Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban

Why Are Gorillas So Strong If They Don’t Go to the Gym?

Published 26 February, 2014
Who says gorillas don't know squat?

Who says gorillas don’t know squat?

Let me start by saying that I don’t actually know much about the topic I’m writing about today and, in a tiny, personal celebration of blissful ignorance, I decided not to try to learn much about the topic I’m writing about before setting pen to paper. I sort of think of this post as a cry for help, so if anyone wants to tell me gently (to spare my feelings), offline (to spare my reputation) what I should  have read before trying to write about this, please drop me a line.

Ok, here’s the thing. Human muscles seem to atrophy with disuse, as anyone will tell you who has had to take a six week hiatus from the gym because of a bunch of gorram injuries. Muscles are a bit like foreign languages and health flexible spending accounts: use it or lose it.

My sense is that many people think that this is a general property of muscles. Or, at least, my sense is that people think that in order for muscles to get big and stay that way, they need to be used.

Don’t get me wrong. I think that’s true of (some, most, all?) human muscle tissue. But just because it’s true for humans, I don’t think that it’s true for other critters, and I don’t think that it had to be true for human muscles, whatever that “had to” might mean.

Part of the reason I was thinking about this is because of the self-control literature I’ve been subjecting myself to, in which people say that self-control is “like a muscle.” In that word “like,” self control researchers seem to have in mind, first, that self control is “like” a muscle in that muscles get tired with use over the short term and, second, that muscles get stronger with use over the long term.

Now, the first part probably has to do with the way that muscles work. Muscles turn chemical energy into mechanical energy. This is accomplished through mysterious processes going on in the cells, and the little power plants that do the work run out of fuel, produce metabolic byproducts, and heat up, some or all of which reduce their ability to produce mechanical energy, which is why each rep is harder than the last one. There are, then, physiological constraints that tissues face over time. This reduction in output is, in short, a necessary side effect.

What about the second bit, the idea that muscles get stronger with use over longer time scales? Or, in the same vein, why do human muscles seem to get weaker over the long term if you don’t use them.

Which brings me to gorillas. I don’t know about you, but I’ve spent a fair bit of time watching gorillas in zoos, not to mention Gorillas in the Mist, and they strike me as, in a word, lazy. Juvenile gorillas do seem to frolic a bit in the enclosure, but adult males seem to punctuate their bouts of sitting around munching on foliage with short intervals of sitting around not munching on foliage. Ok, sure, in the wild, right, every now and then two male gorillas will get into a fight, and I’m sure that provides a robust work out. And of course in zoos, no such battles occur because no zoo would put potential rivals in the same enclosure, and risk the loss of a precious gorilla.

Lazy zoo gorillas, then, don’t seem to get much of a workout, but those dudes are huge.

So, from my completely informal observations that gorillas in zoos are A) lazy and B) buff, I infer that there’s nothing intrinsic about (gorilla) muscles that requires that they atrophy with disuse.

If human muscles atrophy if unused, but gorilla muscles don’t, then it seems that some sort of explanation is required.

My guess is that the relationship between how much you use a muscle and how big it gets is a design feature, not a byproduct, and this relationship varies across species.

For gorillas, my guess is that no matter what sort of life you’re leading, you might need your muscles at any given moment. In the case of males, this is either to defend the harem against rivals, or, on the other side, fight to take over a harem. If such attacks might occur at any time, then muscles must be kept robust more or less continuously, independent of whether you’re working out regularly. As with everything else, there’s a tradeoff, and the metabolic cost of maintaining the muscles is a good investment insofar as the defenses must always be manned.

Maybe something different is going on with humans. People are unusual in many ways. In How the Mind Works, Steve Pinker quotes Ambrose Bierce’s Devil’s Dictionary, which defines humans thusly:

Man, n. An animal so lost in rapturous contemplation of what he thinks he is as to overlook what he indubitably ought to be. His chief occupation is extermination of other animals and his own species, which, however, multiplies with such insistent rapidity as to infest the whole habitable earth and Canada.

That last part is relevant to the present point. People live and probably have lived in tremendously different ecologies. The ecology probably influences which muscles are worth paying the metabolic cost to maintain. Are you doing a lot of persistence hunting? Probably you want to invest in big leg muscles. Paddling a kayak? Best to have big upper body muscles.

And of course the best way for the system to know which muscles are worth investing in are the one that are being used. So, a good design feature is to build up muscles for tomorrow that you’ve been using a lot today. Other muscles, by virtue of the fact that you’re not using them, aren’t worth the cost. So, unused muscles are hung out to dry.

