Do sea shells all spiral in the same direction?

28 November 2010

Question

I noticed that all the sea shells with Spiral growth patterns (I have not yet seen otherwise) all grow in the same direction. What would the reason for this be? What forms or creates sea shells to "grow"?

Answer

Diana - It sounds like you've got a right-handed shell there which is called a dextral shell. You do get other shells which are left-handed and they're more sinister called the sinistral shells, but there's no real obvious reason why you get more right-handed shells right now than you do get left-handed shells. Many people think that if you have all shells within a certain population, which are the same "handedness", it's much easier for them to mate with each other. So therefore, if you get one turning up that's left-handed, it's going to be difficult for the right-handed one to mate with it. But looking back over paleontological records, you do get periods when more left-handed shells appear and then you get periods when more right-handed shells appear, and it just seems to be something that fluctuates and changes with time. At the moment, we're getting mostly right-handed shells.

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