Throughout history, we humans have been drawn to the biggest of questions.
Where do we come from?
Is there a God?
Do we as a species have the capacity to overcome our differences and work together to build
a better future for us all?
And of course, perhaps the most profound of these big questions: do eels have testicles?
OK, so maybe I’m slightly overstating the importance of that last one - the hunt for
eel gonads might not have quite the same scientific glamour as the search for dark matter or a
theory of everything.
But, oddly enough, it’s a question that’s had a hell of a lot of attention over the
years in the scientific community.
Because, as weird as it sounds, eels lack balls.
And I don’t mean that in some vague idiomatic way, either - they don’t get all weak at
the fins at the thought of extreme sports or routinely back down from fights.
No.
They literally don’t have testicles.
But if that’s the case, how on God’s green earth do they reproduce?
Well, before we get onto that, what exactly are eels?
While they kind of resemble snakes that have gone into hiding underwater on account of
being so monumentally ugly, they’re actually a kind of fish.
But for multitudinous reasons they’re remarkably different to pretty much any other fish species
you care to mention.
Take European freshwater eels, for example.
They lack scales, for a start, and can breathe air through their skin.
That ability allows them to survive out of water for up to 48 hours, and they’re surprisingly
nifty movers on land – they can even climb.
They hibernate in the winter if it gets too cold by burying themselves in mud, a trick
they also employ if the pond they’re living in happens to dry out in the summer.
They can live to almost 100 years of age, their blood is poisonous, and they’re also
remarkably difficult to kill, and will keep on swimming for hours even after you’ve
cut off their heads thanks to a decidedly stubborn nervous system.
All in all, eels are pretty bloody odd.
And that’s before we even get to their troubling lack of testes.
So, how does an animal without reproductive organs create offspring?
Believe it or not, this conundrum has occupied some of humankind’s most brilliant thinkers
for at least a couple of millennia.
Aristotle was probably the first to grapple with it, but the great Greek philosopher and
thinker was as perplexed as anyone else by the eels’ lack of Crown Jewels.
Still, as the father of western logic, he did manage to come up with a fittingly logical
explanation.
Eels don’t have reproductive organs, according to Aristotle, because they don’t reproduce.
And if they don’t reproduce, he reasoned, they must come to life through some other
mechanism.
Ultimately, he concluded eels spontaneously come into being when rainwater mixes with
mud.
Not one of his finest moments, that, but considering he basically invented science, I think we
can give him a pass on this one.
As you’re no doubt aware, Aristotle’s influence on science loomed large long after
his death.
And for that reason, the belief eels came to life out of nothing was widely accepted
as scientific fact for some two thousand years, though others did come along to put their
own hypotheses forward as to exactly how the process worked.
Roman author Pliny the Elder, who died in the aftermath of the famous eruption of Mount
Vesuvius that buried Pompei in 79 AD, believed eels came into being from the partially shed
skins of other eels.
Others felt certain eels sprouted from sea foam or burst into life when sunlight hit
open stretches of water in a certain way.
The Scots thought eels started out life as beetles, and the English were convinced they
were born when hairs from horse tails fell into river water.
I know I know; nobody comes out of this with much credit, but hey - those were simpler
times.
It took a while, but eventually people began to question whether it was really possible
for an animal to just come to life from nothing.
After all, the very idea seemed to violate the laws of nature mankind had slowly been
uncovering in the millennia since Aristotle met his maker.
One man who could firmly be considered a sceptic was Sigmund Freud.
And yes, I do mean that Sigmund Freud.
You might be wondering what the most famous psychoanalyst in history has to do with mankind’s
hunt for eel goolies, and I’ll admit it is a little weird to see him crop up in this
story.
But then again, if you know anything about Freud, you’ll know the guy was absolutely
obsessed with genitals, so the fact he was once interested in eel nuts perhaps shouldn’t
come as much of a surprise.
In 1876, when Freud was still an enthusiastic medical student at the University of Vienna,
he traveled to the city of Trieste in north east Italy, a stone’s throw away from the
Slovenian border.
The purpose of the trip was simple - Freud wanted to do something nobody else ever had:
get his hands on a nice set of eel balls.
To that end, he took himself down to the city’s port each morning to meet the fisherman coming
home with their catch, from whom he would buy as many eels as he could afford.
Then he went back home to begin the dissections.
Freud spent several months in Trieste, and it’s thought he worked his way through as
many as 400 eels during that time.
The gory task seems to have gotten to him, too, because he sounded on the verge of losing
his marbles in one letter to a friend, where he confessed: “All I see when I close my
eyes is the shimmering dead tissue, which haunts my dreams."
It’s no wonder he decided to take his career in another direction not long afterwards.
Especially when you consider all that hard work eviscerating eels hadn’t brought about
the discovery Freud was hoping for.
He’d found some interesting looking bits and pieces inside the abdominal cavities of
several large specimens, but there was nothing he could definitely, conclusively claim to
be an eel testicle.
Freud had failed.
Still, he wasn’t the only one sceptical of the stories of miraculous eel origins,
and ten years later in 1886, a breakthrough came.
French zoologist Yves Delage had been keeping an odd, leaf-shaped marine creature known
as a leptocephalus in a tank in his lab for several months when, quite unexpectedly, the
strange little beast turned into something else entirely.
Yves had observed something that would change our understanding of eels forever.
You see, eels are metamorphic creatures, and they go through 6 distinct stages in what
can only be described as one hell of an odd lifecycle.
They start out as leptocephali much like the one Yves kept in his fish tank, before turning
into transparent glass eels.
Glass eels become elvers, elvers become yellow eels, and yellow eels become silver eels,
which are basically the eel’s endgame form.
The funny thing is, science had known about all of these individual animals for a long
time - fisherman had been catching them and people had been eating them since time immemorial.
