Decoding the Remarkable Algorithms of Ants

Emily Singer interviews Deborah Gordon in Quanta:

You called the harvester ant algorithm the “anternet.” Why?

I worked with Balaji Prabhakar, a colleague at Stanford, to figure out the algorithm that the harvester ants are using to regulate foraging. He pointed out that the algorithm is similar to the Transmission Control Protocol, which regulates data traffic on the Internet to make sure that data don’t go out unless there’s enough bandwidth. Both systems use simple, local feedback to regulate activity. I think we might be able to find other algorithms that ants use to solve engineering problems that we haven’t thought of yet. I am interested in the idea that evolution might produce different algorithms in different systems to solve the same problems.

But for evolution to produce algorithms that help the colony, evolution must work at the level of groups, not just individuals.

From the perspective of evolution, the colony is really the individual, because it is the colony that reproduces. Ants don’t make more ants, colonies make more colonies. So if we think about how ant behavior evolves, we have to look at colonies.

How do decisions made by individual ants alter the behavior of the colony as a whole?

In the desert, water is an important constraint. Ants lose water just being outside and meandering around. But they get their water from the seeds they eat, so they have to spend water to get water. No individual ant is making the decision to save water and stay home. But small differences in how ants respond to interactions can add up to big differences in how colonies forage, which in turn affects how many offspring colonies have. We found that natural selection favors the colonies that conserve water. I call it “the rewards of restraint.” I think this is the first study that’s been able to track the evolution of collective behavior in a natural population of animals. A simple, local behavior — how ants respond when one meets another — is being selected for because of the outcome for the whole colony.

More here.