30 December 2009

If you want slimy gossip (and bad evolutionary speculations)...



Despite being almost 125 years old, the dozen or so, some short, some long, articles on mollusks in volume 21 of Hardwicke's Science Gossip kept me occupied today for several hours while I was accompanying my wife during her hospital visit.

Some ideas from more than a century are surprisingly relevant to our current thinking as in this example. But others could be quite absurd by our standards; however, even then by providing an ephemeral window into the minds of the contemporary scientists, they help us understand how and along which paths science has progressed since then. For example, in an article in this volume of Science Gossip, the British malacologist T.D.A. Cockerell dicussed the banded shells of some helicid snailis, such as Cepaea nemoralis and then presented some evolutionary speculations:
...it would seem that form from which the now existing helices were developed had five definite bands, like H. nemoralis; or perhaps, we may go still farther back and say that the form from which all the Gasteropoda sprung, the first type of the Gasteropod shell-bearing Mollusc, was banded. The reason for this speculation is that the bands are always in the same relative position in the Gasteropoda when they are developed, the band just above the periphery being specially characteristic.
Just because the bands are always on the same positions on snail shells, one cannot conclude that the last common ancestor of all Gasteropods had a banded shell. There are probably more snail species that have bandless shells than banded shells. Therefore, Cockerell's logic would force one to conclude that the last common snail ancestor had a bandless shell.

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