Tuesday, April 22, 2008

Earth Day

This albino gray squirrel greets me every morning as I approach the College Commons for my coffee. I call it Whitey Bulger. Somewhere in its genome is a missing instruction for making pigment. A recessive gene inherited from both parents? A mutation? One wonders if lack of pigment makes the squirrel more likely prey for the red-tailed hawk that is often circling overhead.

I don't know the size of the squirrel genome. A rat's genome has about the same number of base pairs and genes as a human, so I would assume the squirrel is in the same ballpark. Somewhere among those 30,000 genes is Whitey's distinguishing inheritance.

And among all those genes too is the squirrel's place in the history of life on Earth. In the April 10 issue of Nature, an international group of more than a dozen scientists describe the most complete attempt yet to suss out evolutionary relationships based on sequenced genomes. The researchers worked with a huge genetic data base drawn from 21 phyla, including 11 animals for which no genomic data was previously available. By and large, the results confirm the familial relationships previously established from anatomical similarities and differences. The evolutionary history that is writ large in an organism's physical appearance is writ small in the DNA. Some new and interesting relationships were also discovered.

And yes, there we are, in the full-page phylogram of 77 species, Homo sapiens, snuggled up with Gallus gallus, the red jungle fowl, our closest relative in the sampling, and tucked between the sea squirt and a wormlike lancelet. Together we four represent the phylum Chordata, characterized by "backbones" (or a primitive precursor thereof).

What a succinct little corner of the animal kingdom! Just look at some of the other animals swimming around on the cover of Nature, including assorted worms, jellyfish and a sea spider. Where is Homo sapiens? We are the journal itself. We are the researchers from the United States, Sweden, United Kingdom, Denmark, and Germany who together compiled the phylogram. And isn't it a wonder that in seeing our place in the grand unfolding of life on Earth we cannot manage to get along better among ourselves -- and with the other creatures of the planet.