  • http://www.darwiniandemon.com/ Rolf Muertter

    I’m not an expert either, but it does sound like a reasonable hypothesis. One way to test it would be to look at other mammals with similar ecological flexibility and see if their muscles show a similar response. The funny thing is, I can’t think of any, and I think I know why. The reason why we can be so ecologically flexible is because we don’t just evolve genetically, but also culturally. So the need to hit the gym to become buff could be another example of gene-culture coevolution.

    • Also not an expert

      Would you consider the response of muscles in animals bred by humans for specific purposes to show a similar response? Referring specifically to horses and dogs, there are certain breeds which are naturally more muscular, more lithe, etc – but this is also modified by their behavior. The animals that become ‘buff’ from heavy exercise for work or sport will lose their muscle tone if they lapse in their activity. But perhaps similarly to the difference between humans and gorillas, a thoroughbred bred for racing will not have the same baseline heavy musculature as a quarterhorse bred for ranch work. Not a ‘natural’ evolution, sure, but comparable?

      Also, while gorilla muscles don’t seem to atrophy if unused, is there any evidence that they can also build up muscle through extra activity and then lose it if they return to their baseline sitting and munching? It may be that humans and gorillas (and chimps, for that matter) have a similar response to increase or decrease of muscle tone, but gorillas/chimps have a much higher baseline for the reasons that Rob suggested.

      • http://www.darwiniandemon.com/ Rolf Muertter

        No, it’s not similar because we are talking about individual-level flexibility. Individuals have to be flexible because cultural evolution happens much faster than genetic evolution, so it’s not determined in advance what kind of cultural environment we will end up in. But the particular environment determines which muscles are needed the most, and that can change several times in a lifetime. Another thing to consider is that our brains are metabolically very expensive, so we can’t afford to waste any resources on building muscle that may never be used.

  • James Goodman

    Hard to poke holes in that, especially the focus on fighting. I vaguely remember reading that male-male competition accounts for 90% of the differences in strength between men and women (I cannot remember the study sorry!). I think the study said that on average human females are 50% of male strength in the upper body and 70% in the lower body.

    To be a real nit-picker though, I point out that a traditional body-building workouts (ie set, rest, set, rest, set, rest, on to new set, rest, set, etc) are not naturalistic in terms of fighting, and better approximate labour and chores. Fighting (actual fighting) is very random in terms of the muscles recruited, which is best approximated by doing your weights in a circuit (CRT) with little to no rest (see http://www.scars.com). Your overall strength and muscle efficiency responds very quickly to this type of training, but the gain in size is much less than in body-building, which is more repetitive and tends to focus on one or two areas of the body per workout.

  • Channing Walton

    Gorillas eat small trees after ripping them apart, quite a work out: https://www.youtube.com/watch?v=4amRA0jl0qI

  • kliban

    Prefacing an essay with an admission of ignorance is like saying you practice charity, but only with yourself.

  • kliban

    I guess I wonder what basis you have for thinking that gorilla muscles don’t atrophy with disuse. Imagine a gorilla who spent ten years in a zoo released back into the wild. I bet his age cohort fellow wild gorillas would totally dis his general limpness. I, also, do not know much about gorillas, but I would guess that part of a gorilla’s advantage is mechanical, based on thicker skeletal bones and broader cross sectioned muscles, resulting in the appearance of freakish strength even among zoo pampered silverbacks.

  • Marc

    The human uterus has muscle that doesn’t atrophy from disuse. It waits years and years and then contracts. The internet just told me it’s the strongest muscle by weight. So if muscles don’t inherently atrophy from disuse, it makes sense that the relationship between use and bigness can be set as a design feature.

  • http://ostrovletania.blogspot.com/ Andrea Ostrov Letania

    Gorillas would be even stronger if they worked out. But even a lazy gorilla is stronger than us because of genetics. But same is true of bears and tigers.

    But this applies to humans as well. If Mike Tyson took it easy, he would still be able to kick most people’s ass. Imagine a lazy Tyson vs Einstein who worked out. Tyson would still be more buff and stronger than Einstein. Genetics.

Copyright 2014 Robert Kurzban, all rights reserved.

Opinions expressed in this blog do not reflect the opinions of the editorial staff of the journal.

Evolutionary Psychology - An open access peer-reviewed journal - ISSN 1474-7049 © Ian Pitchford and Robert M. Young; individual articles © the author(s)
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