G. Ledyard Stebbins George Ledyard Stebbins , Jr. ( January 6 , 1906 -- January 19 , 2000 ) was an American botanist and geneticist who is widely regarded as one of the leading evolutionary biologists of the 20th century .
G. Ledyard Stebbins George Ledyard Stebbins , Jr ( 6 January 1906 -- 19 January 2000 ) was an American botanist and geneticist . He was one of the leading evolutionary biologists of the 20th century .