62
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Science & technology
To carry out their study, Dr Muotri and
his colleagues grew and examined hundreds of organoids, each a mere half-millimetre in diameter, over the course of ten
months. To probe individual neurons
within these they used tiny, fluid-filled pipettes that acted as electrodes small
enough to maintain contact with the surface of an individual cell.
Neurons probed in this way proved
electrically active, so the researchers went
on to employ arrays of electrodes inserted
simultaneously into different parts of an
organoid to study its overall activity. They
looked in detail, once a week, at each of the
organoids that were chosen for examination. This revealed that, by six months of
age, the electrical activity in different parts
of an individual organoid had become
synchronised.
Such synchronicity is also a feature of
real brains, including those of preterm human infants of about the same age as Dr
Muotri’s organoids. It is regarded as an important part of healthy brain function. So,
to check how similar natural and organoid
brain waves actually are, the research team
ran those waves obtained from their organoids through a computer program that
had previously been trained to recognise
the electrical activity generated by the
brains of premature babies. This algorithm
proved able to predict to within a week the
ages of laboratory-grown organoids 28 or
more weeks old. That suggests those organoids are indeed growing in a manner similar to natural human brains.
Brain work
If further research confirms this opinion,
then for medical science that conformity
with natural development could be a boon.
Neuroscientists have long been held back
by the differences between human brains
and those of other animals—particularly
the brains of rodents, the analogue most
commonly employed in medical research.
The purpose of the work that Dr Lancaster,
Dr Muotri and others involved in the field
are engaged in has always been to produce
better laboratory models of neurological
and psychiatric diseases, so that treatments may be developed.
And, although it may be some time in
the future, there is also the possibility that
organoids might one day be used as transplant material in people who have had part
of their brains destroyed by strokes.
For ethicists, however, work like this
raises important issues. A sub-millimetre
piece of tissue, even one that displays synchronised electrical pulsing, is unlikely to
have anything which a full-grown human
being would recognise as consciousness.
But if organoids grown from human stem
cells start to get bigger than that, then the
question that was posed back in 2013 becomes pressing. 7
The Economist August 31st 2019
Genetics and sexuality
There is no “gay
gene”
But biology does in part determine
sexual orientation
I
n 1993 a region of the human genome
called xq28 was linked to male homosexuality, and the controversial notion of a
“gay gene” was born. Those research findings have not been replicated. But it was
never going to be that simple: decades of
genetic research have shown that almost
every human characteristic is a complex
interplay of genes and environmental factors. A new study, published in Science this
week, confirms that this is the case for human sexuality, too.
The study, the largest ever into this difficult topic, was conducted by an international group of scientists working with
23andMe, a personal genomics firm. It
used what is called a genome-wide association study (gwas) on 408,995 individuals
in the uk Biobank, a British health resource, and 68,527 American 23andMe users—all of whom remained anonymous
and consented to the study.
A gwas involves scanning a person’s
dna for tiny variations in the genetic code
(simple changes in the As, Ts, Gs or Cs) that
correlate with a given trait. The participants were divided on the basis of whether
they answered yes or no to the question
“Have you ever had sex with someone of
the same sex?”—a woolly proxy for sexual
orientation, even in the absence of little
white lies. The figures the gwas produced,
therefore, relate only to a single act, not to
whether someone identifies as gay.
The researchers found five genetic
Just part of the spectrum
markers that were significantly associated
with a reported homosexual act by one of
the participants in the study. None of those
markers was on the x or y sex chromosomes and their total combined effect accounted for less than 1% of the variance.
This is because the behaviour is the result
of the aggregate effort of hundreds or thousands of genes, whose individual effects
are infinitesimally weak. Totting up all the
thousands of tested genetic variants accounted for between 8% and 25% of the variation in people’s self-reported homosexual acts. These variants also overlapped
with other traits, such as a smoking and an
openness to new experiences.
Interestingly, only about 60% of the genetic variants identified in the study were
shared by both sexes. Most behaviours
show more overlap between the sexes than
this, intimating that male and female homosexuality, or at least sexual adventures,
may be quite different. David Curtis of University College London notes that what
overlap there is “suggests that there could
be specific factors affecting same-sex attraction rather than simply being attracted
to males versus being attracted to females.”
The riddles go on
Conscious of the tricky subject matter, the
scientists are at pains to anticipate any
misunderstandings or backlash. They collaborated with lgbt advocacy groups
throughout the study.
