Autism, Oxytocin, Rationality, & Extreme Male Brain Theory
All of the research questions that I could think of along with all of the material pertaining to them that I could find
NOTE: This is one of my unfinished articles. It’s been sitting unfinished on my dashboard for a couple months now, so I figured that for once, I’d actually follow the methodology of the blog (and the very title of the blog) that I’ve sworn myself to [more here] and just click the publish button. Maybe the embarassment of having unfinished work floating around will motivate me to finally finish it. Then again, the general topic is so peripheral to my main interests that I may never get around to finishing it.
Recently on twitter, the following anecdotal reddit thread [1] was brought to my attention.
The TLDR of the authors’ stories is that he is autistic, that he started spraying oxytocin nasal spray up his nose, and that when he does so, he feels that his autism is cured, that his social anxiety vanishes, that eye contact is no longer so uncomfortable, that he enjoys the company of his family to a greater degree, and that he can intuitively understand peoples’ feeling and social dynamics rather than having to engage in a draining task of consciously choosing every aspect of his behavior after logically figuring out what is socially appropriate to do.
The picture the author paints of what it’s like for him to not take oxytocin—is that everybody is playing a game whose rules were never explained to him, that he constantly feels negatively judged for breaking these rules, that he constantly feels anxiety about the prospect of breaking the rules again in the future when he’s forced to play again, and that people refuse to explain the rules of the game to him when he asks for them to be clarified. He gets the sense that when he asks for guidance, the other party sees the request as being analogous to being asked to define basic grammatical words/functions such as “and”, “the”, or “as”; such questions are often interpreted as being asked in bad faith, and when not, this doesn’t make it any easier for the other party to figure out how to answer them.
Encountering the story has since sparked my interest to do some cursory research to see what can be established with any degree of rigour regarding the general topic. An obvious first place to start was to look into any potential connections between oxytocin and autism:
Oxytocin & Autism:
Regarding the raw, correlational evidence, a recent 2021 meta-analysis [2] covering 1233 participants from 31 studies found autistic children to be 0.36sd lower in oxytocin levels than non-autistic children (d= -.36; 95%CI = [−0.61, −0.10]; p = 0.007):
No meta-analytic evidence for publication bias was found. Most studies were of oxytocin levels in the blood plasma of children, but some studies assessed oxytocin levels in saliva and in cerebrospinal fluid, and some studies assessed samples of adults. Effects did not appear to be appreciably moderated by any of these factors:
Ostan(2018) assessed the same sample with regards to both blood plasma and cerebrospinal fluid, and the effect sizes were nearly identical
The studies of saliva mostly agree with the blood plasma studies, but have much heterogeneity
The autistic groups in the adult samples had slightly higher average oxytocin levels (d=0.03) than controls, but the analysis was severely underpowered such that the effect size for adult samples was not significantly different from the effect size from samples of children; the 95% confidence intervals for the were enormous (95%CI = [−0.55, 0.61]; p = 0.92) and encompassed the meta-analytic effect size for children. Accordingly, there was much heterogeneity in the adult samples such that the paper (Andari 2010) with the second largest group difference in oxytocin levels (d ~= -1.9) studied an adult sample.
Thus, under the interpretation that the evidence does not suggest results do be significantly moderated by age,—the assertion that “The same effect probably also exists in adults.”—is more strongly supported by the results from the child samples than—the assertion that “There is no significant evidence for any effect among adults.”—is supported by the results from the adult samples.
Hypothetically however, if in the future it comes to be that new evidence is able to properly support the claim that the effect is moderated by age in this way, one potential hypothesis I had to offer was that the nature of Autism partially has to do with developmental biological phenomena such that some people naturally grow out of their Autism with age towards becoming indistinguishable from the typical person. If it turned out to be that this were true, then any study which follows a sample of Autistic children into adulthood would actually be comparing oxytocin levels among a normal group to oxytocin levels among a group comprised of both normal and Autistic people; the declining effect size wouldn’t be due statistical error, but due to an artifact of sampling problems. However, I’m only aware of one large study [3] which is capable of testing this, and it found that Autism is just as common among Adults as it is among children [3]. In the study, adults of various ages completed a phase 1 assessment, and another phase 2 assessment later on. The study was thus able to capture variance in age due to people being born in different years, and also variance in age due to individual subjects getting older. Controlling for year at birth, age was unrelated to the prevalence of Autism, and additionally, year at birth was also unrelated to the prevalence of autism [3]. In addition to falsifying my hypothesis, this is also interesting because it suggests that any popularly-perceived increases in rates of diagnoses for Autism are exclusively due to changes in diagnosis practices given that in this study, the constant standard of diagnosis did not correspond to any sort of differences in prevalence across birth year.
The results of the meta-analysis thus discussed [2] are also broadly consistent with another n=1422, 2021 meta-analysis on the same subject [5] which broadly covers the same material.
Randomized Placebo-Control Trials:
We do not however have to only rely on the correlational evidence. There has also been a meta-analysis of 28 RCTs from 2021 [4] which found the administration of oxytocin to have significant, positive effects on social functioning (but not on other aspects of autistic traits such repetitive behavior) in autistic people. The studies were small (N from all 28 studies only totaled up to 726) and were not pre-registered, but no decline effects were found, and in terms of effects on social functioning, no evidence for publication bias was found.
This is also consistent with the evidence pertaining to effects on the ability to recognize emotions when oxytocin is administered to typical people [6].
One research question which occurred to me was to see whether or not the medications typically given to treat autism (e.g. Adderall & Ritalin) have any effect on oxytocin levels. All I could find on the subject was a small RCT which found Ritalin to have a positive effect on oxytocin levels in certain conditions among children with ADHD [31], so I don’t put too much stock in the idea.
