Have you ever really looked at your hands?

This is a follow-up to It is so difficult to think clearly, in which I mentioned four primary questions of biology and promised to talk about them later, which has become now. The best way is an example: pick a thing and do some biology with it.

The largest context is the founding principle of biology: material thinking. We’re talking about living things as chemical and physical phenomena. The next largest, and hardly smaller at all, is that social ferment of dialogue I wrote about in the referenced thread, which requires disagreement or else it doesn’t happen. To ask a scientific question is synonymous with saying, “some people really disagree about this,” and to address it procedurally is to throw some more material into that discussion in a highly focused way. Therefore the disagreement must be framed as questions. When you say “it goes like this,” and I say, “it goes like that,” the one thing we can agree upon is that the phrase “how does it go?” is valid.

Anyway, I mentioned four primary questions. They, or their topics, are: mechanical operation, interaction with other things, comparison across living things, and history of change. As an evolutionary biologist I tend to think of the fourth as central or as an illuminator of the other three, but that is almost certainly vanity and you may pass it by.

Mechanical operation: how does it work?

You’ll forgive me I’m sure for not providing a gross anatomy dissection and demonstration as classically excellent as this one on my own hand.

I mentioned in the clip but didn’t emphasize that a given muscle can only contract or relax, and therefore nuanced motion, as well as held-immobility, involves multiple muscles. I could have mentioned the properties of the tendons, which are at least as important as those of the muscles.

I didn’t mention the sensory component of the hand and fingers, including both proprioception – knowing where one’s hands are relative to the rest of the body – and analytical sensing, specifically the extensive branching of the nerves at the fingertips.

The hands’ embryonic development could also be a valid topic, including the timing and diffusion of morphogens and the regulation or cueing of specific genes.

There are no basic questions or controversy I’m aware of. Remember how I said that works, that either observations rattle the model, or the model suggests unusual outcomes in certain situations. In this case nothing like that is currently happening, so as I implied in the clip, unless some surprises appear, research questions are going to be applied rather than basic, specifically those concerning healing and health.

What matters most in teaching biology is popular rhetoric vs. understanding. Regarding so-called muscle memory, there is a phenomenon to discuss, but it concerns central nervous system processing. More locally, organs do remodel, which is to say, they undergo a mini-form of development based on use. Obviously this is what muscles do and as you may not know, bone as well, especially at the points of tendon attachments. Therefore local tissue behaviors do occur, but not in the sense of remembering routines and sequences of action.

Ecology and interaction: what does it do?

That word “for,” the hand is “for” this or that or the other, is simply completely off the beam. I’m trying to think about one thing in biology for which it’s a valid and literal verb, and not coming up with much. A critter uses what it’s got to the capacity of everything else about itself.

For humans and many other creatures, the hand is a principal instrument of investigation, confirming, modifying, or replacing what our long-distance senses brought in.

Grasping is obviously going to draw most of our attention, likely not because it’s so amazing in itself, but because it sets up for many of the other activities. especially manipulating.

Not to forget either that an arm is still a leg, in that grasping with one’s hands provides auxiliary support and even locomotive power more often in humans than you might think, and also considering arms’ role in balance even when they’re not touching anything.

The sphere of manual communication is full of fascinating activities, up to and including sign language, which open all sorts of questions, especially when it’s not spelling. What is language, cognitively, when we remove our self-centered obsession on speech? Is there really a hard-and-fast line between syntax and non-syntax based communication?

And combinations too! Sensory, communicative, and manipulative operations factor together into sexual contact, for example. The list goes on and on, including whole subsets such as specific forms of human violence.

Isn’t that more interesting than merely the haiku of “matches the environment?” It’s simply more accurate too, because that matching doesn’t turn out to be as neat as you’d like.

The issue of tools simply has to be reversed, as I mentioned in the clip. It’s another lesson in avoiding the “beauty” trap I described in Adapt this. imagine a creature with a hundred times our dexterity – it might see our making and usage of tools as crude and perhaps deride it as “primitive,” just as we uncritically think of a dog using its paws to open a gate as crude.

One avenue of research that also opens doors into our own perceptions and perhaps limitation thereof, concerns prosthetics, which are especially psychologically dicey for hands. Considering that hands’ appearance and use includes interpersonal recognition, communication, and potential intimacy, the notion of designing them contains all sorts of right-and-wrong triggers; Masahito Mori was right on target when he chose this example for the original Uncanny Valley essay. To date, bionic hands have been utilized by people who’ve suffered injury to their birth limbs, but consider the difficulty people have with prosthetics that function better than what they replace (so far observed regarding legs), and also your response to this situation if it had been fully elective?

Comparison and classification: who has it, and in what ways?

Agilodocodon scansorius, mid-Jurassic

Muscles and nerves are present across almost all animals, including those who aren’t that tightly related to the rest of us when extinct forms are taken into account. Their arrangements and relations to other, often solid parts of the body are legion and play a big role in how we classify animals within the group. That’s why I mentioned the octopus: the basic tissues and processes of its nerves and muscles are like ours, but the arrangements are so different that we consider the octopus “grabbing something with its limb” to be non-homologous to, collectively, you or a squirrel or a honey badger doing it.

