Simplify the following text for a Grade 9 native English-speaking person.
Original: In natural philosophy he asserted Charles Darwin 's theory of evolution unswervingly and set about to prove Darwin 's hypothesis that man arose in Africa ; he was also a devout Christian .
Simplified: In biology he asserted Charles Darwin 's theory of evolution unswervingly , and set about to prove Darwin 's hypothesis that man arose in Africa . He was also a devout Christian .