Trunkedness

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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7 thoughts on “Trunkedness

  1. What a great post! (Attempting to answer all the four questions, wow!). When I read, I wondered if the counter clockwise grass-grabbing might not be HANDEDNESS but might have a naturally-selected reason independent of the elephant’s natural inclination to use one or the other side of the body. Such as the grass pulls easier from one direction.

    • Dave–great point. My initial reaction to the specific example you brought up is that it’s probably not that the grass pulls more easily from one side, because if that original article is correct then elephants are one of those species that have a near 50-50 split on left- and right-trunked individuals (I’m guessing that they do mean in the same population). Presumably, if the grass were more pullable to one side, the majority of elephants would favor that side. Makes you think, why in the world are WE so right-handed? What’s up with that?

      It could be something else, of course–it always could be–and now I’ll be trying to think of how for awhile.

      • This is really intriguing – I originally thought “Oh, handedness, that’s simple. It’s a brain hemisphere thing.” WRONG. A quick overview suggests that handedness is actually quite complicated and very controversial. Epigenetic influences have been suggested to play some role in determining handedness in the womb, while the gene LRRTM1 assorts with left-handedness to some extent. However, it doesn’t appear to show inheritance patterns in a simple Mendelian fashion.

        Interestingly, LRRTM1 has homologs in vertebrates but not in Drosophila or C. elegans (1,2), so we could make a wild leap and suggest that handedness is something that appeared in vertebrates. That’s a huge guess, but let’s do it anyway!

        Taking that as our unfounded basis, we’ll go back to the first vertebrates. To me, a possible explanation comes from specialization. We know that nature is chiral (3) and that this chirality is shown in fossils surviving from the Cambrian – right when vertebrates evolved around the time of the Cambrian explosion! Perhaps handedness then first evolved as a response to chirality of food or prey – similar to Dave’s grass idea.

        Let’s take a completely different and even more unfounded tack. LRRTM1 is associated (somewhat) with schizophrenia as well as left-handedness. We could then view the dominance of right-handedness due to left-handed individuals being selected against for reasons completely unrelated to handedness.

        Anyway, thank you for posting this stuff – it was really thought provoking. My thoughts here only relate to the fourth question, but they’re all pretty intriguing. Also, you are awesome for linking to Kate Beaton in your blog, I am officially jealous.

        (1)http://www.ncbi.nlm.nih.gov/omimDb=homologene&DbFrom=omim&Cmd=Link&LinkName=omim_homologene&LinkReadableName=HomoloGene&IdsFromResult=610867

        (2)http://www.ncbi.nlm.nih.gov/omim/610867

        (3)http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1182695/

        • Who wrote this comment?? I LOVE this comment. From Drosophila to the Cambrian explosion to chirality to Kate Beaton. We should be friends.

          I don’t really have any responses/counters off the bat, because this is all really fun, well-founded reasoning, as far as I can see, and it’s stuff I never would have gotten to in my thinking. As for Kate Beaton, I actually got this blog by clearing out a pre-existing blog of mine (does it say something about me that I already had a blog called “mammalfish” before this class?), and I forgot that I had that collection of links at the side…I should make sure everything there is pc/alright for classes. But anyway! Isn’t she great? I get a lot of silly little Napoleon jokes out of that comic.

  2. Haha, yeah I love Kate Beaton. The Nancy Drew covers she’s done recently are great, as was the Les Mis stuff.

    Where’d you come up with the name mammalfish? I like it, although I think best named blog might be “whythewildthingsare”

    Anyway, I’m Chamith and we should definitely be friends.

    • Agreed very very much on whythewildthingsare, it’s one of the best blog titles I’ve ever seen =D. Mammalfish is an identity I’ve liked for a few reasons: My main intellectual passions are animal behavior and evolutionary biology; my favorite group of critters to study is mammals, but I’ve always had a thing for the sea, and especially cetaceans (mammalfish seems especially appropriate in that respect); and I would usually rather be in water than on land, as would most of my family–we all call ourselves fish, and my uncle, though I never met him, apparently even had vestigial gills (non-functional, of course, but still!)…thus, I come from a family of mammalfish. Humanfish?

      I’ve never written out all the reasons why I like that name before…it reflects a lot of my passions. The Dodo Lives! makes me really happy. It’s optimistically quirky. And the theme you found for it (with its old-fashioned weathered-paper charm) fits the aesthetic of the name, actually, well done.

      I’m now thoroughly convinced that this is the best class assignment ever. We might never have spoken at all if not for this project, and hopefully a lot of people will be similarly introduced. What a cool idea.

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