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In the world I am building I wanted to design a race on a planet which get more full the more calories they eat and then stopping when they have had their daily caloric requirement. I have an idea's on how they would do it physically (sample parts of the food going down their esophagus equivalent and estimating on the amount going to the stomach).

The problem I have is why this race would create this evolutionary tactic in their hunter/gatherer phase. If you find a bunch of berries you would eat as many as you can fit in the stomach, store excess calories as fat, and take the rest back to village for later.

I usually try to find a corollary examples for races I make from earth and I try to be at least a semi-hard on science as to why races are the way they are.

Any ideas would be nice.

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    $\begingroup$ I don't know that they would in their hunter-gatherer phase. Like you said, hunter-gatherer societies typically try to build up stores of food and energy because of how limited food supplies can be. I don't know that you would necessarily see this kind of behavior as an evolutionary trait either. Monitoring caloric intake is useful in modern human societies because of how much excess food we have that's high in sugars, salts, and fats. We're hard-wired to like those things, and so are many of our animal friends because we can store those nutrients for later. (1/2) $\endgroup$ – Pleiades Oct 11 '17 at 23:25
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    $\begingroup$ Early civilizations don't have constant or stable food supplies year-round, which means caloric intake is going to fluctuate anyway. When intakes are lower, that's when you fall back on your reserves to survive through until spring. In other words, I can't really see how this would come about so early unless your race has a constant, stable food supply, which isn't typical of hunter-gatherer societies at all. (2/2) $\endgroup$ – Pleiades Oct 11 '17 at 23:26
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    $\begingroup$ Also, we don't have a daily caloric requirement. We survive on a vast range of caloric intakes, from starvation in the 800 Calorie range up to Michael Phelps consuming 8,000 to 10,000 Calories a day before the Beijing Olympics. The body doesn't have a hard and fast input. It takes what it can get, and modifies how much effort it expends in response. $\endgroup$ – Cort Ammon - Reinstate Monica Oct 11 '17 at 23:37
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    $\begingroup$ We do, however, sample the food's content. We do so with our eyes and with our nose. Our brain puts together a remarkably good model of the content of each meal before we even take a bite. $\endgroup$ – Cort Ammon - Reinstate Monica Oct 11 '17 at 23:38
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    $\begingroup$ humans do this: foodpsychology.cornell.edu/research/… $\endgroup$ – Rick Oct 12 '17 at 16:28
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Your race evolves under circumstances where overconsumption of calories is common and potentially dangerous.

A parallel is seen with salt. Salt is delicious and we need it. But if it were purely delicious and an individual happened into a big pile of it, it would eat it all and get sick and possibly die.

High salt recruits aversive taste pathways Yuki Oka et al Nature 494, 472–475 (28 February 2013)

By contrast, salty taste is unique in that increasing salt concentration fundamentally transforms an innately appetitive stimulus into a powerfully aversive one. This appetitive–aversive balance helps to maintain appropriate salt consumption and represents an important part of fluid and electrolyte homeostasis.

Suppose overindulgence in calories happens often, and there is an evolutionary price that outweighed the benefit of storing away calories for hard times ahead. What could that price be? Refeeding syndrome can happen to people in concentration camps - they are starving and then when they are given all the food they want, electrolyte levels crash and they get arrhythmias or stop breathing. Maybe your race is prone to something like that.

An alternate bitter receptor for high calorie (like for high salt) seems tricky. A different way to evolve stopping when you are full is to make the stomach smaller, like people who have stomach reduction surgery. Or just attribute their satiety to their genetics: the sensation of being full is evolutionarily flexible and under genetic control. https://www.gbhealthwatch.com/GND-Obesity-MC4R.php

One could make a case that humans are already set up as you specify - to stop eating when they are full - of fat. The obesity problem now is due to easy availability of carbohydrate calories, which make an end run around a mechanism that evolved in a time where the only way to eat an immense amount of calories was by eating animal fats. Ketogenic diets work in part because fats are filling in a way carbohydrates are not and people get full and stop eating.

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    $\begingroup$ Salt is a chemical substance. "Calories"are anything. I think for this to be viable you have to explain and constraint how that would work. I believe half way through your posting you realized the difficulty and stated it won't work, maybe delete it then? $\endgroup$ – Raditz_35 Oct 12 '17 at 2:11
  • $\begingroup$ Your last paragraph might be a way to explore, make carbohydrate calories naturally available, so there needs to be a mechanism to prevent the whole race from going full 'Murica $\endgroup$ – Nico Oct 12 '17 at 6:54
  • $\begingroup$ Actually, it can be shown that pretty much any single molecule on its own is not desirable - sugar tastes nice, but have you ever taken just a big spoon of it and eatten it? Salt is just another example. $\endgroup$ – UKMonkey Oct 12 '17 at 14:02
  • $\begingroup$ @Raditz_35 - salt is a single substance. Is bitter? Umami? A receptor pairs a molecule specific detector to a neural input molecule. Many different receptors can share the same neural input - hundreds of different substances are perceived as bitter. Is it such a stretch to think the top 20 molecules associated with calories could be tasted as calorie flavored? $\endgroup$ – Willk Oct 13 '17 at 2:30
  • $\begingroup$ @UKMonkey bad example - kids (including myself, when I was younger) actually do that and enjoy it ;) $\endgroup$ – Erik Oct 13 '17 at 7:54
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There is no known scientific rationale for what you want to happen. Living creatures do not have a "daily caloric requirement." Instead, they maintain their existence by adjusting their caloric output according to what they bring in. If you don't eat enough, you shut down less essential parts. While the US government may recommend 2,000 Calories/day, we can operate on far fewer. As we get near 1,200 Calories/day, our body starts to shift gears to conserve more and more energy. As we approach 500-800 Calories/day, our body will start to shut down bodily functions to preserve energy to support the lower regions of the brain. On the flip side, you have Michael Phelps, who ate 8,000 - 10,000 Calories/day before the Beijing Olympics. There, the vast majority of his caloric intake was expended in his practices.

