by Josephine Livingstone
Is it a coincidence that insect is an anagram of incest? Yes, but it’s a good one. As Nick Davies explained to me, high levels of breeding between siblings is not unusual in insect societies, especially haplodiploid ones (we’ll get to that). “It’s not just an anagram,” he told me, “It’s also a near-homophone.” This has led to a lot of confusion at parties, because Davies is a researcher in social evolution. Insect incest is kind of his thing.
In Davies’s field, they don’t call sex between siblings incest, they call it “sib-mating.” They use a different word because humans and insects are fundamentally different. An ant mating with its sibling means something for ant society in structural terms; a person sleeping with their sister means something totally different, because humans code behavior in cultural terms. Culture, Davies thinks, is more like a network of shareable information and thought. Societies are just “any semi-permanent aggregations of individuals through which at least some cooperation is enabled.”
I’m drawn to Davies’s research for the generosity of its approach: the most encompassing history of life on earth and minutely subtle community dynamics of wasps are part of the same object of study. Davies is a DPhil* candidate in the Mathematical Institute at the University of Oxford, although his day-to-day research takes place in the Department of Zoology. He’s handing in his thesis soon. It’s called ‘Cooperation and Conflict Across the Major Transitions,’ which he admits is very general: “It’s largely a bullshit title that I made up when I didn’t know what I was doing.”
His field conceives of evolution in terms of “major transitions,” summarizing the history of life as a series of shifts between levels: from genes into genomes, cells into eukaryotic cells, and multicellular organisms into societies, which can act as individuals in their own right. Davies’ research focuses on the social Hymenoptera (the order of insects including bees, wasps, and ants), because they form some of the most advanced examples of cohesive societies in the animal kingdom. They’ve also lent us some remarkably powerful metaphors: we talk about the hivemind, swarms, and drones. The queen bee is bossy, and a hard worker is a busy bee. But that language is fairly figurative and long dissociated from its original meaning — social insects have sterile workers who don’t reproduce, drones and queens, who do.
A better working analogy for an insect community is in our bodies. Most of our cells are somatic, or body cells, which don’t really reproduce. But some are germline cells, like sperm or eggs, which get to pass on their specific copy of the genome. While an insect colony comprises many individuals, it can also be thought of as a body made up of bees (!) that sends out its reproductive cells into the world. “That reminds me of Machiavelli’s theory of the state,” I said. Davies pointed out that I meant Hobbes’s body politic.
A lot of different species, from bacteria to animals to plants, have highly social lives: they interact, compete, and cooperate with other individuals. With Laura Ross and Andy Gardner, Davies has co-written a paper forthcoming in Ecology Letters, called ‘The Ecology of Sex Explains Patterns of Helping in Arthropod Societies,’ about the evolution of altruistic behavior in arthropod societies. Davies got a little frustrated while explaining it to me, since it had been difficult enough for him and his collaborators to distill their findings into a 5,000-word article.
In the Hymenoptera, only females contribute to colony tasks. Whenever you see an ant scouting or foraging for food, “It’s a girl ant,” Davies said. The males are produced late in the colony lifecycle: they go out and mate, then die right away. In termite societies (which fall in the cockroach order, Blattodea), both sexes help out, and there can even be sex-specific task specialization — females might be soldiers, males might be workers. Traditionally, Davies said, this phenomenon has been explained by the theory of “kin selection” (organisms are driven to ensure the success of their relatives as a means of preserving their own genes) first outlined by the evolutionary biologist W.D. Hamilton. But why do both sexes help in termites, whereas in the Hymenoptera only females help?
Like humans, termites are diploid — they have one set of chromosomes from their mother, and one from their father. In the Hymenoptera, however, males are haplodiploid, meaning they only have one set of chromosomes, inherited from their mothers, while females have the usual two. Because of this, we see what Davies called “some weird relatedness asymmetries,” between the sexes. If you’re a termite, you’re related to your siblings by one half, no matter your sex. In a Hymenoptera colony, however, females are more related to their sisters than their offspring.
Hamilton hypothesized that organisms helped out their relatives depending on how related they were to each other. Your children share part of your genes, but so do your uncle and cousin and grandma, so acting altruistically to ensure their survival is almost as good as investing in your own offspring. Overall, then, Hamilton thought that high relatedness between sisters might explain why females help in the Hymenoptera. But that doesn’t really work: not only are haplodiploid females more related to their sisters than they are to their own offspring, they’re also less related to their brothers, and these two effects cancel out. It was an elegant hypothesis, but not a true one.
Davies, Ross, and Gardner’s new paper asks: if Hamilton’s haplodiploidy hypothesis doesn’t explain the sex of helpers in animal societies, what are some factors that might? Pre-adaption, when a trait used by an organism for one purpose is co-opted for another, is one. For example, the social descendants of solitary wasps have repurposed their syringe-like ovipositors — originally used to lay eggs inside figs, or other insects’ bodies, or other insects’ larvae — as a sting, for colony defense. This may be one reason why females, not males, defend the colonies of bees, wasps, and ants.
Sib-mating is another potential factor. As a general trend among animals, females spend their energy on making offspring, while males spend their energy on competing with other males for mating opportunities. But when a species has high levels of sib-mating, the males might be especially willing to invest in help instead of reproduction, since they’d otherwise be competing with copies of their own genes. Sib-mating could therefore promote helping by males rather than females.
Anyway, I shouldn’t give away the ending of the paper. Look it up in Ecology Letters soon if you want to know more. When Davies was talking about insects helping out their mothers, I couldn’t help but think it was adorable. But I instantly felt guilty for anthropomorphizing the bugs. “It’s inevitable,” he said. “It happens to everybody.” When Davies was first starting out, he wasn’t that interested in insects. Now, he thinks bees and ants are cute. He works in a lab with a bunch of microbiologists, and he’s heard them coo over E. coli.
It struck me that people must often want to talk to Davies about evolutionary psychology. “Yeah, they do,” he said. “It’s too bad.” He worries that some people might assume that he’s racist, or sexist, or a weirdo; one of those people who chalks up human difference to the experiences of the ‘cavemen.’ (The caveman idea, in principle, is not the problem, Davies said, but culture makes everything more complicated.) “If I don’t really want to talk to someone about evolution,” Davies said, “I will say my work has no relevance for humans, and that I never think about humans at all.” I don’t think that’s true, but it seems like a good strategy.
Davies told me that he got into science because he wanted to know what makes the world work; it didn’t occur to him as a young kid that philosophy or art might hold those answers. “I could imagine myself as a scientist,” he said, “but couldn’t imagine that I would ever even meet, say, a writer.” It was funny to hear him say that, because Davies also acts and does comedy. Although he didn’t like biology much at school, the older he got, th龙凤论坛爱上海e more he understood that the science of life led held answers to the biggest questions. He grew “less interested in what planets were made of and more interested in what being alive is made of.” Davies gradually realized that evolution could hold a partial answer to that question, and that wisdom and comfort might nestle among ants as much as it lies between the pages of big novels. “That was all I needed,” he said.
*DPhil means the same thing as PhD: they’re abbreviations of the same Latin phrase with the words in a different order. I think.
Photo: Alan Taylor