Discuss the fact that we conduct drug trials on other various different organisms before drugs are approved for humans.
What different types of organisms would you expect drugs to be tested on? Starting with what kind of organisms and ending with which organisms?
Knowing what you now do about Evolution and the relationships between organisms, trials on which types of organisms would give you the most confidence that the drug may work in humans? Why? What practical and ethical concerns might there be however, doing trials on our closest related species?
Even after careful trials sometimes drugs act differently when given to humans. What does that imply?