Monday, February 15, 2010

The little organ that wasn't

I visited the Leonardo Da Vinci exhibit at the High Museum of Art in Atlanta on Saturday. Not being much of an artist myself, I was nevertheless intrigued to see one of his anatomical sketches on display. The sketch was dated to approximately 1492 and depicted sections of the human head. Da Vinci's notes mentioned the rete mirable, the "marvelous network" underlying the brain.

The rete mirable looks like a little sack of worms. It's a complicated net of arteries blood that occurs at the entry of the arteries into the brain. According to Galenic medicine, the rete converted the "vital spirit" of the blood into "animal spirit." Animal spirit was a vaporous stuff that the brain used to send signals to the rest of the body.

There's only one problem with the rete: It isn't really there. The first to notice its absence was Mondino in the early 14th century. In the 16th century, Vesalius, the famous reformer of anatomy and corrector of Galen, diagnosed the problem: The rete is prominent in some quadrupeds, like cattle, but it is absent in humans. Since Galen based much of his anatomy on dissection of animals, he likely just assumed that humans had a rete as well. There was some resistance to abandoning belief in the rete (where else would animal spirit be made?), but that changed as more and more anatomists began dissecting cadavers for themselves.

What's the moral of the story? I think it's a nice caution about dogma-driven science. Different readers are now thinking very different things. Creation sympathizers are thinking that evolution is a dogma and is crippling true science. Those favoring evolutionary interpretations think that creationism is the epitome of dogma-driven pseudoscience. It's an all-purpose allegory.

How can I as a creationist seriously caution against dogma-driven science? Why not? The thing about creationists like me is that we're just a bit more blatant about our dogmas than others. That affords me the opportunity to be more rigorous in re-examining my dogmas. In other words, though I accept the inerrancy of Genesis, I relentlessly re-examine my interpretation of Genesis, since that is far from infallible. I'm sure that won't satisfy some people, but I'm not really worried about that.

P.S. In the 1960s, the function of the rete was finally worked out: The arterial network of the rete is surrounded by a network of veins, and the rete works like a radiator. As blood flows into the brain, it's cooled by transfering heat to the cooler venous blood flowing back to the heart. It's apparently important for maintaining brain temperature in animals that pant through their noses.

Forrester, J.M. 2002. The marvellous network and the history of enquiry into its function. Journal of the History of Medicine 57:198-217.