The researchers suggest that this apparently innate hesitation may be an evolutionarily acquired behavior that helps infants avoid a common danger.
Below, I've adapted the experiments used in the study so that you can perform it on your own baby.
Age range: 8 to 18 months
Research area: Cognitive development
Seat your baby in a high chair or have him sit on an adult's lap, and present him with a small potted plant. (Basil and parsley plants were used in the original experiment). Use a stopwatch to track how long it takes before he touches the plant.
Next, present him with a familiar object, such as a small lamp or a wooden spoon, and again measure the time to first touch.
Finally, if you have a medium- or large-sized seashell available, present it to him and again measure the time to first touch.
Your baby will take longer to touch the plant than the other objects.
In the original experiments, babies between 8 and 18 months were presented with real plants, artificial plants, novel objects that were structurally similar to plants, seashells, and familiar objects such as a lamp and a spoon.
On average, babies hesitated for more than nine seconds before they touched the real or artificial plants, but they were willing to touch the other types of objects sooner. For instance, they waited only three seconds to touch the seashells, four seconds to touch the familiar objects, and about five seconds to touch the novel objects.
This hesitation about touching plants appears to be very widespread among infants. Indeed, more than 95 percent of the infants tested took longer to touch the plants than the novel objects.
From an evolutionary point of view, a reluctance to touch plants benefits the infants by making it less likely that they will touch or ingest toxic plants or be injured by thorns or skin irritants.
This is not the only example of an apparently innate behavioral response among babies to a common threat. In Experimenting With Babies, I write about a 2007 study in which babies showed a similar response to images of spiders; other recent research has shown that babies also exhibit a fear response to images of snakes.
Even though your baby may have some built-in faculties that help him detect and avoid certain common threats, the fact is that during the first few years of life, those faculties are not nearly enough to keep him out of harm's way. You, as his caregiver, must remain ever vigilant and ready to intervene. Fortunately, at least in the case of plants, it appears that you've got a little extra time to react. For your child's safety, don't let risk compensation neutralize that advantage.
Wertz, Annie E. and Wynn, Karen. "Thyme to touch: Infants possess strategies that protect them from dangers posed by plants," Cognition 130:1(44-49), January 2014.