Saturday, July 2, 2011


I'm still here! And I've brought you more of your favorite! Cepaea Nemoralis!

One of Charles Darwin's insights into unraveling the mechanics of speciation by natural selection was that in any species there is variation. In a way it seems dumbly obvious: take human siblings. No too individuals are identical. Darwin bred pigeons so he also knew that this variation could be manipulated, in this instance by human intervention, but he took the leap to imagine (correctly) that nature could also manipulate this variation. These variations are, in essence, the stuff of evolution, the stuff of speciation. So to give you an idea of the amount of variation, in this case color variation, a single species can exhibit I went out this morning and shot a number of snails on the wall outside my house. This is what I saw:

11 different snails with 11 different patterns. Browns and yellows dominate the color variation in c. nemoralis but you can see oranges, tans, even one that was almost totally white. I wonder if there is some environmental factor but if so it must be quite acute since these are snails that were found in range of only several meters.

High levels of variation tends to be "good" for a species. It means that if the species (say c. nemoralis here) did need to start evolving towards one of these colors (say for camouflage) the genes are already present and the snails that were expressing those genes would survive more easily. Pretty quickly the ones with the "best" color would be all that was left. You might also imagine conditions in two parts of the species' range changing in different ways, one favoring one color and the other area favoring another color. That's exactly how you get speciation.

I hope to keep documenting the variation in color of c. nemoralis in our area and see if it changes year to year or season to season.


  1. Hi Paul,

    I really wanted to contact you about an article you wrote for Yahoo associated content titled Origin of Whales.

    I'd email you, but I didn't see an email address anywhere - and I was having trouble leaving a comment on the Yahoo site.

    There was a detail you misrepresented in the article.

    You said: "The most observable vestigial feature for Basilosaurus and Dorudon are their tiny "hind-limbs." They are really nothing more than a collection of small bones without even a pelvis to support them, embedded in the muscle wall."

    I'm not sure where you got that information, but Dorudon and Basilosaurus definitely do have a pelvis to which the hind limbs are connected. They aren't merely embedded in the muscle wall, but are thought to have protruded. They had complete digits and everything. I just recently photographed the bones and am in the middle of writing a paper on the subject.

    Sorry to bring this information into your nice looking blog - but I felt it was an important enough detail to bring up.

  2. Hi Aaron,

    Thanks for your comment. I have to say I don't remember exactly which source I used for that bit of information. I'll dig into my sources and see if I can find it. I very well may have just misinterpreted something I read. I know I originally got interested in the topic from reading Carl Zimmer but his science is generally pretty sound from what I know.

    Don't be sorry to bring it up here. I'm always happy to be corrected and the origins of cetaceans remain an interest of mine. I'm glad to have some new information.

    I'd love to hear more about your work on the fossils if you still feel like emailing I'm reachable at: