In article ,
"P van Rijckevorsel" wrote:
Keith Michaels schreef
A snail shell forms an exponential spiral because the direction of
new growth is proportional to all the growth that has come before.
If the growth direction is offset on the Z axis then it forms a helix,
or coil. Starting the helix in one direction (left or right) is
reinforced by subsequent growth. There is probably a predisposition
to handedness based on unit shape, and a randomizing component like
environment (temperature etc.) or a mutation that gets things going
in one direction or the other.

+ + +
Reminds me of an experiment they did to estimate the proportion of left-
versus right-handed shells in sea snail shells. This involved a lot of
manufactured plastic snail shells (sponsored by Shell) which were dumped in
the sea. At various points along the coast they counted left and
right-handed shells. It proved that watercurrents performed an advance sort
and deposited different shells at different points along the coast. You
could "prove" any proportion of left- versus right-handed shells by
selecting a collecting spot.

The same sorting by currents has allegedly been demonstrated for
rubber thongs lost overboard.


Cheers, Phred.

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LID