Answer:
Because chimpanzee 98.6% of our DNA.
Step-by-step explanation:
Human share more of its DNA with chimpanzees than with monkeys or other groups. We also both play, have complex emotions and intelligence, and a very similar physical makeup. With the shared DNA's, some of other DNA's in human have evolved such as the forkhead-box P2 transcription factor which is involved in speech development, have undergone rapid evolution in the human lineage. According to Jane Goodall Institute (is a global community conservation organization that advances the vision and work of Dr. Jane Goodall. By protecting chimpanzees), "Dr. Goodall made a revolutionary discovery when she observed that the chimps in Gombe(Gombe National Park, Tanzania) were making and using tools." Therefore, I believe the reason why Chimps where used to reconstruct the behavior of early man and woman was because of the shared similarities between humans and Chimps which higher tham any other primates.