Simplify the following text for a Grade 10 native English-speaking person.
Original: John Maynard Smith , FRS ( 6 January 1920 -- 19 April 2004 ) was a British theoretical evolutionary biologist and geneticist .
Simplified: John Maynard Smith , F.R.S. ( 6 January 1920 -- 19 April 2004 ) was a British theoretical evolutionary biologist and geneticist .