Sunday, March 20, 2011
(Picture from here.)
Let me tell you a story told to me.
Back before the end of the Cretaceous when I was still in graduate school I was studying neurophysiology. I had the opportunity to work in a lab that was experimenting California Sea Lions. During that time, Sam Ridgway came to the University and spoke on his research with dolphins and other marine mammals. Doctor Ridgway told the following story as I recall. (Any mistakes are purely mine and cannot be attributed to him.)
They were working with Gray Seals.
They had built a water proof box with a hole on one of the top ends. Over the hole they had constructed an air tight "bell" so that gases could be examined. The box was then filled with water.
The seals wore a harness that recorded EKG and temperature and had been trained to take a breath at the opening and go down to the other end of the tank and hold down a button. Then, on a signal, the animal came back to the opening and breathed. The gases were then analyzed. They were looking at CO2, EKG, etc.
Now, Gray seals are excellent divers with recorded depths of greater than 1500 feet. Some of their habitat includes pack ice so they have to be able to manage a sealed environment. Going down a couple of feet in a box and holding down a buzzer for a few minutes wasn't even taxing them. So one of the researchers got a bright idea.
When the seal took a breath and went down to the other end they closed of the opening.
Two things happened quickly. The seals heart beat dropped to about 3 beats/minute. The seal then went to the top of the tank and breathed out. The bubbles collected at the top of the box. After a moment, the seal then neatly sucked that air back up.
When the seal was allowed to breath again the heart speeded up and a significant amount of CO2 were blown in through the opening and analyzed.
The behaviors are brilliant: dropping the heartbeat reflected a lowering of metabolism. Other research has shown that circulation in the flippers is reduced when undergoing a dive. The seals body has shut down the periphery and preserved the core systems: brain, heart, lungs. The lungs are a storage are of oxygen but metabolism reduction reduces the demand. Seals have been shown to be quite tolerant of high levels of CO2 in the blood stream.
But the CO2 is still a problem.
CO2 is highly water soluble-- much more soluble in water than in air and much more soluble than O2 under the same conditions. Hence, the behavior of breathing out against the pack ice surface (i.e., the top of the box) to get rid of the CO2 and breathe in the "purified" O2.
A neat trick.
But the reason for the story isn't just extolling the wonders of animal adaptation. Bradycardia in marine mammals is voluntary. They can be taught to do it. The behavior the gray seal used to get rid of CO2 was similarly voluntary. The adaptation here was behavioral not physiological.
This is an important point. Creating a physiological adaptation is expensive. There are developmental considerations, biochemical consequences, and it takes a long time. Behavioral adaptations are much more quick to achieve and once the organism has created one behavioral adaptation the mechanism for further behavioral adaptations is already in place.
Nowhere is this more apparent than in human beings. We've so completely committed to behavioral adaptations that physiological adaptations other than those that serve behavior have become hard to discern. We no longer have an obvious ovulation cycle. Our reproductive practices are as varied as there are tribes on the planet. Our child rearing strategies are equally varied except in one respect: we are committed to rearing children. In this we are consummate K-strategists (see here) in that we invest in the quality of offspring at the expense of the parents.
We have so committed to behavioral adaptations that we develop a model of the world to which we adapt rather than the real thing.
By this I mean that humans abstract the world into a model, analyze the model and react to the world as if it were the model. Hence, cultural institutions, religion, superstition and science. One could argue that the main difference between science and other forms of modeling is that science submits its models to the rigor of testing and discards them when they don't measure up.
We are what we do and we do what we do because of what we are.
PS: I'm sorry I've been a bit hap hazard of late. Work has been, well, tough. I'll do better.