How do ants find the shortest path?

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When starting Myrmecos Blog a few years back I resolved to avoid discussing creationism. People have strong opinions on the topic, hardly anyone ever changes their mind, and when they do it’s not because they read a blog post. Plus, creationism is so free of technical substance that it’s actually rather…boring.

Argentine ants find the shortest path between three nests.

I’ll make an exception for ant-related creationism, though. Especially when it illustrates a salient feature of ant behavior.

This week creationist William Dembski stepped into myrmecology with a rather odd argument:

Colonies of ants, when they make tracks from one colony to another minimize path-length and thereby also solve the Steiner Problem (see “Ants Build Cheapest Network“). So what does this mean in evolutionary terms?

In ID terms, there’s no problem — ants were designed with various capacities, and this either happens to be one of them or is one acquired through other programmed/designed capacities. On Darwinian evolutionary grounds, however, one would have to say something like the following: ants are the result of a Darwinian evolutionary process that programmed the ants with, presumably, a genetic algorithm that enables them, when put in separate colonies, to trace out paths that resolve the Steiner Problem. In other words, evolution, by some weird self-similarity, embedded an evolutionary program into the neurophysiology of the ants that enables them to solve the Steiner problem (which, presumably, gives these ants a selective advantage).

What’s the trouble with Dembski’s opinion?

In assuming the ants display a programmed neurophysiology, he misses the mechanics of how ants really solve problems.

Ants find the shortest route because of three simple facts:

  1. Ants follow pheromone trails
  2. Pheromone trails degrade over time
  3. Short paths take less time to traverse

When two points (say, two nests, or a nest and a food source) need to be connected, ants may start out tracing several winding pheromone paths among them. As ants zing back and forth down trails, pheromone levels build up. Long trails take more time to travel, so long-trail ants makes fewer overall circuits, more pheromone dissipates between passes, and the trails end up poorly marked. Short trails enable ants to make more trips, less time elapses between passes, so these trails end up marked more strongly. The shortest trail emerges.

Here’s a simulation showing digital ants selecting the shortest of 4 possible routes. Note how and where pheromone concentration builds:

Do you see what’s going on? Individual ants do not need to be smart for a colony to find the shortest route. There’s no need for a programmed problem-solving neurophysiology, as Dembski suggests, either divinely designed or naturally selected. Rather, the solution emerges organically from the summed actions of many individuals. It’s a classic case of swarm intelligence.

In missing the point of the ant study, Dembski’s post becomes a non-sequitur.

In Dembski’s defense, his error is a common one. Ant societies share enough superficial similarities to human ones that the tendency to anthropomorphize is strong. It is too easy to assume ants solve complex problems the way we humans do, with smart individuals applying brainpower to puzzle them out. Real ant colonies are more subtle than that, their decisions arising instead from the complex interplay of thousands of individuals.

23 thoughts on “How do ants find the shortest path?”

  1. I do have to hate on Dembski for at least one thing, though. He makes his ‘refutation’ excessively wordy to try to convey some sense of thought behind it, because you know how pinheaded intellectuals try to confuse the working man with their elite jargon. In fact, people who actually know what they’re saying can make their explanations very understandable. I actually had to read Dembski’s explanation twice (what a waste of time), but understood Alex’s by simply scanning his.

  2. “People have strong opinions on the topic, hardly anyone ever changes their mind, and when they do it’s not because they read a blog post.”

    While I agree that creationists probably wont change by reading random blogs…I think they can change their minds if we actively engage in discussion/dialogue with them. And I think biologists have a responsibility to do so!

    “American biologists are in a state of war”- Richard Dawkins

    We gotta keep on fighting and never give up!

  3. Hi Alex,

    I’m one of the authors on the ant network paper, and I was mortified to it cited on Dembski’s website. I’m overjoyed that you and others in the blogosphere have taken the time to post responses. Thank you!!

