Flightless birds:
Presumably they once flew, what is the advantage of losing this ability even IF they spend most of their time on the ground? Seems to me the ‘flyers’ would have a huge advantage when it comes to staying out of a predators way.
Mightn’t it have something to do with lifespans? (WAG)
As a species becomes larger & more localized, lifespan increases… longer-lived individuals within the species breed more, selectively breeding out flight in favor of size and lifespan?
That’s my guess, anyway. I have no evidence, but I’ll spend this whole Dope-less weekend looking it up.
Unless I get drunk instead.
There doesn’t need to be an advantage. If there are few predators, it might just come down to who can find food most easily, or who looks bigger, or who gets the gals, or whatever.
Evolution isn’t really “survival of the fittest” it’s more “survival of the ones who happen to get by at that particular time”. Which, I admit, isn’t quite as snappy.
With some of the flightless birds from small islands, I can imagine that having wings could be a disadvantage if the bird has to root around in dense undergrowth.
Darwin’s definition of ‘fittest’ was, IIRC, adapts to environment. A trait dwindling away from non-use takes a lot longer than a gentic advantage coming in. And I still contend the not getting eaten would be a bigger advantage than being big.
And dodos weren’t big or long lived.
And given the compactability of wings, I doubt that they could be SO much more of a disadvantage in undergrowth that the wingless one would be ‘fitter’. I mean, look at what a moose can go through with that rack!
It doesn’t have to be a huge advantage; the birds with smaller wings might just be able to get into places that teeny bit quicker than their larger-winged buddies, thus being able to exploit extra food resources which, when population tops out for the island, suddenly becomes a survival trait.
For the moose, the considerable reproductive advantage of having an impressive set of antlers to bash rival males presumably outweighs the slight disadvantage that they might snag on something.
Well, squeeze me. I baking powder.
In re-reading your OP, I take issue with your premise. You said that “§resumably they once flew.”
You are doing the presuming here. Who says they once flew? Cite?
I’m sensing your unspoken agenda. Why not just spit it out?
There is nothing in D’s theory which prohibits concomitant and divergent evolution. One of the arguments that Fundies love is “If we (humans, not Fundies) evolved from apes, then why are there still apes? Huh? Smart Godless science guy?”
What Fundies fail to acknowledge is that HUMANS DID NOT EVOLVE FROM APES.
Let me state that again, for those who didn’t get it the first time: HUMANS DID NOT EVOLVE FROM APES.
The best evidence available, however, indicates that humans and apes evolved from a common ancestor. Please note the difference.
There is nothing in D’s theories which excludes the possibility of different species, with different attributes, evolving from a common ancestor.
The dodo was one such branch of the common tree which had no natural predators and was perfectly adapted to its own environment… until the dominant life-form of the planet decided to exploit it.
I’m gonna stand by my original WAG… that it was more advantageous for some birds to breed for size and strength (ostriches are huge, MEAN fuckers) than for aerodynamics. The beauty of S.O.T.F. is that it proves itself repeatedly, without outside variables or modification.
Fundies: Spell my name right.
WAG: flight requires well developed flight muscles. Muscle mass requires feeding. If a bird with a ground-based lifestyle gives up flight in exchange for lower food requirements then that can be seen as a positive advantage.
For some types of flightless birds who arrived on relatively unpopulated islands, they simply may not have needed to fly anymore. A newly formed volcanic island in the middle of nowhere woudn’t have any predators to escape from, and could have plenty of food at ground level. It doesn’t just take a set of wings to fly; the whole body of the bird is modified for flying - light bone structure, ceratin types of feathers, loss of some pairing organs to reduce weight, generally small body size, the need for a lot of food due to the high metabolic rate needed to power flight muscles and coordinate associated movements, and so on and so forth… it’s really quite demanding and “expensive” biologically to keep an animal air-worthy. If you root around in the mud all day eating worms and have no one to run away from, it’s not such a huge disadvantage. There used to be all kinds of flightless birds on the Hawaiin Islands; lots of food, no predators - some species became flightless, other retained the ability. Think of it more as filling a niche as opposed to cut-throat competion between two “versions” of what a bird should be. Unfortunately, once the polynesians arrived, they quickly wiped out the flightless geese by eating them = introduction of a predator.
