The evolutionary relationship between many organisms can be traced back to a common ancestor. A common ancestor is an individual from which two or more related species could have evolved. With the passage of time, organisms change and diverge from their common ancestor to form new species. The following evidence for evolution demonstrates the concept of the common ancestor. DNA, RNA, the genetic code and protein synthesis are similar in all organisms. The greater the genetic and molecular similarity between species, the closer their common ancestor. Humans and chimpanzees have 98% of their genes in common. The remaining 2% is what distinguishes these two species from each other. Humans did not descend from chimpanzees but from primitive humans. However, at some point in evolutionary history, primitive humans and primitive chimpanzees probably diverged from a common ancestor. Diabetics can use insulin from cows and pigs because insulin from these animals is almost identical to human insulin. In addition, hemoglobin in humans, which has almost 600 amino acids, is almost identical to hemoglobin in all other vertebrates. This similarity in chemical structure demonstrates that all vertebrates can be traced back to a common ancestor.