Wednesday, November 19, 2014

My Year of Darwin 11/19/2014 To see eons of evolution, look anywhere

 Charles Darwin

"every detail of structure in every living creature (making some little allowance for the direct action of physical conditions) may be viewed, either as having been of special use to some ancestral form, or as being now of special use to the descendants of this form - either directly, or indirectly through the complex laws of growth." Charles Darwin, Origin of Species 1st edition (on Kindle)

I really like this quote because it explains something I've been trying to explain to my sophomore biology majors. That, despite the emphasis on adaptation in the course, most of what you see in an organism has nothing to do with that organism adapting/evolving those features. Very very little of an organism can we contribute to adaptation in organisms and most of an organism is the result o inheriting those traits. Take the gray squirrel for example. The most basic functions, metabolism for instance, have been with us for several billion years. The backbone of the squirrel for hundreds of millions of years; hair, perhaps a 100 million years, the rodent skull tens of millions; and the squirrel group are perhaps at least 10 millions years old. So what of the gray squirrel?  No idea, but I suspect that gray squirrels have been with us since the end of the Pleistocene. 


  1. Did you mean the beginning, rather than the end of the Pleistocene? (ie ~2.6m BP rather than ~12k BP) On a side note, while the family as a whole certainly has a longer fossil record than more successful johnny come latelys like Muridae do you have an opinion on the idea that Sciurus represent "living fossils"?

  2. Yea, I just checked out the Interesting. I wasn't sure of the details (and I would never commit it to memory if told). If the skeleton (just one aspect of the phenotype) is ancestral then sure - a living fossil but I'd be OK with that.

  3. The thing that fascinates me about squirrels is how little cosmetic differentiation you seen along the way from Megazostrodon ~200m BP (through Protungulatum and Douglassciurus) to modern Sciurus; its seems like they are essentially the "base model" of mammals.