Children seem to be born with an innate distrust of plants

Evolutionary psychology

Thyme to touch

Nov 16th 2013 |From the print edition

SPIDERS and snakes can be dangerous, so it is not surprising that people are wary of them from birth. But plants? Odd as it may seem, to be afraid of plants—at least when young and ignorant about which are useful and which harmful—might make good evolutionary sense.

The manicured lawns, ornamental trees and bushes, and intensively bred fruit and vegetables which are modern humans’ experience of the plant kingdom are hardly typical of what their ancestors would have encountered in the evolutionary past. Many of these would have been packed with poisons, covered with toxic hairs, furnished with sharp spines or thorns, or possibly all three. A preliminary study, published in Cognition by Annie Wertz and Karen Wynn at Yale University, suggests infant children are indeed, if not exactly afraid of plants, then certainly wary of them.

Dr Wertz and Dr Wynn began by showing a group of children aged between eight and 18 months six objects: a real parsley plant, a real basil plant, a realistic but fake parsley plant, a realistic but fake basil plant, and two strange artefacts. The first artefact was made from two blue cardboard cylinders painted with a yellow stripe and decorated with fabric leaves like those of the fake basil, but dyed black and arranged to hang downwards. The second was the same colour as the plastic parsley, but made of pipe-cleaners and beads.

The children (who were sitting on a parent’s lap at the time) were shown the objects in random order, and their reactions filmed. When Dr Wertz and Dr Wynn had the results analysed, they found that their “volunteers” responded identically to the fake plants and the real ones, taking an average of 9.9 seconds before reaching out to touch them. That contrasted with 4.4 seconds to reach out and touch one of the strange artefacts.

This showed reactions to plants and novel artefacts are different, but not whether it is plants that are repellent or novelty that is attractive. To check that, the researchers did a second experiment, this time using sea shells (non-plant natural objects), spoons (familiar objects children touch frequently) and lamps (familiar objects children do not touch frequently) and also the two novel creations from the first experiment.

The children reacted rapidly to all of these (an average of 3.4 seconds for the shells, 4.6 seconds for the spoons and lamps, and 6.4 seconds for the novel artefacts). Plants—whether they are real or artificial—really are outliers.

Some biologists speculate that children’s famously finicky attitude to eating up their greens is actually a sensible reaction to a world where lots of plants are toxic. This study suggests this hypothesis might be right, and that, to the frustration of parents everywhere, phytophobia is indeed a child’s natural lot.

From the print edition: Science and technology