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.
Plant Dangers
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.
https://gizmodo.com/are-humans-hardwired-to-detect-snakes-1453865235
“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.
https://gizmodo.com/the-psychology-of-hating-food-and-how-we-learn-to-love-476720251
But are infants also sensitive to
the dangers of plants, the same way they appear to recognize the dangers of snakes and spiders?
To Touch or Not to Touch
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.
https://gizmodo.com/artificial-plants-could-one-day-power-your-home-464881436
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.
They crafted the second artifact out of green pipe cleaners
to test if babies don’t like to touch green objects. The object also mimicked
plants’ swaying movement when disturbed.
After testing 47 infants, who were between 8 and 18 months
old, the researchers found that the babies took, on average, 5 seconds longer
to touch the plants and artificial plants than the novel artifacts.
Importantly, the infants didn’t have any social information about the plants,
as they didn’t see anyone touching those specific plants.
As part of the experiment, Wertz and Wynn also gave the
parents a questionnaire about their babies’ experiences with plants. On a
five-point scale (1 being “never” and 5 being “nearly every
day”), the survey probed how often the infants see their parents handling
plants, how often the babies touch plants and how often the parents stop their
infants from touching plants.
The infants’ own experiences with plants didn’t affect how
long it took them to touch the plants in the experiment. Oddly, however, babies
who saw their parents caring for plants more often actually took longer to
touch plants, though the researchers don’t know why.
Given the visual differences between the fabricated objects
and the plants (both real and artificial), Wertz and Wynn decided to test if
the infants were just more interested in touching novel things. They also
tested if the babies were more prone to touch objects that are manmade
— it could be the case that the infants think anything manmade is made to
be handled, and anything that’s not a manmade object should be treated with
some care, Wertz said.
They repeated the first experiment with 44 babies, this time
using the same fabricated objects, seashells (natural objects) and spoons and lamps
(familiar manmade objects that the infants were allowed to touch and not allowed to
touch at home, respectively). The babies weren’t reluctant to touch any of the
objects in this experiment, but they did take a little longer to touch the
novel fabricated objects than the seashells, spoons and lamps.
The results suggest that babies may have a natural aversion
to plants, which protects them from the potential dangers of plants, Wertz
said. And it’s not that babies are afraid of the plants — instead, they
instinctively employ this protective behavioral strategy when they identify an
object as a plant. Of course, this raises the question: Why would the infants
have touched the plants at all?
“With the experimental setup, we very much stacked the
deck against ourselves,” Wertz explained. Specifically: The babies were in
a bland room with a single object placed in front of them. Part of the reason they
ended up touching the plants may be because the plants were the only thing around to touch,
but Wertz is interested in seeing what happens under normal experiences.
Interestingly, there is some anecdotal evidence backing up
the results. “What tends to happen when I present this study, is that I have
people who have kids come up to me and say, ‘Oh yeah, that’s right: My kids
go for everything, but leave the plants alone,'” Wertz said. “Or
they’ll say, ‘My kids put everything in their mouths, but not the
plants.'”
Wertz and Wynn are now testing how infants rapidly acquire
information about which plants are edible. They also want to look at possible
cross-cultural differences in infants’ plant aversions, as well as how nonhuman
primates interact with plants. Another interesting research avenue is to
determine how infants identify objects as plants.
“There’s lot that needs
to be done and a lot of gaps I want to fill in,” Wertz said.
Read the study
in the journal Cognition.
Top
image via Anna Jones/Flickr.
Videos via Wertz & Wynn/Elsevier.
