The naked mole-rat queen rules with a $5 molecule: not urine, a skincare ingredient
The signal that suppresses reproduction in naked mole-rats has finally been found: only the queen produces isopropyl myristate. Add it to a colony that has lost its queen and the peace holds; stop, and the succession war breaks out. The same molecule turns up on breastfeeding women.
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Which female becomes queen is set by social environment, not genes
Naked mole-rats are one of the very few social species among mammals: a colony has just one breeding female, called the queen, while the other females do not reproduce and instead forage, defend the nest and care for the pups. The structure resembles a bee colony, but a queen bee's fate is settled before she is born, whereas in principle any female naked mole-rat could become queen. Melissa Holmes says this is not a genetic trait — the social environment is what controls it — which leaves the question of exactly what signal makes one female the queen and suppresses all the rest. Earlier work looked for a pheromone in the queen's urine, and found nothing at all.
Only queens make this molecule, and any lab can buy it for $5
The team collected odours of all kinds from more than 450 animals across 16 colonies, the hard part being to pick the queen out of a heap of mole-rats piled on top of each other. They found one volatile molecule produced only by naked mole-rat queens: isopropyl myristate. It is structurally simple, common in plastics and skincare products, and a lab can buy it for about $5. Gary Lewin says that made the experiments extremely easy: you simply order it and run behavioural tests. By contrast, rodent pheromones had been assumed to be in the urine — and the queen's urine contained nothing.
Add the molecule back and the colony stays calm; stop and war starts
Brain scans show that isopropyl myristate activates the odour-processing regions of worker brains and keeps other females out of a sexually active state — in effect an ‘odour contraceptive’. In a colony that has just lost its queen, adding the molecule keeps everything quiet and the workers behave as though she were still there; stop adding it and the high-ranking females immediately start fighting each other for the throne. The authors think the mechanism is clear: whichever female becomes pregnant first starts producing the molecule, and thereby suppresses every other female. Melissa Holmes calls this the holy grail of research on naked mole-rat social structure.
The same molecule shows up on breastfeeding women, and nobody followed up
isopropyl myristate is not unique to naked mole-rats. Gary Lewin mentions a study from years ago that measured the volatile molecules given off by the breasts of breastfeeding women; isopropyl myristate was among them. The researchers put the mixture on a cotton swab, and newborns would begin sniffing at it and even try to suckle. But he says that paper stands alone — nobody took it further. Now that the molecule turns out to have such a strong social effect in naked mole-rats, researchers may want to look again at whether it does anything in other mammals.
Two planets less dense than cotton candy, and Hannibal's impossible calorie budget
This week's Highlights carry two stories built on numbers. The first is a pair of newly discovered exoplanets, close to Jupiter in size but more than 20 times lighter, less dense than cotton candy and among the lowest-density planets known; they orbit the same star, with periods of 232 days and 139 days. The second is the metabolic accounting for Hannibal's crossing of the Alps: the most likely route required 15 days and 230 tonnes of supplies, and even with enough food, holding body weight would have been impossible — the war elephants are projected to have lost 4%. Neither segment connects to the main thread, but both are enough to reset your intuitions.
Games research studied experts; the interesting judgment happens before the first move
Games research has long concentrated on experts, but Katie Collins's team is interested in what a novice judges on first hearing the rules. Subjects read the rules of different games and then predicted who would win, whether the game would end in a draw, and how much fun they expected it to be. The team modified tic-tac-toe and Connect Four — a three-by-three board where two lines are needed to win, a five-by-five board where three in a row wins — to produce rule variants that nobody has ever seen. The core question is not ‘how do you play well’ but ‘before the first move, how does the human brain judge whether this game is worth playing’.
Novices run a few shallow, probabilistic simulations, not deep optimal search
The intuitive gamer model the team proposes imagines the novice as running fast, shallow, probabilistic goal-directed mental simulation. Fast means only a few simulations — more than 1, fewer than 10. Shallow means the players inside the simulation do not think very far ahead. Probabilistic means they assess which action is good but do not always choose the best one. The same model accounts both for people's judgments about new games and for the data from their first actual play. Katie Collins says this shows novices are not entirely unsystematic, but you should not expect them to match the optimal predictions of classical game theory.
Near-optimal play may need little compute, and AI could model your intuitions
The first AI use for this model is saving compute: in many situations you can get close to game-theoretic optimal without heavy simulation or enormous amounts of computation. A system could work the way an intuitive gamer does, doing only a small amount of thinking to judge quickly whether a given path is worth exploring. The second use is AI as a thinking partner: with a more accurate model of human computation, an AI could simulate the user's judgment and point out in advance that ‘you probably think a given position turns out one way, and it doesn't’. The next step in the research is to move from analysing existing games to how people create new ones, which is closer still to open-world games.
In their own words · checked verbatim
we can just buy this stuff for. Basically $5.
Gary Lewin4:05
once someone's pregnant and they're making isopropyl marate. They're going to be the queen and nobody else can be the queen.
Gary Lewin4:05
This is like.The Holy Grail for naked Muor research for those of us interested in the social structure.
Melissa Holmes4:05
Games are a really nice framework to think about so many aspects of. What makes life so interesting?
Katie Collins11:49
Engaging in fast.Flat.Probbilistic in goal directed mental simulation.
Katie Collins16:09
So there's systematicity in how people think about a game for the first time, which is really, really cool.
Katie Collins17:21
you could imagine doing something that's kind of like the intuitive gamer where you just do a little bit of thinking to make a quick judgment for whether that path is worth exploring
Katie Collins18:42
Figures
| Cost of buying isopropyl myristate | about $5 | 4:05 |
| Scale of the naked mole-rat sample | more than 450 animals across 16 colonies | 4:05 |
| Mass of the two exoplanets | roughly Jupiter-sized, but more than 20 times lighter | 10:34 |
| Exoplanet orbital periods | 232 days and 139 days | 10:34 |
| Number of known super-puff planets | only a few dozen | 10:34 |
| Supplies needed for Hannibal's Alpine crossing | 15 days, 230 tonnes of food | 10:34 |
| Projected weight loss for the war elephants | about 4% | 10:34 |
| Normal daily foraging time for African elephants | 14 hours/day | 10:34 |
Glossary
- isopropyl myristate
- A volatile ester molecule common in plastics and skincare products; this study shows it is also the naked mole-rat queen's reproductive-suppression signal.
- naked mole-rat
- An East African underground rodent that lives socially the way bees do, with only one breeding female in the colony.
- super-puff
- An exoplanet close to Jupiter in volume but extremely low in mass, with a density below that of cotton candy.
- intuitive gamer
- A computational model that explains how novices evaluate a new game, using fast, shallow, probabilistic goal-directed mental simulation.
How to listen
Behavioural ecologists and chemical ecology researchers, engineers working on AI reasoning and cognitive modelling, and founders looking for an example of ‘chemical signals controlling an organisation’.
The Hannibal segment in Highlights has nothing to do with the main thread and can be skipped; the other two stories are both worth hearing.