Anything that is collectively accepted among a population as a desirable trait or characteristic.
It can literally be anything.
For ducks, it's webbed feet, colorful plumage, unruffled feathers, symmetrical eyes, the ability to fly, and a solidly colored bill.
It varies between species and then among populations. The origin of it lies in the history of an organism's survivability.
We have come to prefer symmetry and color. This was actually explained to you previously in this thread by another poster.
There's a reason that you prefer colorful ducks over darkly colored newts, for example.
You aren't a duck. Your admiration for calm and color ducks does not come the same part of your brain that tells you which human you should mate with.
Your concept of beauty based on survivability is very different from your concept of beauty based on "liking" something.
Not normally. When in captivity, animals do things to alleviate their desire to mate - but those impossible crossbreeds are not the norm.
Given a healthy population, ducks will choose ducks to mate with. Geese will choose geese, swans will choose swans and herons will choose herons.
Why do you think that is, if not for what I've described?
Survivability.
Organisms are genetically predisposed to select what they know works - this is exactly why abnormal physical characteristics are not preferred among populations.
If you had no feeling receptors on your skin, would you know what heat was?
If you had no pleasure receptors in your brain, would you feel pleasure?
http://www.nyas.org/publications/detail.aspx?cid=93b487b2-153a-4630-9fb2-5679a061fff7
https://en.wikipedia.org/wiki/Evolution_of_the_eye
http://evolution.berkeley.edu/evolibrary/article/eyes_01
http://learn.genetics.utah.edu/content/selection/eye/
https://www.scientificamerican.com/article/evolution-of-the-eye/
The answer is the egg, as it evolved long before birds came along.
The question seems paradoxical because it's flawed.
The brain preceded the eyes.
If a tree falls in the wood and no creature of Earth had the ability to interpret vibrations through the air or ground, does it make a sound?
Photosensitive cells would be drawn to light sources - this would be both beneficial and problematic to primitive organisms eking out their existence. Similar organisms with similar photosenstivities would be drawn to the same sources, increasing the competition for resources. It was this very competition, however, that led to variation among the populations and eventually to you and me, and to our more complex eyes.
It doesn't. That's a nonsensical question.
Sight is not beneficial in a lightless cave environment, for example. It's actually a hindrance because it serves no purpose in that setting and an organism that has grown to rely on sight will be at a huge disadvantage to those who rely on their other, more useful, senses.
Of these two fish, which do you think would fare better in an underground lake?
It didn't. You keep asking bad questions.
Yes.
It very much matters. I'm attempting to answer those very questions - you're just pretending it was all magic, done by an invisible man who lives in a non-physical world that has never been proven to exist... Tell me how I'm wrong.
That's a great philosophical position to hold - but it's not physically how you came to exist.
You have multiples indepdent systems that keep your body working, just like everything else that's alive on this planet. Your systems, and mine, are no more special than the nematode's.
Modern computers have predecessors, don't they? They have more primitive and less complex versions of themselves that came before them, right? Why do you think the human "machine" is any different?
There would be some parts that randomly fit together, yes. And some of those parts would work. Evolution only keeps what works. That's how life is. Things that don't work get thrown in the "trash". Over time, lots of small random changes accumulate and something would come out of that cement mixer. It wouldn't be a computer as you know it - no. But it would be something.
Survivability.
We don't.
We are all of the same species, with only mild variations among our cultural environments. It is to be expected.
short answer, survivability.
Cultural homogeny
Evolution isn't linear, so no. They'll become something different from what they currently are, but that doesn't necessarily mean like us.
Not true at all. Ask yourself we we aren't more hairy - or where skin color comes from.
Everything is a trade off.
Except for all the creatures that dominate us...
Philosophy.
Genetics says otherwise.
Wrong.