However, our muscles, these nerves, and these bones are a single biological thing: no one has it except for the tetrapods, and this one group only modifies it in specific ways. We’re talking about a fine example of raw anatomical homology without parallelism or convergence gumming up the place.

Taking it somewhat self-centeredly to the mammals, and with a warning for cuteness, this gives you a good look: Raccoon eats grapes with hands. You’ll find exactly the same thing among many marsupials, rodents, carnivorans, and of course, primates. It’s easy to miss because we’re most familiar with cats and dogs, or with hooved animals.

In research terms, I think the mammalian hand is also a bit underserved. Although I deeply love the following image and those like it, they are unfortunately focused on extreme modification rather than on the most frequent and highly similar basic form.

I’d like to be corrected on this, but research may be lacking regarding mammals whose hands are mostly unmodified it and what they do with them, especially opportunistically and experimentally.

Evolution: what is its history, how has it changed?

What is its history: converting the above comparative classification into a phylogeny. New vocab, concerning looking at a thing in a given species:

  • plesiomorphy (-ic); when referring to more than one species, add “sym-” to the front – what you have is what you got from previous species
  • apomorphy (-ic); when referring to more than one species, add “syn-” to the front – what you have is modified from previous species

Therefore to speak collectively of ourselves with everyone else featuring this particular structure, the hand is symplesiomorphic, retained with little or no modification from a very old origin, going all the way back to the origin of Tetrapoda. I say “salamander hand” because modern salamanders are the creature with the most numerous symplesiomorphic anatomical features relative to the origin of Tetrapoda. Many changes have occurred since in that front foot, ranging from minor to major, evident in probably hundreds of thousands of species … but not ours or our ancestors.

You know what a hoof is, right? A fingernail, or on the feet, toenails. Granted that the columnar front limb of an adult modern horse is a bit harder to spot as an arm or hand, but it’s there, and much easier to see in other hooved mammals. I never began a pig dissection by opening the bodies, but led a discussion comparing the animals’ basic and externally observable anatomy with the students’ own (the latter conducted mentally). Getting rid of that “backwards knee” nonsense was one benefit, as was the occasional “hey! the male has nipples” “so do you” exchange, but I could always count on the silence that would fall over the students as they looked at the feet and flipped their own hands back and forth, or rubbed their thumbs across the nails of their middle two fingers.

Regarding the classic paw, I know this is like a broken record (“repetitious” for younger readers), but it’s remarkable how consistently people assume that it’s the “animal” structure from which “the human hand” is derived, rather than the other way ’round. Bat wing, hoof, whale fin … all of these are derivations – we’d call them advancements except that they’re “animal” and we are exalted Mannn, whose every feature simply must be “advanced,” right?

As I briefly mentioned above, plenty of creatures whose hands are quite specialized and in many ways simplified still use them in hand-y ways, every so often. Their minds are not truncated like their fingers are.

Right about here my cameraman could no longer contain himself

But only humans have unique opposable thumbs! … pause … wait for it … no indeed they do not. This is one of the pleasing falsehoods that litter modern biological science, and nothing more. The medial digit of the tetrapod forepaw is always set lower than the others, with a distinctive attachment more to the side of the inner wrist bones than extending straight forward from them.

You can see the pet-rat people enthusing all over the internet about their little ones’ “freakishly human hands,” missing the point I’m making here – that rats, humans, and many other mammals retain the ancient dexterous arrangement. The picture is a little bit deceptive in that the visible thumb isn’t foreshortened; the rat thumb is much smaller than ours. But it’s there and it’s not weak.

The general narrative would seem to rely on the nonsensical idea that just prior to the origin of humans, the relevant animal lost all anatomical, social, cognitive, and ecological identity, such that the nascent human had to invent these things from scratch, and therefore if any nonhuman has things like us, it’s “amazing.” It all comes of laboring under the historical curse of disconnecting physical anthropology from zoology at its inception, which seems almost impossible to shake. I give all credit and much gratitude to those anthropologists who struggle to do so, against their own discipline’s vocabulary and traditional pedagogy.

For example, in this linguistics course webpage, Dr. Kemmer presents the standard anthropological narrative from Wikipedia and annotates it with useful questions. I draw attention to her questioning what “semi-opposable” means, and how without quite saying so out loud, she allows as how anthropology courses and the general narrative ignore what other mammals do with their fully-opposable, often more opposable thumbs, and focus on nonhuman primates only through a lens which diminishes them into practice-versions of humans.

lorisThe zoological observation is that several other primates outdo us in exactly the variables lauded as so amazingly human. For opposition, see the potto with the reduced-index-finger grip I described in the clip; and for opposition that beats all the opposition, see the loris.

Closer to home, in Hominid thumb strength predicted by high resolution magnetic resonance imaging and force measurements in living subjects, the authors show that other hominids cannot be shown to have lesser or even different thumb gripping strength from human test subjects. It is also not apparent to me from any available data that they lacked thumby-agility compared to ours.

To conclude for the philosophers: these four questions are our biological epistemology, obviously interrelated and yet distinct in precisely what’s asked and how observed variables feed into answering them.

Links: Stephen Jay Gould’s The Panda’s Thumb (the essay, not the book of that title)

Next: Itsy bitsy critters in an itty bitty poo


One thought on “Have you ever really looked at your hands?

  1. Pingback: Fitter than thou | Man nor Beast

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