Science Questions

Do sea shells all spiral in the same direction?

Sun, 28th Nov 2010

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Question

Ronen asked:

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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http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1182695 RD, Tue, 23rd Nov 2010

Good question!  ... And good answer also, RD!!

Most illuminating!

esp. the reversed genitalia bit   !!!
peppercorn, Tue, 23rd Nov 2010

Ronen asked the Naked Scientists: 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"? What do you think? Ronen, Tue, 23rd Nov 2010

Just like humans, molluscs are mostly right handed. Left handed shells are far rarer at the moment - but looking back through time, the fossil record reveals periods when shells have flipped from right handed to left handed and back, through the eras. I don't think we have a good idea yet, why that might be! Oceans Helen, Wed, 24th Nov 2010

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