Mexican jumping beans use random walk strategy to find shade: study | Hacker News Reader

Mexican jumping beans use random walk strategy to find shade: study

arstechnica.com

125 pointsStratoscope53 comments

err, I maybe hugely mistaken but is this an example of a real life of the following joke: "a scientist had this experiment going wherein everytime he rung a bell the grasshopper would jump. He clips one of the grasshopper's legs and rings the bell to see if the grasshopper would still jump and it did. He repeated the clipping process till the grasshopper had no legs. He wondered if it would still jump ... and it did not. He muttered to himself that hence that proves grasshoppers use their legs to hear"

am wondering it this is an example of a teleological thinking?

Yes "random walk" is not a strategy, it is a model. This article basically just says:"Jumping bean motion can be modeled with random walk", which isn't really suprising.

Yah, this article is basically nonsense. The beans jump more when hot, and less when cold, meaning they are more likely to stay put when jumping into the shade, and if too hot they'll keep jumping.

"These results suggest that diffusive motion [random walks] in Mexican jumping beans does not optimize for finding shade quickly," the authors concluded. "Rather, Mexican jumping beans use a strategy that minimizes the chances of never finding shade when shade is sparse."

I’m not sure what alternative strategy they are hypothesizing that would find shade more quickly, though?

it seems like the bugs have only one motor function - move in a random direction - and only one input sensor - temperature. What other strategies are available to them than random walk with a probability of movement based on a function of temperature and time?

I don't know either, but is it possible they are concluding that the bugs have only the function "move in a random direction" based on their observations?

If the bugs had the functions 1) move in one direction and 2) turn, then they might have observed a circular or spiral path.

Put a blindfolded human in a zorb on an uneven patch of desert and I would be impressed if they could manage more than one bounce in the same direction in a row. Not sure what mechanism would enable a jumping bean to reliably bounce ‘forwards’.

Right, but that conclusion is teleological.

First, they have no evidence that evolution could create a jumping bean that jumps in a straight line. It seems that the direction the bean moves is a function of the uncurling larvae but also the shape of the bean. Possibly such a movement could have evolved, but the authors are presenting this like the random walk improved the larvae's fitness function.

Second, the conclusion that a straight line would find shade quickest, but only for a small percentage of larvae, is obvious and doesn't result in anything scientifically new. Of course if you draw straight lines from any point in all direction, the straight lines that happened to intersect with the shade will be the fastest path to the shade. But just as obviously, heading in a straight line in a random direction is not the most efficient way to find shade.

If they had the freedom to evolve any search strategy possible, there are plenty of search strategies that will uncover shade faster than a random walk. But the larva don't have the ability to select any search strategy they want, they're blind and have no senses besides their current temperature. They have no way of knowing which direction they're facing. Therefore a random walk is simply all that is available to them, it's not a strategy.

Exactly! Many motions in nature can be modeled as either Brownian motion or Lévy flight.

Jumping randomly(edit:in a random direction) when it is too hot is a strategy. And apparently good enough for survival of this species. The bacterium e. Coli uses a similar, or identical strategy of turning("tumbling") in a random direction when the environment conditions are not favorable, and then running straight while the conditions are good. You can guide a blindfolded person to a goal of your choosing just by telling them "hot" or "cold".

Maybe the name of the strategy should be "directed random walk".

Isn't it only a strategy if you've established that they are capable of movement in direct line? Otherwise the most you could say is natural selection selected for shell shape that produces random walks.

I.e., it's a strategy at the species scale, but not the individual scale.

But, maybe that's my mistake of not knowing how these words are used in biology.

It's not the shell that produces random walks, it's the larva of a moth living inside the bean. The larva cannot see the environment, it can sense the temperature, so jumping in a random direction is a means (or a strategy) of the larva with the goal of achieving optimal temperature. It works well in their environment, because the temperature rises if they are exposed to direct sunlight, and a few jumps in a random direction might just get them to shade to a lower temperature. In the shade, they stop jumping.

