Vacancy Chain

What are common to hermit crabs and humans? A bit unsettling to hear that question? Sure. Much as I find the question difficult to answer, you might be more eager to tell me the difference between a layman and a sociologist. Well, that's another reasonably interesting question.

I find the answer to both questions after my recent reading of Scientific American article about hermit crabs, by Ivan Chase.

Most of us know three facts about hermit crabs: they're crustaceans, we often meet them near shorelines, and they've got their own mobile seashell homes. In that article, the professor of sociology gives us details of the animal so precise - and so easy to relate to what we're sharing the same behaviour - that I realize what is meant by professor's gift. It was a summer morning, children's footsteps everywhere at low tide along the beach. We can picture an avid sea kayaker wading into a shallow tide pool on Long Island. He was fascinated by a small hermit crab running toward an empty snail shell he dropped into the water a few minutes ago. The curious sociologist wrote, "almost quicker than I could follow, the crab pulled itself out of its old refuge (smaller in size) and thrust its vulnerable abdomen into the (more spacious) snail shell I had dropped." Before he left the scene, another hermit crab discovered the first one's discarded "home" and, after a most intricate three-dimensional inspection, worked out that the new lodging measured bigger than its own. Without second thought, the second crab exchanged his lodging. What next? Read on: "About 10 minutes later a third crab found the second's old home and claimed its prize, abandoning a small shell with a large hole." 

The curious sociologist doesn't stop at discovering the animal behaviour. He is eager to learn the beauty of a well-orchestrated "vacancy chain" - an organized method of exchanging a more desirable possession abandoned by another individual. By individual, he's referring to animals with relatively simple brains and nervous systems, say, hermit crabs, limpets, lobsters, fishes, octopuses and woodpeckers. 

How about humans? Good. Is there room for a broader application of the same vacancy chain strategy among ourselves? Yes indeed. Automobile industry, I was told, depends a lot on this vacancy chain. That explains why car dealers have been so eager to take the old vehicles of any new car buyers in trade (and sell those old cars to yet other buyers).