
Prenatal testosterone linked to long-term effects in females with male twin - bookofjoe
https://phys.org/news/2019-03-prenatal-testosterone-linked-long-term-effects.html
======
Symmetry
Given that women with lower digit ratios[1] aren't socialized any differently
than women with higher digit ratios I'm very unsurprised at this result.

[1][https://en.wikipedia.org/wiki/Digit_ratio](https://en.wikipedia.org/wiki/Digit_ratio)

------
burger_moon
My girlfriend has a twin brother. Since they were born in Haiti and we live in
the US I'm not sure how relevant this study would be towards her, meaning the
socioeconomic changes between living in those two countries is pretty wide.
How does prenatal test affect someone after they've gone through puberty? I
just don't see how that can be attributed towards college graduation or
marriage rates. Is that not a far reaching statement to associate the two?

~~~
tofof
> How does prenatal test affect someone after they've gone through puberty

The test doesn't affect them. Hormone levels during development are the
primary way the body controls development, so even small alterations in
hormone levels in utero would be expected to have large physiological
consequences.

> Is that not a far reaching statement to associate the two

Luckily, the field of statistics gives us ways to reason about whether or not
to believe an observed effect.

In this case[1], the researchers used data on 100% of Norwegian births from
1967-1978 (n=728,842) including 13,800 twins. From these large n's the
researchers are able to get the statistical power to measure these effects at
the level of precision they did. The p-values for all the reported effects are
presented in the appendix [2] and ranged from <.001 to .054 for the outcomes
reported to be different.

It's worth noting that many of these differences had already been observed in
multiple previous studies. The difference in marriage rates, for example,
already appeared in a study analyzing records of 18th and 19th century
(1734–1888) Finns [3].

So, in summary, while these statements are interesting, they're in no way an
overreach, given the amount of data analyzed.

1:
[https://www.pnas.org/content/early/2019/03/14/1812786116](https://www.pnas.org/content/early/2019/03/14/1812786116)

2:
[https://www.pnas.org/content/pnas/suppl/2019/03/14/181278611...](https://www.pnas.org/content/pnas/suppl/2019/03/14/1812786116.DCSupplemental/pnas.1812786116.sapp.pdf)

3:
[https://www.pnas.org/content/104/26/10915?ijkey=2c55ba770f14...](https://www.pnas.org/content/104/26/10915?ijkey=2c55ba770f147fc77c50ea606af9ddb341ab5347&keytype2=tf_ipsecsha)

~~~
burger_moon
Being statistically illiterate, could I get an explanation of of "The p-values
for all the reported effects are presented in the appendix [2] and ranged from
<.001 to .054 for the outcomes reported to be different." I looked at the
link, but I'm still not sure what the table means, or how I could explain what
this means to someone else who doesn't know stats.

I'd like to share this with her, but neither of us know stats so the
significance is kinda lost.

~~~
tofof
Sure.

P-value is the universal* way of expressing statistical likelihood. It
corresponds to a percentage: p=.05 just means 5%, and p=.001 means 0.1%, etc.

It's often inaccurately explained as the likelihood of getting our results
through chance alone. That's wrong for reasons that are technically important,
but not in a way that really inhibits understanding of the strength of results
that have small p-values.

* It has flaws, and a growing number of researchers believe it should not have the prominent importance currently placed on it.

\---- Stop reading here if you're already satisfied. ----

We want to measure if there's a difference between two groups. So, we take
measurements of a portion of group A, and measurements of a portion of group
B.

Mathematically, we assume that what we've actually done is sampled from the
_same population_ both times. If that's true, our data sets should be quite
similar to one another, but of course there will be some difference just due
to noise.

So, we compute mathematically the chance of seeing a difference at least as
large as the one we see between our data sets, _if that assumption is true_.

We decide beforehand on a small error rate. If not otherwise stated, 5%
(p=.05) is the universal standard.

If we find that the likelihood of observing a same-or-larger difference
between the populations is smaller than that already-small 5% chance, we
REJECT our assumption that the samples came from the same population, and
conclude that the populations must actually be different.

In other words, we conclude that we measured an actual difference that
contrasts two mathematically-separate populations.

------
nikbackm
Similar for cows.

[https://en.wikipedia.org/wiki/Freemartin](https://en.wikipedia.org/wiki/Freemartin)

~~~
tofof
Critically, however, freemartins are a form of microchimerism. They literally
have cells with Y chromosomes in their bodies, received from the male twin
through the shared chorion. You're correct that there is a shared mechanism -
they receive testosterone and anti-Müllerian hormone through this link, which
are primarily resonsible for masculinizing the freemartin.

