How the cheetah gets its noms

June 18, 2013 • 5:58 am

This article has been hanging around my neck like an albatross. I’ve been sent it by several readers, but it’s not terribly exciting, and I’m reporting on it more as a duty (and because it’s on a felid) rather than to impart any scientific information.  (UPDATE: after writing this piece, I decided that the results are more interesting than I imply here.]

The results, taken from a new paper in Nature  (reference below) are about how cheetahs (Acinonyx jubatus) run when pursuing prey.  There’s not much new save for the quantitative data, but the paper’s publication (and the ensuing publicity in places like The New York Times) appears to derive largely from its use of gadgetry: special collars fitted on cheetahs that give data on their location (within 0.2 m), their speed, and their acceleration.

Here’s an example of the publicity in the journal itself (read the “speed test in wild cheetah” box).  As Matthew commented to me:

BTW you might want to poke fun at the splash that Nature had on its front page (see attachment). Talk about
the bleedin’ obvious. As a pal responded on Twitter, “I knew that when I was 8 years old”. They’ve changed it since.

Picture 2

Matthew adds this: “Even the opening two paras of the accompanying news item are really stupid.”  Here they are, and yes, we sort of knew this already:

The cheetah crouches in the undergrowth. When a young antelope strays a little too far from the herd, the cheetah explodes out of the bush — and, with a burst of speed unrivalled in the natural world, brings down its next meal.

Or so we have assumed. But the first study to collect data on the animal’s movements in the wild reveals that, contrary to popular opinion, a cheetah’s sheer speed is not its only weapon when it comes to hunting. Its success as a predator also hinges on its lightning reflexes and its ability to accelerate faster than a Ferrari.

Well, the Ferrari part is interesting, I suppose, but what’s new here? I’ll distill it down to a few points.

First, the methodology.  The authors attached special, solar-powered collars to five wild cheetahs in Botswana, and monitored 367 runs at prey over a period of 17 months.  For each run they tracked the animal using GPS technology, and measured its speed and acceleration.  Here are the highlights:

  • 94 of the hunts, or 26%, were successful.  Most of the prey were impalas (75% of prey items), but cheetahs also took warthogs and Thompson’s gazelle.
  • Cheetahs hunt by stalking.  Starting from either a slow walk or a stationary position, they accelerate rapidly. This much we already knew.
  • The average run length was 173 meters, and the average frequency of a run after prey was 1.3 times per day. That means that they have a successful hunt about once every three days.
  • They can run fast: the already-published top speed is 29 meters/ sec (104.4 km per hour or 64.8 mph), substantially faster than racing speeds for greyhounds (18 m/sec), horses (19 m/sec) and humans (12 m/sec; Usain Bolt’s 100 m record).  The collar data substantiate this, showing a top speed of 25.9 m/sec (58 m/hr or 93 km/hr). That’s important because it’s hard to measure running speed in captive cheetahs (they’re trained to follow a bait over a predetermined distance), so we didn’t know how close the “captive” speed was to speeds attained in nature.  The mean top running speed during a chase, though, was about half that: 14.9 m/sec (53.6 kph or 33.3 mph).
  • The rates of acceleration and decleration are extreme. The acceleration rates aren’t expressed in any terms I really understand: the highest was 100 W/kg (can some reader translate that in to m/sec/sec?). That rate is about four times that of Usain Bolt’s acceleration in his world-record 100m dash.  But they can speed up by 3 meters/sec and slow down by 4 m/sec (6.7 mph and 8.9 mph respectively) in a single stride.  They can accelerate, then, faster than a Ferrari (at least according to the New York Times), and decelerate from their average chase speed to a standstill in less than four strides.  That’s pretty amazing.
  • The deceleration often occurs right before turning, enabling them to maneuver with great dexterity, something you’ll know if you’ve seen videos of cheetahs hunting. (I’ve put one below.)
  • Finally, their ability to speed up and slow down rapidly, as well as to corner tightly, comes, according to the authors, from their “ridged footpads,” nonretractable claws (see picture below), their flexible spines, and their tremendous muscle mass. According to the authors, “the locomotor (limb and back) muscle accounts for 45 ± 4% of body mass in captive cheetahs. . . major propulsive muscles such as the hamstrings. . at the hip and gastrocnemius at the tarsus have 64% and 60% longer movement arms, respectively, than in the greyhound.  . “

The photos below show the collars, the forces impinging on hunting cheetahs, their nonretractable claws, and the posture they assume during deceleration.

After rereading the article and writing this, I guess the findings aren’t so humdrum after all!

