Friday, December 2, 2011

Hurling words and turds, an evolutionary link

Humans are excellent throwers. Even poor throwers, or famously ridiculed ones, are still pretty skilled compared to other species with grasping hands. We're so good at throwing things, it's hard not to wonder why. 

This is when you say, "Our arm anatomy, dummy. That's why humans are good throwers."
Our shoulder, arm, wrist and hand anatomy is mostly very similar to other primates' but the differences are critical to our ability to throw so well. (See here for more in-depth discussion of head-to-glutes-to-toe throwing anatomy.)  Once the arms were freed from their locomotor role their anatomy could respond to different selective pressures (or not) and one of those pressures might have still been locomotion (arm swing) and another was likely throwing, considering the benefits of action-at-a-distance for obtaining food, avoiding predators, and interacting (not so nicely) with other humans. 

But it's not all about the arm. Insert a chimpanzee's brain into a human's body and it'd be a safe bet that Frankenzee couldn't throw like Frank Reich... or any of us. That's because throwing well by human standards isn't just about human limb anatomy, it's about controlling that human limb anatomy with the human brain. 

Some popular and well-supported explanations for the origin of throwing are brain-based. The coordination of the body's movements and timing of those movements relative to the distance and velocity of a target is nothing less than genius. This same sort of coordination is required for language which is why hypotheses compare and even link throwing evolution to language evolution. Bill Calvin fleshed out an idea in The Throwing Madonna where he hypothesized that throwing enabled the evolution of language because both are controlled in large part by lateralized functions in overlapping regions (Broca's area) of the left hemisphere.

So it's only because of our big and specialized brains that we can both talk trash and sink a clutch three-pointer.

There's a field of research on understanding the biology, biomechanics, and physics of throwing behavior but only a subset of that research is rooted in an evolutionary, comparative approach. (For one good example, see Neil Roach's work.) As mentioned above, this is because few other species actually throw. However, lucky for us and despite their lackluster ability, chimpanzees do love to throw s--t.

This week some researchers who are interested in the neurobiology of throwing published a paper that made use of this hilarious habit--made famous the world over by zoo visitors with cameras and youtube accounts.

Like the study's authors, if you hang out around chimps long enough, their variation just screams out at you. For one, they vary in how they scream out at you.  But they also vary in their penchant for throwing. And this observation might cause you to ask yourself, If throwing is a brainy activity are the brains of the chimps who like to throw s--t any different from the brains of chimps who'd rather not? And if they're different, how are they different? What parts of the brains are different? Is there anything else about the chimps who like to throw s--t that separates them from those that don't?

These are the questions that Hopkins and his mates asked in their paper.

First they divvied up 78 chimps at the Yerkes National Primate Research Center into those who "reliably throw" (poop and food, mostly) and those who do not. I could not find more details on how this distinction was made, but if you spend your days at the YNPRC it's probably pretty obvious who the' THROWING+' and the 'THROWING-' are. (And you'd probably best learn fast before the s--t hits the man.)

Then they anesthetized each of them so they could MRI their brains to test for any brain anatomy differences.  (This was hopefully, and probably legally bound to be, coordinated with a necessary physical exam for each of these animals so the trauma was for good, health-related cause.)

To test for behavioral or personality differences, they performed the 'Primate Cognition Test Battery' or PCTB (Herrmann et al., 2007) on each of them.

When they compared the brain scans, they found that THROWING+ chimps had significantly more white matter relative to grey matter in the inferior frontal gyrus, which is the homolog to Broca's area in humans. And they also had significantly more white matter in the motor-hand area of the precentral gyrus, which is associated with handedness. Increased white matter is important because it indicates more myelinated interneurons that connect different cortical regions, suggesting to the authors that "learning to throw may alter the connectivity between premotor and primary motor cortex in the chimpanzee." (p. 44)

For an adaptive hypothesis in humans to come from this we'd need to parse out causes and effects. (The authors acknowledge this issue that haunts so many comparative studies.)

When they compared the results of the PCTB the only significant difference was that THROWING+ chimps scored higher in "communicate" points.

Hopkins et al., 2011
As far as I can tell, this "communicate" score comes from tests of a task called "comprehension" where experimenters gaze and point at targets and apes are assessed on how they respond, and another task called "production" where apes are assessed on whether they produce communicative signals (such as manual gestures) to indicate where food is hidden in hopes that an ignorant human will find it and give it to them.

This all seems so far removed from chimpanzees throwing s--t doesn't it?

Especially considering that the authors discuss these findings in support of the connection between language and throwing in human evolution.

Despite all the dots that need to be connected, throwers' brains did have more white matter in potentially significant (to throwing and language) centers of the brain and throwers did outperform non-throwers in "communicate" tasks on the PCTB. How else do you explain these things without throwing as part of the explanation, and maybe significantly so?  And if you're on board with that, how about throwing as a critical precursor to language... as the means for laying down the neural tracks that were later used for language?

Evolution of one wouldn't have occurred without evolution of the other one first. Why not? This isn't so scandalous. Just about everything else exists because of what came before. 


Anne Buchanan said...

Great post, Holly! I especially like your concluding paragraph. I haven't read the paper, but (or rather therefore) I'm confused about the significance of the brain differences between throwers and non-throwers. Is the idea that the increase in white matter pre or post-dated becoming a thrower?

Ken Weiss said...

