Twenty-three chromosomal rearrangements separate man and macaque -- except for some humans it's 24:
... But scientists have also documented some rearrangements that are not hazardous or that are even beneficial. This year, for example, scientists discovered that some Northern Europeans carry a large inverted segment on one of their chromosomes. This inversion boosts the fertility of women who carry it.How many such flips before you have a new species?