gene flow or migration between two populations will help maintain similarities between the species, therefore preventing (or slowing down) the process of speciation. and when the environment changes rapidly, this can cause an overall decrease in population size because of a failure to adapt adequately to environmental changes. i hope this helped <3
Pollution caused the environment to become more darkly colored, so moths were selected to be blacks and greys. Before pollution they were white and lighter colors. <span />