Tuesday, December 22, 2009

A gram of divinity

Looking back on my 45 years walking The Path, nothing has so boggled my imagination as the metamorphosis of the woolly bear caterpillar. Here is how I described it in Natural Prayers:


Of course, the totality of the transformation is to some extent illusory. What remains constant through all the stages of metamorphosis is information. It's all there, at the heart of every cell, in the DNA, blueprints for making a woolly bear and a tiger moth. There are clusters of cells in the larval caterpillar that are destined to become anatomical features of the adult moth, dormant, awaiting a chemical signal that will make them surge into activity. The warmth of spring releases hormones from glands in or near the brain. These cause the caterpillar to build a chrysalis and begin metamorphosis. Previously dormant adult cells begin to multiply. They take their nutrients from superceded larval cells, which are transformed into a kind of nutrient soup for the benefit of the growing adult organs. The woolly bear's six stumpy front feet are turned into the tiger moth's slender legs. Four bright wings develop, as do reproductive organs. Chewing mouth parts become adapted for sucking. In two weeks, the rearrangement of atoms is complete. The chrysalis breaks.

That was a decade ago. The brain-secreted hormone that triggers the transformation had been known for a long time. Now, in the 4 December issue of Science, researchers at the University of Minnesota and the University of North Carolina identify the receptor of the hormone and its signaling cascade, taking us closer to unraveling the chemistry of what would appear to be an inexplicable mystery. Here is the abstract of their report. Don't worry about understanding it; I don't. But we get the drift. Drosophilia, by the way, is the ever-helpful fruit fly.
Holometabolous insects undergo complete metamorphosis to become sexually mature adults. Metamorphosis is initiated by brain-derived prothoracicotropic hormone (PTTH), which stimulates the production of the molting hormone ecdysone via an incompletely defined signaling pathway. Here we demonstrate that Torso, a receptor tyrosine kinase that regulates embryonic terminal cell fate in Drosophila, is the PTTH receptor. Trunk, the embryonic Torso ligand, is related to PTTH, and ectopic expression of PTTH in the embryo partially rescues trunk mutants. In larvae, torso is expressed specifically in the prothoracic gland (PG), and its loss phenocopies the removal of PTTH. The activation of Torso by PTTH stimulates extracellular signal–regulated kinase (ERK) phosphorylation, and the loss of ERK in the PG phenocopies the loss of PTTH and Torso. We conclude that PTTH initiates metamorphosis by activation of the Torso/ERK pathway.
Does understanding the chemistry of metamorphosis disenchant the world. In a sense, yes. But in a more important sense, no. It replaces one enchantment with another -- bigger, more encompassing. The metamorphosis of the woolly bear becomes part of the biochemical fire that animates the world. The two blockquoted passages above -- from Natural Prayers and Science -- do not stand in opposition. They complement each other. Mind and heart. Knowledge and feeling. Science and poetry go hand in hand.