Fruit eating possibly linked to primates' large brain evolution (2017) | Hacker News Reader

Fruit eating possibly linked to primates' large brain evolution (2017)

science.org

90 pointsrajnathani63 comments

Also semi-relevant is the Drunken monkey hypothesis: https://en.wikipedia.org/wiki/Drunken_monkey_hypothesis

> Drunken monkey hypothesis proposes that human attraction to ethanol may derive from dependence of the primate ancestors of Homo sapiens on ripe and fermenting fruit as a dominant food source. Ethanol naturally occurs in ripe and overripe fruit when yeasts ferment sugars, and consequently early primates (and many other fruit-eating animals) have evolved a genetically based behavioral attraction to the molecule.

How does it relate to larger brains?

After a night of Ethanol my brain feels quite swollen.

We needed to evolve bigger brains in order to raise the floor of dumbness brought on by throwing back a few with the boys.

Also the Stoned Ape Hypothesis: https://science.howstuffworks.com/life/evolution/stoned-ape-...

What a great username.

Humans aren't more attracted to ethanol than other mammals which do not regularly consume fruit. Give a dog or a horse or a goat or a racoon some booze and it'll be back for more (don't actually do this).

Elephants are known to get drunk and attack villages. https://www.google.com/amp/s/amp.theguardian.com/world/2010/...

Talk about a tragicomedy! Thanks for sharing.

Fyi that link is broken for me.

Yeah weirdly redirects to a favicon

[edit]

Oh some weird google amp prefix, what is this supposed to do?

here's the real link: https://www.theguardian.com/world/2010/dec/03/elephants-drun...

But that’s elephants for you. Let them get a couple of pints in and they’re just a pack of 10,000 lb hooligans.

>Humans aren't more attracted to ethanol than other mammals which do not regularly consume fruit

Well, it's not about attraction "given the chance", but about persistent attraction. In other words, "other mammals" might also by chance consume alcohol (or ripe fermented fruit) and get drunk and like it, but they didn't pursue it actively or have alcoholics...

Other mammals aren't intelligent enough to do so.

Well, the theory mentioned above is that this is not a coincident, but a causual relationship (perhaps through a self-reinforcing feedback mechanism): that humans got "intelligent enough to do so" (and further progressed way above that level) by being prone enough to do so

Mammals are pretty good at causal inference when it gets them fed. Guinea pigs' #1 priority in life is screaming when they hear you open the fridge.

Go hang out with some monkeys (https://www.youtube.com/watch?v=pSm7BcQHWXk).

How would you know that? I don't disagree, because I don't know either. But I consider that you might know, and I don't know how that would occur. Curious.

I don't think it's true for more intelligent animals like pigs

https://sivertimes.com/tame-wild-boar-in-poland-went-on-a-be...

Even fruit flies can get drunk.

> don’t actually do this

Don’t make me so curious to test your hypothesis then.

Sounds like this is in the same vein as the Cooking Hypothesis? Basically that control of fire led to cooking which led to greater nutrient acquisition from foods ( because more foods can be made edible, cooking reduces the energy cost of eating raw by "pre-digesting" them, and reduces losses by allowing the creation of basic broth style foods ) in turn leading to larger brains and our own evolution

I heard that raw foods contain the very enzymes that our body uses to digest them. Like how an apple decays on its own over time. Those enzymes get destroyed during cooking so your body has to use its existing enzymes. Not sure if this is accurate information, so I'm mentioning it in case someone knows more about this subject.

In that case, why would we develop enzymes? We just always had them?

And what about animals that eat only raw food? Does that imply that they wouldn’t be able to digest cooked food?

this almost sounds like you may be confusing it with natural digestive enzymes that are deactivated during cooking, like the kind that exists in pineapples to help it stave off insects ( if you eat them raw they'll digest part of your tongue and thus give you a raw tongue; heat deactivates those enzymes )

From the NPR link [0]:

> The researchers analyzed the brain sizes and diets of over 140 primate species spanning apes, monkeys, lemurs and lorises and found that those who munched on fruit instead of leaves had 25 percent more brain tissue, even when controlling for body size and species relatedness.

