Infants as young as six months old tend to expect that plants are food sources, according to a new research.
However, they can do so only after an adult shows them that the food is safe to eat, researchers said.
The findings show that, after watching an adult put part of a plant and part of a human-made object in her mouth, infants at 6- and 18-months of age preferentially identify the plant as the food source.
"Young children's decisions about what to eat are, famously, not determined by simply copying adult behaviour," Annie Wertz and co-author Karen Wynn noted.
Wynn and Wertz of Yale University hypothesised that, instead of imitating an adult's behaviour outright, children tend to go for specific types of entities - in this case, plants - but only when an adult does so first.
They tested their hypothesis in four experiments.
Full-term 18-month-olds were presented with a realistic-looking artificial plant and an obviously human-made artifact, each of which had dried fruits attached.
The infants watched an experimenter take one fruit off each object - the plant and the artifact - and place it in her mouth as if eating it.
The fruits were then taken off the plant and the artifact and the infants were asked, "Which one can you eat?"
The infants showed a clear preference for the fruits that came from the plant, despite the fact that they saw the same social information - the experimenter "eating" the fruit - applied to both objects.
The experiments further showed that the eating action was crucial to this plant-based bias: When the experimenter placed the fruits behind the ear, or merely looked at the plant and artifact instead of performing an action, infants chose randomly.
Younger infants, who have little to no experience with solid food, also showed evidence of a plant-based bias: Six-month-old infants looked longer at in-mouth actions when they were performed with fruits from the artifact, suggesting that this violated their expectations for edibility.
"Together, these experiments show that infants use social information from adults to rapidly and selectively identify plants as food sources," said Wertz.
"More broadly, this suggests that humans, unlike some other non-human primates, don't simply consider anything that goes into the mouth to be food. Instead, they also take the type of object into consideration," said Wertz.
The research was published in the journal Psychological Science.