Final answer:
It is true that Darwinian evolutionary theory focuses on individual traits and differences, and Rachels' moral individualism suggests that ethical considerations should take these differences into account.
Step-by-step explanation:
The statement that Darwinian evolutionary theory emphasizes the similarities and differences between individual animals and that Rachels' theory of moral individualism suggests we should be sensitive to these traits in determining morality is true. Darwin's theory indeed focuses on the role of natural selection in shaping individual traits which can lead to the survival and reproduction of organisms. In a similar vein, Rachels' moral individualism proposes that ethics should account for the individual characteristics and capabilities of beings when making moral judgments. This approach is resonant with evolutionary perspectives on personality development, such as life-history theory and costly signaling theory as described by David Buss, which explore the adaptive significance of individual traits.