Fish with teeth specialized for scraping algae occur in both Flower Lake and Blue Lake. Some biologists argue that because such specialized characteristics are rare, fish species that have them should be expected to be closely related. If they are closely related, then the algae-scraping specialization evolved only once. But genetic tests show that the two algae-scraping species, although possibly related, are not closely related. Thus, the algae-scraping specialization evolved more than once. The reasoning in the argument is flawed in that it ['takes a sufficient condition as a necessary one', 'appeals to the authority of biologists who may not be representative of all biologists with expertise in the relevant area', 'infers merely because something was likely to occur that it did occur', 'infers a cause merely from a correlation']