Do you know if T sensitivity has been examined for differences by race? For example, imagine that blacks produced twice as much of the T receptor. This should get them somewhat more masculinization at the same concentration of T.What I think is undeniable is that "masculinization" is not simply a function of circulating testosterone levels and Rushton's notion of testosterone as a "master switch" that neatly explains myriad racial differences is overly simplistic at best.
Racial variation exists in the Androgen Receptor gene, but there's no reason to assume this variation underlies global differences in "T sensitivity" between races, or that racial differences in "masculinization" in a given domain should imply similar racial differences in masculinization in every other domains. Ultimately, the androgen/AR pathway signals/regulates genes, which themselves vary between populations. Without knowing what's happening downstream of the AR, racial differences in the AR gene are not terribly informative.
To give a concrete example of variation in the AR gene failing to predict a racial difference in a phenotype:
The most-studied polymorphism on the Androgen Receptor gene is a CAG repeat found to be "inversely correlated with transcriptional activity by the androgen receptor". Blacks average fewer repeats than whites, implying increased transcription by the AR in blacks. Intra-racially, a lower number of CAG repeats is associated with higher sperm concentrations. If those facts led you to predict black men have higher sperm counts than white men, you predicted wrong.
Could the differences in sperm concentration in various geographical areas be related to the ethnic origin of the studied populations? From the results shown in Table 3 it seems that the MSC of healthy men might be lower in Africa and South East Asia compared to other parts of the world.I'm unable to find direct comparisons between white Americans and American blacks, but the evidence I'm aware of is consistent with lower sperm counts in the latter: autopsy weighing indicates American blacks have smaller testes than whites. Another autopsy study:
[Semen quality and male reproductive health: the controversy about human sperm concentration decline]
The mean sperm density among the fertile population in this series was 71.2 million/ml which is statistically greater than the value of 46.8 million/ ml observed in the infertile marriage population (P<0.001). The mean sperm count reported in the literature for the Caucasian fertile population is higher, with a range between 79-137 million/ ml [Seminal analysis in fertile and infertile Nigerian men]
For these preliminary studies, testes from five non-Hispanic Caucasian, five Hispanic, and five African American males of ages 28.2 ± 1.3, 27.8 ± 1.6, and 28.2 ± 1.3 years, respectively, were evaluated. Based on this small sample of men, there were no statistical differences among groups, respectively, for paired parenchymal weight (44.8 ± 5.3, 40.7 ± 1.8, and 34.8 ± 4.6 g), for daily sperm production per gram of testicular parenchyma (4.9 ± 0.3, 5.1 ± 0.7, and 4.3 ± 0.5 X 106/g), or for daily sperm production per man (224 ± 36, 211 ± 35, and 157 ± 33 X 106).These findings are not statistically significant due to the very small sample sizes, but they are consistent with the other evidence.
12 comments:
You didn't link to Guy White's post where you argued with Peter Frost in the relevant threads, so I'll put it here for the benefit of readers.
Very interesting post. You have done some really good work on Rushton’s theories -- which so many take as the gospel.
On a related subject, I have heard of a study by Masters and Johnson that found that white men had larger penises than blacks and other non-whites. Are you familiar with that study, n/a? And if so, do you know how authoritative that study is?
DS,
I find no evidence Masters and Johnson ever published a study of that sort. I think the numbers misattributed to Masters and Johnson may actually come from a large internet survey.
n/a,
You may be right. However, I did a quick internet search and I found a study by Masters and Johnson referenced many times. Here are a couple of the sites that I found that mentioned the study:
http://www.uwire.com/Article.aspx?id=3750780
http://www.sex-project.com/myths.shtml
It’s somewhat hard to believe that so many people can be either mistaken or lying.
"Without knowing what's happening downstream of the AR, racial differences in the AR gene are not terribly informative".
Testosterone and Greenland Inuit
"Testosterone has a wide range of physiological, morphological, and behavioral effects that in one way or another improve male reproductive success, particularly under conditions of intense sexual competition. These effects may be achieved not only by raising the concentration of testosterone in the bloodstream, but also by making androgen receptors more effective or by converting testosterone into the physiologically more active DHT (5α-dihydrotestosterone). Because such changes multiply the actual impact of testosterone on the human organism, we may underestimate this impact by looking only at blood testosterone levels. For instance, East Asians have the lowest incidences of prostrate cancer, yet their blood testosterone levels are intermediate between those of white and black Americans. They do, however, have less 5α-reductase than either white or black Americans, this being the enzyme that converts testosterone into DHT (Greenlanders are genetically predisposed to a lower activity in testosterone to 5α-dihydrotestosterone turnover and to lower AR activity,."
This may not make them any cleverer
Testosterone miscellany ,
"in an animal model, "cognitive-enhancing effects" of "5alpha-reduced androgen [metabolites]" were recently demonstrated".
[John Manning has a hypothesis about the androgen receptor increasing neural speed and G when it has the structure considered insensitive(long glutamine chain).]
A mating system that would evolve big testicles is the opposite of one that would select for a particularly masculinized physique.
