Haha, I Have not read everyone's response, and even if I did, its sometimes a little ambiguous to fully grasps some of the people's point of views on what seems to be a pretty abstract concept.
I do see a major trend though. The comparison of skill, talent, practice and hard work. Your computer's definition is a bit misleading. It says the capacity to do something, then goes a head to give two meanings involving talent. Perhaps the word "ability" is misleading and not so much the computer definition. I have the ability (capacity definition) to perceive what we understand as "colors". When I say something is red, most people can generally agree that is red, or at least a type/shade of red. That is not a special skill or talent really. Although some people are deficient in this, it does not mean I have a special talent to understand red. I merely have the capacity to understand red, and other colors.
But TO understand red... is that "natural" ability? Well, maybe.. maybe not. I was born without being color blind. So my genetics say I am able to see color. However, "what is red" can be seen arbitrary, or scientific. I grew up being told that when I see a color of a certain characteristic, I was taught how to identify it by giving it a name (red, green, yellow). That was a learned ability (identifying red) based on genetics (I use genetics to describe my whole being without breaking it down by each system, like attributing credit to a functional occipital lope and cones of my eyes and what not.).
Think of this... Color (as a noun) is defined: "The property possessed by an object of producing different sensations on the eye as a result of the way it reflects or emits light." (Googled "What is color") So what if we have a can of paint... the paint is open and we clearly see what we perceive as red... but then we close the paint can... There is no light, and no eyes to see the paint... Is it still red? (If a tree falls, and nothing is around to hear it.. Does it make a sound?) Granted, I highly doubt the chemistry of the paint changed, but there is no light (or eyes)... So maybe an essential ingredient was removed...... (I put this scenario together because it seems to show that one can understand red as a color, understand red as a result of light, understand red because I was taught what "red" is, and because it shows I have the capacity to try and negate red really exists [in the absence of light] )
So back to topic here... Along with the sense of sight, I was fortunate enough to be born with a sense of hearing. Like seeing different shades of red, I can hear different sounds. Maybe I can see and hear differently, perhaps "better" then another individual based on my genetic make up. Perhaps I can see and hear worse then another individual.
But why? Well.. It can deal with my brain and how my sensory perception developed. This is nature.
But at the same time, at a very young age I was constantly surrounded by music playing on my grandmas radio. I now have a deep love for Irish/Celtic music. Also, on long car rides, I remember hearing certain songs. These songs left a permanent nostalgic feeling. Most times when I hear Billy Joel - Piano Man, I am taken back to a point deep in my memory where I was sitting in my grandpas blue car, I believe in Manhattan (I remember being in the right or middle lane of the road approaching/ about to go under the L. (To those not familiar: L means Elevated Train, frequently found in nyc) Then my memory jumps to being in McDonalds and something involving a man in costume dressed with a quarter moon as his head.. He was a piano player... (weird now that I try and explain it instead of thinking about it..) These are examples of the environment playing an effect on my understanding of music. If I hear that opening scale run of piano man, I can pretty much recognize it, even out of context. (As in, I can associate that pitch/ scale to that song, and then recognize it out of the song... Like I can it is played in C Major, and I can more readily identify C Major because of it. Well, that song and because C major is the easiest scale in music.. it "The People's" Scale as I once heard, and I played it so many times in my piano classes.) That is nurture having an effect on my understanding and perception of sound.
Thats mostly about understanding music, and hearing it and what not. I doubt a child is born with the ability to pick up a guitar and just start strumming what he hears in his head. He has to learn what noise strings make, and at what fret as well. However, that child can have a predisposition, such as good "muscle memory," and a body type that more easily build up strength, dexterity etc (general motor ability stuff, functional nerve impulses that dictate what the muscles are supposed to do and such). These together is what I think people are calling "natural ability" It does not have to mean a natural ability to play music, but it seems like inherent qualities that facilitate the understanding of to how to hear and manipulate certain sounds.
I hope I didn't bounce around too much... I was kind of just rattling off what the voice in my head is telling me to say....