This flexibility is incredibly important from an evolutionary perspective. Food supplies are never reliable. If you can't scale your output to match your input, you will die and be replaced by a species that can. There is no known species that doesn't engage in this sort of flexible operation. It's fundamental to how life as we know it functions.

To come up with a species that doesn't have this, one is going to have to reach well beyond realistic science. Consider the Octospiders from Clarke's Rendezvous with Rama. That species is a highly advanced species with many peculiar traits. One of them is that they have to be taught to recognize the feeling of hungry. Their babies are born with a truly blank slate, and one of the first tasks of the nursery technicians is to teach the babies to eat before they starve just sitting there.

In such an environment, one might have "daily caloric requirements" in the form of instructions dictated to you. You may consciously be aware of the food you eat and stop when you reach the level dictated by your society.

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  • $\begingroup$ Yes, but how much variation is there in a hunter/gatherer society? An athlete with 10k kcal a day is something that didn't even exist 50 years ago. And i dont think eating less has been specified as a problem, only more. However I agree that one needs to be careful with that premise. $\endgroup$ – Raditz_35 Oct 12 '17 at 2:15
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    $\begingroup$ @Raditz_35 There's definitely a fair bit of variation. Depending on the culture, we see a 200 calorie/day difference due to seasons (it takes more energy to keep warm in the winter). Also, consider the difference in caloric intake on a hunt vs. after the animal has been killed and must be eaten before it spoils. $\endgroup$ – Cort Ammon - Reinstate Monica Oct 12 '17 at 2:55
  • $\begingroup$ 200 is a lot less than the 9500 you implied. Depending on activity (leg workouts .. ) and the season, I am more hungry sometimes myself. I think we already have that mechanism, no need to worry about it. Btw I've heared such athletes talk about how one can still be hungry after 10k + just because they require so much energy $\endgroup$ – Raditz_35 Oct 12 '17 at 3:00
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    $\begingroup$ Living creatures do not have a "daily caloric requirement - The current thought is that this is, in fact, quite the case. There may be a daily caloric consumption and the relative contribution to where it's funneled to depends on your activity (if you exercise a lot, less is available to reproductive cycle, regenerating, fighting illness and so forth).Could you add your sources to the Olympic dietary intakes? $\endgroup$ – AliceD Oct 12 '17 at 10:27
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    $\begingroup$ @AliceD Source added! $\endgroup$ – Cort Ammon - Reinstate Monica Oct 12 '17 at 14:04
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What kills people?

On our world we have gone hungry fairly often, and starving still is a fact of life in many parts of the world. But if there has always been enough to eat something else would bother them.

Say like Eloi they had all the food they cared for always available, perhaps overeating or having excess fat would be a major problem.

If to escape predators they typically hide in tight places, there is some poison common in their environment that could accumulate in fat or the stable food supply wasn't fast replenishing and was easily damaged by over harvesting, limits of consumption may selected for.

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    $\begingroup$ I agree that evolutionary pressure has to be the driver. But I think one of your plausible scenarios, the poison accumulating in the fat, is less likely. They'd probably evolve a non-fat calorie storage mechanism, or would adapt to the poison, because low amounts of available food would still kill them. I like the other idea about predators and survival tactics to escape these. $\endgroup$ – CodeMonkey Oct 12 '17 at 13:33
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Body fat is a very efficient way to store extra calories on living creatures. Unfortunately there is not an equivalent procedure to storing water, This is interesting as water is just as important for life but it can actually kill some people when they over drink.

What if, we turn off the ability to store extra calories in the same way. All the sugars you eat would go right to the blood stream, thinning out your blood. The more your people eat the more "light headed" they would feel, as they wouldn't be getting enough oxygen.

The lack of oxygen would be a natural way for your species to know they are over eating. Unfortunately not having access to body fat would create a number of other issues.

You would also have thrill seekers who would eat to much high caloric foods just for the weight less feeling they get.

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This is not as hard as it seems.

Take away the evolutionary advantage of storing excess calories. One way to make sure that this evolutionary trait never developed is by making your species always having had an abundance of food. For example your species is rather small compared to many herbivore animals that they could effectively hunt (with poisoned spears). To top that off, maybe they have a good way to preserve this meat.

If food is pretty much guaranteed to be available at any time, but people still had to eat to survive, it would make sense that people would still enjoy food and have an evolutionary impulse to eat, but not to overeat, which in the end does weigh you down, is time-consuming and potentially harmful when food is spoiled.

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