Simplify the following text for a Grade 5 native English-speaking person.
Original: The earliest expressions of the basic concepts were by R.A. Fisher in 1930 , J. B. S. Haldane in 1955 , but it was W. D. Hamilton who truly formalized the concept , in works published in 1963 andâ '' most importantlyâ '' in 1964 .
Simplified: The first to write about the concept were by R.A. Fisher in 1930 , and J.B.S. Haldane in 1955 , but it was W.D. Hamilton who truly formalized the concept .