(Science Week, day 4!)

A question that can entice both children and adults: what would it feel like to be something else – a bat, a mouse, a bird, even a tree or a primitive multi-cellular organism? Perhaps in early grade school, a teacher's answer might consist entirely of an invitation to "imagine," and such imagining is a wonderful thing to try. But even more profoundly wonderful: the question is indeed a scientific one because it presumably does have an answer, and because, while there's no clear path to a human knowing it firsthand, we can inform the imagination by learning more about ourselves and other animals.

Even before you had any detailed knowledge of brains or of nervous systems, perhaps you thought to wonder what exactly is happening after you decide to lift your arm and actually do it. Perhaps you one day learned a little about the brain sending impulses down through the spine and out through the extremeties, of individual muscles that contract and relax at these messages.

It could be said that we know firsthand what it's like to have four legs, as we have two arms and two legs which simply correspond with the front and back "legs" of cats, sheep, and other quadruped mammals. This correspondence is called homology, and studying the relationships between all animals has revealed much more than that. I recall hearing from biologists that the single hoof of a horse essentially maps to the third digit of the hand or foot, evolved to massive prominence. If you can imagine what it would be like to have such well-reinforced middle fingernails that you could bend forward, plant them on the floor like small anvils, and comfortably walk on them, there's reason to believe that you're at least on the path to accurately imagining what it's like to be a horse – more accurately, say, than if you were imagining walking on your elbows. The open wings of a bat, as you can see when light illuminates the bones beneath it, begin at the bat's "shoulder" and span the four mammalian fingers like a giant webbed hand, leaving the small "thumb" hanging out on its own. Imagine wearing a vampire-like cape which you could open and flap as though dramatically playing block chords on a piano with four fingers of each hand. Contrast that with a bird, on a different branch of the evolutionary tree, whose skeletal "fingers" are different enough that a bat would have to make its own imaginative leap to comprehend embodying one of those.

Those are mental journeys made all the more fascinating and rewarding when thus informed by science. But let's now recede to the even more abstract, and finally wonder, as I recently did, what it would be like to be an arachnid with eight legs, seemingly relatively equal. Arachnids are much more distant relatives to humans than bats and birds, and homology has much less to offer. It was easy enough to imagine our arms as two additonal legs. But four more? What could it possibly feel like to have one more arm, perhaps protruding from the torso? Or to have two, independently commandable like our two fimilar arms, in addition to our two familiar arms?

I don't know about you, but this was where my intuition finally began giving way to speculation. A thought arose like "this may be beyond my ability to imagine directly, even by metaphor. Perhaps I can't genuinely imagine it, but I can believe that two more arms and two more legs would feel natural if I really had them. So perhaps the best I can do is to trust that."

It then occurred to me that the human body, though only four-limbed, is still complex. We certainly do learn to control more than eight parts of our body, even simultaneously. Perhaps a spider just feels somehow like we do when controlling, say, our four limbs, eyes, nose, and mouth? Or our hands? I almost blinked at that realization. We have ten fingers and can control them independently. Heck, I realized: I'm a pianist, for goodness' sake! I know exactly what it's like to control ten "legs" with individual timing and precision. I'm typing rapidly on a physical keyboard right now. Contrariwise, an arachnid must spend its life practicing dexterity of the legs, but might marvel, lost for an intuitive hook, at the notion of mammalian fingers. It's still hard to know how to proceed to attempt to imagine that fingers are legs, but perhaps we shouldn't find the notion of each other's experienced bodily structure so alien as we initially might have. So we take one step in the imagination only to find many more still to take. A reflection on the scientific nature of the question, nonetheless, made its contribution to the one.

Of course, there's much to wonder about beyond the movements of limbs. We know arachnids have dazzlingly different eyes, and the feeling of weighing under an ounce seems like it must be an unrecognizably free one, perhaps like the opposite of having to push and shoulder mud in a bog. It's already apparent: the first steps to imagining those aspects of being something else, too, are informed by nature and reality.