Getting a Grip
Shubin opens this chapter with an anecdote about the first (and only) time he taught gross anatomy. It is odd for a paleontologist to teach medical school level courses, but it happened. Shubin relates how he was fine with the torso, cadavers are so modified as to be almost unrecognizable as humans.
His moment of epiphany came when they got to the hands. You see, the hand is quintessentially human. Our internal torso structure is very similar to pigs and other mammals, but the hand. The hand is different. The hand, with the opposable thumb, is a signature human structure. It is our ability to grasp, to manipulate, to make our dreams into reality.
To Sir Charles Bell in 1822, the hand was the perfect design. He thought that it was evidence for God because it was perfectly built for us as tool users.
Sir Richard Owen thought the same, but being an anatomist in the 1800s, he had a wider experience to draw on. Sir Owen first described the gorilla. He coined the term ‘terrible lizard’, what we know as dinosaurs. He began to see the pattern.
One bone, two bones, bunch of little bones. Bat, horse, gorilla, human… dinosaur all had exactly the same limb structure.
Sir Owen found the same thing while examing everything from skulls to backbones. There is a fundamental ‘design’* in all vertebrate land animals (and marine mammals too).
The rest of the chapter is devoted to those details and the fossils that show a steady progression from true fins to pure one bone, two bones, lots of bones.
Now the interesting thing is that Tiktaalik has the arm setup and musculature to do push-ups. That sounds weird, but when you consider the environment, it’s useful. The flat body, the eyes on top of the head and the powerful limbs allowed it to push through marsh, and lift out of the water. There were massively huge predators in the area and the ability to move to locations were predators couldn’t move into was useful.
We can even see our own fetal development in these fossils, how our elbows and knees rotate from what they looked like hundreds of millions of years ago into the ‘proper’ position that allows us to walk and swing from limb to limb.
There’s a lot more detail than what I discuss here. Only to someone who is biased against the evidence could ignore it.
*In the sense of how it actually looks rather than the sense of it being designed by a deity.
Boisvet, C. A., Mark-Kurik, E., & Ahlbert, P. E. (2008, December). The pectoral fin of Panderichthys and the origin of digits. Nature. 406, 636-648. doi: 10.1038/nature07339.