section_path: Historical development/A second synthesis
section_name: A second synthesis
paragraph_text: A second synthesis
  
  Ernst Mayr recognised the key importance of reproductive isolation for speciation in his Systematics and the Origin of Species (1942). W. D. Hamilton conceived of kin selection in 1964. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today. A second synthesis was brought about at the end of the 20th century by advances in molecular genetics, creating the field of evolutionary developmental biology ("evo-devo"), which seeks to explain the evolution of form in terms of the genetic regulatory programs which control the development of the embryo at molecular level. Natural selection is here understood to act on embryonic development to change the morphology of the adult body.