In contrast, this mechanism is thought to be only testosterone exposure in
utero.

A better comparison, then, might be intra-uterine position in mice [1]. This
is similarly a pure testosterone-exposure mechanism (no microchimerism).
Briefly, mouse pups are arranged in linear fashion within the uterine horn,
and so a given (non-end) female pup has 0, 1, or 2 males adjacent to her.
There are clear physiological and behavioral differences in these 0M, 1M and
2M mice, corresponding to the level of testosterone exposure.

[1]:
[https://en.wikipedia.org/wiki/Prenatal_testosterone_transfer...](https://en.wikipedia.org/wiki/Prenatal_testosterone_transfer#Mice)

------
formichunter
I have a twin sister, twin brother talking, and unfortunately this study does
not show credence for me. She's smart as a whip, in a lawyer way, as I'm more
math/science. We both make six figures and both are very career focused. I had
to laugh at this study...she used her words like a dagger to defend against my
constant barrage of physical torture growing up. It was a very contentious
relationship.

~~~
pcstl
You do realize that the point of the study is not that every single woman who
has a male twin will not be successful, right?

------
gubbrora
Worse career AND love life. So it just messes them up in general rather than
make them more androgynous?

------
Causality1
So if prenatal testosterone has such a deleterious effect on females, what
effect does it have on males? How do all those metrics they measured for the
girl half of the twin pairs compare to their sibling?

~~~
dooglius
"Unlike the females, the researchers found that male twins do not experience
long-term consequences of being exposed to a female twin in utero."

~~~
Causality1
That's not what I asked. I asked what effect in utero testosterone had on
boys. Did they have lower metrics than their sisters? Did boys with higher
levels of in utero testosterone have lower metrics than boys with lower levels
of in utero testosterone?

~~~
ska
I'm not sure how they would go about experiment design for this.

In the case of twins they know the mechanism for increased testosterone, and
they have a big control population. Short of everyone having a prenatal
hormone measurement (which presumably is not done typically) how would you
identify the subjects?

------
codeisawesome
Why is “marriage rate” a factor in determining “life success”?

~~~
tofof
The researchers never once use the term 'life success'. [1]

That a behavioral difference (marriage rate) seems to be influenced, in
females, by in-utero exposure to testosterone (independent of any effect on
fertility rate, at that) is certainly a scientifically relevant finding. Links
between psychology and biology are still infrequent.

1:
[https://www.pnas.org/content/early/2019/03/14/1812786116](https://www.pnas.org/content/early/2019/03/14/1812786116)

~~~
codeisawesome
Agree. But it was listed clustered with “college/school graduation likelihood,
wage earnings, fertility (again hmm for this one)” and other indicators which
are arguably termable as life success metrics (or any other suitable
verbiage).. my point is that “one of these things is not like the others”.

~~~
tofof
Marriage rate differences have already been shown to be correlated with
hormone levels.[1][2] Measuring whether such a difference exists for the level
of exposure in-utero simply by having a male twin is interesting. If anything,
the natural interpretation of this data would be to expand the range of
behavior (marriage rate) considered 'typical' for females.

Similarly, fertility differences have been observed already for e.g. mice
exposed to different levels of testosterone in utero. The 'freemartin' cows
mentioned by another poster here are infertile for a similar reason. Hormones
play a huge role developmentally and are almost 100% responsible for
morphological sexual anatomy.

There's no agenda present in measuring these outcomes. These are exactly the
outcomes that would be expected naturally to be different. If anything, the
unusual inclusion is the economic and educational factors.

1:
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5501487/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5501487/)

2:
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3540120/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3540120/)

------
undoware
additional testosterone means you read as (and possibly are) queer more often,
which in turn means you gotta pay the butch tax. This result, correctly
interpreted, will be unsurprising to most queer and trans people.

------
toolslive
any advantages for the females with a male twin, like increased athleticism ?

~~~
tofof
Previous research has shown females with a male twin to be more proficient at
mental 3d-spatial tasks.

As that paper explains in its introduction, this is "probably the most robust
_cognitive_ sex difference", emphasis mine, which is why it's interesting.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4438761/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4438761/)

------
belorn
With smaller data sets I find the summary to be less valuable than the actual
paper. In this case we are talking about 4,533 twin pairs where one is a male
and the other female. The female twin had a 2.8-percentage point higher
probability of dropping out of high school compared to other female students,
and a similar 1.9-percentage point lower probability of graduating from
college.

