How can specied evolve to have a big trait that is composed of little traits that by themselves are harmful?

Question

I never understood how birds evolved to be able to fly. Sure flying is a great evolutionary tool, but to fly you need hollow bones, wings, and small awkward legs. Individually these traits are harmful, so how could the random mutations of hollow bones or wings be succesfull along the way until the birds could fly. Random mutations are very slight and it takes a long time to evolve even a minor change.

Answer 1

The first 'birds" were actually arboreal lizards that learned to escape predators by jumping from limb to limb. The ability to jump well soon resolved to a body shape that was aerodynamic then later to one that could glide as some squirrels now can do. Gliding eventually gave way to limited flight, then full flight. Limited flight became full flight over time by the evolution of the traits you described.

Answer 2

Your last sentence is absolutely correct, and forms the basis of an understanding of evolution by adaptation. However, there has been plenty of time to evolve - about 4 billion years since life started on Earth. The harmful effects would come into play if all these things happened individually, without all the other changes occurring. However, over time, all these changes may have occurred slowly, but collectively. That is, legs got smaller while bones became lighter and wings adapted from front legs etc. leading to the birds we know today. It should be noted that birds have also lost the power of flight, after initially having it, notably ostriches, emus, kiwis and of course dodos. All of them lost the use of their wings for flight because there was no need to fly, and it became a disadvantage to have wings. Based on the size and functionality of the wings, the kiwi and emu would have lost them first, then ostrich and finally, the dodo, who still had proper wings, but useless for flight. Why is it, do you think, that they were created like this? Why bother with very small wings at all?
Think about that.

Answer 3

> "to fly you need hollow bones, wings, and small awkward legs. Individually these traits are harmful,"

No, they're not. Not at all. A lighter animal is a more agile animal, harder to catch. They don't need full flight for these things to be advantageous.

Have you ever tried to catch a chicken or a wild turkey? Watch how they run. Even though they are flightless, then run while flapping their wings and can get up a good bit of speed ... even gliding for short spurts. They can hop up onto ledges or branches several times higher than they are. This kind of running, then hopping, then gliding, and eventually full flight are all incremental improvements that all take advantage of slightly lighter bone structure.

But yes, evolution is just the accumulation of tiny advantages, no matter how slight.

Answer 4

The traits you mentioned may be harmful in some cases. They are still an advantage if you need to fly. Evolution often sacrifices in one area to give a greater advantage in another. Birds may have started out as leapers and then with the ability to glide to another tree. Eventually they developed the hollow bones and features that allowed them to have powered flight.

Answer 5

First, your premise would be totally false for an arboreal organism. Second, hollow bones and wings are not objectively harmful and " awkward legs " is subjective. I do not think the legs of herons are awkward.
That is all I have, as I am going off line now. Hopefully someone will flesh this out for you.

Answer 6

Lifeforms "adapt" to their environment through natural selection. Only those lifeforms that can adapt to an environment survive. So, whatever adaptations occur are beneficial, not harmful.