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Author | Topic: What drove bird evolution? | |||||||||||||||||||||||||||||||||||||||
PaulK Member Posts: 17827 Joined: Member Rating: 2.3 |
I suspect that the "system birds use to rotate flight feathers on upstrokes" may refer to the swivelling wrist joint which is found in no other living vertebrates. It is however found in the Maniraptoran dinosaurs and is one of the major lines of evidence supporting the dinosaurian ancestry of birds.
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redwolf Member (Idle past 5817 days) Posts: 185 From: alexandria va usa Joined: |
Bats aren't a counterexample. They don't fly anywhere near as fast, as far, or as high as birds do.
The basic reality is that birds need the kinds of hearts and lungs they have, and no other creature seems to have them. How are you going to evolve something like that? Why and how would anything which didn't fly end up with them and how would anything which did fly (the way birds do) function without them? Flight feathers same thing, beaks same thing, tail feathers same thing, light bone structure, same thing.....
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crashfrog Member (Idle past 1493 days) Posts: 19762 From: Silver Spring, MD Joined: |
Why and how would anything which didn't fly end up with them and how would anything which did fly (the way birds do) function without them? Why do flightless birds have them, then?
beaks same thing Not same thing. Not all birds have beaks, remember?
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
redwolf writes: Bats aren't a counterexample. They don't fly anywhere near as fast, as far, or as high as birds do. And yet they do fly, so flight itself doesn't require these elements. The flight of modern birds may require them, but this poses no problem for them being absent in their present forms in an ancestral bird which may also not have flown as high, fast or far as modern birds. This seems to be pretty much baseless assertion, do you have any evidence that all of these things are absoloute prerequisites for flight and have no use in a non-flight context. Beaks seem a particularly strange as a choice given, as has already been mentioned, the number of non birds which have them. TTFN, WK
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coffee_addict Member (Idle past 503 days) Posts: 3645 From: Indianapolis, IN Joined: |
Wounded King, I have to ask. What the heck is in that jar (your avatar). I thought it was brain but it doesn't look like brain.
The Laminator
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redwolf Member (Idle past 5817 days) Posts: 185 From: alexandria va usa Joined: |
quote: Flightless birds have evolved/devolved from flying birds. That is microevolution, which nobody disputes. (Micro) Evolution is good at LOSING features and complex capabilities; it is not good at producing them. Sort of like cutting hair; it's easy to cut it off, and much harder to put it back on if you cut off too much. In the cases of the ostrich, moa, and other larger flightless birds, in the ones which survived the changes in gravity which killed off the larger dinosaurs, they had gotten too heavy to fly (~30-lb limit in our present world) and the wings became vestigial. In real life, you not only cannot evolve a complex capability, but having lost the tiniest bit of such a capability, you can't ever even get the tiny bit back. Thus in the case of the domestic chicken we observe a 2-lb forest bird having been bred into a 6 - 8 lb domestic bird which still has the wings for a 2-lb bird, and can fly just well enough to hop up into trees and over fences. Now, with all the billions of chickens around, with them not having been kept in fences or cages untill very recently and with all the billions of such which must have escaped and become feral over the millenia, if there was anything to evolution at all, you'd think that some small number of those would have retaken the air, that you'd look overhead, and there their progeny would all be. As I noted however, having lost even part of the ability to fly, in real life, it doesn't come back. Now, the coelurosaur/bird ancestor needed flight feathers, wings, and a baker's dozen things he didn't have, while the escaped chicken HAS all of those things and lacks only the tiniest iota of whatever is involved in full flying capabilities. Moreover, the coelurosaur bird-wannabes would have been starting from a microscopic numeric base while the escaped chicken is working from a base of billions. If the chicken can't make it that final quarter inch, how is the "bird ancestor" supposed to make it the thousand miles??
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1.61803 Member (Idle past 1530 days) Posts: 2928 From: Lone Star State USA Joined: |
redwolf writes: Umm...I thought this changes in gravity theory was previously discussed in another thread and the consensus was that it was NOT a scientific verifiable fact. *edit typos. In the cases of the ostrich, moa, and other larger flightless birds, in the ones which survived the changes in gravity which killed off the larger dinosaurs, they had gotten too heavy to fly.. This message has been edited by 1.61803, 07-14-2004 01:53 PM "One is punished most for ones virtues" Fredrick Neitzche
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Its a beluga whale embryo, naturally.
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1.61803 Member (Idle past 1530 days) Posts: 2928 From: Lone Star State USA Joined: |
And I thought that most people just eat beluga caviar..
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crashfrog Member (Idle past 1493 days) Posts: 19762 From: Silver Spring, MD Joined: |
In real life, you not only cannot evolve a complex capability, but having lost the tiniest bit of such a capability, you can't ever even get the tiny bit back. How about those stick insects, that evolved wings, lost them, and then evolved them again?
