In the spirit of this divisive holiday, here is an intriguing article about how bacteria in your gut may be secretively manipulating your deepest emotions. A study done in fruit flies showed that fruit flies preferred mating with other flies that had been put on the same diet (either malt sugar or starch). The intriguing part is that when the flies were treated with an antibiotic, this preference disappeared.
Who is the culprit? Lactobacillus plantarum, a Gram-positive bacterium found in dairy products and other fermented foods. It is thought - researchers are not entirely certain - that the bacteria alter the flies' pheromone levels, making them more attractive and attracted to similar members of the opposite sex. The question arises...how much of this actually applies to humans?
An important concept put forth by the researchers is the holobiont. Rather than considering just the parts directly connected to an organism, we should take into account all its "normal flora" - the diverse hordes of microbes that inhabit the body, from our skin to our gut. Although it's initially mildly disturbing to think that 90 percent of the cells in our body are not our own, we should take into account the host of tasks they perform for us. When our normal flora are destroyed - for instance, by a long-term antibiotic - we too are destroyed, unable to digest food and plagued by infections that our normal flora would have otherwise caught.
So the holobiont theory certainly applies to humans. What about the influence on mating preferences? Hard to say. But if our resident bacteria can chew our food for us and protect us from hostile (albeit microscopic) strangers, I think I'll trust their judgment in choosing a suitable mate.