[ intro ] Where there’s life, there’s other life
that’s looking for a free ride. A parasite is an organism that lives on or
inside another organism, and it gets its nutrition at the expense of
that host. It may not always be pretty, but parasitism is an extremely successful
life strategy. Among animals, for example, around 50% of living species are considered
parasitic. And this isn’t a new technique. Many of the parasitic strategies we see today
have been employed for millions of years, and when we’re lucky, we can find evidence of them in the fossil
and archaeological record. So here are six superlatively old parasites
-- among the oldest of their kind that we know
about so far. Now we humans like to think we’re pretty
special, but we’re still animals, and we have our
fair share of parasites. Among the worst are schistosomes, a group of flatworms that cause the disease
schistosomiasis. According to the US CDC, schistosomiasis is
second only to malaria as the most devastating parasitic disease
in humans, with more than 200 million people infected
worldwide. These little worms can cause rashes, chills, anemia, organ damage, and
even cancer. And they also have the distinction of being
some of the most ancient human parasites on record. A 2014 study reported evidence of a human
infected with schistosomes in a Syrian archaeological site dating to
at least 6000 years ago. The evidence didn’t come from the worms
themselves, but from their eggs. A close look at the pelvic region of one human
skeleton revealed that the sediment contained tiny objects, only 130 micrometers long, that turned out
to be schistosome eggs. See, for these worms, our bodies are a nice
place to make babies -- they lay their eggs inside our guts, and our
bodily functions carry the eggs off into the world. And it’s actually our bodies’ reaction
to the eggs that causes all those nasty symptoms. The fact that eggs were found around the pelvis
of this ancient individual, but not near any other body parts, is a good
sign that this poor person had a gut infection. This is the oldest known example of this kind
of parasite in humans , and it raises the question of how this human
ended up infected. Before infecting us, the worms spend an earlier
part of their lives inside water snails. Humans commonly pick up the parasites while
wading in freshwater. So maybe this infected person wandered into
the wrong stream, but there could actually be a more interesting
explanation. At the same ancient settlement, there are signs of crops that wouldn’t normally
survive in the local dry climate, which leads scientists to suspect the farmers
were employing an early form of irrigation. So, it could be that by redirecting water
to their crops, the locals accidentally provided a pathway
for one of our oldest parasitic foes. In other words, this ancient infection could
be a clue to human advancements in agriculture! Now, if you wanted to check for intestinal
parasites and you didn’t have access to an intestine,
the next best option is poop. And it was inside of some ancient poop -- a type of fossil called a coprolite -- that a 2019 study identified the oldest known
parasite DNA. The coprolite in question came from a rock
shelter in Argentina and was dated to around 17,000 years old. Fossils and artifacts show that this site
was home to lots of mammals over the years, like ground sloths, horses; even humans later
on. But based on the size and shape of this particular
poop, researchers suspected it came from a big cat. And while they examined it, they noticed lots of tiny eggs inside that
looked like they belonged to nematodes, or roundworms. To confirm their identifications, they extracted
ancient DNA, which revealed that they were right on both
counts: the poop came from a puma, and the eggs belonged
to the nematode species Toxascaris leonina. Today, this is a species that infects the
guts of cats and dogs, both wild and domestic, all around the world. And as of that study’s publication, it’s
the oldest DNA evidence of a parasite, but its age also reveals something about the
parasite’s history with its hosts. It’s been widely thought that, in the Americas, these parasites jumped from domestic animals
to wild species. But this infected cat is too old to have met
humans in this part of the world -- or to have exchanged worms with their fluffy
companions. So it seems these parasites have been plaguing
wild cats since before our species got involved -- meaning that there’s more to learn about
the history of these worms. Now, while we and our feline friends have
to worry about being infested with eggs that wreak havoc inside our intestines, some insects have more… dramatic concerns. Certain wasps lay their eggs inside other
insects. After the eggs hatch, the newborn larva feeds
on the host for a while before bursting out of its body like the xenomorphs from the Alien movies. These wasps are called parasitoids. They’re not true parasites, since only the
young are dependent on a host, which their life cycle usually kills. Even so, it’s a winning strategy. It’s estimated that between 10 and 20% of
all insects are parasitoid wasps. And as you might expect, this somewhat terrifying
strategy has been around for a while, going back at least 35 million years. This lengthy history was revealed in a 2018
study that examined fossilized fly pupae from southern France. A pupa is the cocoon-like phase these flies
went through between being larvae and adults. And the researchers found over 1500 that had
been preserved in this stage of life. But what was most intriguing -- and kind of
disturbing -- is that when they used X-ray imaging to peek
inside the pupae, they found that 55 of them were occupied by
parasitoid wasps that had hatched and developed inside. Most of these wasps were already adults, and
they seem to have been waiting for the right time to emerge from their hosts. Some parasitoids today will sync up their
adult emergence with their host species, so that there’s plenty around for the next
