Have you ever sniffed babies’ heads before? This question seems very odd, but this is the main topic I will talk about in this research paper.
On a baby’s head, a chemical called Hexadecanal (HEX) is emitted. HEX is also emitted from human skin, saliva, and feces, but it is most particularly abundant on babies’ heads. In a prior study, researchers found out that Hexadecanal has a relaxing effect on the mice that have smelled it. Inspired by this research, Mishor and her colleagues examined if HEX also has a relaxing effect on humans.
Relationship between HEX and Human Aggression
In their study, a total of 127 participants participated in a money distribution game, in which the players had to distribute a sum of money (~9$) each round. In fact, the game was programmed to provoke participants’ anger by resulting in an unfair distribution of money. During the game, the experimental group had a HEX scent strip on their upper lips while playing the game, but the control group had an identical strip on their lips, but without the scents.
When the game was over, the participants were given a choice to select the loudness of noise that would blast their imaginary opponents. As a result of the experiment, men who had scented HEX responded 18.5% less aggressive, while women who had scented HEX responded 19% more aggressive than the ones who didn’t. Consequently, the first study showed that HEX blocked aggression in men, while it triggered aggression in women.
Deeper Study
To identify a deeper relationship between aggression and HEX, the scientists further extended their research. They used fMRI to study where and how in the participants’ brains HEX affects aggression. The fMRI scans showed increased activity in the brain regions implicated with aggression and social cues in men exposed to HEX than the controls and decreased activity in women exposed to HEX. The fMRI scan once again showed the relationship between HEX and aggression.
Human Signaling Pheromones or Not?
The study co-author describes that this study does not conclude that HEX is a pheromone. An important criterion for it to be considered a human signaling pheromone is to let people emit more of the chemical when feeling aggressive, which HEX does not. Beyond the scope of the current study, HEX is missing a key component to be labeled as a human signaling pheromone. However, HEX can be considered as a molecule that is emitted by the human body that affects human behavior.
Hypothesis
The researchers hypothesized that the effects of HEX on human aggression might be related to the survival of babies. In the animal world, maternal aggression has a direct positive influence on offspring survival, whereas paternal aggression has a negative influence on offspring survival. This is based on the information that maternal aggression is usually headed towards the intruders, while paternal aggression is often headed towards the offspring themselves. Therefore, if babies had a mechanism that triggered aggression in women but blocked aggression in men, it would possibly increase their survival. If this hypothesis is correct, it could be said that babies effuse HEX to survive by increasing women’s aggression and decreasing men’s aggression.
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