DescentBB

New Scientist vol 180 issue 2421 - 15 November 2003, page 34

Human chimeras were once thought to be so rare as to be just a curiosity.
But there's a little bit of someone else in all of us, says Claire
Ainsworth, and sometimes much more...

EXPLAIN this. You are a doctor and one of your patients, a 52-year- old
woman, comes to see you, very upset. Tests have revealed something
unbelievable about two of her three grown-up sons. Although
she conceived them naturally with her husband, who is definitely
their father, the tests say she isn't their biological mother.
Somehow she has given birth to somebody else's children.

This isn't a trick question - it's a genuine case that Margot Kruskall, a
doctor at the Beth Israel Deaconess Medical Center in Boston,
Massachusetts, was faced with five years ago. The patient, who we will
call Jane, needed a kidney transplant, and so her family underwent blood
tests to see if any of them would make a suitable donor. When the results
came back, Jane was hoping for good news.

Instead she received a hammer blow. The letter told her outright that
two of her three sons could not be hers. What was going on?

It took Kruskall and her team two years to crack the riddle. In the end
they discovered that Jane is a chimera, a mixture of two individuals -
non-identical twin sisters - who fused in the womb and grew into a single
body. Some parts of her are derived from one twin, others from the other.
It seems bizarre that this can happen at all, but Jane's is not an
isolated case. Around 30 similar instances of chimerism have been
reported, and there are probably many more out there who will never
discover their unusual origins.

While cases like Jane's are the extreme, researchers now think that
there's a little bit of chimera in all of us, and what was once seen
as a biological oddity may serve a vital function. We may owe our
lives to being chimeras.

...most
probably go through life utterly unaware of their unusual constitution.
\"They are probably dramatically under-diagnosed,\" Kruskall says, \"and also
dramatically rare.\"

...
Animal studies of chimerism suggest that
this is indeed common.
...

But the story doesn't end there. There is growing evidence that chimerism
in one form or another may not be so unusual at all. In fact, some
researchers now think that most of us, if not all, are chimeras of one
kind or another. Far from being pure-bred individuals composed of a single
genetic cell line, our bodies are cellular mongrels, teeming with cells
from our mothers, maybe even from grandparents and siblings. This may seem
a little shocking at first. The thought of playing host to cells from
other people may offend your sense of individuality. But you may have
those outsiders to thank for keeping you healthy.
...

While microchimerism may force immunologists to rewrite their textbooks,
it may also prod us into seeing ourselves in a new light. Rather than
being isolated individuals, perhaps we should see ourselves more as a
collective - an individual made of many other different individuals. On
one level, you are you, a person with your own thoughts and feelings. But
zoom in one level and you are a supercolony of individual cells, some
cooperating, others competing. Zoom in to the level of your genome, and
you find individual chromosomes and genes, all jostling to get through to
the next round of natural selection. It's all a question of perspective.

De Rigueur wrote:I'm not sure why this is supposed to be shocking. A person's genetic material still comes from his/her parents, right?

Birdseye wrote:already done it pal

Shadowfury333 wrote:I don't see how it changes that much, as if your mother's chimeran twin's ovaries produced your egg, there is no aunt to speak of, as that DNA would've fused with that of your mother, thus it is irrelevant as far as parental bonds go.