FIGURE 1-1 Two ways to study the process of speciation, which is visualized here as a continuum of divergence from a variable population to a divergent pair of populations, and through the evolution of intrinsic barriers to gene flow to the recognition of “good species.” (A) Using “the spyglass,” the process is studied by attempting to look back to see the details of speciation from the vantage point of the present. (B) Using “the magnifying glass,” the mechanisms of reproductive isolation are studied in partially isolated divergent ecotypes, which are used as models of an early stage of speciation.

the appropriate focus of research in speciation genetics (Ting et al., 2000; Masly and Presgraves, 2007; Mihola et al., 2009; Phadnis and Orr, 2009; Willis, 2009).

A different view of speciation genetics is now gaining in popularity: the population-level analysis of how ecology and genetics interact in various situations to cause the evolution of barriers to gene flow (Schemske, 2000; Schluter, 2001; Via, 2001). By analyzing partially reproductively isolated ecotypes or races, the genetic changes contributing to reproductive isolation can be studied before they become confounded by additional genetic differences between species that accumulate after speciation is complete. Indeed, studying barriers to gene flow in populations that are not yet completely reproductively isolated may reveal important aspects of the process that have never been seen clearly before. This approach is particularly suitable for the analysis of speciation under divergent