Your answer should be tissues.
Rocks? not quite sure about this one but good luck and hope this helps! :)
Answer: The common ancestor of humans and chimpanzees had 24 pairs of chromosomes, and at some point in the human lineage, two chromosomes fused end to end, providing some selective advantage.
Explanation: Humans evolved in a different way due to external factors and at some point in the human lineage, two chromosomes blended giving humans a selective lead.