Can art be a natural thing, or must it be man made?(details)

Art is defined as a work done by a human, with further description, depending on your source, to include specifics such as asthetically pleasing.
I would update that to include animals. Some elephants, and primates have been known to be expressive with visual art.
There are birds which apparently have only one set of sounds, without variance, but many are known to experiment, mimic, or steal new sounds.
There is certainly natural occuring beauty, but it cannot be called art. While natural beauty has inspired a great portion of all art, it is the intentional act which defines it as art. In fact, quite a lot of art has no beauty, and is meant for shock value, or other emotional stimulation.

In the last century there have been efforts to expand the definition of art – readymades, conceptual art, performance art. If Duchamp could declare a urinal as a form of art, I don’t see why you couldn’t display a spiderweb as art.

Art requires intent.
And, as I see it, a deliberate focus on the visual appearance. Form should not be the direct, unmodified result of function.

Beauty is in the eyes of the beholder, so only man can conceive art.

sexist.

Art is whatever you think it is.

If a person thinks it is art, it is art. However, we generally think of art as something that was deliberately created by humans to be art. You could consider a sunset to be a piece of art, but it’s a complete accident.