My rudimentary understanding of human history and anthropology tells me the folllowing:
For most of human existence - like that of most animals, I suppose - life has been hard. Staying alive has involved physical struggle, be it fighting, farming, cutting down trees, whatever.
That’s not to say that brains haven’t been important too, but without industrial-age technology the vast majority of us needed to do heavy-duty shit with our bodies pretty regularly - heaving around swords, ploughs and horseshoes was everyday life.
It’s probably not a stretch to say that those who had strong and capable bodies were more likely to successfully produce and rear offspring than those who didn’t.
Not to mention, the majority of us are sexually attracted to muscular/fit bodies to some degree or another - one presumes that is genetically hardwired to some extent.
However, my rudimentary understanding of biology interjects with…
Some people are genetically predisposed to natural, automatic well-defined musculature and physical strength. The vast majority of us aren’t. Even with the right diet, humans are mostly either ‘fat’ or ‘scrawny’ by default - being physically strong takes effort.
Fair enough, you might say, those who have needed to be strong get that way by doing the things that they do; stonemasons, one would imagine, get brawny quite quickly out of necessity, while painters do not. But why would evolution, in her wisdom, deign that only those who lift heavy things regularly get buff? Why not just programme DNA so that everyone is ripped all the time? There is no disadvantage to scribes, court jesters and candle-makers being able to bench press 200lbs - and potentially an advantage, should any of them encounter an emergency that requires sudden brute strength.
(As an aside, plenty of animals are far stronger relatively speaking than humans - and its not because they put the hours in at the gym, they are just built that way. So why aren’t we?)
The answer that immediately springs to mind is that by not devoting its energies to producing chiseled abs, the body can direct its attentions to other, more important duties. But what are they? And following this logic, those who are physically fit would then suffer deficits in other areas of areas of biological well-being, which doesn’t seem to be the case - injured professional athletes notwithstanding.
That duty is “not starving”. If our current musculature along with our tools are sufficient to survive long enough to reproduce for most people, those with naturally more muscles will not have a very big advantage once you take into consideration the extra energy required to build muscles that might not even be needed.
For the vast majority of human existence, almost all humans had to physically work hard in order to survive and reproduce. So they’d get strong by the “normal” methods – exercising their muscles. With that in mind, it wouldn’t seem to be any advantage to be “naturally” strong and muscular when everyone would become strong and muscular, even as a child contributing to hunting and gathering, just through normal behavior. Only relatively very recently (the last few thousand years) has any significant portion of humanity not had to physically work hard in order to survive and reproduce, so there hasn’t been much time for evolution to have an effect on this. Further, there doesn’t seem to be any significant reproductive advantage for “naturally” muscular people, AFAICT. In the modern world, physical appearance seems to be a relatively small portion of how mates are chosen, species-wide – I’ve seen no data that suggests that physically attractive people have more babies than physically unattractive people (keeping in mind that much of what is considered attractive is cultural rather than biological).
Homo sapiens first appeared around 300,000 years ago. Agriculture first developed about 12,000 years ago. For most of human existence getting food was the main struggle - extra muscle mass to support was an evolutionary disadvantage except in very specific scenarios.
I’m sure real scientists could answer better than I, but one factor may be that muscles require oxygen. Strength is the advantage that creates have in a particular environment, but more muscles would reduce our endurance. We would have been less able to chase other animals down. One of the ways that primitive tribes still hunt in Africa today is simply by hunting in teams and wearing down their prey. We’re slower than other animals but we can keep running, keep them moving, to the point where their bodies overheat and they can’t run anymore.
More muscles might take away more energy that’s required to feed our growing brains, which is what really the thing that made us more ‘human’. As Andy said above, in the past, we exercised naturally a hell of a lot more than we do now, so we were perhaps more muscular in the past, but being a lot more muscular might have been a disadvantage in an evolutionary sense.
In a nutshell. Evolution doesn’t necessarily select for what we may describe as “muscly”.
It does select for “muscly enough to useful” and that might cover a very wide range of musculatures indeed with none having the upper hand.
That all could change of course but that really significant human traits of intelligence and tool making tend to cushion us against the evolutionary pressures that other creatures experience and that steer their structural development.
Also keep in mind that for complex organisms like humans (as opposed to bacteria or fruit flies) evolution happens over a very long timescale. Genetically, humans haven’t really changed for some 10,000 years, if not longer. If you could go back in time and take some caveman’s baby to the modern day, she’d become the same music-listening, cellphone-clutching, fashion-conscious, YouTube-watching kid as anyone else. So stonemasons, painters, or reality TV watchers are a mere blip on the radar and aren’t a factor. We change our environment (literally and metaphorically) so often that what may seem like an evolutionary advantage in one place/time can quickly become a disadvantage. There’s no stable environment for evolution to select for or against.
