by Kathleen Sai-Halasz
This article was written by a student at the Wheeler School. Brown's chapter of The Triple Helix collaborates with the Wheeler School to engage high school students in science journalism.
It is a common misconception that all forms of communication between humans are through verbal or body language. That is, all communication of emotional states of people is through the sense of hearing or visual channels. However, through recent experiments conducted by researchers at Utrecht University, this theory was challenged as researchers showed that people could communicate though chemosignals as well (1). Chemosignals are chemical signals the human body gives off, often through sweat, through which people can interact. Jasper H. B. de Groot and colleagues chose to focus their experiment on the emotions of fear and disgust, and found that chemosignals given off of one person while experiencing one of these emotions can induce the same emotional state upon the inhaler (1). This supports the idea that forms of communication are not limited to eyes and ears, and that through the effects of chemosignals, people can communicate their emotions without needing to hear or see the other person.
Researchers at Utrecht University tested the hypothesis that it is possible to transfer an emotion from one person to another through the fumes the sender’s sweat gives off (1). Researchers chose to work with the emotions of fear, scientifically known as sensory acquisition, and disgust, also known as sensory rejection (1). In this experiment, only males were chosen as the senders because they produce more potent sweat signals, whereas only women were chosen to be used as receivers because they are shown to have a more acute sense of smell (1).
Researchers induced fear or disgust in male subjects by having them watch gross or terrifying movie clips. Each male was to watch both clips, separated by a week’s time, and meanwhile had strict rules of hygiene to follow, in order to prevent sweat contamination (1). While the males watched the videos, clean compresses were placed along their armpits to collect any sweat. These compresses were then stored and frozen (1). Each female receiver was then placed in an individual cubicle where the subject’s sniffing, eye movement, and facial-muscle activity was measured (1). After having defrosted the compresses, the females were told to smell them, and therefore inhale the chemosignals (1). The females who inhaled the sweat produced during a gross movie made, and maintained, a face of disgust: a crinkled nose and squinting eyes (1). Likewise, those females that inhaled the sweat produced during a terrifying movie mimicked an expression of fear: the widening of the eyes, narrowing of vision, and a stronger inhalation (1). The team also speculated that these chemosignals are not limited to disgust and fear, but that chemosignals may also exchange emotions of excitement, anger, sadness, and more (1). Therefore, researchers concluded that through chemosignals, emotions could be transferable between people and cause a state of emotional synchronization (1).
Human chemosignal research is relatively new, so there have not been substantial applications of the use of chemosignals in technology. However, chemosignals are only naturally transferred when people are within close proximity of each other (1). Therefore, in any crowd of densely packed people such as at concerts, bars, or dances, it is possible that chemosignals account for many emotional transmissions that, in essence, cause a unanimously shared emotion (1). However, this close-distance range of chemosignals communication limits its potential impact. Because chemosignals can only communicate the state of the sender when the receiver is within close proximity, and because chemosignals are also completely subconsciously emitted and inhaled, it means that any futuristic technological advances using chemosignals are unlikely to make a large impact on society’s social structure. In total, the range of technological applications of chemosignals seem narrow at this point, because it is so subtle and requires such close proximity. The potential applications that result from utilizing chemosignal-based emotional communication would probably be limited.
However, this does not mean that chemosignals are irrelevant; it seems that chemosignals contribute to the very base of human nature: reproduction. Research at the University of Chicago was conducted to test the theory that exposing women without children to chemosignals given off by other, regularly breastfeeding women while they are nursing increases the women receivers’ motivation to reproduce (2). The senders in this experiment were asked to eat a low-sulfur diet to ensure that there would be no contamination of chemosignals, and were then instructed to wear compresses in the bras that they nursed from (2). These compresses would then absorb the saliva of the child as well as the mother’s chemosignals through her sweat (2). Similar to the experiment conducted in the Netherlands at Utrecht University, these pads were then frozen and stored. Women who had not yet had children were then selected to become the “receivers” in this experiment (2). The receivers were not informed of the nature of the experiment, to counteract any bias, and were then instructed to smell the compresses once in the morning and once at night for several weeks (2). Within two months, the receivers showed a 24% increased in physiological desire to reproduce (2). This confirmed the hypothesis that chemosignals can affect women’s desire to reproduce: a miraculous finding of human nature (2).
If you don't want one of these, hold your breath around mothers who breastfeed their children. [image via]
Therefore, these chemosignals not only affect mood, as mentioned in the previous study at Utrecht University, but also might lead to an increase in evolutionary fitness (2). Women who are more driven to reproduce will, in theory, create a physical and social environment suitable for raising children (2). Chemosignals could help to promote evolutionary fitness through community stimulation in which women encourage other women to try to conceive children by the transfer of these chemosignals (2). For example, in many rural regions of the globe, the percentage of conceptions is significantly higher when the main food source is in season. Therefore, as theorized by the University of Chicago researchers, if there are women breastfeeding their children when said food is off-season, their chemosignals have the possibility of encouraging other fertile women without infants to try harder to reproduce (2). Meaning, chemosignals stimulate reproduction all year long to counter the scarcity of conceptions when the main food source is in the off-season (2). This in turn has the potential to increase the size and strength of said community. Through these chemosignals, women have a great opportunity to strengthen the evolutionary growth of humans.
Although further research must be done to test these hypotheses regarding evolutionary fitness, it is possible that these chemosignals played a role in the long-term survival of human populations. If the inhalation of chemosignals influenced women’s desire to conceive, it is plausible that chemosignals could have been beneficial during the times in our species’ development when maintaining a healthy population was difficult. Certainly, many other factors contribute to the urge to reproduce besides chemosignals, such as stigmas of human culture. Many cultural “norms” for women, developed over centuries, seem to indicate that having children is the ultimate goal (3). Although subject to debate, biological factors can potentially play a role in the desire for children as well (3). Nevertheless, the idea remains that chemosignals could have contributed to the growth of humanity during times of struggle.
By any means, the study of chemosignals is still quite shallow in the realms of great evolutionary discoveries, but it is important that we continue such research as it may hold some clues that drive human and population growth. We are, above all else, social animals, and evolution has led to the creation of many subtle forms of communication between humans. Often these occur so unconsciously that we did not even know they existed, such as chemosignals. The human body is remarkably and acutely equipped to communicate, interact with, and influence other social beings, and it is the study and understanding of these behaviors that will perhaps allow us to harness them. In the coming years, with the continuation of similar research on human interaction, we can more accurately understand the role of chemosignals in human evolution, and how it could potentially influence future population development.