How can a butterfly be related to evolution, natural selection and sexual selection?
For the butterfly, its evolutionary story began around 30 million years ago, according to the fossil record. Insects evolved wings to get from place to place and to reach more sources of food--in this case, flowers. Butterflies also evolved in order to migrate when Earth's temperatures cooled.
Natural selection is the process by which certain members of the population die out and are not able to pass along their genes. This is how traits more fit for a certain environment in a species are able to be inherited. Since butterflies are a prime food for birds, many developed protective coloration, either to blend in or to ward of predators. Some butterflies are able to blend in with leaves or to look like an unopened flower when the insect is still, while others are brightly colored which in the animal world often symbolizes poison. Some butterflies are harmful if eaten by other organisms, while others have simply evolved to have the poisonous colorings. The insects who did not have these genes for survival, such as bright colors, were destroyed by predators.
Sexual selection is where butterflies choose the best mates in order to increase the chances of their offspring's survival. Butterflies only want to mate with robust, healthy butterflies who do not have any genetic defects. Malformed butterflies, while they may survive in the wild, probably will not mate and their genetic material will not be passed down to further generations of butterflies. Outside of natural selection, this is one other way that a species can ensure its own survival. It is not learned behavior--it is something that is ingrained into them.