The 4 species of great apes; gorillas, bonobos, chimpanzees, and orangoutangs; each have 24 chromosomes. In a rare stable chromosomal disruption, some 7-8 million years ago, two chromosomes fused together in our common ancestor which gave rise to the homo genus with our 23 chromosomes. What is additionally astounding is that breeding seemingly would have had to have occurred between different species with a different number of chromosomes.