Jellied eel, anyone?
But it had always been assumed they were different species entirely.
Nobody had ever realised they were all the same animal at different stages of its lifecycle.
Although Yves witnessed the metamorphosis first hand, it took a decade or so for his
discovery to be widely accepted.
That might be because it went against conventional wisdom, or it may just be that people didn’t
take poor old Yves too seriously.
You see, he had a habit of making outlandish statements, and in later life would famously
claim to have ‘calculated’ that the Turin Shroud - which some people believe is the
fabric Christ was buried in after the crucifixion – had a 1 in 10 billion chance of being
a fake.
I’d really love to see your working there Yves.
Anyway, it was with the discovery of this highly unusual life cycle that the missing
piece fell into place to help science finally understand why eels lack testicles.
Not because they spontaneously come to life from mud, not because they’re remarkably
energetic horse tail hairs, but because they grow reproductive organs only when they need
them in their final, mature form.
And you have to hand it to them; it does sound like a sensible system.
Because, as any guy will tell you, when you aren’t using them genitals don’t half
get in the way.
So, one of the oldest questions in the animal kingdom had finally been put to bed.
But, rather annoyingly, the answer brought with it a question of its own.
Because the first stage of the eel’s life cycle - the leptocephalus - was a marine creature
- it was found only in the ocean.
Which neatly explained why poor old Sigmund had never stumbled across so much as a sniff
of testicle during his 400 dissections - by the time eels reach their mature stage – which
can take anything from 7 to 70 years - they’ve left our shores far behind.
So, that being the case - where exactly do all these millions of eels bugger off to each
year?
In 1904, Danish scientist Johannes Schmidt was asking himself the very same question.
Luckily, Schmidt was a doer.
When he came across a question that left him scratching his head, he didn’t just shrug
his shoulders and go make a sandwich.
He went out and found the answer - even if it meant dedicating his life to the task.
Which is why, over a period of some 19 years, Schmidt carried out the biggest survey of
leptocephali ever completed before or since.
He was particularly interested in their size - and for good reason.
Because, as he slowly built up more and more data, he began to realise something - the
closer he got to a certain point in the Atlantic Ocean, the smaller the leptocephali he netted
were, until eventually, they couldn’t get any smaller.
He’d found the eel’s spawning grounds – smack in the middle of the Sargasso Sea.
Not only was that rather fitting - because much like the creatures who go there for a
bit of ‘sexual eeling’, the Sargasso itself is a bit of an enigma - it was also pretty
staggering.
Because it meant European freshwater eels were undertaking a previously unknown migration
of some 6000 kilometres to have their young.
The Sargasso is the only sea in the world that doesn’t have a single land border.
Instead, it’s surrounded by a vortex of ocean currents that completely encircle it
on all sides.
It’s a sea within a sea, if you like, and its border currents act a bit like a plug
hole for the Atlantic.
That’s why, as well as millions of randy eels, it’s also home to the North Atlantic
garbage patch - hundreds of square kilometres of ocean filled with rubbish.
Nice one, humans.
Despite Schmidt’s conclusions, which are still accepted today, nobody has ever actually
seen eels mating in the Sargasso Sea.
In fact, even with all our fancy technology, nobody has ever seen eels in the Sargasso
at all.
Despite the fact we’re pretty confident millions of them make the journey there every
year.
And in keeping with that somewhat patchy understanding of the behaviour of our slippery friends,
we don’t really know how the tiny eel larvae born there make it the 6000 kilometres back
to Europe, either.
Their strange, leaf-like shape is thought to help with drifting, but some researchers
believe active swimming plays at least some part in the trip.
We also don’t know how long the journey takes, or even how long eels stay in their
larval state - estimates range from as little as 6 months to as many as 3 years.
So yeah, we may have found their balls, but eels still seem to have plenty of other secrets
hidden up their sleeves.
Well, sleeve, I guess.
We’ve mostly been covering freshwater eels in this video, but eels don’t get any less
weird no matter which bit of the family tree you’re looking at.
There are snipe eels that look a bit like nightmarish lassos, slender moray eels that
can grow to be 4 metres long, and European congas that can weigh as much as 110 kilos.
Rarely seen gulper eels live at depths of up to 3000 metres and are a confusing mix
of disturbing and cute - kind of like what might have happened if Nintendo had decided
to turn Kirby into a horror franchise.
And then there are parasitic snubnosed eels.
These disturbing little living horrors use their powerful jaws to burrow into the bodies
of larger fish, where they just… make themselves at home.
Typically they can be found snuggled up alongside the spines of species like cod and halibut,
but they’ve also been known to burrow directly into the abdomen of gravid fish where they
promptly devour thousands of unhatched eggs within the space of just a few minutes.
In 1992, two parasitic eels were even found to have made a cosy residence in the still-beating
heart of a 400kg Mako shark caught near Montauk in New York State.
I should probably mention electric eels, too.
Not because they can deliver an electric shock of close to a thousand volts - although they
can - but because they aren’t actually eels at all - they’re a kind of knifefish.
Bit of an embarrassing slip there, hey science - although not an especially uncommon one.
Killer whales aren’t whales - they’re members of the dolphin family.
American buffalo are actually bison, honey badgers are most closely related to martens,
and horny toads are in fact lizards - and, I might add, no more desperate for sex than
any other animal out there.
Knifefish imposters aside, eels are some of the weirdest animals ever to have existed
on planet earth.
But while there are still plenty of mysteries left to uncover about these strange and elusive
creatures, we do at least finally know for sure that, yes, they do have balls.
I’m sure you’ll all sleep easier tonight now that’s been cleared up.
Which should give you plenty of time to vividly imagine a parasitic snubnosed eel eating its
way through your chest and taking up residence in your heart.
Thanks for watching.