His work on the theory of population genetics made him one of the three great figures of that field , together with Sewall Wright and J.B.S. Haldane . He was one of the founders of the neo-Darwinian modern evolutionary synthesis . His work on the theory of population genetics also made him one of the three great figures of that field , together with Sewall Wright and J.B.S. Haldane , and as such was one of the founders of the neo-Darwinian modern evolutionary synthesis .