"Chimps live in polygamous groups where several males may share a female. And when a female chimp ovulates, she does a lot of monkeying around: they copulate up to 50 times a day with a dozen different males [Although that's a simplification - females become more selective in their mating around ovulation and high-ranking males have a substantial reproductive advantage according to paternity tests]
Gorillas weigh four times as much as chimps, but chimps’ testicles weigh four times’ as much as gorillas’. Anatomical clues about a species’ mating system: the bigger the balls, the more polygamous the females. [Note however that polygamous chimps females are relatively free agents. Gorilla females are the property of a single male as one of his harem, Gorillas are polygynous]
Unlike chimpanzees, silverback alpha males take possession of a harem of female gorillas. Gorillas rarely have intercourse, because for males with a harem, sexual access is guaranteed. Therefore, [they] only needed a small amount of sperm and, consequently, a small payload. So, gorillas evolved testicles that were small "
Male-male competition sellected for Gorillas that areg especially large and muscular. While African agriculturists are not bigger than north Europeans it ought to be remembered that humans fight with throwing weapons. Luckily a test of the abilty to explosively orientate oneself to a flying object exists.
Wikipedia Running back - race
"In recent years running back has been almost exclusively a position for African-American players; Brian Leonard is the only white running back in the NFL aside from backups.[1] There have been no white starting running backs in the NFL the last few years."
I think the power to weight ratio and type of spatial awareness useful for surviving ballistic violence is clearly superior in African Americans.
Moreover "despite their low 25(OH)D levels, blacks have lower rates of osteoporotic fractures".
Tod,
I said downstream, not upstream. Obviously, variation upstream of the AR -- which may include any number of factors in addition to circulating testosterone and DHT concentrations -- matter as well, but your copy-and-past is not very relevant to discussion of black-white differences.
"A mating system that would evolve big testicles is the opposite of one that would select for a particularly masculinized physique."
Not really.
As for the position of RB being primarily "a test of the abilty to explosively orientate oneself to a flying object", you obviously know nothing about football. Note: "Running".
Please show me statistics indicating blacks are better at catching footballs or evidence that blacks have advantage over whites in any aspect of "spatial awareness".
As for throwing ability . . .
David Smith,
"It’s somewhat hard to believe that so many people can be either mistaken or lying."
It only takes one dishonest person to put the misinformation out there. I don't find it at all surprising that many people repeat information on the internet without checking references.
Here is the internet survey which I believe is the ultimate source of the numbers.
http://www.sizesurvey.com/result.html
"Surprisingly, it would appear from Figure 5, that contrary to popular myth, Black males have shorter erect lengths than their Caucasian counterparts. However, due to the small sample size and large variation in lengths, this "difference" is not statistically significant. The average flaccid length among Blacks however was 93.8mm (3.7") compared to 87.7mm (3.4") for Caucasians, which may be responsible for the impression that Black men have greater erect dimensions. Again, I emphasize that these observations must remain tentative."
"It is also interesting to note that the vast majority of Black subjects stated that they tended to be well endowed; an opinion which was not borne out by the results of this study."
, you obviously know nothing about football.
Guilty, but those who do - and run the teams - are also in thrall to similar ideas.
Cornerbacks are a better illustration of where black superiority is clearest. To be clear;I think these abilities originated with selection for avoiding projectiles
"There are no white starting cornerbacks in the NFL out of 64 players who start at that position. In fact, there are no white cornerbacks in the entire league". www.castefootball
Knowing everthing about football and trying pick the best team also puts one at risk of buying into the 'myth'.
n/a,
I agree that there exist further variables along the road from T to masculinization.
If there's one way to more or less find out if the androgen system has much to do with race differences in masculinity, it's probably by looking at the expression levels of the entire androgen receptor transcriptome, by quantifying RNA.
To be sure, this approach would not capture every influence that goes into masculinity. For example there are probably genes - let's say, some gene controling muscle mass - that are indeed in the androgen transcriptome, and have the exact same expression levels between races. Yet there might be a polymorphism in the protein itself which differs by race and contributes to racial muscle mass differences.
And yet, if 85% of the genes in the androgen transcriptome were significantly more intensely expressed in africans than in asians, we could it least say it's "very likely" that differences in the androgen system (whether it be in T levels, DHT levels, receptor density, receptor activity) contribute to the race difference in masculinity.
In practice, I think there may be a signal/noise problem in actually doing this, because RNA quantification is not quite that precise. I don't know for sure, but I think that if every gene in the transcriptome were expressed 1.2x more in africans, it might be difficult to show that convincingly.
Tod,
I hear that most chimp offspring are sired by the chief and a couple of his amigos. Do you happen to have read anything on why this is? Sperm competition? Females mate with all, but mate more with the alphas - or favor the alphas especially during peak fertility? Female reproductive tracts somehow assist fertilization after alpha matings but resist it after beta ones?
What convinces you that most homicides are/were done with missile weapons? As far as war goes, that's not the impression I got from _War before civilization_. And what about the role in sexual competition of nonlethal fighting?
"A mating system that would evolve big testicles is the opposite of one that would select for a particularly masculinized physique."
Well, maybe. I understand your points about sperm competition. But why is it that gorillas *are* so polygynous? Is gender dimorphism for muscle the cause of that? I mean, suppose they were all mega-muscular, yet all the males were equals. In that case, the secure hyper-polygyny we see in real gorillas (which obviates sperm competition) would not be the case. Which way is upstream, causally, and which way is downstream?
It’s somewhat hard to believe that so many people can be either mistaken or lying.
Considering white men are known for their propensity to lie, and that blacks are probably less likely to with-hold their numbers, and that "East Asian" included Southeast Asian, that survey is completely worthless
Case in point, in the survey "results" over 25% of men are gay or bisexual. The fact that white men would believe these numbers goes to show how decades of "size" propaganda about blacks has bruised their egos.
Post a Comment