Category Archives: Evolved posts

Nature Study: snail body colour

Evolved posts, Nature Study,

snails.jpg

We were walking through the woods when we found this little group of snails having a party in the middle of the path.  It looked like they were eating lichen. And the strange things is that two of them are beige and two are dark grey, even though they seem to be the same kind.  Why is that, I wonder.  Here is one thing I discovered by doing a search on the Internet:

There is geographical variation in body colour in the land snails Cepaea nemoralis and C. hortensis along a transect of 88 samples from the north of Scotland to the Pyrenees. Paler body colour is associated with higher mean daily maximum temperature in both species. Laboratory experiments show that dark-bodied snails heat up more rapidly and reach a higher equilibrium temperature than do pale snails when exposed to radiant energy. Climatic selection favouring pale body colour in warm areas and dark body colour in cold areas is probably responsible for the association with climate.

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Antonia was busy with a play date all day.  I spent the morning reading a book by myself (!), and the afternoon on my translation project, which is nearing completion.

The chimpanzee genome project is pretty cool, actually

Evolved posts

These people said:

“Evolution “cannot be subjected to a test” because it is something that supposedly occurred in the past and is not occurring today. And before you jump all over that, natural selection (changes within a species that are occurring at present) is not evolution, and there is no recorded instance of a new form or function being observed to have developed through natural means.”

I thought I would jump all over them.  Even though I wasn’t smart enough to figure out how to leave a comment at their blog, I can understand this one.  People who expect to see radical visible changes in organisms in a handful of human generations, e.g. since we discovered evolution, are missing something.  A grip on timescales possibly?

Approximately 500,000 generations (about 250,000 each, from our common ancestor) are estimated to separate us from chimpanzees, our closest relatives, a process that took about 6 million years.  Whether this has produced significant differences in form or function is bound to be a subjective judgement. So check out the chimpanzee genome sequencing project, for something a bit more precise.  Wikipedia gives quite a nice summary, and there’s about a million other things on the net.  It’s a fun thing to research and it underlines the fact that a grasp of genetics is absolutely essential to anybody hoping to understand evolution.

Personally, I’m impressed by just how many genes have changed in so short a time, how few of the changes are visible, and how few changes you need to create visible differences (like chihuahuas from wolves).

For evolution happening today, see here.  It mostly concerns nasty little things like resistance in organisms we can’t see and would rather be without. So as well as getting a grip on large time scales, you need to get familiar with small spatial ones, and with processes as well as morphology.

For the rest of this little discussion, see here and here. I have to go and teach my kiddie something before lunchtime now.