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According to Jared Diamond's Guns, Germs and Steel (pp 125-126), the domestication of local grains (e.g. wheat, barley) and pulses (e.g. peas, lentils) lauched food production (farming) societies in many areas. Grain crops have the advantage of being fast-growning, high in carbohydrates and high yield per area cultivated. Their low protein is made up by pulses which are often >25% protein (e.g. soybeans has ~38%). This makes these two types a good combination. The author proceeded to list many parallel combination of grains (or cereals) and pulses in many early farming communities:

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My question is, given their lack of knowledge about biochemistry, how did these societies learn about the advantage of pulses' protein contents and the importance of balanced carbohydrate-protein diet? Or did they unconsciously do it, for example were there some evolutionary/selection process that caused people who consumed balanced diet to survive and produce more offstring? If so, what made this combination invariably "win" in many areas?

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    Protein content and balanced carbohydrates are merely words we attach to successful strategies. Societies that employ successful dietary strategies succeed. Groups of people who center their diet on cotton candy and soda (or their contemporary equivalents) aren't healthy enough to form a successful society. One doesn't need to understand theory to succeed. – Mark C. Wallace Jun 28 '14 at 20:08
  • @MarkC.Wallace good point, thanks. Edited the question – user69715 Jun 28 '14 at 21:02
  • Here's an experiment that many graduate Life Sciences students are asked to attempt: Try going a mere 72 hours eating only one food group of Protein, Carbohydrates, Dairy and Vegetables/fruits. Stick strictly to the regime, so no mustard or bun with a hot dog, no cheese, anchovies or pepperoni with your pizza, etc. If you are not starting to feel quite ill by 72 hours you were cheating somewhere. As a society we have lost touch with many of our body's most basic signals, and it is really not so difficult to figure out what is necessary to live healthily. – Pieter Geerkens Jul 1 '14 at 15:48
  • @PieterGeerkens but what about Mongols, Inuit, Hawaii islanders ..etc were all these people all able to get a varied diet? I feel like the Inuit really only have access to meat – Hao S Sep 4 '18 at 2:31
  • @HaoSun: Meat is both protein and fat, unless your butcher has over-trimmed it. My comment above mistakenly had Dairy where it should have had Fat. – Pieter Geerkens Sep 4 '18 at 9:50
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What made you think they know about the protein content? Evolutionary pressures would have drove humans to develop instincts for foods that contain the nutrition we need to survive (i.e., cravings). There is also a common human preference for diversity. Those factors alone would have pushed early civilisation into cultivating multiple crops.

Additionally, as MarkC.Wallace points out, societies which adopted a good diet would have been better equipped for success than those who didn't. Now, cultivation of pea and lentil seemed to have begun at the advent of human agriculture in the old world. The evidence points to a tradition of human hunter and gatherers living off food including pulses, before farmer societies came about.

That is to say, those tribes that did not feed off both staple carbohydrates and high protein pulses (and others) was out competed by those who did. As the successful tribes learnt to start growing their food, they would have begun by growing the food they already ate. Hence the farming societies "knowing" about eating pulses.

  • "What made you think they know about the protein content?" Well, we do have a taste receptor for protein. And this seems to be evolutionary very old (as in: "invented" before fish came to land). Please see my answer for more along these lines. Also, very roughly at the same time they started to grow another type of food they were already eating: meat and eggs. – cbeleites Aug 8 at 19:40
  • @cbeleites That's exaclty what I said in the next sentence though. My point was that they didn't need to explicitly know about protein for the evolutionary instinct to work - since OP was asking how they knew this without biology and chemistry. – Semaphore Aug 8 at 21:36
  • Sorry if I was ambiguous. (You do have my upvote, btw) What I try to say in addition to what you said is to say more specifically "your" instinct is actually a rather precise and accurate sensing of protein intake (in that sense we do know the protein content, just not consciously - but that's in no way necessary for reflecting that as pulses are good to eat and therefore worth while trying to cultivate) and that that ability is not part of the neolithic revolution but much older. – cbeleites Aug 8 at 21:56
  • It's all evolution. People ate things that tasted good and those which were traditional. Nutritious foods become traditional, because people who eat them tend to reproduce more. Biological evolution leads to good tasting stuff, and social evolution leads to good traditional stuff. – Mark Olson Aug 9 at 2:07
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Summary: we do have evolutionary very old taste receptors that detect proteins, and we probably have rather well regulated protein intake. Knowing that this is protein is not necessary to achieve this.

OTOH, while grains + pulses are good protein sources, of course meat, fish, eggs and later on milk are even better sources of protein (higher protein content wrt. dry matter).


given their lack of knowledge about biochemistry,

They may not have had our knowledge about biochemistry, but they did have the biochemistry:

how did these societies learn about the advantage of pulses' protein contents

Humans have the so-called umami taste receptor which senses amino acids/protein.

and the importance of balanced carbohydrate-protein diet?

That's where the sweet taste receptor comes in, which detects digestible carbohydrates: the amylase enzyme in our saliva splits monosaccharides [sugars] off the starch (carbohydrate). It's closely related to the umami taste receptor. Bitter receptors are also related (and are in fact a whole family of receptors detecting a wide variety of substances).

Incidentally, sweet and umami are two basic tastes that are unambiguously pleasant. That is, they just had to follow their palates, the link protein - advantage is hard-wired in humans.

Salt is pleasant or unpleasant depending on sodium deficiency, bitter unambiguously bad [but we can learn to accept it in order to have other benefits - think coffeine], and sour becomes acceptable only if offset with sufficient sweet; I'm not up to date about fatty acid taste receptor research, but AFAIK, some receptors have been identified.

As for the balance of the diet, in a way that probably didn't matter as much back then as for us Westerners now: until lately most humans experienced hunger and starvation every so often. So the question of balancing a choice between overabundant food types and limiting your food intake was a non-question.
Plus, humans like food diversity, even if they get food that is nutritionally balanced, which would tend to lead to a more balanced diet.

Or did they unconsciously do it, for example

Probably mostly unconsciously. But I would not bet that the idea pulses should be mixed into the grains was never expressed: I've met what I consider an example of specific appetite for protein, and know of others that they did make the experience that "protein really helps" in the context of long distance hiking. Similarly, without the name protein it's just possible that someone somewhere vocalized the impression that grains + pulses are better than just grains.

It has been demonstrated that rats have an innate specific appetite for protein that kicks in in case of protein deficiency or high protein need (pregnant rats)(see wiki page linked above for source). In humans, there are also indications that protein intake is actually important for the regulation of overall food intake, and takes (to a certain extent) precedence over energy intake (protein leverage hypothesis) [Gosby et al.: Testing Protein Leverage in Lean Humans: A Randomised Controlled Experimental Study, PLOS One, 2011].

Again, this hints at a situation where pulses may have been highly valued right from the beginning - at least where meat, fish and eggs were scarce, and milk for adults was not yet an option. If high-protein sources are available, then of course, additional carboyhdrates without much protein is fine. Keep in mind that very roughly speaking at the same time (after all, domestication of the first grains wasn't something that happened in just a few years, we're talking about a period of a few 1000 years), not only agriculture started but also domestication of goat, sheep, cattle, chickens.

Also, the protein leverage hypothesis (and the fact that this hypothesis is just under study more or less now instead of being centuries-old wisdom that has been subjected to rigorous study decades ago) may point to this important regulation of protein intake being not so easy to detect during "real life nutrition situations". Which would make a conscious decision to work towards farming pulses as well as grains unlikely.

were there some evolutionary/selection process that caused people who consumed balanced diet to survive and produce more offstring?

Yes, and that evolutional/selection pressure is happening since far longer than the "groups of people"/"societies" that @MarcCWallace and @Semaphore write about:

We share the T1R taste receptor family not only with mammals but with vertebrates in general. And, as this question is mainly about protein, there is indication that the sweet receptors are variants of the (older) umami receptors. Yarmolinsky et al.: Common Sense about Taste: From Mammals to Insects, Cell, 2009. Older here is sometime between when fish decided to take over land and before mammals evolved!

(Note that this means we have the ability to detect protein since long before we became humans, but that doesn't necessarily mean that protein precedence and craving for variation are as old: they could be driven by occupying our ecological niche more recently. Still, my personal guess is that the importance of protein is also old.)

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    When I was younger and much more active I very much had a specific appetite, otherwise thought of as cravings. I wasn't always consciously aware of what was being craved, but a tiny nibble would immediately let me know if I was tasting the craved food or not. My strong belief is that all healthy humans probably possess this capacity if they practice exercising it; but it may be suppressed when too many foods have a sugary flavour. – Pieter Geerkens Aug 8 at 19:52
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    @PieterGeerkens: I think so, too (and I've met people who are quite good at this and others who aren't, and some who tell that they had sports training to learn ignore those senses). But unfortunately, even the "outer" chemical senses smell and taste are hardly cultivated in our culture. Not to speak of the inner chemical senses (hunger, thirst, specific appetites etc.). Of course rigorous scientific study of these senses in humans is often difficult (or even unethical) wrt. interesting questions such as whether those senses are innate or learned (or to what extent). – cbeleites Aug 9 at 0:24
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A detail worth considering is that high-protein pulse crops also happen to be nitrogen-fixing. In other words, higher protein crops would have also improved the quality of the soil. Growing them together with cereals would have noticeably increased productivity, even if the nutritional benefits were less obvious.

  • Also, different crops are ready for harvest st different points in the season. So societies that mix up their crops in order to reduce feast/famine swings automatically increase overall nutrition as well. – Pieter Geerkens Aug 9 at 2:12
  • @PieterGeerkens. Interesting point, but is there any correlation between that and protien? In other words, do pulses mature either faster or slower in general than cereals or other crops? Seems plausible but I have no idea. – Brian Z Aug 16 at 11:25
  • Where I live, peas are typically ready to harvest in June but corn and wheat take another 6 to 8 weeks before harvest. – Pieter Geerkens Aug 16 at 11:30

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