[MUSIC]
One Sunday morning sun came up and pop out of the egg came a very hungry caterpillar.
On Monday it ate through a whole apple, but it was still hungry. On Tuesday it ate some broccoli
and died.
[MUSIC]
Plants are the richest source of nutrients on earth. Bacteria, fungi, insects and
animals of all shapes and sizes depend on them for energy. Even animals that eat meat
ultimately rely on plants, and we’re no exception!
[SALAD SCREAMING]
But it’s not always in a plant’s best interest to get eaten. They lack an immune
system like we have to fight off foreign invaders, and while some of them put on intimidating
outfits, many plants have turned to chemical warfare in order to fight off nibbling and
gnawing enemies.
Like Paracelsus said, “the dose makes the poison”, and unfortunately for plants, we
don’t really mind many of their chemical countermeasures. We find them delicious, actually,
or sometimes stimulating, and in trying to avoid becoming food they’ve accidentally
created some of our favorite flavors. Or like you say in Canada and the UK, flavours. Fla-voooours.
Take mustard. Now humans love that spicy zing,
but insects hate it. Plants in the genus Brassica, which includes a whole host of our favorite
edible plants, manufacture chemicals called glucosinolates that lead to bitter flavors.
To most insects these spicy compounds are toxic, even deadly, so mustard and its relatives
are usually off the menu. But that’s not true for one group of insects.
Cabbage butterflies have stumbled upon a way to detoxify these spicy poisons, their own
chemical countermeasure countermeasures it let their caterpillars feed on a food source
that’s unavailable to other insects.
It’s coevolution, culinary edition. In a coevolution relationship, a change in one
organism drives the natural selection of a new trait in another organism. We see this
all over nature.
The idea of coevolution was introduced about 50 years ago by Paul Ehrlich and Peter Raven.
Although even Darwin had predicted it, they were among the first biologists to describe
this sort of cooperative evolutionary arms race in detail, and they used cabbage butterflies
and Brassica plants as one of their prime examples.
Just this year, scientists were able to peer inside the genomes of these two species and
In evolution, new traits don’t just fall out of the sky. Long ago in the mustard plant
family, thanks to an error in DNA replication, a gene was duplicated. Since the plant now
had an extra copy that it didn’t need, this new gene was free to explore some mutations,
try something new, you know, really find itself.
In some individuals, that new function was synthesizing a toxin, and the plants with
that new trait survived and reproduced better than plants that didn’t have it. Caterpillars
who, through their own random mutations, were able to better tolerate or inactivate the
toxin also survived better and reproduced more. This cycle continued, with new mutations
making more or different toxins, and the hungry caterpillars who couldn’t adapt went sayonara.
We see this all over edible plant world.
Fruits like apricots and peaches contain actual cyanide in their seeds to defend against herbivores.
Castor beans contain ricin for crying out loud.
If you’re an insect, alkaloids like nicotine and caffeine are potent neurotoxins, we even
created a whole class of insecticides based upon them, but they’re pleasurable stimulants
to us.
Citrus plants have devised a second use for caffeine, not using it for defense, but lacing
their nectar with the chemical so bees become flying flower junkies.
Monarch butterflies have figured out how to use a plant toxin for their own good, the
milkweed they eat as caterpillars is poisonous to other animals, but they store away chemicals
from the plant’s latex sap inside their bodies, basically becoming flying little poison nuggets.
The tannins that give wine and tea their sharp flavor grab on to and disrupt the digestive
enzymes of bugs. They also bind to proteins in our saliva, which is why you get that sort
of astringent mouthfeel when you drink a glass of cabernet.
The hops we add to beer offer antimicrobial compounds along with their bitter flavor,
fighting off bad bacteria while letting the brewers yeast flourish.
Most of the defensive chemicals used by plants have a bitter taste, because bitter is nature’s
way of saying: maybe don’t eat this and also because plants don’t have hands
so they can’t draw that skull and crossbones thing.
Not all botanical weaponry is bitter, though. Chili peppers produce a compound called capsaicin,
which gives them their fiery burn. But capsaicin only works on certain targets. Feathered dinosaurs,
I mean birds, lack the molecular receptors necessary to feel the heat, so they can pop
chili peppers like candy, but if mammals like us eat them, with our spice-sensitive taste
receptors, then
Lucky for us, our bodies have figured out nutritious uses for many of these chemicals,
from vitamins to antioxidants. Even though most of our favorite flavorable plants are
technically little poison factories, don’t worry, the benefits of eating fruits and vegetables
far outweigh any risks. So don’t use this an excuse to not finish your broccoli.
Next time you take a bite of your favorite plant, you might have a very hungry caterpillar
to thank for that zip, that zest, that zing.
Stay Curious