Survival of the Scrappiest

As biologists, we are trained not to anthropomorphize.  Scientists are supposed to remain rational, and it is easy to attach human characteristics to animals when they appear to show human habits.  But it happens anyway.  It’s inevitable, and we need to accept it rather than completely deny it.  And besides, it can lead to some reflections on principles of biology.


For example, take hermit crabs.  They are everywhere here along the coast.  They inhabit abandoned snail shells, and need to find a new shell to live in as they grow bigger.  To do this, they can scrounge around for an unused snail shell, but in this area of such a high hermit population density, most good shells are already taken.   What is far more common is to steal one from a larger crab.  But the only way to do this is for a smaller crab to challenge and evict a crab that is larger than itself, and then escape with the larger shell.  This fight can take a while, and in the meantime a whole line of smaller crabs will grab on to the challenger, waiting for his shell to become available so one of them can move up a size.  If the challenger wins, everyone plays a game of musical shells with the largest crab left naked and homeless.

So if you think about it, hermit crabs are a race of underdogs.  They can only grow bigger in size if there are enough scrappy crabs that can take on someone bigger.  The bigger the crab, chances are the more upset victories it’s achieved.  Or it’s a cunning little bastard who let others do the fighting and then moved into an available shell.  But either way, it’s not simply selection for the biggest and meanest.  Just the meanest.

Come at me, bro!
              Come at me, bro!

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