Why Bugs Bite the Bullet for Brothers

The side-blotched lizard is one of the few large organisms that show altruistic behavior.

There are many reasons – and most of them are completely understandable – for people to sacrifice themselves for the good of others. Friends sacrifice themselves for the sake of each other like Spock taking a lethal dose of radiation for the Enterprise’s crew. A husband or wife may bite the bullet for the benefit of his or her spouse, like Jack volunteering to become a human popsicle in the frozen Atlantic. These examples seem to take human emotions and rational thought in order to occur.

But emotions and rational thought can’t explain why some insects will die in order to help the greater good. Even single-cell amoebas show the trait. For these few species, there must be some reason for an individual to make the ultimate sacrifice.

Whatever that reason is, whatever makes self-sacrifice spread through a population, it doesn’t really make any sense from an evolutionary biologist’s point of view. After all, Darwinism is survival of the fittest, so it would make sense that all of the individuals sporting a self-sacrificing genetic mutation would quickly kill themselves off.

Dictyostelium discoideum is a type of slime mold that is altrusitic via a mechanism known as green beard targeting.

Instead of strict Darwinism, scientists have come up with the notion of inclusive fitness theory. The idea is that individuals carrying the altruistic genes will die in order to save genetically similar individuals that likely also carry the altruistic gene, thus spreading the practice of self-sacrifice. In this sense, being altruistic in order to save a family makes sense in that because a family shares genes, saving the whole saves more genes than saving oneself.

This last example is known in evolutionary biology as kin selection. But the story doesn’t stop there. A recent study published in the journal Proceedings of the Royal Society by researchers funded through the BEACON Center for the Study of Evolution in Action led by Michigan State University asserts that it is the ability to recognize the genes that make the most difference.

The team of researchers used the computer analysis software called Avida to simulate three different mechanisms of promoting inclusive fitness theory. One trial used kin selection. The next used similarity targeting, which assumes an individual can recognize genetically similar individuals fairly reliably regardless of their lineage. The final method relies on the organism having a recognizable trait that immediately identifies it as a carrier of the altruistic genes. If such a marker were – say – a green beard on a human, we’d automatically recognize carriers. Thus, this mechanism is called green beard targeting (aren’t scientists silly?)

I mean come on, could you miss this guy in a crowd?

Though an organism expressing a trait being altruistic only to other organisms expressing the same trait and thus proving they are also altruistic may seem far-fetched, it has been proven in nature. True, it hasn’t been shown in mammals, but it has appeared in the slime mold Dictyostelium, certain types of yeast, a bacterial plant pathogen and the side-blotched lizard.

As one might expect, the results showed that when given a choice, natural selection will use the method that most accurately allows altruistic individuals to target their altruistic gene-carrying brethren. But only up to a point. A result popped up that the scientists did not expect.

Except under very special circumstances, natural selection opted for the similarity targeting system over green beard targeting. The reason for this, say the researchers, is that green beard targeting doesn’t allow the differentiation of the level of altruism. I’m not exactly sure what this means, but I think it’s saying that it only lets Mother Teresa sacrifice herself to save Jesus and Gandhi – which is no way to grow a population – and prevents her from sacrificing herself for a semi-altruistic individual such as myself.

However, if the species exhibits multiple genetic markers – for example different colored beards – each demonstrating the level of altruism present, the genetic trait takes off like gangbusters.

What’s the real-world meaning of this newly coined term of “identical beard color targeting mechanism?” Absolutely nothing.

“Although we have shown that identical beard color targeting can maintain high levels of altruism, it is unlikely that natural, biological organisms use it as an altruism-targeting mechanism,” reads the paper. “We consider it improbable because identical beard color targeting requires an even more unlikely phenomenon to be caused by a single gene than is the case for green beard genes.”

So even though this finding has very, very, very little real world applications, other than confirming a suspicion that seemed suspiciously obvious to me, at least now you know a whole lot more about the topic.

On a related note, I recently read about a new theory via Wired Science that claims we’re just thinking about altruism in insects all wrong. It’s easily explained if you look at the colony as a whole as the organism, and not the individual insect. By this view, ants sacrificing themselves for the greater good are no more unusual than a white blood cell doing the same. There’s probably some interesting social dynamic research to conduct in that vein.

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About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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