The bulk of hominin evolution occurred close enough to the equator that arguments for the seasonality of fat storage seem tenuous at best. The simple fact of it is that wild humans are not able to consistently overshoot TDEE with energy intake. Look at every thing you ingested yesterday and consider how much more energy it would have taken if you had to do everything involved in hunting down the animal(s), digging up the tubers, gathering this and that...walking to a waterhole. It all adds up to a lot of energy.

Because our general satiety signals are based on a particular food volume threshold, we're going to struggle to remain lean if we eat pretty much anything evolutionarily consistent while sitting on our asses.

The beauty of living in a modern society, with modern healthcare, ample food, and it's relative "safety" (when's the last time you had a rib broken during a poorly-planned mastodon hunt?) means that we suffer significantly less physical stressors.

In my own weightloss journey, I've found that physical stressors (overtraining, under-sleeping) are just as (if not more) detrimental to fat-loss goals than even binging.

What does that mean to the OP?

Hunter-Gatherers have been, and are stressed. Bacteria, illness, injury, feast/famine, predators, all play into the stresses they have, and we as modern humans only endure on a moderate-to-nonexistent level (generally). I know this is quite contrary to the Paleo authors that romanticize the virtues of being a re-enactor but it only takes about 4-hours of Nat Geo specials on Malaria or parasites to prove them wrong. During times of stress at a hormonal level, your body will store fat regardless of what you eat.

The combination of putting our hormones into a state where we are not stressed (eating adequately, sleeping appropriately, exercising appropriately) and eating an ancestral diet, result in an optimization of body weight (the skinny gain mass, the fat lose it). This is consistent with an evolutionary survival standpoint. People who are dangerously skinny won't have the constitution to withstand the rigors of survival, and people who are obese will not be able to keep up with evolution to hunt, kill, and eat.

Introduce severe physical stressors to even the most staunch paleo dieter, and he/she will retain fat and water. The amount of tolerated stressors will be higher, and the recovery will be quicker, but it will still happen.

In short - It's not simply "what you eat", but "how you live" that determines how and when you retain fat.

I always thought tracking, working in groups and with tools were more important survival skills than running. You would never get that fat in the wild either since you had to either hunt or gather your food which is a lot more work than going to a store.

From an evolutionary perspective, the ability to gain weight when food is plentiful is a survival trait. It is necessary to stay alive in circumstances where food isn't always plentiful and readily available, i.e., nature.

I disagree with the premise that storing excess fat had survival benefits. Excess fat impacted man's most important survival ability--running.

You know the old joke "I don't have to out run the bear, I just have to out run you" has some truth in it. The slowest animal in a herd or pack is always the one that gets picked off by predators. In early humans, the fat guy would be the slowest one.

Early humans were known to hunt in packs. A fat human would have had a difficult time keeping up with the rest of the hunting group. This would have put the fat human at a survival disadvantage also.

Also, the fact that we have a mechanism to regulate our body fat (leptin) would suggest that we're supposed to maintain a specific level of fat, not put on unlimited amounts of fat.

The logic of your argument lies in applying universal quantities to the premises but in reality it is only reasonable to apply particular quantities as in; "all foods that are incongruent with our evolutionary past are foods that cause us to eat excessively and become fat" rather than "some foods that are incongruent with our evolutionary past are foods that cause us to eat excessively and become fat."

If we take the first statement, the "all foods..." and assume that it is true then the contradictory statement must be false, i.e.-"some foods that are incongruent with our evolutionary past are not foods that cause us to eat excessively and become fat." But if we can think of at least one food that is incongruent with our evolutionary past that does not cause excessive eating and fatness, then this argument is disproven. I'll let you decide if there is at least one neolithic food that fit's that description.

However if we examine the particular quantity version of the argument, "some foods..." and assume that it is true then the contradictory statement must be false, i.e.-"no foods that are incongruent with our evolutionary past are foods that cause us to eat excessively and become fat." But as in your second paragraph we know that it is likely that the statement is false, also Melissa HGL's answer concurs. So the bottom line is this; we can't think in black and white. Much of what we are talking about has to do with what is most likely to occur, not what will always occur. If you stick around this community for awhile then you'll find that a consensus on low-carb does not exist.

Consider as well that if the human body was optimized for a particular level of macronutrients then a dramatic change in both total amount and availability of all macronutrients and also an increase in macronutrients which were scarce could have a dramatic change in effect. Also consider that a person of say 150 pounds who is at 10% body fat would have 15 pounds of fat, at about 3500 calories per pound that person may only burn 1/15 of their fat completing the equivalent of a marathon. While fat storage for lean times may be necessary the levels of fat storage we see today likely exceed the point of diminishing returns.

Building 20lbs or so of fat during summer is a survival trait. Becoming morbidly obese is not.

There's no debate over the body's ability to store dietary fat. The point usually made though is that it is self-regulating. You can only eat so much fat and protein before your (healthy) body screams at you to stop. But your body will happily store more fat than many would like, and if you never stop eating then it's never going to be used and can start to cause problems. And many do seem to still struggle on 'paleo' because they're still eating in abundance and not eating 'natural' foods. Still, there's a good deal more to health than bodyfat percentage. And there's a big difference between an extra spoon of coconut oil and the kinds of modern 'foods' being promoted by the industry.

Yes, we are optimized to store fat at certain points, that's why you will find plenty of pictures of foraging people with some fat on them, particularly women. But it was often seasonal and not enough fat to be pathological.

But if you want to be permanently thin on a paleo, yes, you are going to have to override the natural inclination to gorge sometimes.

And the idea that carbs cause weight gain because they are carbs or that they were scarce in the Paleolithic is not universally accepted here.