Researchers at Stanford University compared the genetic code of humans to chimpanzees and ended up with some amazing results.  They found 510 gene segments in chimps that are missing in humans, nearly all of them switches that turn nearby genes on or off.  By looking at what the genes did, they were able to explain some key differences between chimps and humans including why humans have big brains and why the human penis is not covered with prickly spines. 

- ‘Cuz the spines would break the condom, duh!