In an effort to discover the characteristics we humans supposedly inherited from organisms found in the Cambrian explosion, scientists have sequenced the genome of the acorn worm. "It's an ugly beast," says UC Berkeley professor John Gerhart, leader of the project. Coauthor Daniel Rokhsar boldly claims, “Acorn worms are marine invertebrates that, despite their decidedly nonvertebrate form are nevertheless among our closest invertebrate relatives." "Acorn worms look very different from chordates, which makes it especially surprising that they and chordates, like humans, are so similar on the genomic, developmental and cell biological levels," Gerhart adds. Chordates include humans and other vertebrates as well as a few invertebrates, but not acorn worms. Chordates, if only as an embryo, have a bundle of nerves like a spinal cord supported by a cartilaginous notochord, a body that extends past the anal opening, and a series of openings in the side of the throat (pharyngeal slits). Reflecting the evolutionary presumptions that guide his interpretation of genetic comparisons, Gerhart says, "I'm interested in the origins of chordates, which, of course, came from non-chordates, and hemichordates like the acorn worm are the closest we have to this lineage. So it's important to compare the development and genomes of our group, the chordates, with the hemichordates if you want to know what characteristics the common ancestor really had."
"The Mouth Forms Second"
Evolutionists think acorn worms, which have not changed significantly since their preservation in the Cambrian fossil record, are a living representation of the evolutionary link between vertebrates and invertebrates. All vertebrates and some invertebrates — like acorn worms — are deuterostomes, a word meaning "the mouth is second." The mouth in deuterostome embryos develops "second" — after the opening for the other end of the digestive tract. This "deuterostome" pattern of embryonic development is found not only in acorn worms but also in starfish, sea urchins, fish, and all other vertebrates, including humans. Evolutionary scientists believe that this embryologic pattern is the evolutionary footprint of our shared history with these animals through a common deuterostome ancestor that presumably lived 570 million years ago.6 This genetic study, in the opinion of the authors, confirms evolutionary relationships between these very different kinds of animals, as well as humans.