[0] https://www.npr.org/sections/thesalt/2017/03/27/521423216/wh...

Kinda funny to think about because leaf-eaters tend to have larger more complex gut microbiomes. Your gut microbiome has been called "the second brain" because the majority of neurotransmitters (including over 90% of all seratonin) originates there.

It almost seems like there's a tradeoff between the two "brains"

This would explain why pandas, koalas, and sloths (all leaf-eaters) are often thought of as "dumb" lol

The neurotransmitters in the gut do _not_ make it across the blood-brain barrier, and there certainly isn’t a direct tradeoff between behavioural complexity and the stew of monoamines in your gut.

Prucalopride and other gut motility meds that contain neurotransmitters often have depression/suicide warnings, so some sort of information transmission is happening, even if it's not that the transmitters directly cross the barrier.

Can't really explain elephants in that case.

Elephants actually do eat a lot of fruit as well. But yeah it was definitely a playful hypothesis and not a serious proposal. I'm sure if I researched it for even 10 minutes I could find a lot of examples that disprove it

>Kinda funny to think about because leaf-eaters tend to have larger more complex gut microbiomes. Your gut microbiome has been called "the second brain" because the majority of neurotransmitters (including over 90% of all seratonin) originates there.

Leaf eaters also tend to have larger jaw muscles and attachments for same.

That tends to limit the size of the brain case, as that space is needed for the chewing apparatus and supporting skeletal features[0].

[0] https://www.nature.com/articles/news040322-9

Fascinating, thanks!

I remember seeing a lecture by an anthropologist who showed a graph that mapped the size of different primates vs what percent of their day they spend just chewing food. Chimps spend about 60% of their days just chewing for example. The trendline was a surprisingly effective predictor for other primates. Except for humans. Based on our mass we would expect humans to spend around 70% of our day just chewing. Instead it's less than 10%

Another point of evidence that supports the hypothesis put forth in the OP

That's funny. If I had a bigger brain I too would munch on fruit instead of leafs. I think they have it backward causation wise.

If you had a bigger brain, you would automatically have access to fruit? That seems backward causation wise

It is also quite possible that harvesting fruits requires more brainpower (advanced spatial understanding, good memory, motor functions etc) which gave rise to the evolutionary pressure for cerebral development.

[Hmm, seems authors have considered that possibility] but Further down the article:

>He suspects that diet allowed, rather than drove, the evolution of big brains.

Well, why?

[Edit: removed question about (flying) frugivores, don't know how I missed the easy explanation, thank you] [

>Also, why don't fruit eating birds or bats have big brains?

Because big brains are aerodynamically impractical?

It would probably be more of a weight issue that an aerodynamic issue. And not for the brain itself, but rather for the strong neck necessary to support a large organ so far from the body's center of mass while in flight. It might put evolutionary pressure to reduce the neck length, which would have far reaching consequences for birds.

They go into the fruit finding is harder than leaf finding in the article.

flying creatures I would guess have a huge pressure to eliminate weight.

Even so, several bird species are among the smartest we know. Crows, parrots. I wouldn't call them bird-brained as a pejorative.

Indeed, the Corvid family (crows, ravens) has been show to do some pretty complex problem-solving.

I imagine that occupying a high perch out of danger and watching the goings-about by many creatures below, it helps to have a brain that figures out the behaviors of other animals, like squirrels, foxes, etc. That's a really theory-of-mind activity; modeling the thoughts of other animals (and the information available to each) to predict their behavior.

Many animals have enough brain power for efficient foraging. The most brainpower-demanding thing humans do, apart from science - but that came later, is interacting with other humans. Coordinating, but also scheming and deceiving.

Harvesting fruit requires more brainpower than hunting, for instance? Wait for the fruit to appear, in the tree that you remember it always appearing in, then climb up and grab it. That doesn't seem to require much brainpower.

