What evolutionary event or process or whatever you want to call it caused birds to take to the air? I was thinking about it today and i just couldnt figure out why something would have to fly. I know alot of you will probably say “to escape from predators” but i was thinking that there really isnt much “chasing” in the animal kingdom for them to run from (with the exception of alot of big game, of course), most predators rely on the element of surprise and not the big chase. So what was so neccessary to them up in the air that they absolutely had to develop wings and get up there? And (i know this sounds pretty crazy, but…) could it ever happen to humans?
Oh, and please, pretty please, just this once, dont turn this into a religious debate. If you cant at least “assume” evolution for this one discussion then please stay out of it.
In the time that the birds were evolving, I think there was a lot of hot pavement… this lead to bigger and bigger steps to cross the parking lot, hence, wings… heheheh
The advantages of flight include escape from predators. I don’t think it’s helpful to dismiss this advantage out of hand. After all, you’ve probably seen a lot of birds take wing once they’ve been scared by something. They’re keeping an eye out for potential threats, and when they see one they fly away. It would be disastrous for an organism to stop looking for and trying to avoid predators just because the predators are trying to be stealthy.
That’s not the only advantage of flight. Flight allows birds access to territory that might otherwise be inaccessible: islands, cliffs, treetops, etc. It also allows birds a very effective way to seek prey/food, potential mates, and suitable territory, they can cruise over miles and miles of ocean and land, seeing much more than they would if they were ground-bound. It also allows birds to migrate vast distances, for example taking advantage of North American resources and territory in the summer and taking advantage of Central or South American resources and territory in winter.
The advantage is that it is possible to make a living and reproduce if an organism uses flight. Before birds, there weren’t any large vertebrates (with the exception of flying reptiles a long, long time ago) taking advantage of the ability to live using flight (the insects had been doing it for eons, and look how they made out! Like bandits!! :)). The process of filling unfilled niches is called an adaptive radiation, and that’s what happened when birds developed flight.
I don’t think I understand the question exactly but I’ll try to answer.
While most predetory animals do stalk their prey there is a pouncing aspect to final attack. Once the predator get within a certain distance it would take a fairly dense prey animal not to noticed. Most predators stay outside this range of detection. The predator then pounces. And if he does it right he gets the prey. But there is a last instant where the prey can respond and escape.
I’d say that predators were the primary cause, but things don’t evolve because they must or die, in all cases. If there is an advantage to evolving, then a species could.
Also the wings didn’t need develop all at once. Imagine this senario:
A proto bird lives in tree and escapes from predators by jumping to adjacent trees. This species has a better chance at surviving if it can jump to trees further away. It develops stuctures (proto wings, strengthed chest muscles, lighter body type) to allow it to glide to further and further. Eventually sustained flight is achieved.
People like to think that flying is difficult for evolution, but it is actually fairly easy. It has evolved four completely seperate times. Pterosaurs, insects, birds, and bats. There is obviously a huge advantage to flight and the obstacles aren’t to high to achieving it.
Not only has full-fledged flight evolved four times, but you see some pretty impressive gliding, too. Give them a few million years, and maybe (or maybe not) flying squirrels will truely fly, for example. There’s also flying fish, which can stay airborn for a few minutes, and I’ve heard that there are some species of snakes which flatten their bodies and glide from trees for their attack.
There are a couple of lines of thought on this - the traditional “birds came from gliders” to the more recent “birds came from chasers” idea.
Gliders: Birds evolved from arboreal ancestors (prior to Archeopteryx, whose scales developed into feathers as these structures were more likely to cushion or soften (deliberate) falls from trees. Surviving falls allows one to pass these features on to offspring. As feathers became more effective, gliding behavior increased in complexity to include flapping and sustained flight. Why are they falling from trees? Predator avoidance and chasing prey can both be considered.
Chasers: Birds evolved from terrestrial ancestors which chased (insect) prey, enclosing them with their scaley/feathery forelimbs. As with the glider scenario, scale/feathers aid in gliding, resulting in being quicker than the prey (and thus more likely to pass these structures and behavior to their offspring). Predator avoidance is also a possibility, but the emphasis is on foraging behavior. (This is J. Ostrom’s theory.)
The glider theory has difficulty with the fact that there are few (if any) bipedal arboreal reptiles and the ancestor to Archeopteryx was most likely bipedal. A gliding arboreal quadriped would have to undergo substantial changes to become a winged biped (as oppose to a glider like a flying squirrel or a true flying quadriped like a bat). The chasers have difficulty in demonstrating how that type of foraging behavior would develop anything as complex as wings.
