Until recently it was widely believed that only a limited number of species could reproduce through parthenogenesis, reproduction by a female alone. But lately, as interest in the topic has increased, parthenogenesis has been found in a variety of unexpected cases, including sharks and Komodo dragons. So the number of species that can reproduce through parthenogenesis must be increasing. The reasoning in the argument is most vulnerable to criticism on the grounds that the argument ['takes ignorance of the occurrence of something as conclusive evidence that it did not occur', 'takes for granted that because one thing follows another, the one must have been caused by the other', 'overlooks a crucial difference between two situations that the argument presents as being similar', 'equates mere interest in a subject with real understanding of that subject']