Insects (class insecta, with 29 orders) o o o. From thorax extend 3 pairs of legs, 1-2 pairs of wings: most successful order: beetles. The trait: improves the organism"s chances of survival and reproduction. Eventually spreads through entire population by natural selection. Evolution is change over generations in the proportion of individuals with a certain trait. o o. New traits and new combinations of traits arise through. Individuals with favourable traits will have higher fitness. Should such trait be heritable, eventually population will have it. Not all differences between populations are the result of natural selection. Genetic drift and gene flow cause populations to change genetically. Larvae feed on vegetation, adults on nectar: different mouthparts. Mate choice: struggles only some males can overcome. Intra-sexual competition & mate choice: males have bumps on dorsal prothorax for defending territory and mating, females prefer larger. Intra-sexual competition & mate choice: males to intimidate or court, females prefer louder hisses.