We grew opposing thumbs. We learned to walk upright on our legs. Why didn’t we evolve with wings so we could fly. If we could fly, we would have an advantage for finding food, protecting ourselves from predators, etc. So why can’t we fly? Any ideas?
Bones are too dense would be one reason. I’m sure there are others.
Q
If we evolved massive wings that were bigger than our bodies, we still wouldn’t be able to fly?
There you’re getting into an area of biophysics I don’t feel qualified to answer, copperwindow.:), but I think then also we’d more massive muscles to move those big wings.
Good to meet you, btw!
Quasi
Have we met?
Yeah, just now. Here. 
Q
Ah.
Not while remaining human, no.
If we start with a 50kg human we would need a massive wingspan, IIRC about 30 metres. That’s comparable to a decent sized aircraft. We would also need pectoral muscles to move those wings. Those muscles would weigh at least another 40kgs which means correspondingly large leg muscles to enable us to run. So that’s 40kg of extra flight muscles and 20 kg of extra leg muscles meaning that we now have to lift a 110kg weight, which means a 100 metre wingspan and another 90kg of muscles to move those huge wings. But now we need correspondingly large leg muscles to move those huge flight muscles…
Do you see where this is going?
The problem is that an animal built even vaguely like a human cannot achieve flight. We are too heavy to start with, and almost 1/4 of our weight is in our legs, which are useless for powering flight, but they still need to be able to carry the flight muscles. So every time you scale the flight muscles you need to scale the legs even more, and vice versa. It’s a feedback loop and at no stage can the result fly.
There have been some much larger than human-sized animals that have managed to take to the air, anything up to half a tonne, but they did so at the expense of greatly reduced legs, quadripedal locomotion, greatly reduced utility of the forelimbs, loss of teeth, reduced brain size and so forth.
An animal simply can not remain even vaguely anthropoid and manage to fly.
he might mean having wings on our backs but retaining our dextrous hands out front (even more unlikely.)
Evolution doesn’t just equip animals with what they need because they need it. It’s (generally) a case of ‘whatever works least worst now, is best’.
In order for us to have wings, there would have to be a point where our ancestors developed something that could have later become wings, but was also useful or at least not detrimental in its own right. There’s no particular reason why such a change must happen (so maybe it just didn’t), and even when such changes do happen, and even when they’re advantageous, sometimes circumstance has other ideas and the line dies out for some other reason.
And even if the line itself doesn’t die out through any fault of its own, it could be out-competed by another mutation or species that has a better long-term survival/breeding rate.
If hypothetical flying humans existed and they had to sacrifice brain capacity, tool use, communal living, agriculture, etc. in exchange for flight, they may have simply been out-bred by the landlocked humans who channeled limited resources into ultimately more useful pursuits.
Flight also takes a lot of energy, and with the advent of successful land-based hunters, there may not have been large/dense enough prey left for the large flying creatures. As for vegetation, I don’t know if a ruminant stomach could be supported by the typical wing configurations…
What? You mean, you CAN’T? :eek:
Heck, I can fly!
Well, it’s not really flying, more like soaring.
No?
Gliding, with a really steep angle of decent? 
Ok, ok… Falling with style! :rolleyes:
And that’s my final offer! 
Yep, JBD, and one can don the so-called “bird-suit” as a sky diver and soar a bit longer than normal free fall, but I think that’s about it.
Q
Or to look at another way, our ancestors did eventually evolve flight - just not in our branch of the tree. For an example of what humans might have been, look here.
I’d say that one reason we didn’t evolve flight is that vertebrates happened to evolve with only four limbs. Wings are so specialized that having a pair of them means that you sacrifice a pair of limbs for pretty much any other purpose. Being a specialist in tool use and in flight at the same time would be hard to pull off with only one pair of upper limbs. If vertebrates had evolved with six limbs, the human-equivalents in that world could have evolved wings and hands at the same time.
I suspect it could be done if you made them a lot smaller. We know from the existence of very short people that an intelligent species can be much smaller than the average modern human. And getting 20-30 pounds in the air is a lot easier than getting 150-200 in the air. Basically think “flying monkey”, not “angel”.
flying is easy. you just throw yourself at the ground and miss.
The practice sessions hurt like hell, though.
*<whump!>
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There are a couple of valid answers. First, there is hardly ever a good answer to “why not” questions when it comes to evolution. Usually, all we can say is just that that trait never happened to show up, or if it did, it didn’t work. There’s no mechanism for evolution to provide us with stuff because it’s cool.
Secondly, flight is a hugely specialized and expensive thing. Animals that fly have their entire bodies changed and adapted to make it possible - hollow bones, huge wing muscles, etc. The entire bird group lost their teeth just to lighten the front end a bit. The expense is evidenced by the fact that whenever flight becomes no longer necessary for survival, it’s quickly lost, as in all the myriad of flightless birds that evolved on small islands where there were no ground predators. The point being that flying is more than just slapping a pair of wings on a critter and off it goes. If we were to take a modern human and modify it just the bare minimum to allow it to fly, it would be so radically different from us that we could in no way still call it “human”.
Fruit bats are vaguely anthropoid, for sufficient values of ‘vaguely’
With evolution - every advantage comes with a trade-off; as others mentioned, you have to lose a lot of weight to achieve anything small or light enough to fly. Consider someone who is super-fast or super-strong; those muscles take a lot more energy to maintain, meaning these are the first to starve to death in times of famine (common in hunter-gather days). Someone getting light enough to fly but not quite there, OTOH, is weaker than the rest when it comes to competing for food or mates. Our big advantage is our brain (which explains why we can now fly better than birds) - but a brain like ours (like mine) is heavy and needs a lot of food - one item I read said one third of our calorie consumption goes to feeding the brain. So Mother Nature has to decide - brains or wings?
Basically evolution pauses when the result is “good enough” - we run fast enough to chase down the wildebeasts on the sahvanna - not by speed but because we can run for hours and they can’t. We are 5 or 6 feet tall because any taller would starve to death fastest in tough times, but does not gain enough food-gathering advantage to pay for the extra need. We can’t see infrared, or like hawks, because our eyesight is good enough for hunting; super eyesight only is only useful for hunting if you can drop out of the skies onto whatever you see… not when it takes you ten minutes to run up to it.
I would be curious what the speculation is about the evolution of birds or bats - what environmental circumstances were that preceded full flight but allowed the process to happen without putting the animal in a too vulnerable situation. One suggestion I have is that it was a somewhat dense jungle situation where there was plenty of opportunity (like flying squirrels) to climb to a jump-off point and glide a long ways. Also, I suspect the ability evolves frst in very tiny creatures who are light enough that they can fall from extreme heights and not injure themselves, due to low weight and slow terminal velocity. Once those creatures can fly, then evolution pushes the limits in terms of size vs. ability.