This term is usually used to refer to something that is not found in nature. For example, a skyscraper is unnatural because it has to be constructed. However, to use this definition requires you to exclude humans from fitting into nature. If you include humans in nature, then all of our actions are also natural, including the things that we construct. This would mean that cars, computers, and cloning are all natural. And since things constructed and created by animals are all considered natural (honey and beehives, dens for burrowing animals, etc), this seems appropriate.

However, this leads to everything that we see and do being natural, and therefore, nothing is unnatural.

The term is also often applied to behavoir that people claim is only done by humans, and not by animals. But one must wonder if such so-called unnatural behavoir would instantly be considered natural if animals are found to perform that behavior.

This last point is of interest because many opponents of homosexual rights claim that such behavior is unnatural. However, homosexual behavior has often been observed in animals of various species. So would they still claim it is unnatural?