If you think about it, the whole concept of twins sounds like science fiction: genetic
duplicates who share a womb and the same DNA?
But unlike zombies, cyborgs, and shark tornados, twins are a true-life example of how crazy
biology can be — and the fact that they look alike barely scratches the surface of
all the interesting things about them.
Here's everything you never knew about nature's own version of human cloning.
Identical vs. fraternal
Unless you slept through your high school health class, you know how babies are made:
the sperm fertilizes the egg, which becomes a zygote, and nine months later —
"(alien chirps)"
Just kidding.
Actually, you get one of these — unless that single zygote splits into two embryos,
resulting in two babies who are identical right down to their DNA.
But that's not the only way to get two kids from one pregnancy: sometimes, the mother
will release two eggs, each of which are fertilized by a separate sperm.
That's when you end up with fraternal twins, who do share a womb, but unlike identical
twins, don't share any more DNA than ordinary siblings.
"We're not identical twins."
"Oh NO?!"
Different fingerprints
From their faces to their genetic profiles, identical twins emerge from the womb sharing
virtually every physical characteristic — except, oddly enough, their fingerprints.
But why?
The answer is that fingerprints are a product of environment rather than genetics: all those
whorls, loops, and ridges are formed from the outside in, when a fetus presses its developing
fingers against the walls of the womb.
Since identical twins occupy different positions in the amniotic sac before birth, they each
end up with different, unique patterns on their fingertips.
That makes fingerprinting the one and only way for police to tell which of the two twins
committed a crime — so if a guy wants to rob a bank and let his twin brother take the
fall for it, he's gonna have to wear gloves.
The disappearing twin
Back before "ghosting" became a sketchy thing that people do on OKCupid, twins were doing
it to each other — in the womb.
It's called fetal resorption, and it's one of the eeriest things that can happen during
a twin pregnancy: an initial ultrasound reveals two developing babies, but somewhere along
the way, one of them simply vanishes.
Where'd it go?
"I ate my twin in the womb"
It sounds shocking, but that's pretty much how it works: one twin sometimes doesn't make
it through the early states of the pregnancy due to chromosomal abnormalities, and its
remains are absorbed by the surviving fetus.
Different families, similar lives
In the event that a pair of twins are separated at birth, they often grow up to lead bizarrely
parallel adult lives.
The studies surrounding this subject are a little shady — one is even locked in a vault
that can't be opened until 2066 — but the results don't lie.
In one example, a pair of twins reunited in their thirties to discover that they had independently
developed similar personalities, political views, and quirky movie taste — and had
both studied film in college and edited their school newspapers before finding work as writers.
Bonding in the womb
According to Scientific American, twins get a head start on their social skills even before
they're born.
By the 14th week of gestation, twins start reaching out to each other in the womb, and
by Week 18, they'll touch their partner more often than they're touching the walls or themselves,
and with more deliberation, patience, and focus.
They're also extra careful when touching their twin's eye region — because even when you're
a fetus, nobody likes getting poked in the eyeball.
Mirror images
Roughly twenty-five percent of identical twins come with an interesting twist: they still
share all the same genes, but their physical features are flipped, so that looking at their
twin is literally like looking in a mirror.
If one twin is right-handed, their mirror twin might be left-handed.
One might have a unique birthmark on his left leg; the other would have the same birthmark
on his right leg.
But it gets weirder: the mirror effect also occurs in twins who develop certain health
issues, so that if one develops, say, a tumor on his right lung, his twin will develop one
on the left.
Their own language
Before the adult world saddles them with past participles and dangling modifiers, a certain
percentage of twins learn to talk exclusively to each other in a language only they can
understand.
The phenomenon is called cryptophasia, and it happens in about forty percent of twin
pairs — and usually, it doesn't last past toddlerhood.
But in at least one case, a pair of twins hung on to their language for so long that they
ultimately had to be sent to separate schools in order to learn to converse normally with
other people.
They're multiplying
Since 1980, the rate of twin births has jumped up 76 percent, hitting an all-time high in
2014.
Where's this twin-vasion coming from?
For one, women are waiting longer to have kids — and women in their 30s or older are
more likely to hyper-ovulate, which increases the chances of a multiple zygote situation.
Plus, there's always the magic of science: more and more couples are turning to in-vitro
fertilization when they can't get pregnant the old-fashioned way, but since not all those
embryos end up being viable, doctors will often implant a few at a time.
Sometimes, the result is a healthy baby — but sometimes, more than one of those embryos
takes, resulting in multiples.
Different dads
Remember how fraternal twins result from a woman producing two eggs, and how each egg
gets fertilized by different sperm?
"Hey, we're gonna make babies!"
That means that if the timing, genetics, and environmental factors work out just right
—or in other words, if mom releases two eggs and gets down with two different guys
in short succession — you get what's known as heteropaternal superfecundation… or,
uh, grounds for divorce.
"Andrew, you are NOT the father!"
The phenomenon occurs much more frequently in dogs than people, since female dogs produce
multiple eggs and don't usually practice monogamy.
But it's been known to happen with people, too: one couple in Vietnam was worried that
one of their baby twins might have been switched at birth, until tests revealed that the twins
had different fathers.
Awkward!
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