Posted by: Rob Viens | July 27, 2012

Darwin Discovers the Missing Skink

Still not able to travel the countryside, today Darwin walked the shores of a nearby island (which, presumably due to its isolation, was safe from revolutionaries). At some time (I think after Darwin’s visit) Rat Island (off the coast of Montevideo) was used for political prisoners. But it seems for now, it was a safe place for a stroll. Darwin writes:

“I had no opportunity of taking a long walk.— so that I went with the Captain to Rat island.— Whilst he took sights I found some animals & amongst them there was one very curious.— at first sight every one would pronounce it to be a snake: but two small hind legs or rather fins marks the passage by which Nature joins the Lizards to the Snakes.” (July 27)

Two things of interest here:

(1) What Darwin is describing is a skink (family Scincidae)– a lizard with such reduced legs that it is sometimes mistaken for a snake.  This confusion is furthered by the fact that they also often move with a writhing motion like a snake. Some species have lost their legs entirely.

Five-lined skink (from the Information Archives):
Five Lined Skink

There are over 1200 species of skinks, but, interestingly, a search of the Reptile Database revels only one species found in Uruguay – Aspronema dorsivittata, the Paraguay Mabuya (shown below – also from the Reptile Database).

Paraguay Mabuya

A few bits of general information on the skink clan:

Skinks are found around the world and live in a number of different habitats.  Some live in trees and others burrow in the ground; some are adapted to cold latitudes, others to equatorial climates; and some eat primarily insects, while others expand their dinner menu to include worms, slugs and sometimes even small mammals. Many skinks , particularly those with longer tails, have the ability to lose the tail (a way to escape predators), and better yet, the tail can later be regenerated.

There is even one genus of skink (Prasinohaema) that is the only known vertebrate to have green blood (which results from a toxin that builds up in the bloodstream).

(2) I know a lot of scholars suggest that Darwin’s first real references to evolution occur later in the voyage, but man, referring to the “passage by which Nature joins the Lizards to the Snakes” seems to imply the beginnings of the concept of speciation.  I suppose that it could be like saying that there is a continuum of shades of grey between black and white.  And that is probably part of the meaning here.  But I can’t help but wonder if Darwin was considering more.  Interesting insights into a great mind… (RJV)

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