1. In the "DNA clock", some nucleotide changes cause amino acid substitutions in the encoded protein (nonsynonymous changes), and others do not (synonymous changes). In a comparison of rodent and human genes, rodents were found to accumulate synonymous changes 2.0 times faster than humans and nonsynonymous substitutions 1.3 times as fast. What factors could explain this difference? How do such data complicate the use of molecular clocks in absolute dating?
2. Imagine that Pangea were re-formed today. What might be some of the environmental effects, and how might these changes influence life on Earth?