I beleive the main advantage of loosing the flying ability were the metabolic savings received from maintaining the highly modified “flight systems”. Meaning you didn’t have to eat as much, could grow bigger and have even fewer predators and competitors to contend with, and even take advantage of new food sources (digging up roots?) that your little seed-cracking cousins couldn’t. It doesn’t even have to be an isolated island… ostriches apparently suffered no disadvantage being big and flightless; even in an environment packed full of some of the nastiest and biggest predators to be found anywhere.
Manetout: You apparently don’t know much about moose. They do more than occasionally “snag” on something. A ranger, Rick, believe it or not, at Rocky Mountain Natnl Park, told me that moose tangle not only in each other but trees as well and DIE because of their huge antlers. This seems to me to be more than a “slight” dis-advantage. And couldn’t the same case be made for a birds wingspan? Peacocks…
FarmerOak: You are right, sir, I presumed. And I belive in divergent evolution. BUT, if these birds we are speaking of never flew shouldn’t we be studying them to find out the purpose of proto-feathers, instead of the Archiopterix(sp?).
I’m sorry, I don’t have a cite, but I betcha that they did fly at one time.
FarmerOak: I think that there are flightless birds that can reasonably be assumed to have descended from flying ones, notably some of the birds on various Pacific islands, but you’re right, we shouldn’t assume that this is the case for all of flightless species.
With a few exceptions, flightless birds are found on small islands that had no bird predators prior to the arrival of humans, along with pigs, rats, snakes, and other eaters of birds and eggs.
Exceptions are things like ostrichs, which are 8 feet tall and mean as hell when full grown. Also birds like cassowaries, which aren’t so big but have been known to kill the hunters trying to kill them. In other words, they’re big enough, mean enough, and well armed enough to fight off their enemies.
And then there are penguins - but penguins do still sort of fly, in the water rather than the air. Even then, they tend to live and nest in spots with few predators, like Antartica and islands in the southern hemisphere.
warmgun wrote:
Well… they stood about 3 feet tall, about the size of a large turkey, which is definitely towards the larger end of the bird spectrum. It’s a little hard to determine how long they lived, seeing as they’ve all been dead a few centuries.
If there are no predators about and no pressing reason to keep flying there is a tendency for species of flightless birds to evolve. Flying is very expensive from a metabolic viewpoint, requiring enormous amounts of food - whoever said “eats like a bird”, meaning very little, never owned one. Giving up flight means not having to find as much to eat, which can be very important in a resouce-poor island.
[whisper]
I bet they did, too.
[/whisper]
That having been whispered, there have been a couple of posts since this was brought up which absolutely support divergent evolution.
The Perfect Master has, of course, addressed this issue repeatedly. Whether it be wheels, humans or why we still have apes, the subject HAS been addressed.
The BEST explanation of the mechanics of this that I’ve ever seen appears in “Why Things Are, Volume II: The Big Picture” by Joel Achenbach, who is the Perfect Master’s logical successor.
(By stating the above, I do not mean to suggest that The Perfect Master will ever die, but that he will one day become so disgusted with our ignorance and lack of fealty that he will choose to Achieve the Next Level. And who are we to question this wisdom?)
In response to a question from Achenbach, the Harvard paleobiologist Stephen Jay Gould states “Evolution isn’t an optimizing principle.”
I would LOVE to quote the whole piece here (buy the book!) but I do not wish to antagonize our incredibly overworked, underpaid and, frankly, quite sexy, moderators with copyright issues.
Upshot: Evolution operates on the principle, “if it ain’t broke, don’t fix it.” An organism is not a new car, to which can be added features and options. If something works for a given creature, and, therefore, for a given species, it tends to be perpetuated.
Ostriches kick ass. So they don’t fly. Neither do you. They’ve found their niche, and they fill it pretty well.
Almost as if it were PLANNED that way…
(Did I mention how attractive moderators tend to be? Must be some sort of genetic thing going on there…)
Well, you’ve got me there, yes, I know very little about moose and only slightly more about the deer that we have here in the UK, so maybe the snag thing is more than a “slight” disadvantage, but if it outweighed the reporoductive advantage gained by having the antlers, guess what… there wouldn’t be any moose (or more likely we’d have moose with no antlers (like we have birds with no flight)
Yes, the same could be said and in fact was said (by me):
Peacocks? interesting, because their native habitat is dense jungle (Cite) - they do have large tails that would get snagged if they were to try to walk through dense undergrowth with the tail in the display position, but it isn’t a problem because they don’t try to do that, in fact when folded, a peacock’s tail is quite compact and offers little resistance to movement (the little resistance that it does cause is again, presumably outweighed by the reproductive advantage of having it (or there wouldn’t be any peacocks).