As an aside, one popsci claim I’ve heard of before is that oxytocin acts as a hormone which increases instinctive behaviour in general with a few manifestations of this being that it increases people’s trust in their in-groups while decreasing their trust in out-groups. An earlier small, k=8 & 10, n=317 & 505, 2011 meta-analysis [7] on the subject found support for the claim that administering oxytocin increases people’s trust in their in-groups (however this was the question with the smallest quantity of research pertaining to it), and found evidence against the claim that administering oxytocin decreases people’s trust in outgroups [7].
Autistic people should also be somewhat glad to hear that a rather small, k=5, n=223 meta-analysis on the risk of adverse side effects of the administration of oxytocin in autistic people [8] found no increase relative to placebo controls for reports of particular adverse side effects such as nasal discomfort, tiredness, irritability, diarrhea, or skin irritation, or for reports adverse side effects generally [8].
The Oxytocin-Receptor Gene:
Various studies have been done with a candidate gene approach with regards to what is thought to be ‘the’ gene ‘for’ oxytocin receptors (OXTR). Generally however, we should be very skeptical of candidate approaches to molecular genetics [more here & here/here], especially given the largely shared etiology of autism and intelligence [23]. For what it’s worth however, two small meta-analyses of candidate gene studies on the OXTR gene [24 & 25] have purported to be able to have results showing statistically significant effects on autism [24] and sociability [25]. With regards to the rs7632287, this may actually be worth taking seriously for once, as A) the effect size of the allele on autism (OR = 1.44 [24]) is unusually large for any one allele to have on any trait at all, and B) effect size for the allele allele reached a high threshold of statistical significance at p = 0.000005. Given this along with the fact that effects for the allele are replicated in multiple independent samples, and it may actually be reasonable to expect effects for the allele to replicate if examined again in a properly powered dataset.
Autism, Assortative Mating, & Extreme Male Brain Theory:
Here’s another tweet I saw later on twitter [9]:
Immediately, my answer was that such a phenomenon probably does not exist, let alone require such a theory to explain its existence:
Given extreme male brain theory of autism and given genetic similarity theory, it probably depends on the sex of the person in question; for males, no; for females, maybe. Basically, people select for spouses (and even friends) who are genetically similar to themselves, this is also true with regards to autism, autistic people are higher in masculinity than non-autistics people in various ways.
Assortative Mating / Genetic Similarity Theory & Autism:
Various phenomena have been observed which are broadly consistent with an idea known as genetic similarity theory where people will instinctively take a liking to others who are genetically similar to themselves in order to increase the fitness of their genes, even if they aren’t consciously or rigorously aware of what their kinship statuses are with various particular people.
An obvious manifestation of this logic which one would predict to occur is assortative mating, where people select for partners who are similar to themselves and are at an elevated risk of having a falling out with the partners who are especially different than themselves. Indeed, marital partners tend to be similar in attitudes, values, abilities, appearance, personality, ethnicity, behaviours, intelligence, etc [10]. Marital partners also tend to be more genetically similar to each other than random members of the population are to each other [11]. This is also true in terms of platonic, same-sex friends [12], and the background genetic similarity of the communities that friendship groups are formed within does not fully explain the genetic similarity of friends [12]. Pretty much all psychological traits are partially heritable [13], and friends tend to be more similar to each other in terms of the more heritable traits [14]. The longitudinal literature suggests that marital partners do not become more similar to each other over time, but rather that they select for similarity, break up over differences, and tend to have met in places frequented by those like themselves [10]. Additionally, couples tend to be more assortative in terms of the verbal tilt of their intellectual profiles than in the other aspects of intelligence which are less readily apparent [10]. Broadly, a picture of assortative mating is painted where people take a liking to those who are similar (especially genetically so) to themselves, and where people avoid selecting people that they dislike.
With regards to autism, autism is an incredibly heritable trait with meta-analytic heritability figures ranging from 64% - 91% depending on how the trait is defined [15], and of various psychiatric disorders, autism appears to be the one on which mating is most assortative (r ~= 0.46) [16], although there does appear to be a tendency for people who have some sort of psychiatric disorder to end up with a partner who also has some sort of psychiatric disorder without regards to the qualitative similarity of said disorders [16].
As an aside, the manner in which the heritability of autism depends on the definition of autism has to do with the idea that autism (along with various other personality and psychiatric disorders more generally) is continuous with normal variation on the continua of various traits on which the average person can be plotted, with autistic people just being those one the extreme ends of the distributions where differing further from the average becomes maladaptive [15, 17, 18, 19, 20, 21, & 22]; when the criteria for delineating ‘autistic’ from ‘normal’ are made more strict, the correlation between dizygotic twins in ‘autism’ rises, and the heritability of ‘autism’ falls [15].
The Extreme Male Brain Theory Of Autism:
There is a large literature documenting various ways in which autistic people are more physiologically and psychologically masculine than normal people. Given assortative mating for autism, this likely means that autistic women are given an advantage in their ability to relate to men while autistic men are faced with a harder time relating to women as an addition to their already low sociability.
Here’s my attempt to document this literature:
PREVALENCE: An enormous (k=54, n=13,784,284, n(autistic)=53,712) meta-analysis [26] from 2017 found autism to be more common among men than among women [26]. Given the sex differences in… m a s c u l i n i t y…, this is among the most obvious things to expect given an understanding of the condition as a disorder of abnormally high masculinity.
OXYTOCIN: With regards to the role of oxytocin, I’ve seen it claimed [27] that women are higher in levels of oxytocin in blood plasma; the paper I referenced just references a bunch of other papers on the topic, and going off of titles, it looks like a bunch of clinical, non-representative samples. I didn’t find anything else on this other than that paper aside from a meta-analysis showing oxytocin levels to vary with the menstrual cycle [32]. It does seem however that men and women respond differently to oxytocin [27, 28, & 29]. The paper from earlier [27] also reviews a bunch of literature on sex-biased expression of the OXTR gene:
“ Coming from the perspective of genetic variations in nonapeptide receptors, Walum et al. (2012) have found an association between the OTR variant rs7632287 and pair-bonding behaviors in women but not in men, whereas an earlier study found an association of an AVP receptor polymorphism and pair-bonding in men but not women (Walum et al., 2008). Furthermore, numerous studies in the growing OTR literature note sex-specific associations between genetic variants in the OTR gene and personality characteristics (Stankova et al., 2012), neural responses to emotionally salient cues (Tost et al., 2010), hypothalamic gray matter volume (Tost et al., 2010), and empathy (Wu et al., 2012), though other studies in this area have failed to find a sex bias (Rodrigues et al., 2009; Saphire-Bernstein et al., 2011; Feldman et al., 2012). ”
To add to this, I’ve encountered a paper [30] which claims sex-biased microRNA expression to be highly enriched in gene sets involved in autism.
MUTATIONAL LOAD: It is commonly thought that autism is a disorder of the x chromosome and that the increased prevalence of the condition among men is due to men lacking a backup-x chromosome to compensate when mutations arise on it. Indeed, a k=34, n=1542 meta-analysis from 2021 found fragile x syndrome among females to be associated with autism [33]; evidence for publication bias was evident from the funnel plot and confirmed by egger’s test, but the prevalence of autism among women with fragile x syndrome was still 12% after trim and fill correction was done. The genomes of autistic people have been found to be significantly enriched in de novo mutations [34], and there is evidence that autistic women are higher in mutational load than autistic men [35]. A large, high-quality population-based cohort study done Sweden has also found children sired by men over the age of 50 years old to be 1.79 times as likely to be autistic among women and 1.67 times as likely to be autistic among men [36].
It has been suggested that left-handedness is an indicator of mutational load [37]. I have not found any material which directly tests this, but if true, we might predict the prevalence of left-handedness to be higher among autistic people. Indeed, a small, k=21, n=1199 meta-analysis from 2016 [38] has found left-handedness to be more prevalent among autistic people; moreover, a k=144, n=1,787,629 meta-analysis [39] has found left-handedness to be more prevalent among men than among women.
It has also been suggested that homosexuality and transexuality are indicators of mutational load [37]. Again, I have not found any material which directly tests this, but if true, we might predict the prevalence of these conditions to be higher among autistic people. This seems to be the case: A) For its broadest result, one massive, n=641,860 study covering 5 datasets [40] found the prevalence of autism to be 5.53 times as higher (OR = 5.53, CI = [5.06, 6.04], p < 2 * 10^-16) among transgender and gender-diverse individuals than it is among cisgender people;
B) A systemic review from 2015 agrees that there seems to be a tendency for autism and gender dysphoria to co-occur [41]; and C) I’ve come across various small & medium scale studies whose results are consistent with the existence of such an association [42, 43, 44, 45, 46, 47, 48, & 49]
(Note: Keeping with the point of this blog [more here], I have not yet checked to see whether or not any of these papers [42-49] were included in the related systemic review [41]).
DIGIT RATIO: Somebody’s 2D:4D ratio, also sometimes just called their digit ratio, is the ratio of the length of their pointer finger (2nd finger starting from their thumb) to the length of their ring finger (4th finger starting from their thumb). So, for example, if I were to be a genetic abomination whose pointer fingers were twice as long as my ring fingers, then I would have a 2D:4D ratio of 2:1, or more simply, a digit ratio of 2. Having a low digit ratio is often understood to be a marker of having high testosterone levels, or to at least of having been exposed to high testosterone levels in the womb, which, as per the common understanding, would have permanent consequences for the fundamental organization of your physiology. Oddly enough however, I could not readily find material capable of testing either of these claims. This stated, a couple lines of evidence line up with digit ratios having something to do with masculinity:
SEX: A k=116, n=25049 meta-analysis [50] found men to be 0.28sd lower in digit ratio than women on the left hand, and 0.35sd lower in digit ratio on the right hand.
GRIP STRENGTH: A k=22, n=5271 meta-analysis from 2021 [51] found a small, negative correlation (r = −0.15, CI = [–0.20, −0.09]) between digit ratio and grip strength.
AGGRESSION: A k=32, n=13199 meta-analysis from 2017 [52] found a very small, negative (r = -0.036, p < .05) correlation between digit ratio and aggressive behavior (They report the correlation as positive under the logic of taking inverse digit ratios for the sake of ‘simplicity’, but the correlation is negative; those with more masculine digit ratios behave aggressively).
FACIAL MASCULINITY: A very small k=8, n=469 meta-analysis [53] (the authors of the meta-analysis even contributed a majority of the data analyzed in it) found a small, but statistically insignificant negative correlation between digit ratios and facial masculinity. This evidence can neither confirm nor deny the existence of such an association, I’m just including this because it was a research question of mine and this was all the material I could find which addresses.
HOMOSEXUALITY & TRANS-SEXUALITY: Vaguely relevant is this k=34, n=5828 meta-analysis [54] of digit ratio and sexual orientation; lesbian women had higher (more feminine) digit ratios than heterosexual women while gay men did not differ from straight men in digit ratio. Additionally, this k=17, n = 3674 meta-analysis from 2020 [55] found MtF transgenders to have higher digit ratios than cisgender men, but did not find digit ratio differences between FtM transgenders and cisgender women.
(Unrelated): LEFT-HANDEDNESS: This k=18, n=7247 meta-analysis from 2019 [56] found left-handedness to be related to low a low digit ratio on the right hand, but also to a high digit ratio on the left hand; effect sizes were very small. As discussed in the meta-analysis [56], the meta-analysis is also consistent with a very large, n=200741 study [57] which dwarves the meta-analytic sample.
Now for the moment we’ve all been waiting for, do autistic people have lower digit ratios than non-autistic people? Maybe. This k=16, n=2981 meta-analysis from 2021 [58] found autistic people to have significantly lower digit ratios than non-autistic people, but we can see in figure-4A that this finding was driven by a bunch of small studies while the larger studies found no such effects:
Additionally, regarding the analyses for all psychiatric disorders put together, here’s what the funnel plot looks like:
However, I am aware of a rather-large study which wasn’t included in the meta-analysis [59]. It included was 1896 participants, which is singlehandedly 64% of the size of the entire meta-analytic sample. The effect size in the paper is also huge: autistic people were found to be 0.58sd lower in digit ratio than non-autistic people [59]. Given this, I lean towards saying that autistic people probably are indeed low on average in digit ratio.
BRAIN SIZE: A k=126 meta-analysis from 2014 [60] found men to be 3.03sd higher in intracranial volume, 2.1sd higher in total brain volume (although with significant heterogeneity), and 3.35sd higher in cerebrum volume:
Additionally, the gray matter volume difference (2.13sd) was larger than the white matter volume difference (2.06sd), which perhaps indicates male brains to be higher in gyrification/folding. Many of the supplementary funnel plots visually seemed to indicate publication bias, but A) egger’s regression test was not formally conducted; and B) labeling was not done clearly enough to know which funnel plot applied to which analysis.which funnel plot applied to which analysis.
Turning to the research on autism and brain size,
A k=46, meta-analysis [61] found autistic people to be .32sd higher in total brain volume (k=16, n=776, CI = [.16, .49]), with insignificant results for tests for heterogeneity (I^2 = 22%; χ^2 = 19.23, p=.21) and publication bias (p=.43). Regarding intracranial volume (k=4, n=184) and cerebrum volume (k=8, n=318), effect sizes for autism were 0.51sd (CI = [0.20, 0.81]) and 0.62sd (CI = [0.39, 0.86]) respectively.
Another meta-analysis [62] on the subject is larger (k=71, n>5000) and more recent (2015), but with a worse operationalization of the gaps; ASD participants were compared with controls in ‘macrocephaly’ (and ‘brain overgrowth), defined as having a head circumference (or brain volume) greater than 2SD above the mean. As such, with the results artificially dichotomized, effect sizes were expressed in terms of odds ratios. With 822/5225 autistic participants being macrocephalic, the odds ratio for head circumference was 6.74 (CI = [5.24, 8.67], p = 5.20 * 10^-50). In terms of MRI-assessed total brain volume, the odds ratio for brain overgrowth was 1.93 (CI = [1.68, 2.20], p = 1.21 * 10^-21), with 142/1558 autistic participants displaying brain overgrowth.
I however find both meta-analyses to be a bit suspect because they just cover a bunch of low-N studies. In light of this, it is worth mentioning that there exists a longitudinal, seemingly representative, n=889 study of infants from Japan [63] which should lend a bit of extra confidence to these results. Even correcting for sex/age/weight/height, Head circumference was found to be significantly larger in the autistic group than the control group. Head circumference growth rates were also significantly higher among the autistic group, with no such differences existing at birth.
The brain size difference is not just a triviality of a larger skull size and lower brain density. The brain size difference comes with a higher number of neurons [64] and a thicker cortex [65].
There is also a bit of a literature about how the brain size differences relate to some of the various behavioral aspects of autism.
