Not Going to Finish Your Vegetables? Blame Your Genes.

An intriguing piece of research has added an unexpected category of things that evolution may have taught us, down in our DNA, to be afraid of. Plants.

You’ll finish the turkey, maybe two helpings. The mashed potatoes will probably all go (pass the butter, please). And you’ll certainly make room for a mound of that great pumpkin pie. But Aunt Celia’s green bean casserole in gravy? That mushy steamed spinach au gratin? The Brussels sprouts in…whatever that sauce is? There may be more than a bit of green left on the plate when you push the chair back from the Thanksgiving dinner table. And if you get any grief for not finishing your vegetables, you may have evolution, and fear, to blame. Yes, fear.

Some fears – snakes and spiders and heights and the dark – are so ubiquitous that it seems they must be genetic, even though most studies find that infants don’t harbor those fears, suggesting that they are more the result of nurture than nature. Now an intriguing piece of research has added an unexpected category of things that evolution may have taught us, down in our DNA, to be afraid of. Plants.

Yup, plants. Plants are not generally associated with fear. They’re not among the threats used to terrorize contestants on “Fear Factor”. They aren’t the starring bogeymen in Sci Fi or monster movies (although the carnivorous Audrey Jr. was pretty nasty in Little Shop of Horrors, as were the triffids in John Wyndhams’ 1951 The Day of the Triffids).

But as authors Annie Wertz and Karen Wynn note in Thyme to touch: Infants possess strategies that protect them from dangers posed by plants plants have always been dangerous. They protect themselves with all sorts of physical defenses like needles (cacti) and spikey leaves (holly) and thorns (roses), or noxious oils (poison ivy, oak, sumac, etc.). Many plants are laced with a variety of poisons. There’s a reason why Atropa belladonna is commonly known as ‘deadly nightshade’, Cerbera odollam is known as the ‘suicide tree’, Excoecaria agallocha is sometimes called ‘blind-your-eye mangrove’, why the Irish call Conum maculatum (hemlock) "Devil's Bread" or "Devil's Porridge", and Hippomane mancinella is also known as manzanilla de la muerte  or ‘little apple of death’. YUM! (Here is a more a more complete list of dangerous plants.)

So it would indeed make sense if evolution has taught us - encoding the lesson directly into our DNA - to start out with a sense of caution about plants, at least until we’ve been around long enough to learn that the positively hostile looking pineapple, with its thorns and spikes and serrated leaves, is actually both safe and delicious. Wertz and Winn suggest they may have found evidence of that innate fear. They write,

“Human infants, like other non-human animals, possess strategies for mitigating the ancestrally recurrent dangers posed by plants.”

They showed 47 babies (of both genders) between 8 and 18 months old a real basil plant and a real parsley plant, a realistic looking fabric basil and a plastic parsley, and two facsimiles of plants made of pipe cleaners, beads, paint and cardboard, which are clearly more from arts and crafts class than from the garden.

                                 (credit; Annie Wertz, Karen Winn, Yale University)

The kids sat in their parents’ laps and the objects were presented, two at a time in various combinations. The kids were encouraged to investigate the objects with the universal attention getting come-on, “Look what I’VE GOT!” Researchers timed how long it took the babies to reach out and touch the various objects to explore them. It took an average of 4.4 seconds for the babies to reach out and touch the arts-and-crafts-project/faux plants, but more than twice as long, 9.9 seconds on average, to work up the courage to touch the real plants or even the models that looked like real plants. The kids were WAY warier of touching the real plants or the realistic models, than the clearly fake ones.

So is this proof that we have evolved a genetic fear of plants? Hardly. It’s pretty rare that one bit of research absolutely proves anything in any field, and that’s especially true in the fuzzy world of evolutionary psychology, which requires a heavy dose of inference about how our behaviors now might have helped us survive way back when. But something about plants, at least parsley and basil, made those 47 infants wary, and they certainly had not been taught that wariness. Something's going on.

So if you are like me and tend not to finish your vegetables, go right ahead and blame it on evolution, and impress everybody at dinner with your knowledge of that new research that suggests we are born with an innate caution about plants. Although you may want to hold off on the fear part, and suggesting to Aunt Celia that you’re worried her green bean casserole could be fatal.


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