Avian-human: Arms or Wings

Question

I've seen bird-human hybrids before in popular fiction, where they have legs, wings, AND arms. So I was wondering if this was really plausible. Humans don't want to give up the ability to manipulate things with their hands, not even for the power of flight, because that would make things hard in a hand-orientated society. Would it be possible to have hands on the wings, though? Kind of like a harpy? Or maybe it could be a cross between an arm and a wing? Also, ignore the stuff about how we wouldn't be able to fly, and all those other serious issues, for the sake of the question.

Answer 1

If you're dealing with humans as known on Earth, the answer is a resounding no. That would be six limbs, whereas basically all animals (or at least anything more closely related to humans than, say, spiders) evolved from an aquatic ancestor with four limbs plus a tail. Evolution tends to work on a gradual basis: it's not about to conjure new limbs out of nowhere. A six-limbed human, at least on Earth, is flatly impossible without absurd mad-scientist-style experiments.

If you want to try merging arms (with hands) and wings together, it becomes slightly less impossible (but still is absurdity to imagine) if you're willing to look to other ways of flight beyond avians. Bats, for instance, have wings made up of their own skin (instead of growing feathers), which connects their arms to their bodies by much more than just the shoulder, giving a significant flying surface. Mind you, their arms are also incredibly long in relation to their body: if you wanted a human capable of even reasonably effective gliding (never mind powered flying) with such wings, each arm would probably be two metres long at minimum. Bat wings are also incredibly fragile, such that the equivalent of a paper cut would probably pierce them; they heal quickly from small tears, but this is likely to be problematic when scaled up to human proportions.

Still, this is at least something that developed in another mammal, so it's less ridiculous than sprouting two new limbs. Manipulation with such wings, however, is very unlikely; bat "fingers" are the spines in their wings (the thumb sticks out on its own, and as far as I know is basically a vestigial digit), their fingers being used to alter the wing shape. If you wanted to preserve hands in your winged humans, you would need to either sacrifice most of their performance in the air (likely ensuring that wings would never naturally evolve) or accept that hands and wings do not mix in that way and instead rely on the feet to take the place of human hands (which, apart from their beaks, is how birds manipulate and grasp objects).

In short, nature is never going to produce what you're looking for; flight is very energy-intensive and requires considerable specialization. Usable hands at the ends of wings falls under "makes wings no longer useful for chief purpose of flying", and natural selection will typically kill off individuals with such counterproductive traits; wings that cannot be used to even glide effectively are worse than useless, being a huge target that slows an individual down on the ground. Turning feet into new hands while having wings is a more reasonable approach, but still an absurd proposition given Earth's evolutionary history.

Answer 2

Palarran's answer why a species with the six limbs necessary for your species would not naturally evolve on Earth is very reasonable. The only animals on Earth with more than four limbs are invertebrates unlikely to grow to the sizes necessary for intelligence beings.

Of course I could imagine land octopi that start living in trees. They might leap from the trees and glide using a web between their 8 arms. And maybe over time they might modify some of their arms to be wings with a web between them, others to be legs, and others to be arms and hands. But they wouldn't look much like winged humanoids.

But Earth isn't the only planet in the universe. It is quite possible that on many alien Earth like planets the first vertebrate-like creatures that crawl out of the ocean onto land will have six or eight walking fins instead of four, and that land vertebrate-like creatures will thus evolve six or eight legs for walking. Thus those six-limbed vertebrate-like creatures may someday evolve groups of beings with 2 legs, 2 arms, and 2 wings, which fit your description.

It may be noted that many monkey species have a fifth limb, a long prehensile tail, which might theoretically evolve into a more "handy" organ.

And giant ground sloths are believed to have used their tails as third legs to stand on.

I think that some kangaroos sometimes use their tails like legs.

And I can imagine beings like heraldic wyrverns, dragons with one pair of wings and only one pair of legs. They might slither up trees like tree snakes, helped by using one pair of legs like arms and hands, and use the other pair of legs like wings when they glide out of the trees. Possibly an intelligent wyrvern like species might raise their fore bodies upright to use their forelimbs as arms.

https://en.wikipedia.org/wiki/Wyvern1

And don't forget that proboscideans have evolved trunks that serve like arms and hands, a fifth limb. I could imagine a tiny proboscidean-like species starting to climb trees, and evolving feet better suited to climbing along with using their trunks to help climb. And perhaps some of their descendants might evolve wings out of one pair of limbs. And perhaps some descendants of the flying tree elephants might return to living on the ground, walking on two legs while not flying, and using their trunks as hands.

I believe in C.C. MacApp's Gree stories there was a species, the Birds of Effogas, that resembled flying elephants. Although I think their form was the result of biological engineering.

So maybe your winged humanoids could be the result of genetic engineering by a highly advanced society.

Also see my answer here:

Mistaken For Wings? 2