I
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Caldwell, H. K. (2018). Oxytocin and sex differences in behavior. Current Opinion in Behavioral Sciences, 23, 13-20. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.cobeha.2018.02.002
Ziats, M. N., & Rennert, O. M. (2014). Identification of differentially expressed microRNAs across the developing human brain. Molecular psychiatry, 19(7), 848-852. Retrieved form https://sci-hub.ru/https://doi.org/10.1038/mp.2013.93
Levi-Shachar, O., Gvirts, H. Z., Goldwin, Y., Bloch, Y., Shamay-Tsoory, S., Zagoory-Sharon, O., ... & Maoz, H. (2020). The effect of methylphenidate on social cognition and oxytocin in children with attention deficit hyperactivity disorder. Neuropsychopharmacology, 45(2), 367-373. Retrieved from https://www.nature.com/articles/s41386-019-0522-5.pdf
Engel, S., Klusmann, H., Ditzen, B., Knaevelsrud, C., & Schumacher, S. (2019). Menstrual cycle-related fluctuations in oxytocin concentrations: a systematic review and meta-analysis. Frontiers in neuroendocrinology, 52, 144-155. Retrieved from https://sci-hub.ru/10.1016/j.yfrne.2018.11.002
Marlborough, M., Welham, A., Jones, C., Reckless, S., & Moss, J. (2021). Autism spectrum disorder in females with fragile X syndrome: a systematic review and meta-analysis of prevalence. Journal of neurodevelopmental disorders, 13(1), 1-19. Retrieved from https://sci-hub.ru/10.1186/s11689-021-09362-5
Yuen, R. K., Merico, D., Cao, H., Pellecchia, G., Alipanahi, B., Thiruvahindrapuram, B., ... & Scherer, S. W. (2016). Genome-wide characteristics of de novo mutations in autism. NPJ genomic medicine, 1(1), 1-10. Retrieved from https://sci-hub.ru/https://doi.org/10.1038/npjgenmed.2016.27
Jacquemont, S., Coe, B. P., Hersch, M., Duyzend, M. H., Krumm, N., Bergmann, S., ... & Eichler, E. E. (2014). A higher mutational burden in females supports a “female protective model” in neurodevelopmental disorders. The American Journal of Human Genetics, 94(3), 415-425. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.ajhg.2014.02.001
Frans, E. M., Sandin, S., Reichenberg, A., Långström, N., Lichtenstein, P., McGrath, J. J., & Hultman, C. M. (2013). Autism risk across generations: a population-based study of advancing grandpaternal and paternal age. JAMA psychiatry, 70(5), 516-521. Retrieved from https://sci-hub.ru/https://doi.org/10.1001/jamapsychiatry.2013.1180
Dutton, E., Madison, G., & Dunkel, C. (2018). The mutant says in his heart,“there is no god”: The rejection of collective religiosity Centered around the worship of moral gods is associated with high mutational load. Evolutionary Psychological Science, 4(3), 233-244. Retrieved from https://sci-hub.ru/https://doi.org/10.1007/s40806-017-0133-5
Markou, P., Ahtam, B., & Papadatou-Pastou, M. (2017). Elevated levels of atypical handedness in autism: meta-analyses. Neuropsychology review, 27(3), 258-283. Retrieved from https://sci-hub.ru/https://doi.org/10.1007/s11065-017-9354-4
Papadatou-Pastou, M., Martin, M., Munafò, M. R., & Jones, G. V. (2008). Sex differences in left-handedness: a meta-analysis of 144 studies. Psychological bulletin, 134(5), 677. Retrieved from https://sci-hub.ru/https://doi.org/10.1037/a0012814
Warrier, V., Greenberg, D. M., Weir, E., Buckingham, C., Smith, P., Lai, M. C., ... & Baron-Cohen, S. (2020). Elevated rates of autism, other neurodevelopmental and psychiatric diagnoses, and autistic traits in transgender and gender-diverse individuals. Nature communications, 11(1), 1-12. Retrieved from https://sci-hub.ru/https://doi.org/10.1038/s41467-020-17794-1
Glidden, D., Bouman, W. P., Jones, B. A., & Arcelus, J. (2016). Gender dysphoria and autism spectrum disorder: A systematic review of the literature. Sexual Medicine Reviews, 4(1), 3-14. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.sxmr.2015.10.003
Cooper, K., Smith, L. G., & Russell, A. J. (2018). Gender identity in autism: Sex differences in social affiliation with gender groups. Journal of Autism and Developmental Disorders, 48(12), 3995-4006. Retrieved from https://sci-hub.ru/https://doi.org/10.1007/s10803-018-3590-1
Nobili, A., Glazebrook, C., Bouman, W. P., Glidden, D., Baron-Cohen, S., Allison, C., ... & Arcelus, J. (2018). Autistic traits in treatment-seeking transgender adults. Journal of Autism and Developmental Disorders, 48(12), 3984-3994. Retrieved from https://sci-hub.ru/https://doi.org/10.1007/s10803-018-3557-2
Murphy, J., Prentice, F., Walsh, R., Catmur, C., & Bird, G. (2020). Autism and transgender identity: Implications for depression and anxiety. Research in Autism Spectrum Disorders, 69, 101466. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.rasd.2019.101466
Stagg, S. D., & Vincent, J. (2019). Autistic traits in individuals self-defining as transgender or nonbinary. European psychiatry, 61, 17-22. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.eurpsy.2019.06.003
Jones, R. M., Wheelwright, S., Farrell, K., Martin, E., Green, R., Di Ceglie, D., & Baron-Cohen, S. (2012). Brief report: female-to-male transsexual people and autistic traits. Journal of Autism and Developmental Disorders, 42(2), 301-306. Retrieved from https://sci-hub.ru/https://doi.org/10.1007/s10803-011-1227-8
