Simplify the following text for a Grade 12 native English-speaking person.
Original: Besides his work on how environmental factors influenced the evolution of geographically isolated populations and on evolution above the species level , which contributed to the modern synthesis , he also worked extensively in the area animal behavior ( ethology ) .
Simplified: His work on the evolution of geographically isolated populations , and on evolution above the species level , contributed to the modern synthesis . He also worked extensively on animal behavior ( ethology ) .