I just finished the book Your Inner Fish by Neil Shubin. Though I bought the book with a specific interest in learning just how much bony fish there is within us, I want to say at the outset that it has been an enjoyable read in general as a book about the joy of science. I hear so much about the battles between scientists and those who fear science that it’s nice to hear a scientist simply write about what he loves. I know: there are lots of such books out there to be sure; still, this one strikes a chord that I first remember hearing in Carl Sagan.
I remember my father saying “ontogeny recapitulates phylogeny” a number of times during my youth. This lyrical slogan-like phrase indicates that our formation in the womb reflects our formation as a species. It wasn’t until several years ago that I finally looked the phrase up, and found it to be quite outmoded. I still like the sound of it, but it does miss an important point: it’s not so much that we evolved from, say, fish, but rather that we remain as fish to this day.
The fact that we have undergone a multitude of changes does not change the fact that we are modified fish. Many aspects of our anatomy and physiology bear this out. It’s not like all our fish parts were replaced by amphibian parts when we left the water, but rather our fish parts were generally transformed or even reassigned.
Why fish? It’s not that we aren’t amphibians and reptiles as well, but the fish holds a special place for two reasons:
- Fish represent the aquatic origins of life.
- The famous fishiness, albeit temporary, of the human embryo.
It’s not just that we can look at bony fish and note our resemblance to their basic skeletal layout. They do have a spine, head, and limbs. They do have our basic camera-type eye. They do have nostrils. They also have three ear canals that give them a sense of acceleration in three dimensions. Still, it’s much more than that. Remarkably enough, we have retained our gills, in a morphological sense at least. The gills of the embryo are gills that guide the formation of our head and neck.
It’s tempting to think of our inner fish as something we’ve left behind, but who’s to say there’s no going back? Look at our cousins the whales. They stand as proof that the water is not so irrevocably lost to us.
Another less-fishy reflection from the book that resonates with me is the notion that life is self-building. We tend to see creatures as buildings that are built by some builder, but when we look deeply into the formation of creatures, we are struck by how they actively build themselves out of a mere blueprint. And what of the blueprint? That too is continually recreated and redesigned by the living.