Those two numbers seems connected, ie that individuals that have higher risk
of high school drop out have also a higher risk of not graduating. The study
do not cross compare this with male students which also have higher drop out
rate and lower graduation rate compared to female students, but some relation
seems implied.

The study also notes a lower probability of ever having been married by age
32, and lower probability of employment. The article does not explore if the
effect could be exclusively a result of lower education.

As a final thought, the sample size is relatively small and the effect
relatively minor in absolute numbers. The paper does not give out any P values
or confidence intervals for their primary findings. The relative effect is
large, but I interpret that more like a warning flag. In absolute terms we are
talking about 136 additional students born between 1967 and 1978 that dropped
out compared to a null hypothesis. The same number for college drop out was 49
students that did not graduate. With so few individuals having that large
effect on the conclusion I personally will wait a bit for replication studies.

~~~
tofof
> The paper do not give out any P values [...] for their primary findings. The
> relative effect is large, but I interpret that more like a warning flag.

Incorrect. The p-values -- all 85 of them -- are presented in the appendix[1],
linked to in the first paragraph under the 'Results' heading, along with
means, standard deviations, and number of observations. The article text[2]
repeatedly references these tables when making each claim.

> The paper do not give out any [...] confidence intervals for their primary
> findings.

Incorrect. Confidence intervals are presented in 100% of the figures.

> The article does not explore if the effect [on marriage or employment] could
> be exclusively a result of lower education.

Incorrect. They explicitly consider the effect of educational attainment on
future economic earnings.

"Behavioral changes downstream of prenatal testosterone exposure, such as any
effect of disruptive behavior on schooling or educational attainment, are
likely candidate pathways linking male co-twin exposure to later earnings.
Consistent with this interpretation, conditioning on educational attainment in
the earnings equation reduced the coefficient on opposite-sex from −0.086 (SE,
0.021) to −0.042 (SE, 0.014), suggesting that roughly 50% of intensive margin
labor market effects could be explained by educational outcomes that are
upstream of earnings.

> Those two numbers [H.s. dropout rate / college graduation rate] seems
> connected ... some relation seems implied.

These measures are already known to be strongly correlated, along with the
correlations to the probability of inclusion within the labor force and
lifetime earning potential. The paper makes no claims that these four measures
are independent from one another.

The paper does explicitly make clear when findings of independence are
relevant, particularly in usually-correlated variables. In this case I'm
referring to their findings of a fertility rate effect independent from
marriage rate.

1:
[https://www.pnas.org/content/pnas/suppl/2019/03/14/181278611...](https://www.pnas.org/content/pnas/suppl/2019/03/14/1812786116.DCSupplemental/pnas.1812786116.sapp.pdf)

2:
[https://www.pnas.org/content/early/2019/03/14/1812786116](https://www.pnas.org/content/early/2019/03/14/1812786116)

~~~
belorn
> are presented in the appendix[1],

Thank you, missed the appendix. Also see that in the figure page list CI as
95%.

> These measures are already known to be strongly correlated... The paper does
> explicitly make clear when findings of independence are relevant

The first few paragraphs in the article here and the Significance section in
the actually paper imply a strong independence. My point above is basically
that the independence looks to be much weaker than a casual read might imply.
It also boast with the largest study ever done on the subject, which might be
true, but the absolute number are actually quite low with only a few
individuals being responsible for a large effect in the data. That is one of
the biggest warning signs that exist in this kind of research. I thus get
skeptical, at which point I start to look why there seems to be a disconnect.

------
alwaysanagenda
Has nobody recognized that not a single biologist, chemist, neurosurgeon,
hormone specialist, neo-natal specialist, or just general medical doctor
participated or helped produce this study?

Here are the authors:

Aline Bütikofer - Department of Economics, Norwegian School of Economics, 5045
Bergen, Norway David N. Figlio - School of Education and Social Policy,
Northwestern University, Evanston, IL 60208 Krzysztof Karbownik - Institute
for Policy Research, Northwestern University, Evanston, IL 60208 Christopher
W. Kuzawa - Department of Economics, Emory University, Atlanta, GA 30322 Kjell
G. Salvanes - Department of Anthropology, Northwestern University, Evanston,
IL 60208

So we have, two economists, one anthropologist, and two people who specialize
in "social policy."