Cheetah
Figure 1 | Cheetah with collar and anatomical features contributing toperformance. a, Cheetah with a mark 2 collar is shown. b, Gravitational andcentripetal accelerations acting on a turning cheetah; g denotes acceleration dueto gravity, v2 r21 denotes centripetal acceleration, and a is the resultantacceleration (effective gravity). c, Non-retractable cheetah claws that enhance grip. d, Low posture used in deceleration, which prevents pitching and engageshind limb musculature to absorb kinetic energy.

Finally, you can see it all in action in this National Geographic video of a hunt:

___________

Wilson, A. M., J. C. Lowe, K. Roskilly, P. E. Hudson, K. A. Golabek, and J. W. McNutt. 2013. Locomotion dynamics of hunting in wild cheetahs. 498:185-189.

Moar policy: emails

June 17, 2013 • 1:31 pm

Since there has been some discussion on the Internet about revealing private email communications from readers, I want to state my policy upfront. Consider this an addition to my previous promise that I would not “out” (that is, identify) anybody who makes a comment on this site, save for those who physically threaten myself or others.

Since other writers and I also receive private emails, I want to make clear that I will never publish the contents of private emails, or identify their authors, without without explicit permission.  You can be sure, when emailing me—and my work email is readily available—that your communications are confidential.

There is one minor and (I think) harmless exception. If you email me animal or plant pictures, hoping they’ll be posted, I sometimes put up the authors’ comments as a caption.  I almost always try to contact authors first, but sometimes I don’t hear back, and then I go ahead and post.

Even in those cases, though, I will not identify the person who sent me the picture without permission. If you do send me photos or something you think I might want to post, then, please include some information that could be published, as well as how you’d like to be identified. This is not a guarantee that I’ll post what I’m sent—I get far more material than I can use—but a guarantee that you won’t be “outed.”

And, as always, I urge readers to send me photos or other things they think might interest our community.  But please don’t be disappointed if I don’t use it.

kthxbye.

Sean Carroll: There is no classical world

June 17, 2013 • 11:49 am

I’m not a physicist but wanted to direct you to Preposterous Universe, where, in a new post called “There is no classical world,” Sean Carroll mentions an experiment showing definitively that even a macroscopic object—a mirror cooled to near absolute zero—behaves according to quantum rather than classical mechanics.  That is, instead of remaining absolutely still, it vibrates at an amplitude of 0.000000000000001 meter, as predicted by QM.  And they could measure that vibration! There’s a nice animated video that describes it clearly. You will want to see that.

The universe continues to astound me.  I don’t understand quantum mechanics, but that puts me in good company.

Foodtrip!

June 17, 2013 • 9:58 am

In a final attempt to have fun before I start serious book-writing, I took half the day off yesterday to have a food trip.  My ex-student Daniel, who likes his noms, was around, and I invited him to the Birreria Zaragosa on the South Side, near Midway Airport.  In case you don’t know, a birreria is a Mexican place specializing in goat, a vastly underappreciated meat that is best sampled at either a birreria or a Jamaican restaurant. It’s gamey, which I like, flavorful, and, when cooked properly, tender and luscious.

The Birreria Zaragoza is a small, family-run place, unprepossessing but fiercely dedicated to its one dish: goat. It’s local grass-fed goat, lovingly stewed for hours and served in a flavorful broth.

Here’s the inside of the restaurant, which was full of locals chowing down on cabra. If you enlarge the menu (below), you’ll see that it’s almost all goat, with a few quesadillas thrown in as an afterthought.

Interior

Having done a bit of preliminary investigation, I knew that the most highly prized parts of the goat were those parts close to the bone, especially the ribs and the pistole (the shank). Here’s one of the cooks displaying the pistole:

Pistole

One of the best parts of the meal are the tortillas, which are made completely by hand, rolled out by this woman and then flattened in an old wooden tortilla press.  They’re a bit on the thick side, and absolutely delicious: a perfect encasement for the goat:

Tortillas

A superb lunch: a plate of goat (the prized pistole) with a stack of fresh tortillas, lime, chopped onion, and homemade smoked-tomato salsa, all washed down with a glass of cold horchata.

goat dinner

Afterwards we repaired to a Polish place: Bobak’s Restaurant and Sausage company, famed for its sausages and other Polish delicacies. (Chicago, I’m told, has more Poles than any city in the world save Warsaw. And they’ve brought their food culture with them.)

Here are some of their homemade sausages (there are dozens of types):

Sausages 1

Self portrait with kielbasa and Daniel:

Portrait with kielbasa

The various kinds of pickled and preserved fish beloved by Poles:

Fish

A box of kolacky, or fruit-filled cookies. They come with prune, cherry, apricot, and apple fillings.

Kolacky

And my haul for the day: a big $1.79 link of kielbasa wselna (Polish wedding salami), half of which I’ve just had for lunch; paczki, or Polish donuts, pierniki uszatki, or glazed gingerbread cookies; a jar of plum preserves (Polish jams and preserves are cheap and delicious), a jar of pickled beets with onions, and a log of macowiec (poppyseed cake).  You can see my sweet tooth at work here.  This should hold me for a while. . .

