As far as evolution is concerned, genital size doesn't matter — but shape does.
Genitalia are important in the evolution of new species, since compatible parts are necessary for two individuals to successfully mate. Now, new research shows that as two species diverge, evolution acts on the shape and fit of genitalia first, leaving size issues for later.
Using data from scarab beetle populations separated by anywhere from 50 years to millions of years, research led by scientists at Indiana University reveals that both male and female genitalia evolve rapidly and in parallel with one another. But between newly evolving species, genitals diverged faster in shape than they did in size....