Final answer:
Divergent evolution is the process by which a body part of an ancestor evolves into different forms in different lines of descent, often due to natural selection in varying environments.
Step-by-step explanation:
Through divergent evolution, a body part of an ancestor is modified differently in different lines of descent. Divergent evolution occurs when two species evolve in different directions from a common point, leading to structures that share the same basic anatomy but look very different. This process is a result of selection in different physical environments and adaptation to different conditions or challenges.
An example of this is the evolution of the forelimbs of various animals such as humans, dogs, birds, and whales which have evolved to fulfill different functions like grasping, walking, flying, and swimming, respectively. These evolved limbs are homologous structures, indicating descent from a common ancestor while evolving for different purposes over time due to the pressures of natural selection.