The haul

A strange conception of free will

June 17, 2013 • 6:37 am

Just when I think there’s nothing more to be said about free will—after all, we’ve hashed over most of the points here—a new piece comes along with yet another take on the issue.

The latest slant, written by Dr. Peter Tse, is either deeply misguided or, less likely, profound in a way I don’t understand. I suspect it’s the latter, an essay that, in the end, is just a “deepity.”  Tse, a cognitive neuroscientist at Dartmouth College in New Hampshire, has written a 1200-word defense of free will in New Scientist called “Free will unleashed” (unfortunately, it’s behind a paywall, though I give the reference below).

Although Tse doesn’t define free will, he appears to conceive of it as the condition of human behavior when, in a given situation, with all else equal, you could have done otherwise if you reran the tape of life. I used to hold that definition, too, until I realized that if quantum indeterminacy really does play a role in our actions, then it’s possible for us to have done otherwise in a given situation—that is, with all the molecules in the universe aligned in the same way were the situation repeated—even though we’re not really affecting that decision through any kind of conscious rumination. I now prefer to define free will as Anthony Cashmore did in his article on the topic in Proc. Nat. Acad. Sci. (reference below):

I believe that free will is better defined as a belief that there is a component to biological behavior that is something more than the unavoidable consequences of the genetic and environmental history of the individual and the possible stochastic laws of nature.

That excludes any quantum effects from the notion of free will, for I believe that even the compatibilists who post here don’t find their compatibility in quantum indeterminacy.

At any rate, Tse’s insight—his defense of free will—depends on the fact that when neurons fire, causing electrical “spikes,” the firing can change the subsequent way that other neurons fire:

The missing piece is that neurons can rewire each other. Spikes don’t just trigger subsequent spikes in other neurons. Within milliseconds, they can temporarily change the degree to which synapses –; the nerve structures that pass signals to other neurons –; trigger future spikes. This reweighting of a synapse is like changing the combination on a padlock without opening it, and can happen without necessarily triggering spikes immediately. I base this claim on research from the past decade showing that rapid bursts of spikes trigger the opening of specialised synaptic receptors, altering the responsiveness of neurons to subsequent spikes.

This means that a neuron could now be driven by an input that, moments before, might have contributed nothing to its firing. For example, a nerve cell that has just responded to a touch to your forehead could now respond to someone stroking your hand.

This rapid synaptic reweighting could potentially alter the connectivity of an entire circuit, defining new neuronal paths that signals can traverse. Just as railway switches must be flipped to allow trains to pass, synaptic weights must be reset before brain signals can follow one path through a neural circuit instead other possible paths. And if information is realised in the brain at the level of circuits, not just neurons, it is no wonder that listening to spikes in single neurons has not allowed us to crack the neural code.

I’ll concede the idea of “reweighting,” which doesn’t violate my notion of how brains might work. But how does this “reweighting” give us free will? Because it means, according to Tse, that we could have done otherwise.

You might ask, though, how could that be, since the description above is still deterministic ? Reweighting is just a deterministic phenomenon: neuronal firing affects the way other neurons fire. Here he simply sneaks in quantum mechanics (my emphasis), something that he hasn’t defined as part of “neuronal reweighting”:

What does this have to do with free will? Determinists argue that because all particles follow predetermined trajectories, all events, including our lives, unfold as inevitably as a movie. Indeterminists, supported by quantum mechanics, argue the opposite –that all events are random. In either case, whether predetermined or random, there is no room for free will to make events turn out otherwise.

There is, however, a middle path to freedom between these unfree extremes. If the brain sets up criteria for future firing, and if spike timing is made random by the amplification of quantum-level events in the synapse, it is down to chance how these criteria are met. The inputs that meet criteria cannot be predicted –the outcome depends on which spikes coincidentally arrive first.

How does chance interplay with these internal criteria in real life? If I ask you to think of a politician, your brain sets the appropriate criterion in neurons involved in retrieval of information held in your memory. Perhaps Margaret Thatcher comes to mind. If it were possible to rewind the universe, you might think of Barack Obama this time, because he also meets the criterion. This process is not utterly random, because the answer had to be a politician. However, it is also not deterministic, because it could have turned out otherwise.

