Body double
You may think your body and mind are your own. In fact, you are a fusion of many organisms - including, potentially, another person. Words by David Robson, photography by Ariko Inaoka.
Once upon a time, your origins were easy to understand. Your
dad met your mum, they had some fun, and from a tiny fertilized egg you emerged
kicking and screaming into the world. You are half your mum, half your dad –
and 100% yourself.
Except, that simple tale has now become a lot more
complicated. Besides your genes from parents, you are a mosaic of viruses,
bacteria – and potentially, other humans. Indeed, if you are a twin, you are
particularly likely to be carrying bits of your sibling within your body and
brain. Stranger still, they may be influencing how you act.
A very large number of different human and non-human
individuals are struggling inside us for control
“Humans are not unitary individuals but superorganisms,”
says Peter Kramer at the University of Padua. “A very large number of different
human and non-human individuals are all incessantly struggling inside us for
control.” Together with Paola Bressan, he recently wrote a paper in the journal
Perspectives in Psychological Science, calling for psychologists and
psychiatrists to appreciate the ways this may influence our behavior.
(Credit:Ariko Inaoka)
Over the last 6 years, photographer Ariko Inaoka has
captured the special connection between two Icelandic twins, Erna and Hrefna
That may sound alarming, but it has long been known that our
bodies are really a mishmash of many different organisms. Microbes in your gut
can produce neurotransmitters that alter your mood; some scientists have even
proposed that the microbes may sway your appetite, so that you crave their favorite
food. An infection of a parasite called Toxoplasma gondii, meanwhile, might
just lead you to your death. In nature, the microbe warps rats’ brains so that
they are attracted to cats, which will then offer a cozy home for it to
reproduce. But humans can be infected and subjected to the same kind of mind
control too: the microbe seems to make someone risky, and increases the chance
they will suffer from schizophrenia or suicidal depression. Currently, around a
third of British meat carries this parasite, for instance – despite the fact an
infection could contribute to these mental illnesses. “We should stop this,”
says Kramer.
Infiltrating siblings
In this light, it becomes clear that our actions are not
entirely our own. It’s enough to make you question your sense of identity, but
the idea of infiltration becomes even more eerie when you realise that your
brain has not just been invaded by tiny microbes – but also by other human beings.
Even non-conjoined twins could be sharing organs without realizing
it
The most visible example might be a case of conjoined twins
sharing a brain, says Kramer, but even regular twins could have shared organs
without realizing it. During early development, cells can be passed between
twins or triplets. Once considered a rare occurrence, we now know it is
surprisingly common. Around 8% of non-identical twins and 21% of triplets, for
example, have not one, but two blood groups: one produced by their own cells,
and one produced by “alien” cells absorbed from their twin. They are, in other
words, a chimera – a fusion of two bodies – and it may occur in many organs,
including the brain.
Developing together in the womb, twins may swap cells,
making them even closer than we'd previously realised (Credit: Ariko Inaoka)
Brothers from another mother
Women accidentally carrying a "twin's" child
Lydia Fairchild’s paternity test was meant to be straightforward,
proving to the courts that her two sons’ father was the person she said he was.
When the test came back, however, Fairchild herself came up as a blank: there
was no trace of her DNA in her own children.
The courts threatened to convict her of illegal surrogacy –
they assumed it was a scam to gain benefits. Luckily, at around the same time,
a scientific paper reported a similar case in which a woman was apparently not
the biological mother of two of her three children. The reason was that she was
a chimera: a case in which two twins had merged into one body early in
development. Being the product of two different cell lines, some of her eggs
carried a genome that was different from the rest of the body.
Needless to say, the discovery has caused Fairchild to
question her own identity. “Telling my sons about this was the hardest part
because I felt that part of me hadn't passed on to them,” she told the website
Jezebel. “I thought, ‘Oh, I wonder if they'll really feel that I'm not quite
their real mother somehow because the genes that I should've given to them, I
didn't give to them.’”
A chimera brain could have serious consequences. For
instance, we know that the arrangement of different brain regions can be
crucial for its function – but the presence of foreign tissue, being directed
by different genes carrying a different blueprint, may throw that intricate
design into disarray. This may explain, for instance, why twins are less likely
to be right-handed – a simple trait that normally relies on the relative
organisation of the right and the left hemispheres. Perhaps chimerism has upset
the balance.
Even if you do not think you ever had a twin, there are many
other ways you might be invaded by another human’s cells. It’s possible, for
instance, that you started off as two foetuses in the womb, but the twins
merged during early development. Since it occurs at such an early age of
development, the cells can become incorporated into the tissue and seem to
develop normally, yet they are carrying another person’s genetic blueprint.
“You look like one person, but you have the cells of another person in you –
effectively, you have always been two people,” says Kramer. In one extreme
case, a woman was surprised to be told that she was not the biological mother
of her two children (See “Brother from another mother”, left). Alternatively,
cells from an older sibling might stay around the mother’s body, only to find
their way into your body after you are conceived.
However it happens, it’s perfectly plausible that tissue
from another human could cause the brain to develop in unexpected ways, says
Lee Nelson from the University of Washington. She’s currently examining whether
cells from the mother herself may be implanted in the baby brain. “A difference
in the amount, cell type, or the time during development at which the cells
were acquired could all result in abnormalities,” she says.
Nelson has found that even as an adult, you are not immune
from human invaders. A couple of years ago, Nelson and William Chan at the
University of Alberta in Edmonton took slices of women’s brain tissue and
screened their genome for signs of the Y-chromosome. Around 63% were harbouring
male cells. “Not only did we find male DNA in female human brains as a general
observation, we found it to be present in multiple brain regions,” says Chan.
In other words, their brains were speckled with cells from a man’s body. One
logical conclusion is that it came from a baby: somehow, her own son’s stem
cells had made it through the placenta and lodged in her brain. Strangely, this
seemed to decrease the chances that the mother would subsequently develop
Alzheimer’s – though exactly why remains a mystery. Some researchers are even
beginning to wonder whether these cells might influence a mother’s mindset
during pregnancy.
Our knowledge of the human “superorganism” is still in its
infancy, so many of the consequences are purely theoretical at the moment.
Kramer and Bressan's aim with their paper was not to give definitive answers,
but to enlighten other psychologists and psychiatrists about the many entities
that make us who we are today. “We cannot understand human behaviour by
considering only one or the other individual,” Kramer says. “Ultimately, we
must understand them all to understand how ‘we’ behave.”
For instance, scientists often compare sets of twins to
understand the origins of behaviour, but the fact that even non-identical twins
may have swapped bits of brain tissue might have muddied those results. We
should be particularly careful when using these twin studies to compare
conditions such as schizophrenia that may arise from faulty brain organisation,
Bressan and Kramer say.
In general, however, we shouldn’t feel hostile
towards these invaders – after all, they made you who you are today. “I think
it is now clear that our natural immigrants are with us for the long-term, for
better or for worse,” says Nelson. “And I would think “for better” outweighs
‘for worse’
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