Broca, influenced by previous work Samuel George Morton, used the concept of hybridity as his primary argument against monogenis, and that it was flawed to see all of humanity as a single species. Different racial groups' ability to reproduce with each was not sufficient to prove that idea. Under Broca's view on hybridity, the result of a reproduction between two different races could fall into four categories: 1) The resulting offspring are infertile; 2) Where the resulting offspring are infertile when they reproduce between themselves but are sometimes successful when they reproduce with the parent groups; 3) Known as Paragenesic, where the offspring's descendants are able reproduce within themselves and with parents, but the success of the reproduction lowers with every generation until it ends; and 4) Known as Eugenesic, where a successful reproduction can continue indefinitely, between the intermix descendants and with the parent group.