Talent appears throughout the ages at varying degrees...but there is one constant: There's always someone who can draw. If only 1% of the population has an artistic talent, and 1% of those artists can look at a target and then draw an accurate representation of said target, and only 1% of those people actually get themselves in a situation to where their art will be viewed and deemed worthy of saving, and only 1% of those people isn't a total douche, then there's still a couple people with all the above qualities producing good work. Looking at artwork 100's to 1000's of years in age I see inanimate objects drawn with proper scale and dimension...bows, for example: There are people out there who make functioning bows based on dimensions they gained from artwork thousands of years in age.
What's the point of this? Knowing all of the above, I have come to a couple conclusions:
Humans made a dramatic switch from monocular to binocular vision somewhere around the mid-1500's. The obvious most obvious explanation is that mankind developed a second eye. People argue this point with because pictures always show people with two eyes. I think artists simple knew the second eye was coming and compensated so when people look back at their work no one will think its weird. Another, but far less plausible explanation is that our heads suddenly got bigger and it allowed our eyes to gain enough distance from one another to properly identify distance and dimension.
It's either that or people really looked like that a thousand years ago.