsure what these so-called Venus figures represent, so it’s hard to generalize their significance, but many examples have been found.
Come on, have you ever seen a cow?
The reason antelope are slim and agile is because they have evolved to become slim and agile to evade predators, not because there is no such thing as a fat herbivore.
I have.
Your point?
ETA: a cow’s conformation allows for a rumen, reticulum, omasum, and abomasum, along with an enlarged cecum to extract nutrients from grasses. Cows are not obese.
Horses utilize a huge cecum to get the same end result.
But they are very large, which refutes your supposition insufficent calories are available from a herbivore diet to gain weight, even when food is abundant. Buffalo are similar, and are perhaps more relevant, since they share an environment with antelope. The point is that the predator evasion strategy of an antelope is solely to run, which strongly precludes excess body fat, and they undoubtedly have tight regulatory mechanisms that limit the accumulation of body fat even when food is abundant.
As have I. They’re big, and stocky, but not necessarily fat.
Domestic cows (particularly those destined for meat production) have been specifically bred for efficient weight gain. Most of them don’t only eat grass, as well – their diets will be supplemented by other, more nutritious grains (barley, oats, soy, etc.), as well as nutritional supplements.
“Grass-fed beef,” on the other hand, comes from cows which are largely, if not entirely, only eating grass; their meat tends to be leaner, and they tend to take longer to mature.
What “tight regulatory mechanisms” do they have? Food is abundant. They spend all their time grazing, sleeping, observing for predators.
Most nutritionists believe in the calorie theory. If you eat more energy, you store more energy - a calorie from any source is a calorie. Although there is another theory, often said to be discredited but not really adequately studied, called the insulin theory of nutrition. This posits that eating too many carbohydrates makes you fat, and the fatter you get the hungrier you get.
In any case, your body was made, over thousands of years where food was not always available, to use whatever resources it could glean. It is very difficult to lose weight and keep it off - there is a reason diet companies do not publish their data. Your body was built with setpoints to try to keep weight once acquired. The problem is not necessarily too much weight but rather too little activity. Being fit and fat is associated with better health than being slimmer but sedentary.
I’m suggesting any evidence for or against a weight control mechanism may be found in other animals besides humans. I have no idea whether there is anything to find or any need for it. But I think it is more likely not so specific, just part of the many mechanisms that keep an animal healthy. Tests in the lab might be able to determine if any animal will would tend eat without limit when there is a food surplus, but I don’t see that those circumstances arise in nature often enough to evolve a specific weight control mechanism for that purpose.
Perhaps you should clarify what hypothesis you are proposing. That antelope are only slim and agile with little body fat because of the limitations of their diet, and natural selection through predation has nothing to do with it?
I offer no hypothesis, was merely pointing out flaws in your suggestions.
What flaw, exactly? You said:
And yet they are never fat.
What more elementary textbook example of natural selection is there than the fact that any antelope with a tendency to chubbiness got eaten millions of years ago and had no descendants?
I’m honestly scratching my head that everyone now seems reluctant to concede that any mechanism to regulate body fat could ever exist in nature, even in antelope where mobility is so obviously crucial to survival.
I don’t know about this. If, for an example, someone lived to their late 40s in a world where everyone dies in their late twenties, they would have double the chance of producing viable offspring. Therefore, anything that helps humans to live in the long-term would be more likely to pass on their genes than someone who does not.
That’s not an alternate theory. That’s one possible explanation for why people have increased their calorie consumption and therefore gotten fat. Really, there are probably many such mechanisms at work.
It seems obvious that in the absence of physical limits on food intake (including factors like an herbivore’s ability to digest food at some rate), the only relevant factor is appetite. At least in my anecdotal observation, appetite is an extremely powerful motivator and one of the most significant inputs to a person’s mood. I’ve seen no reason to believe that most people deviate more than a tiny amount from what their appetite tells them to eat.
But the body can’t count calories, either. It has to work indirectly. If food has gotten much more calorie dense, or the mix of macronutrients has changed, or there is some other factor that the body has depended on to determine how much you have eaten–then the appetite response will be broken, and the person will end up at a different weight equilibrium.
We could certainly test the hypothesis. Maybe it’s been done already. Take a wild antelope and feed it one of the super calorie-dense diets used for fattening cows (which often includes pure sugar). If the antelope gets fat, then maybe it doesn’t need a feedback mechanism because the natural limits are enough. If it proves impossible to fatten up, then perhaps there is such a mechanism.
We could run the experiment on cheetahs as well…
Well, no. Forcing a system into dysregulation by artifical means does not prove that there is no regulatory mechanism in the relevant environment. Again, that’s like stabbing someone and watching them bleed out and then claiming that proves we have no blood clotting mechanism.
We might well predict that it would be more difficult to force an antelope to accumulate fat than an animal that does not rely solely on mobility to evade predation.
Perhaps not, but your contention was that antelope and other prey animals must have an extremely strong feedback mechanism, so one would hope that’s easily discernible when looking at a spectrum of possible diets. If an antelope can’t physically eat enough to get fat on a wild diet, there’s no need for strong feedback and in any case you’d need to look elsewhere to figure out if such a mechanism exists.
I essentially agree with your hypothesis, though; that something in the modern world has screwed up our appetite response, and as a result people eat more calories than is warranted and end up at a new, much higher, weight equilibrium. It may never have been a strong factor since there are also physical effects that limit weight, but clearly the fact that we have an appetite at all means there is some type of regulation at play.