Here he appears to find free will in the pure stochasticity of individual quantum events.  The problems are twofold: nobody wants to see free will in such indeterminacy, and we don’t even know if quantum effects have an effect on neuronal firing, much less on the behavior that results from such firing. And, absent quantum events, the system becomes purely deterministic. Since Tse thinks pure determinism rules out free will (he’s not a compatibilist), he has to do some fast-stepping to drag conscious “will” into the picture:

Factoring in rapid synaptic reweighting also gets around the argument that free will can’t exist because of the impossibility of self-causation. The argument goes as follows: we act as we do at each moment because of how our brain is physically organised at that time. So because we are not ultimately responsible for the way we are organised then, we are not responsible for the consequences of that action. It had to happen as it did, otherwise a thought could change its own neuronal basis, which is impossible. But with synaptic reweighting, mental events don’t change their present physical basis. They change the neuronal basis of possible future events.

As far as I understand this, though, “synpaptic reweighting” does not get around determinism and is not “self causation”.  Absent quantum events, there’s no obvious reason to ditch determinism simply because when a neuron fires it affects how other neurons will fire.  To me, this seems like semantic gobbledygook.

Tse then raises the problem that a zombie lacking consciousness could still show this behavior, but “we would not say it had free will.” In other words, to Tse, a conscious decision, one in which you can alter future events by thinking about them, is essential for free will.  He then explains, using a food analogy, how consciousness really is important in giving us free will:

If consciousness plays no part in the synaptic reweighting process, there is hardly a free will worth having. (There are many definitions for consciousness, but I define it as all the information that presently is, or could be, voluntarily attended to.) [JAC: note the sneaking in of the word “voluntarily,” which is skirting dualism and, at any rate, doesn’t have anything to do with quantum indeterminacy].

Fortunately, the neural activity associated with consciousness does play a necessary role. One way to demonstrate this is using a thought experiment. Let’s say you are planning a dinner party and play out various possibilities in your mind’s eye. You imagine serving a steak, then realise that one guest is vegetarian, so set criteria “delicious; not meat” among synapses associated with memory retrieval. As described before, whatever comes to mind will meet these criteria yet could have turned out otherwise.

Let’s say spinach lasagne is the first appropriate solution that comes to mind. This solution could only have been reached through intentional manipulation of conscious thoughts, so the neural activity that gives rise to consciousness is necessary for the subsequent act of shopping for spinach. Your brain freely willed the outcome of spinach by setting up specific criteria in advance, then playing things out. Such internal deliberation is where the action is in free will, not in repetitive or automated motor acts.

I don’t get this, for it seems like pure determinism to me.  The “internal manipulation of conscious thoughts” so touted by Tse is simply the working of the meat computer we call our brain. That computer running a program based on your genes and environment.  So how on earth is this the same as “your brain freely willing the outcome of spinach” in a way that your decision could have turned out otherwise? How could it have turned out otherwise? How do we “manipulate” our conscious thoughts? Am I missing something?

As far as I can see, Tse is coming perilously close to saying we have a dualistic free will, but coming nowhere near justifying his claim that our own thinking can change our decisions so that we could have done otherwise.  His ending makes this clear:

This way of understanding the neural code has deep implications. It means that our thoughts and actions are neither utterly random nor predetermined. This counters arguments that free will is an illusion. It shows that the conclusion derived from the dogma of determinism –that mental events, including volitional ones, cannot cause subsequent events –is wrong.

We are not mere automata or unfree characters in a deterministic movie. We can change the physical universe with our minds. For example, it was not predetermined at the big bang when and where aeroplanes would be invented. They were brought into existence by brains that could harness chance to creatively envision a different future.

This does not mean that we require a soul for free will. We don’t. My account is entirely physicalist. But our brains can set criteria, play events out internally, choose the best option, then make things happen. And it could always have turned out otherwise.

Really?

I will grant Tse one thing: I agree with him that the invention of aeroplanes wasn’t determined at the Big Bang.  For between that event and the Wright brothers there were lots of events in which quantum indeterminacy could have played a role.  The configuration of the universe right after the Big Bang, so Sean Carroll tells me, could have been profoundly influenced by pure physical indeterminacy. I’m also willing to grant that mutations—the raw material of evolution—could often be purely indeterminate. And if that’s so, then even the evolution of humans, or of any other species, might not have been inevitable had we, à la Gould, rolled back the earth 4.6 billion years ago, but leaving every molecule in the same place.

But that is not the same thing as saying that if I was planning a dinner party, and rolled back time a few minutes to the moment when I decided what to serve, I could have chosen meat rather than spinach.

Maybe I’m getting something wrong here, and maybe Tse is proposing a type of compatibilism with which I’m not familiar, but it seems to me that he’s simply stringing together a lot of words, mixing them with some findings in neuroscience, and coming up with a type of free will that doesn’t do what it purports to.

_________

Cashmore, A. R. 2010. The Lucretian swerve: the biological basis of human behavior and the criminal justice system. Proc Natl Acad Sci USA 107:4499-504.

Tse, P. U. 2013. Free will unleashed. New Scientist 218:28-29.