It is therefore clear that it is only the outward appearance of the two species that inhibits hybridization. The authors attribute this to assortative mating, the advantage of which is not clear, and it would lead to the rapid appearance of streams of new lineages, and possibly even species, through mutual attraction between mutants.
As a result, it is evident that only the external features of the two species prevent hybridization. The authors suggest that this is due to assortative mating, for which the benefits are unclear, and it would lead to the rapid formation of new lineages and possibly even species through the attraction between mutants.