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Comment by ogoparootbbo | Hacker News Reader

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?

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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)

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