Two possibley simple questions I've difficulty answering...
 

Evolutionary: If humans developed slowly, how did we avoid the problems that make it bad for cousins to marry?

Aerodynamics: How can a seagull turn, hover...still hover, descend, ascend, and continue on now with a 5 year olds sandwhich with barely any wing movement? Airflow control through wings?

Evolutionary:

Here is my take:

Since humans developed from Homo Erecti, there was still a diversity in the gene pool...The groups that were living together probably were related, however, they were not groups that were small enough to cause genetic defects to become prevalent.

Truth be told, marrying and having a child with your cousin would not, in the first generation cause any noticable defects...unless there were some major genetic defects already there. 3rd, 4th, 5th generation of inbreeding would definitely start to show problems. (i.e. cleft chins turning into major birth defects, minor flaws becoming major issues as the inbreeding continues.)

All in all, the gene pool still had enough diversity to deal with many defects...however, maybe some of the human frailty there is today and susceptibility to diseases is due to the fact that the gene pool was limited for a long time...

Aerodynamics:

This would be attributable to the same mechanism that airplanes use (i.e. flaps) to move upward and downward in their flight. The birds are jsut really damn good at it!!

By changing the airflow, as you stated, over their wings, they are able to change the pressure differences between the tops of their wings and the bottom...thereby either creating lift or destroying it.


great questions!!
:)

Xell, if they face into a reasonable wind, birds can remain stationary but still produce lift, just like they would if they were moving forwards. It's really bizarre to watch :)

I've noticed Seagulls at the landfill flapping as much as other birds. I think they probably evolved into limited flapping at the sea where there is usually a steady wind that they can glide on, but some at the dump are willing (and able with the abundant food supply) to work harder.

My brain isn't grasping the aerodynamics of it at all, I still have an odd time trying to understand how minor movements can have such tremendous effect on the birds movement.

Its really hard to comprehend breeding patterns and their effects though. From history middle to early modern ages, supposedly:
Europeans developed many diseases, while the Chinese were supposedly very healthy people before foreign diseases arrived. The same goes for Indians, yet they were less apt to be able to stand hard labor. Europe was the most ethnically diverse, yet they developed the most diseases. How has breeding habits changed since then, we are mixing races and ethnicities even more today.

Wasnt it mostly just the royalty that had problems with inbreeding? The main evolutionary factor that I see during that time is that the populace was subservient to the will of others and therefore outspoken or brave persons were put down. It may say something about the traits we developed. It was hard to be a hero or die-hard yet we look up to heroes and have developed morals today.

Planes don't have to flap their wings, they utilize nothing(mostly besides some stabilizers) but the force of the wind for lift(only magnified by their propellers or jets). The structure of the wing creates more lift on the bottom than the top because more wind is under the curved lower surface of the wind. I only know the basics so I'm not sure how good this explanation is.

Yes royalty has had a lot of problems with inbreeding. Hemophelia is often called the royal disease, because it was passed on in British royalty for many generations.


Like others have said, an eagle keeping its wings stationary is just like your average airplane. The wings are curved in such a way that air passes over the top of the wing faster than it does the bottom of the wing. This creates low air pressure on top of the wing and high air pressure underneath the wing. Things move from higher to lower pressure, so the low pressure air is sucking the wing upward. The bird/plane is attached to the wing, so it gets sucked up too. This phenomenon is called lift. Airplanes are heavy, so they have to propel themselves forward in order to create a strong enough artificial wind over the wing to produce enough lift. Birds are light (hollow bones etc.), so natural wind is often enough to keep them aloft. If there's a lull, they have to start flapping.

Like someone mentioned, sails work on the same principle. I think somebody actually took an airplane wing, stuck it on a boat, and almost broke the wind-powered watercraft speed record.

Man, I would love to have seen that!! :)

I'm referring to how to a seagull can barely move the ends of it's wings and:

- Turn left
- Swoop down
-coast along
- Swoop up

It seems wierd that with such little adjustment to the wings so many different flight movements can be done.

Re: Two possibley simple questions I've difficulty answering...
 

Erm, not sure I really understand that question.

How did we avoid the problems? We didn't. It IS bad for cousins to marry (blood cousins). It's just not as bad as sisters/brothers doing it.

I recommend the following books if you truly do have an interest in genetics and human evolution.

Genome, The Autobiography of a species in 23 chapters - Matt Ridley (ISBN 1-85702-835-X)
The language of the genes - Steve Jones (ISBN 0-00-655243-9)
What evolution is - Ernst Mayr (ISBN 0-465-04426-3)
The day before yesterday - Five million years of human history - Colin Tudge (ISBN 0-7126-6173-5)
The rise and fall of the third chimpanzee - Jared Diamond (ISBN 0-09-991380-1)

Just picked these five off my bookcase (and yes, I have read them all :) ). I have more recommendations if you wish.

Fascinating subject.


Mr Mephisto

Fascinating indeed. Thanks for the recommendations.

Genome and The Language of the Genes are probably the best (ie, most readable) "popular science" titles listed above.

They specifically deal with human genetics, whilst Mayr's book looks at evolution in broad conceptual terms. Diamond and Tudge both examine the emergence of human consciousness. If you're especially interested in this subject, I highly recommend The prehistory of the mind by Steven Mithven.

Diamond is also the author of the excellent Guns, Germs and Steel which examines the development of society, culture, agriculture and civilization.

Happy reading. It really is amazing to learn more about our history and what makes us human.


Mr Mephisto

Airplanes can do exactly the same things. They don't flap their wings but can make the same small adjustments to their wings for similar effects. Next time you fly check out the wings when you're taking off or landing, there are flaps on the rear edge of the wings - I think they're called aerilons.

Try this: make a paper airplane and rip two lines at the back of each of the wings, creating rectangular flaps. Folding both of these up or down will change it's pitch, and having one straight and one bent will do crazy spinny stuff. It's all about adjusting the airflow over the wing.

I'm sure seagulls can do the same thing with their feathers, and from so far away the very minor adjustments are impossible to see.

a little bit off topic, but i found this really cool theory on how humans evolved differently from other apes. It was because one ape started to develop a very aquatic behavior, i.e. the white fat humans have (typical to aquatic mammals), the elevated, more advanced voicebox (again typical to aquatic mammals), and teh fact that humans are one of the only land mammals, and teh only primate, that instinctively holds its breath when put underwater as an infant... there was some more proof but i only remmeber those

The easiest way to understand it is to feel it for yourself. Next time you're driving on the highway, put your hand out the window. Make your hand flat and make it 'fly' with the wind. With your arm loose, try slightly tilting it up and down and you'll see your arm fly up or down with it.

who says the way we are now is not "defective" relative to the way we could have started.......Longevity, strength, health..etc?

New species or common defects among the old ones?

This so-called "Aquatic Ape" theory was proposed by Elaine Morgan in her books The Descent of Woman and The Aquatic Ape.

I believe that today it is more or less considered bumkum by paleoanthropologists, evolutionists, geneticists and the established scientific community.

Mr Mephisto