All good points, FarmerOak. One wrong assumption though - I do fly. Frequently! 
Better cut it out, though. This new administration ain’t gonna put up with your “flying” unless you’ve got a permit, and that permit says “Privileged Class.”
*Physiologically, flying is an expensive business, and when the afvantages of flight no longer compensate for the cost, wings may atrophy and disappear. At least 13 orders of birds are known to contain flightless members( Raikow, 1985 ). As a rule flightlessness is associated with geographical isolation and the relative absense of terrestrial predators…In fact, strong wings may be a handicap to island birds by increasing their chance of being blown to sea and drowned during hurricanes…Avidance of predators can be secured by adopting nocturnalliving, secretive habits, or fleet-footedness…The large flightless, ratites probably survive in the face of moderate predation because of their large size, keen vision, rapid running, and aggressiveness…Absence of terrestrial predators permits the evolution of flightlessness. But why is it favored? Flight muscles are energetically expensive to produce embryologically and maintain. A reduction in these muscle masses then would mean a considerable saving in energy which may be used for other functions such as reproduction, more rapid development, and larger legs ( Ferduccia, 1980; Diamond, 1981 ).
From The Life of Birds, 4th edition, by Welty and Baptista ( 1988, W.B. Saunders Publishing ). 
I might further mention that the large, predatory ratites of prehistoric times appear to have arisen in places where large, predatory mammals were absent, and to have disappeared, presumably outcompeted, when those large, predatory mammals appeared on the scene.
- Tamerlane
A minor nitpick: Humans did decend from apes. My parents are both apes, as are (were) their parents and grandparents before them. Modern humans are apes, as are Homo erectus, Austrailopithecus, and various other ancestral species. The common misconception is that humans evolved from gorillas or chimpanzees specifically, which we did not.
Quoth warmgun:
That depends… How often does this happen? If a moose has a 75% chance of getting entangled and killed before reaching maturity, then yes, that would be a big deal. If, on the other hand, one moose in a thousand dies from entanglement, then you could very easily say that it’s a slight disadvantage.
Don’t you talk about your mother like that.
Aside from the expense of maintaining wings and flight muscles their is the problem of unintentional use.
If using wings provides more of an energetic cost than its survival benefit then any individual without wings will produce more young (on average). Trouble is even the smartest bird can’t do the calculations and will just casually fly onto a roost even if their are no predators within a thousand miles. Any bird that does this is wasting energy for zero survival benefit. So,long as a bird has wing muscles. So any bird that doesn’t have wing muscles in a situation where their are no predators and plenty of food will have an immediate advantage even if it their is no chance of tangling its wing in dense underbrush. Survival of the fittest at work.
Now you can alter the birds thought pattern so that it doesn’t even try to fly, but even if this does occur prior to the loss of the wings the wings will still pose a liability. Time and energy is needed to groom under the wings to remove parasites, protein is wasted on keratin for full flight feathers that will never be used etc. All this for a wing that can never be used for psychological reasons. The wings are going to end up being lost again.
Dodos were at least twice as heavy as any other member of the pigeon group. I think we can safely assume that a loss of flight is necessary to obtain a 5 pound turtle dove.
The largest numbers of flightless birds were found on New Zealand, and included flightless waterfowl, parrots, wrens and nightjars in addition to kiwis and moas. The islands were swarming with predators like the ground dwelling, 20kg adzebill, largely terrestrial wekas, a gigantic 15kg eagle and numerous falcons and hawks. These all were or are predatory on birds, and highly successful. They are of course all birds themselves, but to suggest that flightless birds are found largely small islands (New Zealand has two of the worlds larger isalnds) with no predators grossly understates the truth. Even small islands like the Mauritius?Reunion group have large numbers of predatory birds. It appears to be less a case that lack of predators allows for flightlessness than that there is no advantage to flight if all your predators can fly as well. Like Tamerlane says, it’s an absence of terrestrial predators that’s important. Not an absence of predators.
Well it wasn’t a rattite, but it was flightless and about 500 lb. Bullockornis was quite comfortable living amongst fairly large predatory mammals like thylacines and marsupial lions.