Wednesday, October 26, 2011
A walk in the woods
This past weekend I went for a walk in the deep woods west of Boston with sons Tom and Dan and spouses. The highlight of the day was coming across this beaver dam (click to enlarge).
We were bowled over by the size and engineering sophistication of the dam, as impressive in its own way as Hoover Dam on the Colorado. Constructed by rats.
OK, not rats, but rodents. A huge undertaking of felled trees, rocks and mud, ingeniously placed at the perfect spot along a tiny stream, as if planned by a human engineer. "OK," the engineer might have said to the assembled beavers. "Here's the blueprints. Go to work."
I stand to be corrected, but I think biologists are of the opinion that dam and canal building by beavers is primarily innate. Which means dam building is encoded in beaver DNA -- a four-letter code for assembling proteins that somehow self-construct the beaver's cerebral hardware. And the hardware comes loaded with engineering software.
All this in a package a hundred times smaller than the period at the end of this sentence.
One could think about this all day and never get tired of the wonder of it.
My favorite example of innate behavior is the flight of the red knot, which I mentioned in Skeptics and True Believers. For details of the story I am indebted to Brian Harrington's The Flight of the Red Knot.
The red knot is a small shore bird that each year wings its way more than 18,000 miles, from the southern tip of South America to the arctic islands of northern Canada and back again.
From October to February, the birds live and feed on the beaches and mud flats of Tierra del Fuego, the southernmost land on Earth, excluding Antarctica. Then, they lift off in flocks of hundreds or thousands for the journey to islands of the Canadian archipelago north of Hudson Bay.
Here, in the northern summer, they mate and breed, each female laying four speckled eggs which she and her mate incubate in turns. By mid-July, the female adult birds head south again, and male adults follow a few weeks later. The juveniles fend for themselves until late August, when they too take to the air for the 9,000-mile journey to Tierra del Fuego.
These young birds in their thousands, without adult guides, find their way along an ancient migration route, down across New England's Atlantic beaches, across the Atlantic to Guyana and Surinam, then down along the east coast of South America, arriving at precisely those places along the way where they are sure to find food, eventually joining the flocks that include their parents.
A map of their journey and the knowledge they need for navigation are part of their genetic inheritance. When you consider that they started their lives, like the rest of us, as a single information-packed fertilized cell, their migratory feat stands as one of the great wonders of the natural world. That single cell contains the biological equivalent of a set of charts, a compass, a sextant and maybe something equivalent to a satellite navigation system.
DNA. Proteins. Evo-devo. We understand a lot of what's happening, but my guess is there's still a key discovery to fall into place before our understanding of complex instinctual behaviors is complete, maybe something as revolutionary as the insights of Darwin and Watson and Crick.
Meanwhile, biologists are beavering away.