Friday, November 24, 2006

Strongylocentrotus purpuratus

The November 11 issue of Science reports the sequencing of the sea urchin genome.

Every wader in a tide pool knows this spiky creature. What most people don't know is that we are more closely related to sea urchins than we are to worms or flies. Vertebrates and urchins share a common ancestor, 500 million years ago.

Now we have a complete readout of the 814 million base pairs (compared to the human 3 billion bases) that are the four-letter code for making an urchin, encoding approximately 23,300 genes.

Sea urchins have been standard laboratory animals for over a hundred years, a sort of marine white rat. A century ago Theodor Boveri demonstrated in a famous experiment that a complete set of chromosomes must be present in every cell of a sea urchin for embryonic development to occur normally. The same, of course, applies to us.

Expect now to see even more rapid progress in understanding basics of embryonic development, immunology, speciation -- and a more complete understanding of our place among the myriad creatures of Earth.

Who would have guessed that a history of life over hundreds of millions of years is written in every cell of our bodies, linking us across the eons with creatures that begin their larval lives as tiny bells of transparent jelly afloat in the sea.

This is what the naturalist Donald Culross Peattie called the "most unutterable thing" in evolution, "the terrible continuity and fluidity of protoplasm, the inexpressible forces of reproduction -- not mystical human love, but the cold batrachian jelly by which we vertebrates are linked to things that creep and writhe and are blind yet breed and have being."