What do goosebumps have to do with evolution?

Answer 1

You had an ancestor with more hair that had goose bumps to raise that hair. Evolution is the change in allele frequency over time in a population of organisms.

So, by evolutionary process human populations lost the hair along the way, but the mechanism to erect that hair is still with us because something so trivial does not impact reproductive success and is invisible to natural selection.

Second answer

The hair-raising mentioned above was used by our early ape-like ancestors to make themselves look bigger. For example, chimpanzees, our closest genetic cousins, often raise their hair when competing with other males for mating rights and or the alpha position. Bigger usually equals stronger in nature, so the individuals who could make their hair stand out the most were more likely to scare away competitors.

As the human lineage split form the original ape-like ancestor (the other line becoming chimps), we began to lose our hair to better deal with life on the hot savannahs of ancient Africa. As explained above, hair-raising offers us no survival advantage in the modern world. But the fact that we still have this reflex attests to its effectiveness in the past. Goosebumps are therefore "vestigial." A more extreme example of vestigial body parts would be the non-functioning leg bones located in the rear of Wales.