Spiders and Cladistics

This New York Times science story on a spider taxonomist is of particular interest because it does a good job explaining the matter of cladistics. Hoew do we know who is related to whom?

"His logic is simple: find characteristics of spiders' shapes that independently select the same exact group of organisms. "There are about 1.75 million species on this planet," Dr. Platnick explained. "Select from these all the organisms with abdominal spinnerets to produce silk - about 38,000 species. Repeat this process and select all organisms with modified male pedipalps for copulation. You end up with the same 38,000."

"This congruence of characteristics unites spiders uniquely from all others, he said. Apply the concept with higher degrees of specificity, and species' characteristics emerge.

" "You start with the null hypothesis that they are all the same. It doesn't take long to see that they are not," he said. "Then you divide them into groups of specimens more closely related to each other." "

It is now accepted that, unlike what was previously thought, cladistics can actually demonstrate both relationships and their degrees of closeness.