  4. Alex,

    I think you’re bending over too far backwards when you say, “In Dembski’s defense, his error is a common one.” If a guy makes a claim about biology on an Intelligent Design website, asserting that a trait couldn’t have evolved by natural selection, then it behooves him to do a bit of analysis and study before making his pronouncement. Many biologists, including me, know how this works, and if you don’t you can find out in a few minutes of Googling.

    There’s nothing that can be said in Dembski’s defense, for his ignorance is not the “normal” ignorance of the average person about ants, but a willful ignorance designed to confuse people and push his religious agenda.

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  7. Hi Alex,

    Are you the Myrmecos of ARN? If so, then it’s good to see ya’! I’ve been following Coyne’s blog for a while, which led me here. I agree that hardly anyone ever changes their mind, but it can be interesting, at times.

      1. I dropped out of ARN in 2004 or so. Then I started following TelicThoughts, got invited to join, and was a member until recently. Philosophical differences about banning critics (I’m against it). Now I’ll just try keeping my own blog going:

        http://bilbos1.blogspot.com/

        I’ll have to put your blog on the side so I can learn from the ants.

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    1. Yikes! Jerry Coyne saw the website and “cited” it. I just about died of embarrassment when I read “sighted”. 🙂

  9. I think there’s another point to be made here, specifically to do with your first image – and this is that the Steiner solution that the ants converged upon here isn’t actually the optimum result if the goal is to reduce the total distance travelled by each ant. The optimum for that problem would be for the ants to be traversing around the sides of the triangle.

    The solution to the Steiner problem, on the other hand, minimizes the total path length – it’s the most useful solution where the cost of building the path is much higher than the cost of travelling along it. For the ants, this isn’t the case – they’re just travelling over bare ground, and they lay their pheremone trails down no matter what.

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  11. This isn’t a theology blog, so I’ll keep this short. But I just want to remind everyone that not all Christians are creationists, and if anything Christians who accept evolution are even MORE annoyed at creationists than you are. ID/Creationism not only rests on completely shoddy empirical ground, it also relies on a warped and hyper-simplified theology that views God as an object within reality rather than the underlying presence that is reality itself.

    So Creationists aren’t just doing science wrong, they’re also doing theology wrong, too. Ok, thanks for listening to my rant on radical orthodoxy and for the great ant blog!

    1. Staplovich, ALL Christians have to be creationists, or they’re denying the Bible in its totality and aren’t Christian at all. But I’m much amused that even if Wild is right in his point concerning the ant paths (which I’m not conceding), is this where you people hang your hat? The absence of macro in the fossil record doesn’t bother you, e.g.? The fact that species have devolved rather than evolved doesn’t bother you? It should. The subatomic machinery of the “simple” cell should be spellbinding, but you think that evolved? The fact that life’s origination cannot be explained by evolution and that Darwin’s primordial pond is a physical and chemical impossibility doesn’t bother you at all? Again, it should. If you people are going to knock ID, I’d have thought you would pick something of greater consequence than a debate about how ants find the shortest path. Don’t add pedestrian to your long laundry list of intellectually dishonest inadmirable qualities.

      1. I know these are examples often brought up but I’ll use them anyway:

        If to be a true Christian you need to believe the Bible “in it’s totality,” including – apparently – the Old Testament, since we’re talking about Genesis here, does that mean that if you wear mixed fiber clothing (Deuteronomy 22:11), don’t keep kosher, or fail venerate Jewish traditions and holidays, you are not a true Christian? Every follower of religion to some extent picks and chooses those parts of doctrine which are convenient and believable to him or her. I would ask you to refrain from telling others that their faith or interpretation of scripture is incorrect, but seeing as you have dubbed followers of objective truth -scientists – and personal truth – the (presumably) Christian poster above you – “pedestiran. . intellecually dishonest,” I imagine it’s a lost cause.

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  15. Thanx a lot! The whole thing was interesting.
    Have you wrote anything about the researchers’ wish of creating a human colony like that of ants(of making human colony an ideal one)? Please tell if it is there.
    I was browsing about ants for my biology project. Yours was very helpful. Thank you

  16. Pingback: Groepsgedrag / zwermintelligentie/ robots | Tsjok's blog

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