Pasterski, V., Gilligan, L., & Curtis, R. (2014). Traits of autism spectrum disorders in adults with gender dysphoria. Archives of Sexual Behavior, 43(2), 387-393. Retrieved from https://sci-hub.ru/https://doi.org/10.1007/s10508-013-0154-5
Gilmour, L., Schalomon, P. M., & Smith, V. (2012). Sexuality in a community based sample of adults with autism spectrum disorder. Research in Autism Spectrum Disorders, 6(1), 313-318. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.rasd.2011.06.003
George, R., & Stokes, M. A. (2018). Sexual orientation in autism spectrum disorder. Autism Research, 11(1), 133-141. Retrieved from https://sci-hub.ru/https://doi.org/10.1002/aur.1892
Hönekopp, J., & Watson, S. (2010). Meta‐analysis of digit ratio 2D: 4D shows greater sex difference in the right hand. American Journal of Human Biology, 22(5), 619-630. Retrieved from https://sci-hub.ru/https://doi.org/10.1002/ajhb.21054
Pasanen, B. E., Tomkinson, J. M., Dufner, T. J., Park, C. W., Fitzgerald, J. S., & Tomkinson, G. R. (2021). The relationship between digit ratio (2D: 4D) and muscular fitness: A systematic review and meta‐analysis. American journal of human biology, e23657. Retrieved from https://sci-hub.ru/https://doi.org/10.1002/ajhb.23657
Turanovic, J. J., Pratt, T. C., & Piquero, A. R. (2017). Exposure to fetal testosterone, aggression, and violent behavior: A meta-analysis of the 2D: 4D digit ratio. Aggression and Violent Behavior, 33, 51-61. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.avb.2017.01.008
Hönekopp, J. (2013). Digit ratio (2D: 4D) and male facial attractiveness: new data and a meta-analysis. Evolutionary Psychology, 11(5), 147470491301100501. Retrieved from https://sci-hub.ru/https://doi.org/10.1177/147470491301100501
Grimbos, T., Dawood, K., Burriss, R. P., Zucker, K. J., & Puts, D. A. (2010). Sexual orientation and the second to fourth finger length ratio: a meta-analysis in men and women. Behavioral neuroscience, 124(2), 278. Retrieved from https://sci-hub.ru/https://doi.org/10.1037/a0018764
Siegmann, E. M., Müller, T., Dziadeck, I., Mühle, C., Lenz, B., & Kornhuber, J. (2020). Digit ratio (2D: 4D) and transgender identity: new original data and a meta-analysis. Scientific reports, 10(1), 1-11. Retrieved from https://sci-hub.ru/https://doi.org/10.1038/s41598-020-72486-6
Richards, G., Medland, S. E., & Beaton, A. A. (2021). Digit ratio (2D: 4D) and handedness: A meta-analysis of the available literature. Laterality, 26(4), 421-484. Retrieved from https://sci-hub.ru/https://doi.org/10.1080/1357650X.2020.1862141
Manning, J. T., & Peters, M. (2009). Digit ratio (2D: 4D) and hand preference for writing in the BBC Internet Study. Laterality, 14(5), 528-540. Retrieved from https://sci-hub.ru/https://doi.org/10.1080/13576500802637872
Fusar-Poli, L., Rodolico, A., Sturiale, S., Carotenuto, B., Natale, A., Arillotta, D., ... & Aguglia, E. (2021). Second-to-fourth digit ratio (2D: 4D) in psychiatric disorders: A systematic review of case-control studies. Clinical Psychopharmacology and Neuroscience. Retrieved from https://pdfs.semanticscholar.org/0888/eadb155f3aabddb498d1a783d3c4d4875ae5.pdf
Hönekopp, J. (2012). Digit Ratio 2 D: 4 D in Relation to Autism Spectrum Disorders, Empathizing, and Systemizing: A Quantitative Review. Autism Research, 5(4), 221-230. Retrieved from https://sci-hub.ru/https://doi.org/10.1002/aur.1230
Ruigrok, A. N., Salimi-Khorshidi, G., Lai, M. C., Baron-Cohen, S., Lombardo, M. V., Tait, R. J., & Suckling, J. (2014). A meta-analysis of sex differences in human brain structure. Neuroscience & Biobehavioral Reviews, 39, 34-50. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.neubiorev.2013.12.004
Stanfield, A. C., McIntosh, A. M., Spencer, M. D., Philip, R., Gaur, S., & Lawrie, S. M. (2008). Towards a neuroanatomy of autism: a systematic review and meta-analysis of structural magnetic resonance imaging studies. European psychiatry, 23(4), 289-299. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.eurpsy.2007.05.006
Sacco, R., Gabriele, S., & Persico, A. M. (2015). Head circumference and brain size in autism spectrum disorder: a systematic review and meta-analysis. Psychiatry Research: Neuroimaging, 234(2), 239-251. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.pscychresns.2015.08.016
Fukumoto, A., Hashimoto, T., Mori, K., Tsuda, Y., Arisawa, K., & Kagami, S. (2011). Head circumference and body growth in autism spectrum disorders. Brain and Development, 33(7), 569-575. Retrieved from https://sci-hub.ru/https://doi.org/10.1016/j.braindev.2010.09.004
Truly note-tier note stuff (section 1):
Much of it likely written to only make sense to me:
Meta-analysis of brain size & autism:
https://www.sciencedirect.com/science/article/abs/pii/S0925492715300573
2020 Meta-analysis of MRI studies on autism & brain size:
https://sci-hub.ru/10.1016/j.eurpsy.2007.05.006
Growth in brain size associated with repetitive behavior among autists:
https://sci-hub.ru/10.1016/j.biopsych.2013.08.013
Male-to-Female Ratio in Autism Prevalence Meta-Analysis:
https://sci-hub.ru/10.1016/j.jaac.2017.03.013
Testing the Empathizing–Systemizing theory of sex differences and the Extreme Male Brain theory of autism in half a million people:
https://sci-hub.ru/10.1073/pnas.1811032115
Test of extreme male brain theory: predicted maleness scores higher among autistics:
https://onlinelibrary.wiley.com/doi/abs/10.1002/aur.2537
review of evidence pertaining to extreme male brain theory of autism:
https://sci-hub.ru/10.1016/B978-0-444-53630-3.00011-7
meta-analysis of prevalence of autism among females with fragile X syndrome:
https://sci-hub.ru/10.1186/s11689-021-09362-5
meta-analyses of the prevalence of schizophrenia among autists:
https://sci-hub.ru/10.1007/s10803-017-3328-5
https://sci-hub.ru/10.1016/j.schres.2019.07.050
Schizophrenia, autism, and intelligence profile:
https://sci-hub.ru/10.3389/fpsyt.2020.00187
Stuff on intelligence profile of autism:
https://psycnet.apa.org/record/2008-05020-003
https://sci-hub.se/10.1007/s10803-013-2025-2
https://www.frontiersin.org/articles/10.3389/fnins.2016.00300/full
Autism & anxiety meta-analyses:
https://sci-hub.ru/10.1007/s10826-017-0687-7
https://sci-hub.ru/10.1177/1362361320953253
Large population-based study: Blacks & Hispanics higher in autism than whites:
https://sci-hub.ru/10.1542/peds.2013-3928
Autism, Sex, & Cortical Morphometry:
https://www.nature.com/articles/s41380-019-0420-6
Autism & cerebellar volume meta-analysis:
https://sci-hub.se/10.1016/j.biopsych.2017.09.029
Meta-analysis of sex differences in brain structure: (including cerebellum):
https://sci-hub.se/10.1016/j.neubiorev.2013.12.004
Etiology/characteristics of Autism, and involvement of cerebellum:
https://sci-hub.se/10.3389/fnsys.2013.00015
https://sci-hub.se/10.1007/s12311-012-0355-9
https://sci-hub.ru/10.1016/B978-0-12-418700-9.00001-0
Characteristics of autism:
https://onlinelibrary.wiley.com/doi/abs/10.1002/9781118911389.hautc13
https://www.sciencedirect.com/science/article/abs/pii/0891422295000445
-social impairment
-repetitive behavior
-restricted interests
-masculine intelligence profile
-sensitivity to stimulus
-homosexuality, mutational load, pedophillia, left-handedness
Autism and epilepsy meta-analyses (to do with sensitivity to stimuli?):
https://sci-hub.ru/10.1177/1362361320951370
https://journals.sagepub.com/doi/abs/10.1177/13623613211045029
Autism and abnormal walking styles meta-analysis:
https://sci-hub.ru/10.1002/aur.2443
Meta-analysis of menstrual cycle-related fluctuations in oxytocin concentrations:
https://sci-hub.ru/10.1016/j.yfrne.2018.11.002
IQ, Handedness, and Pedophilia:
https://sci-hub.ru/10.1007/s11194-007-9049-0
Autism & Handedness meta-analysis:
https://sci-hub.ru/10.1007/s11065-017-9354-4
Autism and gender identity:
https://sci-hub.ru/10.1007/s13178-020-00489-z
https://sci-hub.ru/10.1007/s10803-018-3590-1
Meta-analysis: Sex differences in 2D:4D ratio larger on the right hand:
https://sci-hub.ru/10.1002/ajhb.21054
older meta-analysis on sex differences in digit ratio:
https://sci-hub.ru/10.1037/a0012814
Autists have lower 2D:4D ratios than non-autists. This difference is also larger in terms of the right hand. However, among autists, digit ratio is not associated with position on the empathizing vs systematizing spectrum:
https://sci-hub.ru/10.1002/aur.1230
Regional gray matter volumetric changes in autism associated with social and repetitive behavior symptoms:
https://sci-hub.ru/10.1186/1471-244X-6-56
Genetic advancements in autism:
https://sci-hub.ru/10.1007/s10803-020-04685-z
Biomarkers of autism:
https://sci-hub.ru/10.1016/j.cca.2019.12.009
Dutton:
https://www.bitchute.com/video/zUvErnCQFByt/
https://www.youtube.com/watch?v=uUy-lpe8WqM
Sampling, Autism, & IQ:
1) https://molecularautism.biomedcentral.com/articles/10.1186/s13229-019-0260-x
The papers whose authority paper 1 defers to:
https://www.jstor.org/stable/pdf/24806043.pdf
https://sci-hub.ru/10.1017/S0033291710000991
https://sci-hub.se/10.1192/bjp.172.3.200 (this paper only cites a bunch of others)
https://sci-hub.se/10.1023/B:JADD.0000029550.19098.77
https://www.cdc.gov/mmwr/pdf/ss/ss6302.pdf
The enormous emergency department sample study analyzed by paper 1: https://sci-hub.ru/10.1007/s10803-016-2820-7 See supplementary notes 1 & 2 for more.
2) https://www.frontiersin.org/articles/10.3389/fnins.2016.00300/full (‘autism as high iq’ paper):
The papers whose authority paper 2 defers to:
https://sci-hub.ru/10.1111/j.1467-9280.2007.01954.x
https://sci-hub.ru/10.1016/j.bandc.2007.09.008
https://sci-hub.ru/10.1007/s10803-014-2270-z
FSIQ and IQ profile of ASPD vs HFA: dubious sampling practices, but it’s a meta-analysis
https://sci-hub.se/10.1007/s10803-013-2025-2
Truly note-tier note stuff (section 2):
Much of it likely written to only make sense to me:
Random:
Autism and object personification:
https://journals.sagepub.com/doi/10.1177/1362361318793408?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
Meta-analysis of brain size & autism:
https://www.sciencedirect.com/science/article/abs/pii/S0925492715300573
Regional grey matter volumetric changes in autism associated with social and repetitive behaviour symptoms:
https://sci-hub.ru/10.1186/1471-244X-6-56
2020 Meta-analysis of MRI studies on autism & brain size:
https://sci-hub.ru/https://doi.org/10.1016/j.eurpsy.2007.05.006
Growth in brain size associated with repetitive behaviour among autists:
https://sci-hub.ru/10.1016/j.biopsych.2013.08.013
Autism and male brain-ness:
https://onlinelibrary.wiley.com/doi/10.1002/aur.2537Testing the Empathizing–Systemizing theory of sex differences and the Extreme Male Brain theory of autism in half a million people:
https://sci-hub.ru/10.1073/pnas.1811032115
review of evidence pertaining to extreme male brain theory of autism:
https://sci-hub.ru/10.1016/B978-0-444-53630-3.00011-7
Test of extreme male brain theory: predicted maleness scores higher among autistics:
https://onlinelibrary.wiley.com/doi/abs/10.1002/aur.2537
Stuff on intelligence profile of autism:
https://psycnet.apa.org/record/2008-05020-003
https://sci-hub.se/10.1007/s10803-013-2025-2
https://www.frontiersin.org/articles/10.3389/fnins.2016.00300/full
Visuo-Spatial Performance in Autism: A Meta-analysis:
https://link.springer.com/article/10.1007/s10803-014-2188-5
A Meta-Analysis of Working Memory Impairments in Autism Spectrum Disorders:
https://link.springer.com/article/10.1007/s11065-016-9336-y
Autism & anxiety meta-analyses:
https://sci-hub.ru/10.1007/s10826-017-0687-7
https://sci-hub.ru/10.1177/1362361320953253
Large population-based study: Blacks & Hispanics higher in autism than whites:
https://sci-hub.ru/10.1542/peds.2013-3928
Autism, Sex, & Cortical Morphometry:
https://www.nature.com/articles/s41380-019-0420-6
Autism & cerebellar volume meta-analysis:
https://sci-hub.se/10.1016/j.biopsych.2017.09.029
Meta-analysis of sex differences in brain structure: (including cerebellum):
https://sci-hub.se/10.1016/j.neubiorev.2013.12.004
Etiology/characteristics of Autism, and involvement of cerebellum:
https://sci-hub.se/10.3389/fnsys.2013.00015
https://sci-hub.se/10.1007/s12311-012-0355-9
https://sci-hub.ru/10.1016/B978-0-12-418700-9.00001-0
Characteristics of autism:
https://onlinelibrary.wiley.com/doi/abs/10.1002/9781118911389.hautc13
https://www.sciencedirect.com/science/article/abs/pii/0891422295000445
-social impairment
-repetitive behaviour
-restricted interests
-masculine intelligence profile
-sensitivity to stimulus
Autism and epilepsy meta-analyses (to do with sensitivity to stimuli?):
https://sci-hub.ru/10.1177/1362361320951370
https://journals.sagepub.com/doi/abs/10.1177/13623613211045029
Autism and abnormal walking styles meta-analysis:
https://sci-hub.ru/10.1002/aur.2443
Genetic advancements in autism:
https://sci-hub.ru/10.1007/s10803-020-04685-z
Biomarkers of autism:
https://sci-hub.ru/10.1016/j.cca.2019.12.009
Dutton:
https://www.bitchute.com/video/zUvErnCQFByt/
Schizo:
Sex differences in schizophrenia meta-analysis:
https://jamanetwork.com/journals/jamapsychiatry/article-abstract/207514
meta-analyses of the prevalence of schizophrenia among autists:
https://sci-hub.ru/10.1007/s10803-017-3328-5
https://sci-hub.ru/10.1016/j.schres.2019.07.050
Schizophrenia, autism, and intelligence profile:
https://sci-hub.ru/10.3389/fpsyt.2020.00187
Meta-Analysis of Cognitive Performance in Neurodevelopmental Disorders during Adulthood: Comparisons between Autism Spectrum Disorder and Schizophrenia on the Wechsler Adult Intelligence Scales:
https://www.frontiersin.org/articles/10.3389/fpsyt.2020.00187/full
Vasopressin Stuff From Bigot Watch:
https://www.jci.org/articles/view/144450
https://www.science.org/doi/10.1126/scitranslmed.aau7356
https://www.science.org/doi/10.1126/scitranslmed.aat7838
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6750159/
(still need to know sex-differences in vasopressin expression)
Sampling, Autism, & IQ:
Paper 1):
https://molecularautism.biomedcentral.com/articles/10.1186/s13229-019-0260-x
The papers whose authority paper 1 defers to:
https://www.jstor.org/stable/pdf/24806043.pdf
https://sci-hub.ru/10.1017/S0033291710000991
https://sci-hub.se/10.1192/bjp.172.3.200 (this paper only cites a bunch of others)
https://sci-hub.se/10.1023/B:JADD.0000029550.19098.77
https://www.cdc.gov/mmwr/pdf/ss/ss6302.pdf
The enormous emergency department sample study analysed by paper 1: https://sci-hub.ru/10.1007/s10803-016-2820-7 See supplementary notes 1 & 2 for more.
Paper 2):
https://www.frontiersin.org/articles/10.3389/fnins.2016.00300/full (‘autism as high iq’ paper):
The papers whose authority paper 2 defers to:
https://sci-hub.ru/10.1111/j.1467-9280.2007.01954.x
https://sci-hub.ru/10.1016/j.bandc.2007.09.008
https://sci-hub.ru/10.1007/s10803-014-2270-z
FSIQ and IQ profile of ASPD vs HFA: dubious sampling practises, but it’s a meta-analysis
https://sci-hub.se/10.1007/s10803-013-2025-2
Meta-analysis:
Excluding individuals with full-scale IQ below 70 on the wechsler’s test, autistics had an average full-scale IQ of 98.0 and schizophrenics had an average IQ of 90.8:
https://www.frontiersin.org/articles/10.3389/fpsyt.2020.00187/full
Currently used project links for the substack post:
https://sci-hub.se/10.1016/j.biopsych.2017.09.029
https://sci-hub.ru/10.1016/j.biopsych.2013.08.013
https://www.frontiersin.org/articles/10.3389/fnins.2016.00300/full#B6
https://sci-hub.ru/https://doi.org/10.3389/fnins.2016.00300 (currently on brain size stuff)
https://sci-hub.ru/10.1016/j.neuropsychologia.2009.01.012
https://www.tandfonline.com/doi/abs/10.3200/SOCP.146.4.423-439