"Strategy" makes clear sense for humans. A group of people could think some problem through and adopt a strategy to solve it. For any other life we know of, it quickly stops being meaningful. We may sometimes say that cats or dogs or chimpanzees adopt strategies, because we often like to talk about them as agents. But as we move towards less complex/intelligent forms of life, it quickly becomes clear that we're only ever dealing with biased dice throws.

Point being, I wouldn't worry too much about "having a strategy" vs. "natural selection selecting for". It's only ever the latter - perhaps with exception of humans, but that's up to philosophers to figure out.

I think that's right. I don't think the article is imputing "strategic thinking" to the individual larvae. They carry out a strategy, but they probably didn't whiteboard it themselves.

I think it's mainly the ability to start or stop jumping according to temperature. Jumping in a random direction, only when you're too hot, is a strategy for finding shade. Given a pattern of light and shade, that strategy is provably better than never jumping at all, or jumping regardless of temperature. (I haven't proved it, but I think I could.)

I think they're saying a jumping bean "has a strategy" in the same sense that a Roomba "has a strategy." The Roomba has an edge over a traditional vacuum cleaner. But if it's you against the Roomba, you're normally going to win.

Wrong. The model CAN be characterized as a strategy. Why? Because there are better strategies that can be executed. A model is just a description, a strategy is a method for winning. Some methods are better then others.

Given zero information about your surroundings other then the fact of whether you are currently in a shade or currently not in a shade traveling in a straight line is a mathematically better strategy.

Why? Because random walk includes the possibility of going back to the same place of where there is no shade while traveling in a straight line guarantees every move is a new location.

> He muttered to himself that hence that proves grasshoppers use their legs to hear

Not quite, but the location of the grasshoppers hearing organ is actually quite close to the legs!

Many women would say the same about many men, who often don't hear a word that they are saying!

In crickets, which together with grasshoppers are in the order Orthoptera, the hearing organs are actually on the legs: https://en.wikipedia.org/wiki/Cricket_(insect)

Applied Science recently pointed his X-ray video hardware at the Mexican jumping bean:

https://youtu.be/xdpDd7dyU00?t=33

Amazing good quality high-speed x-ray video!

Interesting video. I can’t believe this guy is just live x-raying his fingers like this though…

they come in packs of ten for a reason yaknow!

Sleep soundly, for Ben is no stranger to radiation and imaging and is surely well aware of the risk profile. He mentions it briefly at 10:55 as roughly equivalent to a dental X-ray, which is pretty minor as seen on the excellent XKCD radiation dose visualization: https://xkcd.com/radiation/

If I recall correctly Ben's side hustle before YouTube was making non-ferrous computer peripherals for MRI machines, and his portfolio on YouTube is incredibly extensive including this one from 10 years ago where he made a CT scanner from scratch!

https://youtu.be/hF3V-GHiJ78

I was amazed with the lcd and the vacuum metal evaporation coat applying thing

Always amazed at the order of magnitude jumps in that chart. Why are mammograms 20x stronger than chest x-rays? Who would guess how much safer the nuclear energy stuff is than so many common activities? And brick/stone house doses are kind of astounding.

Even after examining that chart every few years, my intuition still isn't tuned to reality.

Anyone know if this can realistically cause cancer or skmething?

Presumably they've refined the equipment by now, but this guy seriously injured his hands with x-rays around the turn of the previous century: https://en.wikipedia.org/wiki/Mihran_Kassabian

Always wondered about that too. Once got a contrast solution injected into my shoulder (they were going for the tissue around the joint) under a live x ray feed and I could watch them on a screen. I was padded with lead wherever possible, but still, cool experience.

That guy doesn’t get enough props for what he puts out, in my opinion…

This not true:

"Because the outcome of each coin flip is independent of all the others, there is always an equal chance that it will land on heads or tails with each toss. That means that your future final position is independent of your original starting position"

Assuming a fair coin, you will most likely end up approximately at where you started, with a Gaussian distribution. And your final position is extremely correlated with where you started.

In theory, using spherical cows, sure. But in practice there are all sorts of things screwing up the "probability" when jumping. Slope of the ground, windspeed, ground cover, etc.

