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The science of zombies: Will the undead rise?
WASHINGTON, Nov 1, 2019 (BSS/AFP) – Hordes of brain-munching undead
terrorizing neighborhoods make for fun television and movies, but zombies
could never be real… or could they?
There are in fact a growing number of documented examples in the animal
kingdom of parasites that change their hosts’ behavior — and increasing
evidence that humans are not immune to manipulations that are arguably
zombie-like.
It’s a subject that fascinates theoretical evolutionary biologist Athena
Aktipis of Arizona State University, who hosts a podcast called “Zombified”
that applies real-life science to the types of apocalyptic events first
popularized by filmmaker George Romero in the 1960s.
– It’s not unusual –
“If you actually look at the proportion of species overall that are
parasitic in one way or another… more than half of the species that we know
on Earth are parasites,” Aktipis told AFP.
One example is the Ophiocordyceps fungus, which releases spores that infect
the carpenter ant’s body, allowing it to take over the insect’s locomotive
activity.
Eventually, it kills its host by forcing it to leave its nest and bite down
on a piece of vegetation which it gets stuck to as a result of a tetanus-like
infection that gives it lockjaw.
The parasitic fungus erupts out of its host’s head with a mushroom-like
growth called a stroma. At night, when uninfected ants are out foraging, this
growth shoots out more infectious spores and the 2-3 week cycle repeats
itself.
“We’re totally convinced that the behaviors that the ant show are all to
benefit the fungus,” said Charissa de Bekker, an assistant professor of
biology at the University of Central Florida who is carrying out genetic
research on both creatures to better understand the takeover process.
Another example among insects comes from two different wasp species, the
crypt gall wasp and the parasitoid crypt-keeper wasp.
Kelly Weinersmith, a biology professor at Rice University who was part of
the team that made the discovery, said that a healthy crypt gall wasp matures
inside a compartment formed in an oak tree called a “crypt.” Eventually the
larva grows up and chews its way out of the tree. But when the parasitoid
finds crypt gall wasp larvae, it lays its own egg in the crypt, and the
parasite manipulates the host into chewing a hole that is too small to escape
from — such that it can only stick its head out.
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“After they get trapped there, the parasitoid eats (the crypt gall wasp’s)
insides,” Weinersmith said.
“When the parasitoid is done developing, it chews a hole in the head of the
host and emerges through its head, it’s all super creepy.”
– What about humans? –
If you think nothing like that could ever happen to humans, think again.
The single-celled parasite Toxoplasma gondii in fact infects around 40
million Americans, according to the Centers for Disease Control and
Prevention (CDC), and some studies have found that it impacts human behavior.
The parasite “somehow evolved to make a rat get turned on by the smell of
cat urine, so it goes up to a cat and snuggles with it, and then it gets
eaten which completes the life cycle of the toxoplasma — if that’s not
zombification then what is?” said Aktipis.
People can get infected with it by eating undercooked meat — or through
their pet cats, especially when cleaning out their litter boxes.
Some studies have reported an association between brain infection of the
parasite and personality traits such as risk-taking and aggression, though
other research has disputed these findings.
Rabies, likewise, makes animals and people aggressive, and in some cases
makes humans extremely sexually aroused.
There’s even growing evidence that the bacteria in our gut change our
emotions and behavior, including what we want to eat, the subject of another
paper that Aktipis recently co-authored.
– Be prepared –
Certain tropes of zombie fiction are entirely unscientific.
For one, dead bodies decay rapidly, meaning the huge throngs of undead seen
in “The Walking Dead” would naturally become incapacitated as their flesh and
muscle disintegrate within days to a few weeks, depending on weather
conditions.
And it would require a huge evolutionary leap for toxoplasma to do to
humans what it does to rats.
But Atkipis, who organized the cross-disciplinary Zombie Apocalypse
Medicine Meeting last year and plans another such conference in 2020,
believes gaming out such scenarios can be a useful — and fun — way of
thinking about future threats.
She recommends keeping a go-bag of vital supplies like first aid kits, duct
tape that can be used to fashion a shoe or a weapon, and whiskey to sterilize
water and wounds (or drink if things get really bad).
According to its website, the CDC also stands ready to provide assistance
to determine the source of the infection, learn how it’s transmitted and find
a cure, “much like any other disease outbreak.”
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