Post by Admin on Nov 21, 2023 12:52:17 GMT
Both one and yet distinct
Being a twin (as our author knows) cracks open our ideas of the perfectly bounded self and might liberate us all
aeon.co/essays/being-a-twin-helpfully-cracks-open-our-ideas-of-individuality
In Washington state in 2002, Lydia Fairchild nearly lost custody of her three children, when a test revealed that none of them shared her DNA. It turned out that Fairchild’s body was populated with cells from a non-identical twin she’d unknowingly had before birth, making her, in effect, the biological aunt of her own children.
The technical term for Fairchild is a ‘human chimera’: a human being composed of cells that are genetically distinct. The phenomenon can happen artificially, through a transfusion or transplant, or naturally, as in Fairchild’s case, through the early absorption of a twin zygote. Only 100 cases of natural chimerism are documented, but there may be many more. Scientists estimate that 36 per cent of twin pregnancies involve a vanishing twin. Most such twins likely disappear without a trace, but some get partly absorbed into their neighbour. The survivor is unlikely to learn of their lost sibling’s genetic presence, unless an unrelated test or procedure inadvertently reveals it. Go in for a routine cheek swab, come out with a twin.
Many find the idea of unknowingly carrying the vestiges of their twin unsettling. One person I told about Fairchild instantly burst into tears. I’m less perturbed by it, likely because I’ve known I have a twin for decades. My own twin Julia survived our joint gestation (rather than me, what, eating her? Gross!) If I find out I’ve got another one in there somewhere, it won’t be my first rodeo.
What mainly interests me about human chimeras are the philosophical, not the personal, implications. What should we say, metaphysically, about Fairchild and her ilk?
Journalists reporting on Fairchild’s case didn’t quite know what to make of it. ‘She’s her own twin,’ proclaimed ABC News. ‘The many yous in you,’ intoned Ed Yong in National Geographic. ‘A Guide to Becoming Two People at Once,’ wrote Maia Mulko in Interesting Engineering in 2021. Such headlines are clickbait because they challenge a standard presumption of modern Western culture, so basic as to go unstated. Westerners generally think that each person is physically discrete, cleanly distinguished from all other people by their location, solo, within an unbroken continuum of skin.
Actually, though, human chimeras leave this assumption intact. Fairchild isn’t two people in one, because the mere presence of human DNA doesn’t indicate the presence of a person. Any stray hair you leave on your pillow overnight is biologically human, but that doesn’t mean that, every time you shed hair, you’re multiplying the number of people in the room. Personhood requires something more than a particular type of genetic material: it arises only with the larger-scale structural organisation of that material, which permits capacities like consciousness, thought and moral agency. At the macro level that matters for personhood, Fairchild is a singleton.
Still, the one-person-per-body assumption is worth questioning, and there’s a much more convincing example of its violation at hand. Conjoined twins, unlike chimeras, contain only one genetic cell line. But (when two heads are present) they overwhelmingly consider themselves to be two unique, distinct beings, despite sharing a body. It’s typical for them to speak of themselves as individuals, and to develop a personality and tastes different from each other’s. Their families and friends, too, think of them as two people who just happen to be physically attached.
The case of conjoined twins reveals the falsity of the assumption that bodies correlate one-to-one with people. Recognising this has large implications. If one body can contain two people, why couldn’t one person be spread across two bodies? Why couldn’t that person be me, or you?
Being a twin (as our author knows) cracks open our ideas of the perfectly bounded self and might liberate us all
aeon.co/essays/being-a-twin-helpfully-cracks-open-our-ideas-of-individuality
In Washington state in 2002, Lydia Fairchild nearly lost custody of her three children, when a test revealed that none of them shared her DNA. It turned out that Fairchild’s body was populated with cells from a non-identical twin she’d unknowingly had before birth, making her, in effect, the biological aunt of her own children.
The technical term for Fairchild is a ‘human chimera’: a human being composed of cells that are genetically distinct. The phenomenon can happen artificially, through a transfusion or transplant, or naturally, as in Fairchild’s case, through the early absorption of a twin zygote. Only 100 cases of natural chimerism are documented, but there may be many more. Scientists estimate that 36 per cent of twin pregnancies involve a vanishing twin. Most such twins likely disappear without a trace, but some get partly absorbed into their neighbour. The survivor is unlikely to learn of their lost sibling’s genetic presence, unless an unrelated test or procedure inadvertently reveals it. Go in for a routine cheek swab, come out with a twin.
Many find the idea of unknowingly carrying the vestiges of their twin unsettling. One person I told about Fairchild instantly burst into tears. I’m less perturbed by it, likely because I’ve known I have a twin for decades. My own twin Julia survived our joint gestation (rather than me, what, eating her? Gross!) If I find out I’ve got another one in there somewhere, it won’t be my first rodeo.
What mainly interests me about human chimeras are the philosophical, not the personal, implications. What should we say, metaphysically, about Fairchild and her ilk?
Journalists reporting on Fairchild’s case didn’t quite know what to make of it. ‘She’s her own twin,’ proclaimed ABC News. ‘The many yous in you,’ intoned Ed Yong in National Geographic. ‘A Guide to Becoming Two People at Once,’ wrote Maia Mulko in Interesting Engineering in 2021. Such headlines are clickbait because they challenge a standard presumption of modern Western culture, so basic as to go unstated. Westerners generally think that each person is physically discrete, cleanly distinguished from all other people by their location, solo, within an unbroken continuum of skin.
Actually, though, human chimeras leave this assumption intact. Fairchild isn’t two people in one, because the mere presence of human DNA doesn’t indicate the presence of a person. Any stray hair you leave on your pillow overnight is biologically human, but that doesn’t mean that, every time you shed hair, you’re multiplying the number of people in the room. Personhood requires something more than a particular type of genetic material: it arises only with the larger-scale structural organisation of that material, which permits capacities like consciousness, thought and moral agency. At the macro level that matters for personhood, Fairchild is a singleton.
Still, the one-person-per-body assumption is worth questioning, and there’s a much more convincing example of its violation at hand. Conjoined twins, unlike chimeras, contain only one genetic cell line. But (when two heads are present) they overwhelmingly consider themselves to be two unique, distinct beings, despite sharing a body. It’s typical for them to speak of themselves as individuals, and to develop a personality and tastes different from each other’s. Their families and friends, too, think of them as two people who just happen to be physically attached.
The case of conjoined twins reveals the falsity of the assumption that bodies correlate one-to-one with people. Recognising this has large implications. If one body can contain two people, why couldn’t one person be spread across two bodies? Why couldn’t that person be me, or you?