About 150,000 years ago something very interesting happened to the 'human' Y chromosome. Very, very interesting.
Also, why to all the 'other' simians have 48 chromosomes, while we have 46? You can't mate a 48 with a 46. Perhaps a 46 needed to modify a 48 into a 46…
Oh look, chromosomes 2 and 13 have been fused. Perfectly.