Well said.
It’s why I don’t personally like talking about evolution in the context of modern humans – it’s not that we’re not evolving per se, it’s that it’s a moving target and evolution is crazy slow compared to the rate we change our environment. It only ever seems to lead to flawed conclusions.
One thing that no-one has brought up yet is that the human body has evolved to be ADAPTABLE.
Whatever activities an individual engages in - his or her body will change to accommodate and support those activities. This is why body builders and weight lifters develop big muscles. It’s why long distance runners have very lean musculature, why swimmers develop very broad shoulders and probably partially why basketball players are so tall.
Most of us do not need lots of muscles these days, so we don’t develop them. But we could if we needed them and engaged in activities that developed them.
Tall people play basketball because it’s an advantage to be tall when playing basketball. Good swimmers have broader shoulders. (Natural) bodybuilders are people who have genetics that allow for large muscle development. Successful long distance runners have a larger percentage of slow twitch muscles.
Most of the things you listed are a large portion of genetics, not bodies adapting to training. Everyone can build muscle if they train, not all people have the genetics to put on massive amounts of muscle. All people can run longer distances with proper training, not all people have the genetics to be sub-3:00 marathoners. No amount of training will make you taller or give you the lung capacity of Michael Phelps.
There is great variation in human genetics so there are people out there who have the ability to excel at all sorts of things. But not everyone can excel or even succeed at some things.
People certainly have genetic predispositions that make them more likely to excel in certain areas. It is also true that actually engaging in a physical activity will cause the body to develop appropriate to that activity.
How many 7 foot tall individuals do you see who do not play basketball? How many sedentary persons do you see built like Arnold Schwarzenegger?
I agree that basketball is a bad example, but for the rest let’s not confuse world-elite competitive athletes with everyone else who’s “good enough.” The best swimmers may have naturally broad shoulders, but the musculature of swimmers is built from swimming. Bodybuilding is mainly just a visual thing, it has nothing to do with the performance of those muscles. It might be better to look at competitive weight lifters or just weight lifting in general. Again, the super elite may have a genetic predisposition to packing on muscles, but anyone can improve their weight lifting abilities significantly, even if they don’t get the bulging/ripped look (which frankly is what most people are going for). Long distance running is the main accomplishment of human physical evolution, it’s the one physical attribute that we excel at over nearly all other animals. The proportion of slow-twitch to fast-twitch muscle can be changed to some extent with training, but again, we’re not looking at world-class athletes here, but normal people, and they can dial in the fitness of those muscles to the task at hand, to quite impressive lengths.
This is the big answer to the OP’s question. the resting metabolic rate for muscle tissue is much higher than for fat tissue. This means that muscular people need a lot of calories today to stay that way - not just because they worked out earlier today, but because they’ve been working out three times a week for the last ten years.
A person who is genetically predisposed to maintain muscle mass even in the absence of both physical activity and high calorie intake is less likely to get through a period of starvation than a person who is genetically predisposed to have low muscle mass and accumulate fat. Conversely, the latter person may have trouble coping with the rigors of daily life on the savanna outside of those starvation periods. Evolution may have found the sweet middle ground with a body policy that accumulates muscle mass only in response to a demonstrated need for it (and ability to feed it), and lets that muscle mass waste away in response to behaviors associated with scarcity of food (i.e. inactivity and fasting).
First, muscles burn energy much more than other cells. When you are starving, the body gets rid of whatever is consuming too much energy - typically muscle mass. Considering that as mentioned, for much of our evolutionary history, finding enough food was the problem. Them guys with big muscles would starve to death first. The people who laid in fat instead, made it through the slim times to recover when food became plentiful. This problem was likely exacerbated as humans moved into places with more pronounced seasons and accompanying seasonal food shortages.
As mentioned, evolution works slow. Evolution aims for “good enough”, is not fine tuning things if the survival rate is pretty good for everyone. I would suggest that muscles became less of a thing when humans discovered pointy sticks and slings and arrows were pretty effective against someone with huge muscles. Hand-eye coordination, reading human emotions like anger, and running were pretty effective tools too. (A person with huge upper body muscles is likely to be less effective at chasing someone; heck, the best runners are not the ones with the thickest legs, either.) As an example of the speed of evolution, humans from the far end of Europe had no problem reproducing with natives of Tasmania or Patagonia despite generational separation of 20,000 to 50,000 years. DNA does not drift that much.