generation. But these are the oldest known fossils of
parasitoid wasps inside their hosts, and among them, the researchers identified
four brand new species. Two of these species were grouped into a new
genus very appropriately named Xenomorphia. Finding such a diversity of chest-bursting
wasps in one fossil site is a good clue that the parasitoid lifestyle
has been a lucrative and successful strategy for a long time. Now worms and insects are pretty common parasites, but animals also have to be wary of infections
by fungi. And if you thought chest-bursting wasps were
disturbing, might I remind you that there are parasitic
fungi that mind control their victims before erupting from their skulls. Some modern day fungi, like Ophiocordyceps, get inside the bodies of insects like ants
and manipulate the bugs to crawl high up on vegetation. From this elevated position, the fungus reproduces
by sprouting long, spore-covered stalks from the insect’s head
or body. It might be the most horrifying parasitic
strategy on this list, and these fungi have been at it since the
age of dinosaurs. A 2008 study reported an insect preserved
inside a piece of Burmese amber from the Cretaceous Period, about 100 million years old. Emerging from the head of the insect were
two long fungal stalks, each longer than the insect itself. Researchers could even examine the spores
preserved on the stalks. Amazingly, this fungal infection was fossilized
in the act. And at the time of publication, it’s the oldest record of animal parasitism
by a fungus. The researchers identified the fungus as a
close relative of Ophiocordyceps, and so named it Palaeoophiocordyceps. And by comparing this ancient species to its
cousins, they were even able to reconstruct the evolutionary
pathway of this group. Using a method called ancestral state reconstruction, which compares closely-related species to
estimate what traits their ancestors had, the team concluded that this group of fungi
started off as plant parasites. And then at some point in their history, they made the jump to animals and became mind-controlling,
head-bursting terrors. But some even older parasites are actually
a little more familiar to our own human experience: tapeworms! Tapeworms are an infamous group of flatworms
that get inside our intestines and set up shop stealing our nutrients and
laying eggs. And some have been so prolific in this life
strategy that they can grow as long as 25 meters. But we’re not the only ones targeted by
tapeworms. We share this burden with lots of other animals
around the planet -- and throughout time. The oldest evidence of a tapeworm infection
in a vertebrate comes from the Permian Period, around 270 million years ago. And once again, the proof is in the poop -- this time, a spiral-shaped coprolite from
an ancient shark. Because sharks have spiral-shaped intestines
and thus spiral-shaped poop. Inside one coprolite from Brazil, described
in 2013, researchers identified a cluster of 93 eggs,
each around 150 micrometers long. The size and shape of the eggs, plus the way they were grouped together in
a long segment, is just right for tapeworms. At least one egg even contained a partially
preserved larva inside. So this was a shark infested with at least
one tapeworm, but this fossil also provided evidence of
what else the worms went after. Like many parasites, tapeworm life cycles
often include several hosts, such as insects, frogs, or fish, and the worms usually pass from prey to predator when their host is eaten by the next host
in line. And inside this shark poop, alongside the
tapeworm eggs, were bones and scales of fish. So it seems that this shark may have picked
up some parasites during dinner -- and left us with some incredible insights
into the life cycle of some very old tapeworms. Now, throughout this list, we’ve been working
our way back through time, so let’s wrap it up with the most superlative
parasite of all -- the oldest animal parasites ever found. A 2020 study identified parasitic worms from
the Early Cambrian Period of South China, around 510 million years ago. These parasites were part of the one of the
very earliest animal-dominated ecosystems on Earth. But these aren’t intestinal worms -- there’s no poop involved this time. Rather, they’re tubeworms that spent their
lives in sturdy tubes attached to the outside of brachiopod shells. Brachiopods are two-shelled animals similar
to clams, and they’re known from this fossil site
by the thousands. In this study, the researchers found that
about 200 of them had worms stuck on them. Now, hitching a ride on another animal doesn’t
necessarily make you a parasite, and we’ve found older hitchhiker fossils
before. But the authors of this study are pretty sure
that these worms were true parasites, and their main clue comes from the condition
of the brachiopods. The brachiopods with worms on them were significantly
smaller, a clue that they weren’t as well-fed, perhaps
because those worms were stealing their food. See, brachiopods feed by sucking in water
and filtering out tiny morsels, and all these worm tubes were angled with
their opening stretched out toward the brachiopods’ intake area. The worms may have been relying on their hosts
to create a current, and then reaching out and intercepting food
on the way to the brachiopod’s mouth. This is a strategy called kleptoparasitism, which relies on stealing resources from a
host. And these are, so far, the oldest known fossil
parasites, and an amazing indication that parasitism
has been a winning strategy for about as long as there have been animal
ecosystems. Parasites may often be small and undignified,
but they have a huge impact. They cause disease, impact the health of other
organisms, and make up a major portion of the diversity of life. So, the more opportunities we have to study
ancient parasites, the better we’ll understand the intricacies
of life on Earth. And if you want to help us help you understand
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