Simplify the following text for a Grade 9 native English-speaking person.
Original: One of Louis 's greatest legacies stems from his role in fostering field research of primates in their natural habitats , which he understood as key to unraveling the mysteries of human evolution .
Simplified: One of Louis 's greatest legacies was fostering field research of primates in their natural habitats . He understood this helped to unravel the mysteries of human evolution .