As adults, we have a habit of reaching out and touching plants without a second thought. But babies, apparently, aren't so careless. New research shows that infants have an innate reluctance to touch plants — an aversion that protects them from potential dangers, such as toxins and thorns.
In our evolutionary history, we've had to deal with many animal dangers, which helped shape our innate behaviors and abilities. A recent theory, for example, suggested that we've evolved an uncanny ability to detect snakes — the earliest and most persistent predators of mammals. But animals weren't the only things in our natural environment that could do us harm.
"In most modern lives, plants are mostly part of the background and sort of an afterthought," said Annie Wertz, a developmental and evolutionary psychologist at Yale University. "But when you think of humans in their historically natural environment, plants were a huge part of their lives."
Like animals, plants have a number of chemical and physical defenses to protect them from getting eaten or damaged. Certain plant toxins can be deadly if ingested, while plants' thorns, fine hairs and oils can damage tissues. So many animal species developed physiological countermeasures to get around plant defenses, such as vomiting or the ability to break down plant toxins. Some animals even have behavioral strategies to protect themselves from plants.
"Herbivores are known to only eat little bits of unknown plants, so if they have some kind of adverse reaction, it won't kill them," Wertz told io9.
Humans may also have developed ways to deal with plant defenses. Young children, for instance, are naturally averse to the bitterness of vegetables, possibly because plant toxins are commonly bitter. And some researchers have even suggested that cooking arose in part to break down plant toxins.
To test this, Wertz and her coauthor, Karen Wynn, set out to determine if babies are more reluctant to touch plants than other objects. They set up a simple experiment, which involved placing a plant (basil or parsley), an artificial plant or a fabricated object in front of an infant, while the child sat on its mother's lap in a room with no distracting stimuli.
The novel artifacts, Wertz explained, had some features of plants. The researchers constructed one object from two blue cardboard cylinders. They then dyed black some artificial, fabric leaves — the same ones that were on the artificial plants — and strung them around the top of the object. "Maybe babies are reluctant to touch leave-shaped things, or maybe they don't touch things that look delicate," Wertz said.