Answer :
Humans have a substantial effect upon the environment, and the environment provides the selection pressure that directs how natural selection will occur. Two examples of how humans have inadvertently directed the course of evolution are British pepper moths during the industrial evolution and African cichlid fishes in lakes. Prior to the industrial revolution, most pepper moths in Britian were light in color and blended in well on the background of trees with light bark, allowing them to avoid being noticed by predators. During the industrial revolution, soot from factories covered many of the trees in the area, making the bark appear darker. At that time, dark moths, which had been very rare, became much more common.
African cichlids diversified rapidly in the Great Rift Valley lakes. Sexual selection and positive assortative mating led to fishes living at different depths choosing mates with similar color patterns. While these fishes were not yet different enough that they were incapable of reproducing with one another, they functioned as separate species through mate choice. Different colors appeared brighter at different depths due to different amounts of light penetration at different depths. Therefore fishes attracted to the brightest mates were unlikely to move to a higher or lower depth to find a mate when the colors that appeared the brightest differed by depth and ability to percieve color at the depth at which they had adapted. Water pollution from human activity now obscures the vision of these fishes, and species that were once separate through behavioral isolation are now hybridizing and no longer functioning as separate species.