It is a question that has perplexed parents for decades: why do children refuse to eat greens?
Now, two American academics believe they have the answer.
After studying dozens of toddlers as they played with various objects, the researchers noted that they were far more reluctant to grasp plants than artificial items such as spoons or pipe cleaners.
They believe this is because evolution has biologically programmed children to be wary of flora as it may contain potentially hazardous toxins.
Due to a susceptibility to illness or injury in the early years of life, the body has designed an inbuilt defence mechanism that limits a child’s contact with plants, they think.
The researchers believe this is why infants in the study were wary of grabbing plants — and why children turn their noses up when faced with a plate of broad beans.
The findings are published in an academic paper by Dr Annie E Wertz and Dr Karen Wynn, both psychologists at Yale University, titled “Thyme to touch: Infants possess strategies that protect them from dangers posed by plants”.
They wrote: “Throughout human evolution … plants have been essential to human existence. Yet, for all of these benefits, plants have always posed very real dangers.
“Plants produce toxins as defences against predators that can be harmful, or even deadly, if ingested. Some plants also employ physical defences, such as fine hairs, thorns, and noxious oils that can damage tissues and cause systemic effects.”
They added: “We predicted that infants may possess behavioural strategies that reduce their exposure to hazards posed by plant defences by minimising their physical contact with plants.”
To test their theory, the academics studied how children aged eight to 18-months-old reacted when presented with a variety of objects while sitting on their parent’s lap.
In each case they would place six objects, one at a time, in front of the infant while saying “look what I’ve got” and timing how long it took before they clasped the item. Parents were told to keep their eyes shut to minimise their influence. By repeating the same test on almost 100 subjects, the researchers discovered significant variations in the time it took for children to reach out for different items.
On average, it took 3.4 seconds for a child to reach out for shells, 4.6 seconds for lamps and spoons but almost 10 seconds for parsley and basil plants, twice as long as many non-plant items.
Objects that were faked to look like plants also triggered a slow response time.
The authors concluded that trial and error across centuries of human existence had taught infants to be intrinsically wary of physical contact with plants.
“We are not suggesting that infants are actively afraid of plants,” Dr Wertz and Dr Wynn concluded.
“Rather, we propose that once infants identify an object as a plant, they deploy a behavioural strategy of inhibited manual exploration, which serves to help protect them from plants’ potential dangers.”
For parents who have been noting this “behavioural strategy” every time they attempt to spoon some peas into the mouth of their child, this finding should come as a welcome relief, they said.