What backs up a scientific law?

Scientific laws are similar to mathematical postulates. They don't really need any complex external proofs; they are accepted at face value based upon the fact that they have always been observed to be true. Specifically, scientific laws must be simple, true, universal, and absolute.

Explanation:

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.

what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.