Sinistral species & even genera are more common among the land snails. Since
sinistral & dextral species usually coexist & either type appears to have
survived -in an evolutionary sense- equally well, we can rule out the
possibility that one direction of coiling is better than the other. So, the
reason why most gastropods are dextral may simply be that the ancestral
gastropods happened to be that way; a historical accident so to speak.

Aydin

> -----Original Message-----
> From: Morton Kessel [mailto:[log in to unmask]]
> Sent: Monday, September 18, 2000 7:18 PM
> To: [log in to unmask]
> Subject: Chirality
>
>
> I'm looking at shells from an evolutionary standpoint.  There
> are so many
> right handed shells and so very very few left handed shells -
> worldwide
> (which rules out Coreolis effect as a cause).  The most
> common example of a
> "lefty" here in Florida is Busycon contrarium (sinistrum).
> Any thoughts on
> why this should be so would be welcome to me and maybe to the list.
> Mort Kessel
>