Evolution and Extinction: How Populations Respond to Change
Influenza vaccines must be planned before the season in which they will be used. As circulating viruses evolve, their surface proteins can become a poorer match for the immune response the vaccine was designed to elicit. Mutation and selection are operating over months, which makes influenza an exam
How New Species Form: Speciation and Reproductive Isolation
A mule can live and work for many years but is usually sterile. A horse and a donkey can produce this hybrid, yet the hybrid usually cannot pass genes into another generation. Fertilization alone therefore does not establish unrestricted gene flow. To study a species boundary, examine both the produ