Yet the research only scrapes the surface
of the mysterious depths of human sexuality. Unravelling these riddles will be difficult and will inevitably beget misconception and controversy. But at least this study
should add weight to the view that nonheterosexual behaviour is firmly within
the normal, natural spectrum of human
diversity and provide a firm foundation for
future work. 7
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Science & technology
The Economist August 31st 2019
To carry out their study, Dr Muotri and Genetics and sexuality
markers that were significantly associated
his colleagues grew and examined hunwith a reported homosexual act by one of
dreds of organoids, each a mere half-millithe participants in the study. None of those
metre in diameter, over the course of ten
markers was on the x or y sex chromomonths. To probe individual neurons
somes and their total combined effect acwithin these they used tiny, fluid-filled picounted for less than 1% of the variance.
pettes that acted as electrodes small
This is because the behaviour is the result
enough to maintain contact with the surof the aggregate effort of hundreds or thouBut biology does in part determine
face of an individual cell.
sands of genes, whose individual effects
sexual orientation
Neurons probed in this way proved
are infinitesimally weak. Totting up all the
n 1993 a region of the human genome thousands of tested genetic variants acelectrically active, so the researchers went
on to employ arrays of electrodes inserted 上 called xq28 was linked to male homosex- counted for between 8% and 25% of the vasimultaneously into different parts of an uality, and the controversial notion of a riation in people’s self-reported homosexorganoid to study its overall activity. They “gay gene” was born. Those research find- ual acts. These variants also overlapped
looked in detail, once a week, at each of the ings have not been replicated. But it was with other traits, such as a smoking and an
organoids that were chosen for examina- never going to be that simple: decades of openness to new experiences.
tion. This revealed that, by six months of genetic research have shown that almost 5. Interestingly, only about 60% of the geage, the electrical activity in different parts every human characteristic is a complex netic variants identified in the study were
of an individual organoid had become interplay of genes and environmental fac- shared by both sexes. Most behaviours
tors. A new study, published in Science this show more overlap between the sexes than
synchronised.
Such synchronicity is also a feature of week, confirms that this is the case for hu- this, intimating that male and female hotruth
real brains, including those of preterm hu- man sexuality, too.
mosexuality, or at least sexual adventures,
man infants of about the same age as Dr 2 The study, the largest ever into this dif- may be quite different. David Curtis of UniMuotri’s organoids. It is regarded as an im- ficult topic, was conducted by an interna- versity College London notes that what
portant part of healthy brain function. So, tional group of scientists working with overlap there is “suggests that there could
to check how similar natural and organoid 23andMe, a personal genomics firm. It be specific factors affecting same-sex atbrain waves actually are, the research team used what is called a genome-wide associa- traction rather than simply being attracted
ran those waves obtained from their orga- tion study (gwas) on 408,995 individuals to males versus being attracted to females.”
noids through a computer program that in the uk Biobank, a British health rehad previously been trained to recognise source, and 68,527 American 23andMe us- The riddles go on
the electrical activity generated by the ers—all of whom remained anonymous 6 Conscious of the tricky subject matter, the
brains of premature babies. This algorithm and consented to the study.
scientists are at pains to anticipate any
proved able to predict to within a week the 3 A gwas involves scanning a person’s misunderstandings or backlash. They colages of laboratory-grown organoids 28 or dna for tiny variations in the genetic code laborated with lgbt advocacy groups
more weeks old. That suggests those orga- (simple changes in the As, Ts, Gs or Cs) that throughout the study.ǚàr
noids are indeed growing in a manner sim- correlate with a given trait. The partici- 7 Yet the research only scrapes the surface
pants were divided on the basis of whether of the mysterious depths of human sexualilar to natural human brains.
they answered yes or no to the question ity. Unravelling these riddles will be diffi“Have you ever had sex with someone of cult and will inevitably beget misconcepBrain work
If further research confirms this opinion, the same sex?”—a woolly proxy for sexual tion and controversy. But at least this study
then for medical science that conformity orientation, even in the absence of little should add weight to the view that nonwith natural development could be a boon. white lies. The figures the gwas produced, heterosexual behaviour is firmly within
Neuroscientists have long been held back therefore, relate only to a single act, not to the normal, natural spectrum of human
by the differences between human brains whether someone identifies as gay.
diversity and provide a firm foundation for
and those of other animals—particularly 4. The researchers found five genetic future work. 7
the brains of rodents, the analogue most
commonly employed in medical research.
The purpose of the work that Dr Lancaster,
Dr Muotri and others involved in the field
are engaged in has always been to produce
better laboratory models of neurological
and psychiatric diseases, so that treatments may be developed.
And, although it may be some time in
the future, there is also the possibility that
organoids might one day be used as transplant material in people who have had part
of their brains destroyed by strokes.
For ethicists, however, work like this
raises important issues. A sub-millimetre
piece of tissue, even one that displays synchronised electrical pulsing, is unlikely to
have anything which a full-grown human
being would recognise as consciousness.
But if organoids grown from human stem
cells start to get bigger than that, then the
question that was posed back in 2013 beJust part of the spectrum
comes pressing. 7
There is no “gay
gene”
I
-
.
.