Don’t touch? How infants react to thorny plants
Dealing with plants over the course of human evolution appears to have left its mark on the human mind. Previous research has shown that infants seem to hesitate before touching harmless-looking plants. Scientists at the Max Planck Institute for Human Development have now studied how infants aged 8 to 18 months react to plants with dangerous-looking thorns. Their findings have been published in the scientific journal Evolution and Human Behavior.
Plants have many ways to protect themselves from predators. Some harmless-looking plants are poisonous, while others have sharp thorns or stinging hairs. Contact with these different plant defenses can be painful or even deadly to humans. However, knowledge about plant threats is no longer very important in Western industrial societies, where we spend most of our lives in buildings without a lot of direct contact with plant life. This was not the case over the course of human evolution when knowledge about the dangers posed by plants was essential for survival.
The scientists of the Max Planck Research Group „Naturalistic Social Cognition“ examined whether evolutionary predispositions influence human behavior towards plants. To do this, members of the research group observed infant behavior.
The current study focused on the question of whether infants are equipped with behavioral strategies to help them avoid the dangers posed by plants. In particular, does their behavior differ according to whether a plant is obviously dangerous, for example, because it is covered in sharp-looking thorns? The scientists showed 42 8- to 18-month-olds plants, unknown artifacts with plant-like features, as well as everyday objects. Half of each type of object included thorn-like elements. In order to ensure that children were not guided by their parents’ reactions, they sat on their parents’ lap facing towards the experimenter who was presenting the plants and other objects. Parents were asked to keep their eyes closed so that they did not know which object was being shown to their child at a given time.
The findings support previous studies showing that children generally hesitate before they touch plants. Interestingly, infants hesitated to touch all plants, whether or not they had thorns, suggesting that infants treat plants as dangerous regardless of how they look. Even so, infants rarely touched the thorny parts of plants. „It became very clear that infants distinguish between thorny plants and thorny objects. They touched thorny plants much less frequently than the other thorny objects,“ says Aleksandra Włodarczyk, a doctoral student in the Max Planck Research Group „Naturalistic Social Cognition“ at the Max Planck Institute for Human Development. The researchers interpret this behavior as an avoidance strategy to prevent infants from being injured by plants. This occurred even though the participating infants came from the metropolitan area of Berlin and therefore had little contact with plants in their everyday environment.
„We have now seen a similar reluctance to touch plants in infants growing up in Germany and the US. It will be interesting to see how children who grow up immersed in nature react to plants. We are therefore currently investigating this question with young children growing up in villages in the Amazon jungle in Ecuador,“ says Annie Wertz, head of the Max Planck Research Group „Naturalistic Social Cognition.“
Włodarczyk, A., Elsner, C., Schmitterer, A., & Wertz, A. E. (2018). Every rose has its thorn: Infants' responses to pointed shapes in naturalistic contexts. Evolution and Human Behavior. Advance online publication. https://doi.org/10.1016/j.evolhumbehav.2018.06.001