Unlike glucose, fructose (sugar from fruit) is metabolized by the liver, and then converted to fat. Maybe fruit eaters were simply able to store more energy as fat which supplied the nutrition and/or extended survival required to evolve larger brains.

> fructose (sugar from fruit)

For posterity; sucrose (table sugar) is composed of half fructose, half glucose.

The new study's large sample size and robust statistical methods suggest diet and ecology deserve more attention

Maybe someone in need of a PhD thesis topic can do me a favor and spend some time scientifically looking at why half of the human population lives within 200 km of the coast and what impact ocean minerals, including but not limited to salt, have on brain development at the species level.

https://www.reddit.com/r/MapPorn/comments/uxrinu/half_of_the...

Iodized salt was actually a big public health thing in my non-coastal country.

Yeah, it's a thing in the US as well due to the Midwest being historically known as The Goiter Belt.

I'm likely allergic to iodine, but have a genetic disorder that involves misprocessing NaCl -- "table salt" -- among other things (fats as well, which are also significant to brain development, what with the brain being the organ with the most cholesterol). And it happens to be a genetic disorder anecdotally associated with high IQs and indirectly associated with Nobel Prizes in that it is common in a population with a historically high percentage of of Nobel Prizes, outsized compared to the population in question.

Anyway, I'm not good at doing "professional sciency speak" but I have reason to wonder about the role of salt (and related minerals) in brain development and IQ. Iodine is not, per se, one of the things making my radar in that regard.

But thanks for replying

Sorry, I know nothing about salt per se. I just knew that iodine deficiency is not good for brain development.

My wild guess for human population distribution being heavily coastal is: people don't tend to live where there aren't jobs, and the XXI economy (as was the XX, etc.) is ocean-oriented.

In order to test that guess, one might wish to look at the % of the population that doesn't live near a coast, and see how many of them live near a navigable waterway.

My recollection off the top of my head is that cities are strongly associated with navigable waterways.

Which I don't see as a rebuttal for my hypothesis, just to be clear.

Mushrooms may have had some influence: https://bigthink.com/neuropsych/stoned-ape-return/

I just find fruit trees to be extreemly beautiful. Especially an old rugged apple tree, or a fruitting peach tree or orange tree. Something about it clicks in my brain to release happy endorphins.

They tend to occur in sunny areas, provide shade, and provide a habitat for insects and birds. Citrus trees are not always pleasant to be near. Tangentially, the wood of many fruit trees is highly valued in carving and woodblock printing.

Are fruits eaten by primates the sames that those eaten by modern human ?

I strongly doubt about it.

But what we know for sure is modern fruits are causing fatty liver syndrome and metabolism disease in human.

That's probably just a matter of quantities. If you eat a lot of fruit, you're also eating a lot of sugar.

We've been promoting this idea that fruit is inherently healthy and health conscious people have low fat, high carb diet (which cause hunger) and just binge eat fruits and drink juice.

Sure, it's better than preprocessed crap but still a bad diet.

Cue all the people posting YouTube videos on how freelee, the banana girl made them fat in 4 weeks.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4405421/ https://www.nih.gov/news-events/nih-research-matters/how-hig... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8018782/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5893377/

Is there a study showing that eating X amount of apples or Y amount of banana does what you say it does in your last sentence?

I never saw something like that.

Extracting the fructose from fruit and then drinking it is completely different to eating the fruit whole.

Fructose is inhibitor of leptin production. Leptin is used in promoting satiety. So in general we always overeat fructose.

But there's no study?

I can't imagine anyone casually eating 1000kcal of apples or bananas on purpose. There's so much water and fiber in that meal that after 4 apples (~300kcal) you'd feel like you were stuffing yourself against your will.

The study that shows people overeat fruits feels absolutely impossible.

I always felt the high fat diet was more likely...

One question I have is to what degree have domesticated fruit trees infiltrated wild populations? Domesticated fruits have far higher caloric content than wild ones.

> Fruiting bodies, also known colloquially as "shroomz."

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