The Biological Origins of Arms Races

Scientists find new theories and explanations in the weirdest places. For instance, it turns out the answer to how weapons evolved might lie in shit. Biologist ​Doug Emlen of the University of Montana has a ​new book, ​Animal Weapons: The Evolution of Battle (published by Holt) that describes the increasingly outrageous horns and other weapons that dung beetles have evolved, and why it matters. Long story short, he may have stumbled onto a new way to look at evolution after poking through dried poop in East Africa.

I recently called him up to chat about the phenomenon of "sneaky males" and how medieval chainmail helped explain evolution as an  endless series of arms races.

VICE: Your book suggests that the idea of an arms race comes from evolution. Tell me about that.
​Doug Emlen: ​[This is] one of the rewards of jumping out of my comfort zone and reading about military history and human arms races. In beetles, or in ​ungulates, or in any diverse group of animals with crazy weapons, biologists have reconstructed the past: which species branched off from which others when? And you can map on top of that the traits you're interested in, like weapons, and look at how they've changed as these groups have diversified. When you do that, every single time you find that there's lots of cool things happening with the weapons. This one went from one horn to two, this one got a horn on its thorax. We see where arms races started, but you also see lots and lots of cases where the weapons are lost.

Why would a step in evolution take away weapons?
​When you reconstruct the most likely scenario for what happened, you get an ancestor that had big weapons, but a particular lineage lost those weapons. So we have good reason to believe that big weapons disappear often, but we never actually get to see what happened a million years ago unfold. We know these arms races collapse, but we don't know why. But when you turn to the military literature, they have a fairly good idea.

As in human military? Why do our arms races collapse?
​There tend to be very specific situations that will end arms races. One is cost. So long as there are rewards to having these badass weapons, you can pay a pretty hefty cost. But if the cost gets too high, it cancels out, and that will slow things down. When you get cheating tactics, sneaky things that break the rules, that can bring about the collapse. If the technology changes so something that used to be good isn't good anymore, then all of a sudden the best thing you can do is get rid of it as fast as possible.

Can you give me an example?
​The best example is a submarine, which could sink the most enormous battleship in the line. Right from the get-go, battleships almost weren't worth the price, because they were so vulnerable and obsolete. The same thing happened with medieval armor, which got bigger and bulkier until you got the point where these guys had to be hoisted onto their horses. They were helpless, but really well-protected. Once muskets or longbows with steel-tipped arrows came along, you could pierce the armor. It cost a fortune and it weighed a ton, but it made you a sitting duck.

So by cheating, you mean bypassing the normal course, which is escalation, and exploiting some weakness?
You find cheating males everywhere. If only the best-conditioned males can produce these huge weapons, only a very small fraction of the population has enough resources and stature. So what do the rest of the males do? You break the rules. Biologists have known about sneaky males for decades, but we've never thought about it in context of an arms race. And this is happening in animals, all over the place.

So this is a revolutionary development in evolutionary theory, right? You're saying that as opposed to something fairly linear or one-directional, what's really happening all over the planet in these ecological niches, these arms races are repeating over and over.
​That's exactly what I'm saying, although I wouldn't be bold enough to say it's revolutionary. I think it's a new view, and it's an exciting view. It's consistent with what we see in the histories of these groups: We get gains and losses, gains and losses. If conditions are right, an arms race sparks and they get bigger and bigger and bigger. Until they're gone, eroded by cheaters, and then another weapon comes along. All of these things are going to turn out to be cyclical processes of explosive evolution and collapse.

And you learned all of this by digging through shit.
​I did.

Why study nature's dweeb, the dung beetle?
​The truth is, when you get down on your knees and look at these things, they're amazing. Lots of these species have really incredible weapons. Pound for pound, the weapons on the dung beetles are bigger than the weapons on elk or caribou. So all the biology questions I wanted to ask on megafauna, I realized I could ask on dung beetles and do a much better job answering. How are the horns used? What the males doing with these weapons? Why do only some of the males have horns and the little guys don't?

I know you don't have to kill a turd to eat it, so these weapons are all for attacking other male dung beetles?
​At the time, very little was known about what they did with the weapons and it was very clear that different species, even closely related species, had very different kinds of weapons. Some had horns coming from the back of the head, like we'd expect in elk or deer. But some species had a single horn from the middle of the head, like a rhinoceros. There are species that had four or five horns coming off the shoulder blades. Some of the horns were branches. Some were curved. There was a ton of diversity and we knew very little about them.

The species are categorized based on what the males' horns are like?
​If you were to look at 500 species of dung beetle, the most divergent trait is the weapons. Those structures are evolving faster and in more directions than any other thing. It doesn't actually mean the diversity in horns is causing them to become new species. We don't have a link there; there's a good chance it's related to other mechanisms, but the fact is that you've got a ridiculous diversity of beetles and, on top of that, a crazy diversity of weapons.

And they're evolving really quickly?
​Within the group that became the dung beetles, a lot of the diversity is more recent. The genus that I worked on, which has about 2,000 described species, is one of the most species-rich genera of any multi-cellular group of organisms anywhere. That genus is probably only 40 million years old, and that diversity probably only happened in the last 5 or 10 million years.

Is that timescale common with insects?
​It's dangerous to generalize with insects considering there are so many, but if you step back and look at beetles, one out of four multicellular things on this planet is a beetle. No matter how you look at diversity, beetles win. There's lots of groups of beetles that are doing something right, but the dung beetles are certainly have some of the fastest rates of mutation among insects.

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