Final answer:
Variations in behavior and morphology are expected due to the combined influence of genetics and the environment. Behaviors selected by Belyaev and Trut have a genetic basis; however, environmental factors can shape and modify these traits. This illustrates the complexity of the nature versus nurture debate in the development of animals.
Step-by-step explanation:
While the behaviors selected by Belyaev and Trut indeed have a genetic basis, variations in behavior and morphology are expected because of the interplay between genetics (nature) and the environment (nurture). The experiments conducted by Belyaev and Trut with foxes demonstrated that selection could lead to dramatic changes in behavior and physical characteristics over several generations through genetic manipulation.
However, it is also true that an organism's development is affected by its environment. For example, two foxes with the same genetic predisposition for tameness may exhibit different behaviors if one is raised in a stressful environment, while the other is nurtured in a calm one. Additionally, while certain traits such as social behaviors tend to have a significant genetic component, these traits may still be modified by individual experiences.
Morphological changes, like behavioral changes, are also not solely determined by genetics. Nutritional factors can affect the size and health of an organism, demonstrating that the variability in morphology is also subject to environmental influences. It's important to note that genetic variations must exist for natural selection to work on them, but these variations can be influenced or magnified by environmental conditions.