They did not work with these twins, they did not do their own medical research
and assessment. They literally "[used] data on all births in Norway (n =
728,842, including 13,800 twins) between 1967 and 1978 to show that females
exposed in utero to a male co-twin have a decreased probability of..."

This is not meaningful research.

This is playing with statistics and cherry picking existing scientific
literature to produce a headline that propels an agenda.

This is propaganda of the highest order.

~~~
tofof
Why do you suggest fields other than anthropology or economics should be the
qualification for analyzing population-level economic effects?

Are you aware that the vast majority of scientific research is done by PhDs,
not MDs? And that both are doctorates?

> ... propels an agenda. This is propaganda of the highest order.

What's the agenda? And did that agenda apply to the 2011 paper calling for
more research in this area - "Evaluating the twin testosterone transfer
hypothesis: a review of the empirical evidence"[1]?

Was that agenda behind this 2012 Japanese study[2] which examined the ratio of
middle finger to pinky finger in twins? It's the same hormone transfer
hypothesis being examined. What propaganda could there possibly be about the
lengths of one's fingers?

Was that agenda present in 1993? [3]

Does that agenda include propoganda about females becoming better at
3d-spatial mental manipulation tasks? [4] If so, why?

Is propaganda about mouse behaviors part of that agenda? [5] If not, why not?
Still that same hormone transfer hypothesis being discussed.

Perhaps this 1988 paper on intrauterine position of gerbil fetuses [6] and
resulting variance in hormonal exposure from siblings was the birth of this
propaganda agenda?

Or is it more sinister than that, and this agenda extends all the way back to
1959 [7], causing these doctors to 'play with statistics' instead of doing
what they said - applying testosterone in-utero and watching for behavioral
changes? And then I suppose Dr Phoenix would do more 'playing' in 1967 [8]
instead of actually measuring testosterone uptake rates of the various tissues
he avoided actually manipulating eight years prior...

1:
[https://www.ncbi.nlm.nih.gov/pubmed/21893061](https://www.ncbi.nlm.nih.gov/pubmed/21893061)

2:
[https://www.ncbi.nlm.nih.gov/pubmed/22270254](https://www.ncbi.nlm.nih.gov/pubmed/22270254)

3:
[https://www.ncbi.nlm.nih.gov/pubmed/8240211](https://www.ncbi.nlm.nih.gov/pubmed/8240211)

4:
[https://www.ncbi.nlm.nih.gov/pubmed/21094200](https://www.ncbi.nlm.nih.gov/pubmed/21094200)

5:
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3212613/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3212613/)

6:
[https://www.ncbi.nlm.nih.gov/pubmed/3387473](https://www.ncbi.nlm.nih.gov/pubmed/3387473)

7:
[https://www.ncbi.nlm.nih.gov/pubmed/14432658](https://www.ncbi.nlm.nih.gov/pubmed/14432658)

8:
[https://www.ncbi.nlm.nih.gov/pubmed/6020216](https://www.ncbi.nlm.nih.gov/pubmed/6020216)

~~~
alwaysanagenda
Because the presupposition is that testosterone exposure in-utero is to blame.

Without actually addressing this claim by medical professionals, everything
else is manipulation of data to prove a point to address 'social policy' or an
economic agenda.

Moreover, the sample size, location, and dates of birth, are small and narrow,
comparatively speaking. You cannot make sweeping claims like this using such
small data set. But they do, and the "Material and Methods" section of this
paper goes to great length to explain how they've made these extrapolations.

This is statistical sausage.

I have no doubt you could write a similar paper that claims the opposite; that
females with male twins do much better. Just like this team did, you can find,
extrapolate and present data to support the idea.

------
Asparagirl
Cersei Lannister was not available for comment.

------
steventhedev
Notably, they didn't control for social effects by looking at female and male
sibling pairs with an age difference of 10-18 months. How much of this is
parents favoring the male sibling?

~~~
dooglius
"To separate the effects of fetal testosterone from postnatal socialization,
the research team repeated their analyses focusing only on female twins whose
twin sibling—either twin sister or twin brother—died shortly after birth, and
thus they were raised as singletons."

~~~
Mary-Jane
Shouldn't they have monitored both groups, using twins raised together as the
control group?

~~~
tofof
"repeated their analysis"

This effect exists in twins raised as singletons and twins raised with their
brother.