Of course I'm very skeptical about any of these evolutionary just-so stories. But in this case,there are a few important points.

As far as human throwing and throwing footballs as in the first picture, two things are clear:

First, even after 7 million years of evolution, a recent NYTimes story clearly showed that there is no one best way to throw a football properly. Not even how to grip it.

Second, for this to have evolved would more likely have had _intestinal_ rather than neural concomitants. Only once, when, and if our droppings were ovate in shape would the proper throwing challenge have been presented.

I have never observed chimp droppings, even in captivity, so I cannot comment on why they do or don't throw good spirals....

Holly Dunsworth said...

Maybe next they're work on throwing as an evolutionary precursor to tebowing.

Anne Buchanan said...

Given what's known about brain plasticity, and how the brains of, say, musicians differ from those of the rest of us mere mortals, or of how brain areas can be remapped when, say, someone loses his or her sight, I'd bet these brain changes are an effect rather than the cause. If so, and if a chimp learning to throw correlates with his or her communication scores, to me it says a lot about how adaptable the brain is. How do you get to Carnegie Hall -- or the The Chimp S--t Throwing Hall of Fame? Practice, practice, practice?

Ken Weiss said...

Of course, if uniforms were made with the right sleeve and leg length, and hats that fit weird shaped heads, chimps might make very good baseball pitchers (or cricket bowlers). Whether they could throw just fastballs or curves, may depend on brain structure, but think of the leverage with their gangly arms!

And with their facile toes, they could get a good grip on the rubber, too.

Holly Dunsworth said...

The longer the arm, the larger the window of release which is nice if your chimpy brain's unable to finely (i.e. humanly) control the release timing of the projectile. This can give you distance (especially if you're short in stature), but this is not accurate throwing. You need to be able to control fine details of release timing and if you're hunting you need to be able to combine subtle release control with velocity. A shorter arm (especially the forearm) is easier to manage for this, but only if you've got the brains.

Holly Dunsworth said...

Anne, yes! And a good test might be to look at MRIs of professional throwers versus others. Or especially kids who regularly play a throwing sport versus those who do not. Much easier to collect these data. A quick search right now came up with no such thing.

Ken Weiss said...

Ah, yes if you've only got the brains. I never could control a fastball or a curve. Sometimes (as, for example, in Nolan Ryan or others) wildness terrifies batters, and makes them swing recklessly.

I guess if all you have to do is throw droppings to make a show of yourself, any dolt can do that.

Holly Dunsworth said...

hahaha. The one in the video I posted is pretty accurate. Hits the camera which must have been right on the face of the human!

Holly Dunsworth said...

Also, might I add that if we're gonna talk about the aerodynamics of poop: cow pies make good frisbees.

Holly Dunsworth said...

Oh, and then Anne, you'd need to look at brains of the families of throwers too, hopefully some are throwers and some are not.

Holly Dunsworth said...

And a longitudinal study on little leaguers.

Ken Weiss said...

Holly, what a dumb mistake you made! Cows didn't evolve til much, much later than humans! We couldn't have evolved to throw frisbees; it must have come later.

Of course, now that I think of it, this tends to strongly support the Aquatic Ape hypothesis (I really hate to say so!). Not because of droppings--that's a superficial just-so story based on stupid assumptions of forest-to-savannah evolution.

No, the truth is that our accurate throwing abilities evolved on the shores of Lake Victoria (where we evolved to swim), but it wasn't tossing turds that made us human, but skipping rocks on the lake.

Also, if their (cows') ancestors were savannah species, and chimps were in the forest, they'd never have got the idea of frisbee competitions on any lineage's way to human-ness.

Likewise, the brain-evolving human lineages may have been out in the savannah, but do wildebeest or oryx's make aerodynamic pies?

Holly Dunsworth said...

Yes. I can't believe you didn't know that already!

From flinging cow pies to twirling pizza pies to... pie in the sky.

Holly Dunsworth said...

Skipping rocks on the lake... a critical precursor to ennui.

Ken Weiss said...

No, I beg to differ. It can't have evolved if it led to ennui. Rock skippers (presumably male, or is that sexist bias?) would have been sooo, so sexy that they skipped as well as rutted much more than their less skippy contemporaries.

I think few people would agree that being relentlessly involved in expressing one's fitness was boring.

It was the non-skippers who, with no opportunities to do more than watch wistfully, at others 'at it' on the lakeshore (these were, presumably, naturist beaches), would have eventually droned off to bored sleep.

Each generation there were fewer and fewer of them.

One way to test the aquatic hypothesis is to see how many rocks are left on the shores. If hardly any, this proves that they were all skipped into the lake during millions of years of evolution. But if there are still lots of pebbles left, then the whole aquatic hypothesis will sink like a pebble thrown by an inept chimp.

Ken Weiss said...

Probably only that, like drunks in a bar, the modern human ancestors threw the other guys outta there.

occamseraser said...

Homo erectus (both Dmanisi and Nariokotome versions), like their Ardi and australopith ancestors, had little to no humeral torsion. They would have sucked at overhand throwing. Need to CT scan Tebow's shoulder ...

Ken Weiss said...

All of you are thinking too narrowly. Okay, so you reject my aquatic hypothesis. But what about bowling--maybe they bowled big rocks, kneecapping their prey? Or bowling, cricket style--I can't remember how you spin or fast-bowl, but it's so damn awkward that it shows that it may be hard to imagine how our ancestors passed their idle time away....