The context reproductive isolation

NEED GENETICS TUTORING HELP WITH THIS “There is also the terminological problem that reproductive isolation combines traits that reduce gene flow, such as mate choice or fertilization barriers, with traits that select against genes that have flowed, such as hybrid incompatibility. Lumping these two antagonistic features is confusing, since they are unrelated and evolve in very different ways. For instance, whereas it is conceivable that reinforcement might evolve to reduce an individual's tendency to mate with another species and produce inviable offspring, it is almost impossible to imagine that hybrid inviability itself would evolve as an adaptation. This reproductive isolation terminology leads also to a muddled use of the term gene flow as the opposite of reproductive isolation; in other words, gene flow comes to include not only the flow of genes, but also the effects of any natural selection on the frequency of such genes within each population.

Perhaps the most fundamental problem with isolating mechanisms (and specific mate recognition systems) is that species are implied to be qualitatively different from subspecies, races, or forms by their possession of these traits. Races cannot, in theory, differ in either type of trait because only species are defined by their possession. Arguably, by making species seem qualitatively different from races, these terms have spawned a number of special models of speciation where geographic isolation, also known as allopatry, or sudden bursts of evolution in small founder populations (founder events or punctuated equilibria) play important roles. Only such unusual conditions were thought to be able to give rise to new species that differ in isolating mechanisms (or specific mate recognition systems). In reality, there is little to distinguish mate choice and disruptive natural selection commonly observed within species from pre-mating and post-mating isolation between species; and, indeed, it is hard to distinguish species from races in many actual organisms”.

3. Gene flow and natural selection: Another issue arises in the use of the term "gene flow" as the opposite of reproductive isolation. Gene flow typically refers to the exchange of genes between populations through mating and reproduction. However, in the context of reproductive isolation, gene flow may also include the effects of natural selection on the frequency of genes within each population. This usage can lead to confusion when discussing the mechanisms that maintain species boundaries.

4. Species, races, and isolating mechanisms: The passage suggests that the distinction between species and races is not always clear when considering isolating mechanisms. Races, subspecies, or forms within a species can also exhibit traits that reduce gene flow, and it can be challenging to distinguish between these different taxonomic levels based solely on the possession of isolating mechanisms.