One area of support for the chasers comes from a math model of flight evolution suggesting that a biped chasing insects could easily evolve into short-distance flight (Russel Balda is one of the doodlers). I think they even predict that primary flight feathers (the ones on the forelimb farthest away from the body) should develop before the secondaries (the flight feathers on the forelimb closets to the body). So, I imagine ornithopaleontologists are on the search for fossils with primaries but no secondaries. (Avian evolution is not my speciality and there is most likely some newer explanation.)
Like wevets said, don’t dismiss the power of predator avoidance. There’s nothing like not getting eaten to pass your genes on to the kids. Plus, there’s plenty of food in the air (all those other flying objects).
Actually, the general consensus is that feathers evolved for insulation, not as precursors for flight. They were later co-opted for that purpose. This would fit particularly well with the idea that theropods (at least) were warm-blooded, since the smaller species would definitely need some sort of insulation in such a case.
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One which, I might point out, Ostrom abandoned as untenable (at least with respect to the forelimbs-as-insect-nets idea). Others (e.g., G. R. Caple, in 1983) revised Ostrom’s ideas, hypothesizing that instead ground-based proto-birds simply snapped up insects with their jaws. This would involve a great deal of ground-to-air leaping, thus flight could have evolved from there.
However, developing flight for a primarily ground-based forager isn’t terribly practicle in terms of metabolic cost (nor is it even terribly beneficial in terms of actual prey capture). For the size proto-birds are generally believed to be, a small proto-bird would need to catch a couple hundred insects per day. And catching flying insects is hard enough; trying to catch flying insects while learning to fly oneself is nearly impossible (today, only small, highly maneuverable, birds are successful aerial insectivores). It would have been much easier to simply hunt insects on foot. More than likely, however, small proto-birds ate small lizards rather than insects (or at least, ate more lizards than insects); in fact, Archaeopteryx’s teeth are actually more suited for going after fish than anything else (which would also be consistent with the enviornemnts in which they are typically found…).
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And, of course, the chaser model (aka, the ‘Ground Up’ hypothesis) has the problems I mentioned above
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Support for the glider model (aka, the ‘Trees Down’ hypothesis) comes from looking at the anatomy of Archaeopteryx. The forearms were well-muscled - moreso even than the hind limbs. They are also relatively longer than those of other theropods. The claws on the fingers are consistant in form with the claws of modern climbers. The hind limbs were not well-adapted for running. The hallux (inner-most toe) was backward pointing - not to the degree that modern perchers are (and we certainly shouldn’t expect them to be!), but to a much greater degree than any other theropod. The list goes on.
It is thought that Archaeopteryx had become, to a slight degree, secondarily quadripedal, and was largely (though by no means exclusively) arboreal. We see similar arboreality in the modern hoatzin (particularly in the young chicks, which even possess two clawed fingers on each wing).
It is also thought that rather than simply ‘gliding’ down from the trees, leaping from branch to branch might have been more likely. The already-elongated forearms and the presence of feathers for insulation would have been an excellent combination for producing a viable airfoil. (Of course, Dr. Lao mentioned this hypothesis.)
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Another aspect to consider is that flight is among the most efficient forms of locomotion available (one need only consider that modern migratory birds can cover 500+ miles without stopping - something no ‘runner’ could ever achieve!). For a given body size, it requires less energy to fly from point A to point B than it does to run. Oxygen consumption is abolutely higher, O[sub]2[/sub] consumption per distance traveled is much lower, because of the increased speed that flight allows.
Oh, and one more thing… wevets writes:
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Actually, pterosaurs co-existed with the early birds, all the way through the Cretaceous. However, by the Cretaceous, birds had pretty much mastered the whole ‘flying vertebrate’ thing and were starting to out-compete the pterosaurs (pterosaurs, for example, could only dream of the maneuverability that birds had achieved). Like most dinosaurs, they, too, were on their way out.
I should probably point out (before someone else does!) that what I meant by this is that as birds go, only the small, highly-maneuverable ones are successful insectivores. I did not mean to imply that only birds were successful at it! Insectivorous bats, of course, do just fine for themselves
“And (i know this sounds pretty crazy, but…) could it ever happen to humans?”
That is a very interesting question, something that could be extended to: will evolution continue with human at all in the next few thousands years?
My personal hypothesis is that external evolution will stagnate with humans except perhaps for intelligence. Why? Because possibly useful mutation are regarded as unattractive by potential mates. For example, if someone were to grow something that could eventually become wings, it would be very difficult to find someone willing to have children with him due to this genetic “defect”.
We will only tend to change towards the pseudo-“ideal” human sold by us by fashion. (Isn’t that depressing?)
