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Old 11-05-2012, 04:38 PM   #1
tommo123
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Default not sure if HT but...... why do we need to pee?

i know HT is for science and not so much biology but anyway.

some animals iirc don't pee. the water gets recycled and the waste just gets added to the poop. did we just never have a need to evolve this due to having plenty of water around normally or what? europeans may not have had a need but what about people in desert climates? (living in the sahara, aussie aboriginies etc) not much water there so shouldn't an ability like this have evolved there at some point?
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Old 11-05-2012, 06:32 PM   #2
GWestphal
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Well, that is what your kidney does. It can't remove all of the water due to the concentration gradients and also the difficulty of shuttling solids around. Much easier to move a fluid with high solute concentration then to move a powder/paste/solid.

Also the time frame for divergence of this trait would be measured over 10s of millions of years. There simply hasn't been enough generations for said mutations to have occurred.

That would be my 0.02.
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Old 11-05-2012, 09:38 PM   #3
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Condensing everything to solid waste is a relatively slow process that, to my knowledge, is primarily done in small animals where the mass transfer processes have smaller barriers and therefore higher relative throughputs.
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Old 11-05-2012, 09:51 PM   #4
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it's mostly dependent on what type of excretion system is used.
humans use a urea based nitrogenous waste expulsion system, whereas other organisms such as birds excrete uric acid
there are some benefits and costs to each, of which some of the main variables are water loss, energy cost, and toxicity
http://en.wikipedia.org/wiki/Uric_acid#Biology

Last edited by fralexandr; 11-05-2012 at 09:54 PM.
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Old 11-06-2012, 10:07 AM   #5
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Quote:
Originally Posted by tommo123 View Post
i know HT is for science and not so much biology but anyway.

some animals iirc don't pee. the water gets recycled and the waste just gets added to the poop. did we just never have a need to evolve this due to having plenty of water around normally or what? europeans may not have had a need but what about people in desert climates? (living in the sahara, aussie aboriginies etc) not much water there so shouldn't an ability like this have evolved there at some point?
There's another problem - with this that hasn't been pointed out - you're operating under the assumption that evolution has goals. There isn't a "this would be better, so it should evolve." It's "this trait/this mutation confers a slight benefit in survival and reproduction." Mutations/natural variation don't necessarily "have" to provide specific traits that you're seeking.

That is, hypothetically speaking, let's say we have a cave, and we "light" the cave up with a frequency of light that's invisible to us and to animals, say something in the ultraviolet region. There's nothing that says that over the next umpteen million years that animals living in that cave MUST develop eyes that see in the ultraviolet region of the spectrum.
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Old 11-06-2012, 11:34 AM   #6
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Most simply, nature comes up with solutions to the problem of survival.

It doesn't always come up with the best solutions. They just have to be good enough for the life form to reach reproductive age, and give its offspring an adequate chance of surviving. Anything beyond that is a bonus.

And indeed, many solutions don't work. There are far more extinct species than there are living ones. Some vanish through evolution, some vanish because they all die out, when their biology is no longer adequate to ensure continued survival.
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Old 11-27-2012, 11:53 AM   #7
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Quote:
Originally Posted by Jeff7 View Post
Most simply, nature comes up with solutions to the problem of survival.

It doesn't always come up with the best solutions. They just have to be good enough for the life form to reach reproductive age, and give its offspring an adequate chance of surviving. Anything beyond that is a bonus.

And indeed, many solutions don't work. There are far more extinct species than there are living ones. Some vanish through evolution, some vanish because they all die out, when their biology is no longer adequate to ensure continued survival.
I would argue that it does come up with the best solutions. "Best" being subjective.

The difference is that evolution inadvertently weighs the costs along with the benefits. Evolution is not a straight track toward "This is best" but is a constant tradeoff of cost-benefit for various traits.

For instance, the speed of a cheetah, or hummingbird might be a best-case scenario for humans to evolve, but such activity is very expensive (in terms of food/calorie requirements) in a large animal. Further, we would have to give up our upright nature, which again, comes with cost.

So while I would love to fly..Evolution discovered a long time ago that it is simply too biologically expensive for large creatures to fly under their own power.

Last edited by IPlayNaked; 11-27-2012 at 11:55 AM.
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Old 11-27-2012, 06:36 PM   #8
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Quote:
Originally Posted by Jeff7 View Post

And indeed, many solutions don't work. There are far more extinct species than there are living ones. Some vanish through evolution, some vanish because they all die out, when their biology is no longer adequate to ensure continued survival.
every last one of them has been created by god and any single one of them that has died was due to satan. your evolutionary "theories" are so dorky

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Last edited by DrPizza; 11-28-2012 at 02:29 PM.
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Old 11-27-2012, 07:46 PM   #9
mnemonic76
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Default Dorky?

I certainly don't want this thread to be hijacked into a theological discussion, but I can't help but to ask why someone is reading the "highly technical" forum and chooses to simply call the careful consideration of generations of scientists, not to mention the other members of the forum, from all manner of religions "dorky". Seems rather a schoolyard put down. Also, please let me know where to look in the Bible for the verses about Satan making animals extinct.
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Old 11-28-2012, 10:30 AM   #10
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Because. If you can stop/start the flow when you pee, you develop control over the muscles that let you stop/start the flow of other fluids in other circumstances.

Which means you last long enough to be useful in those other circumstances.

Need practice? Drink more water.
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Old 11-28-2012, 12:33 PM   #11
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kegels? ^
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