Friday, February 26, 2016

This little critter was crawling across an exterior wall of my house Wednesday (the picture is rotated 90 degrees to make it look "normal").  I'm far from sure, but I think it's a form of Carolina mantleslug. 

Land slug is the common name for any shell-less terrestrial mollusc.  As the shell-less condition has independently arisen many time during the evolutionary past, there are a great variety of slugs derived from several quite different evolutionary lineages. Therefore, the various families of slugs are not closely related, despite a superficial similarity in the overall body form, but they've all evolved from one common ancestor. 

To be sure, humans did not evolve from slugs, but if you go way, way back in evolution, about 590 million years ago, the lineage that gave rise to humans branched off from that same common ancestor that gave rise to the various families of slugs.  You can consider that common ancestor, by Richard Dawkins' estimate, as our 300 million greats- grandfather.  That would make the present slug not an ancestor, but a far-distant cousin.

Therefore, it's not surprising that 70% of our DNA is the same as a slug's.  The difference between us and them is only in that other 30%. Still, it's startling when we encounter ourselves in an unfamiliar form, separated as we are by 590 million years of separation and 300 million generations,

He was gone by the time I finished unpacking the groceries from my car.  Since there's no way he could have moved that fast, I fear a bird must have gotten him and this picture uploaded to the internet will be his only legacy.   

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