Today's Nature features an essay by Oxford's Tristram Wyatt on pheromones, I quizzed him about these intriguing chemicals:
OxSciBlog: What purpose do pheromones serve?
Tristram Wyatt: Animals use pheromones in all sorts of ways and pheromones are probably the commonest form of communication across all species of the animal kingdom (even though we cannot hear or see the messages).
Sex pheromones are used by many species and it was the silk moth sex pheromone that was the first one identified, 50 years ago this year. Dogs use a powerful sex pheromone as every dog owner will know – though this is one pheromone that we've not yet identified.
Social insects run their whole societies with pheromones, from trails and nest building to alarm pheromones to bring rapid defence of the colony. Social insects also provide good examples of primer pheromones, which have longer term effects on physiology. The queen honey bee sends a pheromone message round the hive which stops the workers laying their own eggs.
Underwater animals use pheromones too – for example goldfish have sex pheromone duets and lobsters do too. Humans undoubtedly have pheromones but none have been chemically identified.
OSB: Do animals send false pheromone signals?
TW: Yes, one of the most spectacular is the bolas spider which synthesizes moth pheromones which are so good that they attract male moths (to their death). Some orchids do a similar thing with the pheromones of wasps and bees to lure them to visit the flower to take on pollen – and deliver it to the next flower when they are duped again by the fake pheromones.
OSB: Why do you think theories about human pheromones are so controversial?
TW: I think we find it disturbing to imagine our behaviour could be influenced by chemicals given off by another human being! Yet at the same time most perfumes are advertised with the promise of just this kind of effect.
There may be a reluctance still to accept that we are mammals – and as mammals it is highly likely that we use pheromones, though there's no evidence for ones with instant effects like the dog or moth sex pheromone.
OSB: What are the biggest questions about human pheromones that remain to be answered?
TW: Well the first challenge is to chemically identify the first one. We are at the stage where we have some phenomena, for example hormonal effects on women when they smell sweat extracts from male armpits, which are pheromonal but the chemicals involved have not been identified.
We're at an early stage of understanding. It has been likened to the way that for hundreds of years doctors used foxglove leaf extracts to help with heart disease but it was relatively recently that the active molecule, digitalis (digoxin), in the leaf extracts was isolated, identified and synthesized.
Another candidate is the pheromone produced by women that appears to mediate the effect of menstrual syncrony in women living in close proximity. Again this has been shown to be produced by the armpits. I know that at least one team is trying to track down the chemical identity of the molecule. If they can find it, a whole new range of drug targets for contraceptive agents may open up.
Dr Tristram Wyatt is based at Oxford's Department of Zoology