1. In the United States, traffic drives on the right side of the road. In Britain, traffic drives on the left side of the road. In most countries that were British colonies, traffic drives on the left side of the road. Define a "frozen accident", and address whether the choice of which side of the road to drive on is a frozen accident.


2. If we lived in a world where everybody had always driven on the left side of the road, what sort of experiment would you do to decide whether this was a frozen accident or the result of selection? Hint-driving is supposed to get you from place to place rapidly and safely.


3. Earlier in 2010, the Pacific island nation of Samoa decided to switch from driving on the right to driving on the left. Why might this cause difficulties? Why is it difficult for a cell to change codon usage, say, switching a "stop" codon to a tryptophan codon?