Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff,
Speaker 1: Lauren vogelbam here. Zombies are a horror trope for a reason.
Speaker 1: For many reasons, really, but one is that we humans
Speaker 1: tend to like the idea of being in control of
Speaker 1: our own bodies and behavior, and in stories, the walking
Speaker 1: dead are reduced to mindless doers of damage and often modernly,
Speaker 1: spreaders of whatever infectious disease has caused the dead to rise.
Speaker 1: There are many real life infections and conditions that can
Speaker 1: alter a person's behavior, all horrific in their own right,
Speaker 1: but none we know of could cause a full on
Speaker 1: George Romero's style apocalypse or the Last of Us style apocalypse.
Speaker 1: In the video games and television series The Last of Us,
Speaker 1: a brain hijacking fungus evolves from the infecting insects and
Speaker 1: other arthropods to infecting human beings. And don't worry, that's
Speaker 1: the only spoiler we're going to give here. But today,
Speaker 1: let's talk about the real life fungi that inspired the series.
Speaker 1: Cordyceps and Afia. Cordyceps are each a genus of fungi
Speaker 1: that are often parasitic to arthropods like ants, spiders, and wasps.
Speaker 1: Fungi in general grow from spores, then consume living or
Speaker 1: dead material like wood in order to grow root like
Speaker 1: structures called mycelium and fruiting bodies like mushrooms that produce
Speaker 1: more spores. But instead of in wood, Cortceps and Affia
Speaker 1: cordyceps tend to grow in arthropods that in itself is
Speaker 1: nothing very special. A fossil evidence of fungi growing in
Speaker 1: insects has been found as far back as one hundred
Speaker 1: and five million years ago, and over a thousand fungi
Speaker 1: with insect hosts are known to exist today. But these
Speaker 1: two genera of fungi can actually change an animal's behavior
Speaker 1: when they're ready to spore in order to spread those
Speaker 1: spores as far as possible. Take, for example, a species
Speaker 1: of Apia cordyceps. The parasitizes carpent durants and hijacks the
Speaker 1: ants behavior during the last days of its life. This
Speaker 1: phenomenon caught the eye of British naturalist Alfred Russell Wallace
Speaker 1: when he was in Indonesia back in eighteen fifty nine.
Speaker 1: Even a newcomer to the area could see that something
Speaker 1: was seriously wrong with some of the ants in the rainforest.
Speaker 1: After all, carbondurants are generally pretty predictable in their behavior.
Speaker 1: They work as a team, and each ant has a
Speaker 1: very specific job, like building the nest, gathering food, or
Speaker 1: caring for the queen. When an ant is infected with
Speaker 1: the fungus, the fungus grows unnoticed in the ant's body
Speaker 1: for a while, feeding on the ant until the fungal
Speaker 1: cells account for over half of the ant's body mass.
Speaker 1: All this time, the ant has been doing its usual
Speaker 1: job and living its life. One day it begins to
Speaker 1: act very differently. Breaking off from the colony. It stumbles
Speaker 1: around by itself all day and night, climbing higher and
Speaker 1: higher into the trees. Eventually, the ant clasps a leaf
Speaker 1: for stem with its strong mandibles and dies. Check in
Speaker 1: a week later, and you'll find the dead ant's body
Speaker 1: covered in a brown mat of hair like structures, with
Speaker 1: a beige stalk having erupted from a place near its head.
Speaker 1: This stalk releases millions of tiny spores that float away
Speaker 1: on the air for more ants to step on, thus
Speaker 1: beginning the whole cycle over again. That chomping onto a
Speaker 1: leaf for stem behavior by the way is how we
Speaker 1: know that this kind of behavior altering fungal parasitism is
Speaker 1: pretty ancient. Leaf scars created by an ant death grip
Speaker 1: have been found on fossils at least forty eight million
Speaker 1: years old. In all that time, carbenter ants have evolved
Speaker 1: some strategies for avoiding these fungi, at least they try
Speaker 1: their best. Many ant species groom each other in an
Speaker 1: attempt to remove spores from their friends, while others fray
Speaker 1: their nests with fungicidal poisons and seal off parts of
Speaker 1: their nests. When infections arise, a whole ant colony will
Speaker 1: relocate if necessary. But how does the fungus affect the
Speaker 1: ants behavior to the extent that it does. It's a
Speaker 1: question that's baffled generations of scientists over the years. Some
Speaker 1: have argued that the ants aren't hijacked at all, that
Speaker 1: certain protocols have evolved in response to a fungal infection,
Speaker 1: and that the individual ants wander off not because they're
Speaker 1: being influenced by the fungus, but to avoid infecting the
Speaker 1: rest of their colony. And despite the tropes about zombies
Speaker 1: and brains, a twenty seventeen study published in the Proceedings
Speaker 1: of the National Academy of Sciences found that it's possible
Speaker 1: that the ant's brain isn't involved in the whole process
Speaker 1: at all. The researchers found that as the fungus grows
Speaker 1: inside the ant's body, its cells create an interconnected network
Speaker 1: of fibers that surround the ants muscle fibers, and that
Speaker 1: it's this network that is most likely coordinating the ants movements.
Speaker 1: They did find the fungus in the insect's head, but
Speaker 1: not in its actual brain. In a press release, the
Speaker 1: lead author of the study, an entomologist by the name
Speaker 1: of David Hughes, said, we found that a high percentage
Speaker 1: of the cells in a host were fungal cells. In essence,
Speaker 1: these manipulated animals were a fungus in ants clothing. Pretty
Speaker 1: much everything except the brain had been taken over entirely
Speaker 1: by fungal cells, which led the researchers to believe that
Speaker 1: the fungus might be preserving the brain for a reason,
Speaker 1: maybe in order to help the ants survive until it
Speaker 1: can perform its final death bite. To be fair, ant's
Speaker 1: brains are pretty small, and they make up for that
Speaker 1: by having clusters of neurons throughout their bodies that help
Speaker 1: control different work, like the movement of a pair of
Speaker 1: legs or receiving signals from an antenna. So although these
Speaker 1: findings are compelling, it's still not crystal clear what's going
Speaker 1: on between these parasitic fungi and their victims. But at
Speaker 1: least it is clear that it would be extremely difficult
Speaker 1: for a fungus to start hijacking human bodies in the
Speaker 1: way that cordyceps and a few cordyceps do with arthropods,
Speaker 1: so that's one less thing to worry about. Today's episode
Speaker 1: is based on the article Meet the Zombie ant Fungus
Speaker 1: that inspired HBO's The Last of Us on how Stuffworks
Speaker 1: dot com, written by Jeslin Shields. Brain Stuff is production
Speaker 1: of iHeartRadio in partnership with how Stuffworks dot Com and
Speaker 1: is produced by Tyler Klang. Four more podcasts my Heart Radio,
Speaker 1: visit the iHeartRadio app, Apple Podcasts, or wherever you listen
Speaker 1: to your favorite shows.