Then it's still dependent on some known inputs: final position depends on initial position, wind speed/direction, ground conditions and gradient, etc etc. There is randomness, but you could make a probability distribution.

Ok? But it won't just converge to 0,0 because everything isn't equal and opposite, there will be some sort of bias that will move the bean away from it's origin.

But once you move to 3-dimensions, with a 3-sided coin that isn't true any more.

Yes it is true. You may be misremembering the fact that an infinite walk in 3D has less than 1 probability of returning to start. But returning to start is still the most likely outcome. How could anything else be more likely?

https://mathworld.wolfram.com/RandomWalk3-Dimensional.html

They definitely chose their words poorly in that sentence.

Karl Friston mentions a similar discovery in this interview: https://www.aliusresearch.org/uploads/9/1/6/0/91600416/frist...

“I first came up with a prototypical free energy principle when I was eight years old, in what I have previously called a “Gerald Durrell” moment (Friston, 2012). I was in the garden, during a gloriously hot 1960s British summer, preoccupied with the antics of some woodlice (small armadillo like bugs—see Figure 1) who were frantically scurrying around trying to find some shade. After half an hour of observation and innocent (childlike) contemplation, I realized their “scurrying” had no purpose or intent: they were simply moving faster in the sun—and slower in the shade. The simplicity of this explanation—for what one could artfully call biotic self-organization—appealed to me then and appeals to me now. It is exactly the same principle that underwrites the ensemble density dynamics of the free energy principle—and all its corollaries.”

I wonder if the simplicity of his proposed wood lice model applies to the jumping bean larvae as well?

Now I await someone pointing a camera at one - to create a random number generator like is done with lava lamps.

They don't really live that long. They can be farmed, I gather it's a couple difficulty steps above "regular" moth ranching.

A moth in a womb kicking about until it gets comfortable? That's pretty cool.

Jumping beans are available for purchase. I haven't bought from these folks; but I've heard good reviews of them: https://www.amazingbeans.com/

https://news.ycombinator.com/item?id=34748479

Not understanding how this is the best strategy to find success. A straight direction would be quicker and travel further.

Speed and distance aren’t what is being solved for.

Maximizing the chance of hitting an arbitrary spot is.

A straight line would require that you know where to go. But the bean (or rather it’s occupant) doesn’t - it has no eyes to look outside. So essentially it decides “it’s uncomfortably warm, let’s go elsewhere” until it’s no longer uncomfortable.

I see what you mean, but it's not necessarily true. You could pick an initial direction and keep jumping that way. I don't know what kind of environment would favour this behaviour, or if the beans can "jump the same way as last time" but it's certainly plausible.

Agreed, but the bean would probably very quickly find an obstacle over which it cannot jump. It would have to change direction then, but that's a much more complex strategy.

Another problem is that the bean probably can't keep a direction even if it "wanted". It uses random walk, quite possibly because it's the simplest to achieve acceptable results.

So you're saying we should CRISPR in some pigeon magnetic direction finding genes to the jumping beans so that they have more choice in their shade-finding strategy?

Perhaps, but even in genetics, there is no free lunch - all that hardware you CRISPR into the larva inside the bean will need energy and material to be constructed and operated. Those resources will come at the expense of something else. It might damage another vital system, or just compete with everything else for fixed metabolic output.

Ultimately, it may turn out that natural selection will remove your "upgrades" simply because metabolic load makes the organism statistically less likely to survive long enough to procreate. Turns out - it's something I hear is particularly apparent in bacteria and viruses - natural selection likes simplicity too :).

Takeaway being, it's easy to splice in arbitrary genes these days - but it's hard to make it an actual improvement.

If you have no idea where to go then a straight direction is likely not optimal as it is literally hit or miss with a high probability of miss if shade is sparse.

This is addressed in the paper. They say a straight line is faster, but much lower odds of success. Overall a worse strategy for survival.

They're not saying it's the best strategy. It's obviously not the best strategy. The bug can't see anything in there.

I need glasses, I thought it was a species of bear I'd not heard of that likes to jump.

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