I take some pleasure in contemplating the relatedness between myself and my dogs. Somewhere, millions of years in the past, we once shared a common ancestor. I like to think there are little bits of DNA that we share in the cells of our very different bodies.
Although I often gaze into the eyes of my dogs, enjoying the oxytocin rush and pondering our shared heritage, it’s not something I would do with say, a fly, or a shark, or that common star of my dinner plate, a fish.
In Neil Shubin’s Your Inner Fish, that’s exactly what the author asks us to do.
Compare yourself to a dog. We’re both mammals, both have fur, four limbs, a spine, a head, a neck, three bones in the middle ear, eyes. Now, a crocodile. Four limbs, head, neck, eyes and spine, but no fur, no mammary glands. A shark? Eyes, a spine, a head, but not limbs or a neck. But before 400 million years ago, there were no mammals, no land dwelling animals at all, and nothing that trotted around on four legs that could move its head independent of its body. So how did that happen? And how can we use fossils of ancient sea-dwelling creatures and even current specimens to divine the path from boneless jellyfish and oozing blobs of goo to the remarkable diversity and complexity of animals roaming the earth today?
Shubin throws in the just the right amount of biographical experience as a fossil hunter in the frozen arctic. Here, he attempts to find a fossil that will prove some intermediary link between the humans of today and our oceanic ancestors.
The Arm Bone Connected to the Hand Bone
The limb bones of all limbed creatures have a common plan: “one bone, two bones, lotsa blobs, five toes,” as Shubin puts it when beginning his exploration. Horses, humans, birds, dinosaurs: we all have it. It’s a great plan for roaming the land and whatnot, but how does something like that come from fins? Fins and limbs are adapted to their specific environments and don’t seem to have a lot in common, besides locomotion. But somewhere along the way, those flippers had to turn into something that would move creatures along on the dry earth.
Shubin shows us how, through discovery of an ancient fish with nascent limb structures. He does the same for eyes, ears, noses, nerves, bones, and teeth. For example, the three middle bones that make up our middle ear in that whole complicated contraption that is the mammalian ear has corresponding bones in reptiles and sharks that perform completely different functions. Hearing in water and hearing on land are two completely different beasts, and require different types of mechanisms.
There is a beautiful interconnectedness to all of life, and even those creatures we might think of as utterly different from us, that we mindlessly consume as food, that we set traps for, that we watch soar high overhead, are still a part of us. We find it very difficult to contemplate large numbers. A million years is something no person will ever experience, and can never really comprehend. But you, and the obnoxious crow, and the annoying gnat, and the doofus dog, all share a past on this geological timescale. We’re probably not the pinnacle, and some day our species will go the way of all species, both dying out, and becoming something new.