When we look at islands across the planet (think the islands of the galápagos and hawaii) we see that there are a remarkable number of island endemic species, species that are found nowhere else. what is a possible explanation for this observation? sympatric speciation on islands is easier than in mainland environments because rates of chromosomal evolution are higher on islands. extinction rates are lower in islands so species that have gone extinct elsewhere persist on islands. sympatric speciation on islands is easier than in mainland environments because levels of disruptive selection are higher on islands. vicariance events are more common on islands than in mainland environments. island isolation promotes allopatric speciation. island isolation promotes allopatric speciation.