[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
