Suppose that you are starting a long-term study of a population of annual, flowering plants isolated on a small island. Reading some recent papers has convinced you that global warming will probably cause long-term changes in the amount of rain the island receives. Briefly outline the observations and experiments you would need to do in order to document whether natural selection occurs in your study population (what requirements must be met to establish that adaptation is happening?). What traits would you measure, and why?

Answer 1

Directional natural selection can be understood as a process by which fitter traits (or genes) increase in proportion within populations over the course of many generations. It must be understood that the relative fitness of different traits depends on the current environment. Thus, traits that are fit now may become unfit later if the environment changes. Conversely, traits that have now become fit may have been present long before the current environment arose, without having conferred any advantage under previous conditions. Finally, it must be noted that fitness refers to reproductive success relative to alternatives here and now—natural selection cannot increase the proportion of traits solely because they may someday become advantageous.