Trunkedness

by mammalfish

Is anyone else REALLY EXCITED about this whole blogging project? I can’t wait to read what you all have to say…

Yesterday in class I was thinking about what I wanted this assigned first post to be about (although I know it’s more of a test-out-the-system endeavor than anything else, why waste an opportunity to think about something interesting, right?), and it occurred to me to write about the most intriguing thing I noticed about the elephants I studied in Tanzania last Fall—a thing which, ironically, had utterly nothing to do with what I was studying about them.

A bull elephant in Ngorongoro Crater, grazing by wrapping his trunk around tufts of grass.

More after the break…

I looked at the behaviors of two young orphaned elephants who are being raised by humans at a private ranch called Ndarakwai in Northern Tanzania. Since the two are so habituated to people, I was able to spend a lot of time in very close proximity to them, and so I noticed a funny thing about how they use their trunks. When an elephant is grazing, it wraps the underside of the flexible hand-like tip of its trunk around a clump of grass, grips it, and rips it out of the ground to transfer it into its mouth. If you look at this photo of an old bull elephant in Ngorongoro Crater, you can see that’s exactly what he’s doing (I would have used a photo of the orphans, but I didn’t get a photo of them that properly illustrated this discussion—this is the only photo I got of an elephant that does). This is fun to watch just on its own—trunks are such weird appendages, but they use them so well—but I started to realize that when the orphans grazed, they almost always wrapped their trunks around the grass in the same direction: counter-clockwise, like that bull is doing up there. They could just as easily have wrapped their trunks to the right, or clockwise, but to my casual observation they never did. Check it out! Elephant handedness! (Or as a friend of mine called it, “trunkedness.”) We all know that we have handedness (dominance on one side or the other), and people who’ve spent a lot of time with horses often find that individuals have a preference in their asymmetrical gaits, but I didn’t necessarily expect to see it in elephants.

As it turns out, though, handedness is a pretty common thing in the animal kingdom. A quick google brought me to this awesome and thorough article (where they also use the term “trunkedness”—humans, man! We think so alike!). They give a nice overview of the animals that show something like handedness, saying that “almost anything with a backbone displays some degree of asymmetry in its preferences.” Also, according to this article, humans are some of the only animals to show a population-wide preference—by far, most of us are right-handed. In other animals, apparently, it’s nearly a 50-50% split in the population, with around half of the individuals having a clear left preference, and half of the individuals having a clear right preference. A professional horseback riding trainer once told me that she had observed that horses tend to do more work with their left sides. Scientific? No! But fun to think about.

A horse at the canter, an asymmetrical gait. This is a right-leading canter, meaning that her right foreleg will stay foreward, as you can see here--and it also means that when she started into this run, she used her left hindleg first. Horses can canter at either a left or right lead, and riders can usually request that they initiate either one, but when left to their own devices most horses seem to prefer one or the other, taking off with either the left or right hind leg most of the time. This horse, Sadie, prefers the right lead that you can see here (if I remember correctly!), so it's easier to get her to comply with a right-lead request.

So, I’ve been thinking about this a lot since I saw the orphan elephants exhibiting this asymmetrical preference (I love that phrase—so many syllables), and I’ve really been wondering why so many animals—or vertebrates, at least—seem to have handedness. So, to wrap this up: why not delve into this with the proximate/ultimate model of thinking about animal behavior? I’ve got nothin’ but time. And maybe anyone who’s interested can contribute! I’d love to hear your thoughts.

Proximate Current: How does handedness work in individuals?

That article I linked to further up has a suggestion or two: The muscles and nerves used to work on one side of the animal’s body are more developed than on the other, leading and/or allowing the animal to use that side more. It would seem, though, if you think about it, that this is at the start a result of asymmetrical preference, rather than an initial cause (unless fetuses actually initially grow with more muscle/nerve development on one side than the other, which they may be). So how does handedness develop in individuals? (What a great lead-in, right?)

Proximate Historical: How does handedness develop in individuals?

From what we know of handedness in humans, it’s an inborn trait (well, maybe, we think so, sort of). But can we extrapolate this to other species? Maybe other animals, in youth, are choosing a side—does the human right-handedness vs. the other-species 50-50%-handedness have anything to do with this?

Ultimate Current: What is handedness for, in a species-wide sense?

That first article has a suggestion for this, as well: Since animals presumably have only so much energy to devote to movement and movement tasks, they need to designate that energy in the most practical way possible. Dedicating more muscle/nerve development energy to one side of the body, and less to the other, means that you’ll have really nice dexterity on that one side (less symmetry, more dexterity), as opposed to having equal development on both sides (more symmetry, less fine dexterity). Basically, this leads to the conclusion that dexterity is more important—at least for these handed animals—than is symmetry. What do y’all think—do we buy any of this?

Ultimate Historical: How did handedness evolve in these species?

If that last ultimate current statement is correct, I guess we can presume that animals in these species that had more dexterity had greater survival rates—and they way they got that dexterity was an asymmetrical designation of their developmental energy resources, leading to handedness. So the handed ones, over time, lived long and prospered, and the more symmetrical ones didn’t. Again, do we buy any of this?

So! In conclusion: If anyone actually read that whole mess, much respect! I certainly had a lot of fun writing about it. If you have any thoughts/criticisms, I would love to hear them, either in person or by comment or whatever. Were there any flaws in my thinking or reasoning? Do you have any more ideas as to the various causes of handedness? Any of you have your own observations of asymmetrical preference in the animal kingdom? What say you?

See you all in class!

~Megan

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