If the chicken can't make it that final quarter inch, how is the "bird ancestor" supposed to make it the thousand miles?? I wasn't aware there was a selection pressure on chickens for flight. How about that beak thing? You keep ignoring the fact that not all birds had beaks. Oh, and if you're going to talk about that ridiculous fiction of "changing gravity", do you suppose that you could address my standing rebuttals in the thread in which we discussed it? Thanks... This message has been edited by crashfrog, 07-14-2004 02:50 PM
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redwolf Member (Idle past 5817 days) Posts: 185 From: alexandria va usa Joined: |
quote: Kind of sounds like there might have originally been flightless versions and flying versions. It's not obvous how fossils could show the difference.
quote: The advantage to chickens (of being able to fly better) would be immense: better access to more distant feeding areas, easier escape from predators, ability to move to optimal climates by season, you name it.
quote: Sorry, but I never saw one that didn't and google searches on "beakless bird" don't turn up anything meaningful or anything indicating that such actually exist.
quote: Basically, you've probably still got a handful of geniuses on talk.origins who would still tell you that the idea of a gravity change was ridiculous, nonetheless they've already lost the war on that one and they don't even know it. A google search on dinosaurs and gravity will turn up 40K hits or more, one of the directors of Los Alamos has told me that the topic is a now a safe one there, and when serious scholars went to put together a documentary on the topic last winter, they came to me and not to the geniuses at talk.origins. How about that? Japanese Office Workers Viewing The basic reality is that the question is no longer even about whether or not gravity changed, but over what caused it. A lot of the web sites which discuss gravity change argue for an expanding earth theory of one stripe or another. My own little book argues against that. http://www.bearfabrique.org/books/books.html
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Loudmouth Inactive Member |
quote: I think you pretty much answered your own questions. I will try and help you along a bit. First of all, humans selected for size, not ability to fly. The ability to fly is still there but it is hampered by the increase in muscle mass, a three to four fold increase in overall weight. Just as an experiment, triple our quadruple your overall weight and see if you can still run. For chickens to fly it would necessitate a reduction in size, something that farmers breed against. Secondly, there is not a selective pressure for flight among domesticated chickens. Given their present mass, it would take several morphological steps for them to fly free once more. In the wild each small step would mean be advantageous, but within their domesticated environment each mutation towards flight is not spread through the population through selective pressures. Thirdly, the mutations necessary for flight would probably take a long time anyway, much longer than the time they have been domesticated. Recently, it has been shown that increased muscle mass can be the result of one mutation in the myostatin gene, so an increase in size within the time frame of domestication is not surprising. What would be surprising is seeing the wing from a 2 lb bird evolve into a wing able to support a larger bird in the same time period without selective pressures.
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Gary Inactive Member |
No one wants chickens to be able to fly well. People want them to be fat, easy to keep in one area, and tasty. Therefore, they breed the fat, tasty, manageable ones. Chickens may have been able to fly a couple thousand years ago but they can't now because humans have selectively bred them.
It might be better for an individual chicken's health for it to be able to fly, and therefore escape being slaughtered, but evolution doesn't work like that. The chickens carrying genes that people like are the ones that have been allowed to survive long enough to breed, so useful chickens are all that's left. Selective breeding is just an extension of natural selection - those that humans deem fittest to eat and sell are the ones that have offspring. Feral chickens might get back their ability to fly if there was selective pressure to do so. If chickens with larger, more usable wings were more likely to breed, then those individuals would have more offspring than others and might be able to regain flight in a matter of a few centuries. Keep in mind though, that these chickens get eaten too, whether by humans or by other predators. I don't think a slightly larger wing would help them much, chickens would have difficulty getting over that hump to become able to fly again. Bird/dinosaur transitional fossils lack many characteristics that modern birds have. They might have evolved large feathers for a variety of reasons other than for flight, to get mates, to keep warm, or for whatever reason. Early birds couldn't fly like most modern birds can either, they could only glide, much like flying squirrels do.
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1.61803 Member (Idle past 1530 days) Posts: 2928 From: Lone Star State USA Joined: |
redwolf writes: except one problem, humans bred them to stay put. The advantage of chickens (being able to fly better would be immense: "One is punished most for ones virtues" Fredrick Neitzche
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redwolf Member (Idle past 5817 days) Posts: 185 From: alexandria va usa Joined: |
Humans never bred chickens to "stay put". We bred them to lay eggs and taste good. Until very recently they were never kept in cages and often ran loose, often becoming feral with feral chickens living for some generations in various areas.
Moreover any other non-flying creature which you might suppose to be evolving into a flying bird would have no plausible way of ending up with wings of the "right size". Evolution would have to take care of that for them and, if that were possible, it would have happened in the case of the escaped chicken long since.
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