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Author Topic: Why don't evolving wings cause problems for a creature before being fully formed  (Read 4303 times)

Offline krytie75

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I understand the process of evolution and I do subscribe to the theory but there are some aspects of it I can't get my head around...

For example, how does a creature evolve wings and become able to fly when the wings will not function until they have completely evolved into a working wing. I can't imagine a creature loping around with half a (non functioning wing), when said stump would probably impede it's ability to survive and cause it's death before it has chance to procreate and spread the stump DNA down into the next generation.

There seem to be many things like this in nature that are too complex to have evolved in 'one step' but would almost certainly have caused problems for a creature before reaching a working stage of evolution.

Thanks in advance for your answers!


 


Offline CliffordK

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It may be difficult to imagine a (flying) bird without fully developed wings.  However, one might be able to look at other examples in the animal kingdom.

For example, a flying squirrel has developed an evolutionary niche where it can glide from tree to tree, or tree to ground.  One can imagine the ancestors to the flying squirrel being normal squirrels that would jump from branch to branch and tree to tree.  Perhaps those that spent less time on the ground were safer from predators, or taking less energy to get from place to place by gliding there.  Nonetheless, the flightless squirrels still could compete, but those that could jump and glide would be selected for, with the better gliders being more competitive than the less effective gliders.  It wouldn't be a big jump to consider future squirrels developing powered flight, if it would actually serve them a purpose.  Perhaps initially developing a method to flap the legs to maintain level flight, then from there move to more upward trajectories.

Now, lets think of a bat.
Perhaps beginning as a mouse that developed an affinity for insects, or lets think of it as a cat-like creature.  Have you ever watched a cat trying to chase a moth?  The ability to jump a little higher would certainly be an advantage.  Again, one could imagine the development of webbing like a duck, but on the front feet to help propel the cat upward, then eventually evolving from jumping to flying.  Echo-location is a pretty extraordinary ability of bats.  However, perhaps it is necessary for nocturnal hunting of insects.  And, of course, there are advantages of hunting at night such as escaping predators.  Some humans have in fact developed the ability to do rudimentary echolocation, so perhaps it is not to big of a jump to think animals might also develop and improve the ability until it is more effective than eyesight. 

Insects, of course, would also be moving from improved jumping to flying to take advantage of the 3 dimensionality of the atmosphere, and to help escape from predators on the ground.  Think of perhaps a grasshopper or cricket with a powerful jump, then eventually developing wings to extend the jumping (which most have).  Over time, the legs might atrophy with the growing of larger wings, and less energy being wasted in flight.

Now, the birds have many optimizations for flight.  However, most people believe that they evolved form a much more bat-like flying dinosaur such as a Pterosaur.  Feathers would have come later as a very lightweight and durable method to improve aerodynamics and conserve weight.  Perhaps beginning as a sort of fur that became optimized for flight.

 

Offline Nizzle

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Feathers might have also evolved from/on skin because they isolate better against the cold, which would be a useful pre-flight adaptation in it's own right, and then later the feather patterns on the upper limbs and tails were perfected and allowed flight.
Let's not forget that the modern day dinosaurs (ie birds) are warmblooded/endothermic while the old skool dinosaurs were either warm- or coldblooded (jury's still out on that), but anyway insulation is important for warmblooded animals..
 

Offline Don_1

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A damn fine question sir/madam/miss, but if you take your question to a logical extreme, you could ask it of just about any part of the body of any of the higher animals. As single celled organisms developed into multi celled organisms and continued to grow bigger, their need for oxygen gradually outstripped the capability for simple diffusion to supply it. But the circulatory system did not appear over night. So you could ask, ‘what use were lungs, a heart, blood vessels etc?’ The point is that these developments must have provided an advantage.

In the case of wings, such a development had already taken place before the birds appeared. Pterosaurs had developed flaps of skin on their forelimbs which enabled them to glide. However, I personally and contrary to Clifford’s statement, do not subscribe to the idea that birds evolved from the pterosaurs.  I think it far more likely that feathers preceded wings. The early feathers would have evolved from the scales of reptilian skin into a downy insulation as protection from cold nights. It may be possible that this development took place on reptiles living at high altitudes, where lower temperatures were more liable.

Just as pterosaurs had developed flaps of skin on their forelimbs, these early flightless birds, the likes of Archaeopteryx, began to develop larger feathers on their forelimbs.

Now this is pure speculation, I think it possible that this was not for the purpose of flight, but for extra insulation against the cold. Being able to wrap a feathery pair of arms around yourself would offer improved insulation. Would these early ‘wings’ have got in the way of normal transit? Possibly yes, but the benefit of extra insulation may have outweighed that minor interference to perambulation and may have proved useful in its eventual provision of the ability to glide over short distances. It is thought that Archaeopteryx would have been a rather clumsy animal.

These larger feathers on the forelimbs would develop into the flight feathers which would enable the birds to glide over longer distances and in a more controlled manner. But flight did not depend solely on the development of feathers and wings. It was the internal development of a bone unique to the birds which would give them the ability of powered flight. The wishbone, which is considered to be the major factor in linking the birds with their predecessors, the dinosaurs, in which some Theropods  also had this fused scapula. But even this is not the end of the story, for the birds also developed system of breathing which is different to that of their reptilian ancestors. As yet, no link or transitional step has been found between the two systems.
 

Offline CliffordK

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I'm going with wings being a better adaptation for hopping and jumping, and feathers, while good insulators due to trapping air, were an adaptation of the need for lightweight covering and wing extensions.   

However, a perhaps a similar idea to Don's for the formation of the wings would be that many animals like to "puff themselves up", to appear much larger than they actually are.  Many birds will do that today.  What better way to do so than stand upright and spread out enormous wings.  A bird with extended wings might look several times as large as one with just ordinary arms.  There would be strong natural selection of any adaptation that would make prey look unappetizing to predators. 
 

Offline CliffordK

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There was an NPR special today about a book:

Feathers, the Evolution of a Natural Miracle, by Thor Hanson
http://www.npr.org/2012/09/04/160539034/conservation-biologist-explains-why-feathers-matter
http://www.feathersbook.com/
http://www.amazon.com/Feathers-The-Evolution-Natural-Miracle/dp/0465020135

I haven't read the book, but it sounded like an excellent review of feathers, and the evolution of feathered animals.

According to Hanson, the feathers began to evolve with the theropod dinosaurs (meat-eating dinosaurs including Tyrannosaurus rex), probably as color, and insulation.  These dinosaurs were primarily bipedal which freed up the arms for other evolutionary purposes, including the development into wings.
 

Offline evan_au

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Here is a genus of lizards which glide: http://en.wikipedia.org/wiki/Draco_%28genus%29

..and snakes: http://en.wikipedia.org/wiki/Chrysopelea

...and marsupials: http://en.wikipedia.org/wiki/Sugar_glider#Gliding

None of them have feathers, or what you would call a working wing...
 

Offline evan_au

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A recent suggestion from fine Chinese dinosaur fossils was that many dinosaur species had feathers.

http://en.wikipedia.org/wiki/South_Polar_dinosaurs suggests that on Gondwanaland, some dinosaurs lived inside the Antarctic circle, where there would have been several months of darkness in winter - a down quilt would have been quite welcome!
 

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