Quote

Wendel and co-workers (Wendel 1989, Percy and Wendel 1990, Wendel and Albert 1992) have proved that the hybridization of diploid AA African cotton and diploid DD New World cotton to produce the tetraploid (AADD) cotton took place one to two million years ago, even before the evolution of modern humans. The current picture is as follows. Six to eleven million years ago, long distance dispersal from Africa led to the evolution of the New World DD diploid species. These 13 species originated in Mexico and radiated from that locus. Some time later, African AA diploids dispersed to the New World. One to two million years ago, these diploids combined to form the tetraploid (AADD). Molecular data suggests that this hybridization occurred only once (Wendel 1995). New World AA diploids have obviously become extinct during the long interval prior to human domestication.