Ernst Mayr has written that Darwin's theory contains five theories that relate to different aspects of variational evolution. These are: 1) organisms evolve over time, 2) different organisms have descended from a common ancestor, 3) species multiply over time or speciation, 4) evolution is slow and gradual, 5) the primary mechanism of evolutionary change is natural selection. What kinds of evidence does Darwin cite to support these different aspects of his overall theory? Be sure you explain why something is evidence for different aspects of the overall theory. What role did Malthus play in Darwin's thinking?