The genetic difference between man and chimpanzeese (depending on the source) is roughly 1 to 1.2 chromosomes (chimpanzee chromosome 19 and 22 and the human chromosome 17)
I think the reason he called this definition -2genes was due to the fact that not all humans are created equally. In some mentally / emotionally deficient case studies, it would appear that in a select group of genetic human failures GHF the normal process of evolution was bipassed in order to preserve the more primative traits of the subspecies. Due to these circumstances, the author of this definition excercised "observational liberties" based on real life experiences and not a controlled biogenetic analysis.
see: observational liberties
see: Blowing sMokE up your ASS!