The theory of evolution by natural selection was proposed at about the same time by both Charles Darwin and Alfred Russel Wallace, shown in Figure below , and was set out in detail in Darwin's 1859 book On the Origin of Species . Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits, or traits that are not helpful or advantageous for survival to become more rare in a population of organisms. This occurs because organisms with advantageous traits are more "fit" to survive in a particular environment and have "adapted" to the conditions of that environment. These individuals will have greater reproductive success than organisms less fit for survival in the environment. This will lead to an increase in the number of organisms with the advantageous trait(s) over time. Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment. Natural selection is one of the cornerstones of modern biology.
The peppered moth used to be a light color with black spots. Occasionally some darker moths were born but they did not blend in well with the trees.When the atmosphere in London became filled with soot because of the Industrial Revolution, the white trees became darker and light colored moths became easier to see on the dark trees. After the Industrial Revolution the trees returned to their original color and light colored moths once again blended in with the trees.
Which moth had a disadvantage before the Industrial Revolution?