The "Advanced" Tunicate

When I was along on my daughter's grade school field trip to the beach at low tide, we found a tunicate. A tunicate looks like a little white blob, soft and shiny like a jellyfish. Surprisingly, they're chordates. The field guide to tidal animals said that they are among the most advanced animals found in the tidal zone. They are not. The author was thinking like a 19th century biologist. Tunicates are chordates. Chordates are the most advanced phylum in the animal kingdom. Therefore tunicates are more advanced than crabs, sea stars, anemones, and snails. That's essentialist logic.

In fact, tunicates are primitive. Some of them are actually colonies of single-celled animals rather than true multicellular creatures. The reason the author of the field guide called them advanced is that they're closely related to the chordates that evolved into vertebrates, a sub-phylum that indeed includes the most advanced animals on the planet. But being advanced isn't essential to being a chordate. The group of things called chordates doesn't exist in the Mind of God as a coherent whole to which general traits— such as being advanced—are to be assigned.The fallacy of treating a phylum or other group of animals as an essential whole leads to various secondary fallacies, such as "if humans evolved from apes, why are there still apes," the idea that "races" are distinct and homogeneous, and E.O. Wilson's theory of animals evolving behaviors that benefit the species.

October, November 2002