Mary Stewart Van Leeuwen
The animal research does show a relationship between increased testosterone levels and later aggression, regardless of the animal's sex or whether the hormone is administered pre- or post-natally. By contrast, males castrated either pre- or post-natally may exhibit the opposite pattern of less aggression, unless they receive injected testosterone to compensate. They may also exhibit sexual behaviors typical of females (and vice-versa for females, if they get too much testosterone). Bear in mind that we know little about how these effects would generalize from isolated, lab-raised animals to those in natural settings: rodents and primates are, after all, quite sociable species. And human babies, given their much longer period of post-natal development, are even more susceptible to social influence: their long-term survival literally depends on it. Moreover, the most distinctive biological feature of humans is the plasticity of their brains. The legacy of a large cerebral cortex puts us on a looser behavioral leash than other animals, with the result that, more than any other species, we are built for continual learning—for passing on what we have created culturally, not just what we are inclined to do genetically and hormonally. We are, it seems, hard-wired for behavioral flexibility.
In the absence of direct hormonal manipulation, suppose we were to separate nature from nurture by randomly designating some boy and girl infants to be raised as the other sex after they're born, to see just how much (or little) they remain stubbornly "masculine" or "feminine" despite the reversal in gender socialization. But, ethical considerations aside, this wouldn't even begin to approximate a double blind experiment—in the sense of controlling for expectancy effects—because the cat would be out of the bag (so to speak) as soon as the babies' caretakers began changing their diapers. All this is to say that when studying human gender traits, gender identity, or sexual orientation, essential conditions for inferring cause and effect—the manipulation of one factor (sex) and the control of others (social as well as biological)—cannot be met. It means that "all data on sex differences, no matter what research method is used, are correlational data," and as every introductory social science student learns, you cannot draw firm conclusions about causality from merely correlational data.
"Eunuchs Made So by Others": Some Lessons from History
This methodological uncertainty makes for constant debates between adherents of gender essentialist and social-constructionist camps, as the books to be reviewed all attest. Readers might wonder why the list includes historian Mathew Kuefler's study of eunuchs in the late Roman Empire, and Kathryn Ringrose's corresponding one on eunuchs in Byzantium. Very simply, few brain organization theorists read history to find connections between their own research and past cultural practices, such as that of castrating a non-trivial percentage of males in the Greco-Roman and Byzantine eras. This was of course not a controlled experiment, but it was a practice that lasted several centuries in the Roman West, as well as the Byzantine East and beyond, with many surviving texts (including some biblical ones) commenting on it. Kuefler and Ringrose try to connect the biological and cultural dots, with a stronger emphasis on the latter. They also examine the reciprocal impact between male castration and church law and practice, appealing to sources like medical texts, sermons, hagiographies, historical narratives, law codes, biographies, and standards for church office holders.
In both Rome and Byzantium, the theories of Aristotle, Galen, and Hippocrates were the accepted basis for doing science and medicine. Obviously, these scholars did not know about genes or hormones as those terms are used today—in fact, Aristotle believed that only fathers contributed any "seed" to fetal development. But they and their descendents were often astute clinical observers, and though castration of males (by removal of the testes and sometimes even the penis) was technically illegal within the Roman Empire, it occurred nonetheless. It was even more common in the barbarian hinterlands, resulting in a steady export of eunuchs to metropolitan areas like Rome and Constantinople. Over time, it was noted that the results of castration varied, depending on when it occurred. If done after puberty, eunuchs might still be able to have erections and orgasms, even though they were unable to reproduce. If done before, the longer-term dearth of testosterone resulted in tall slender bodies, beardless faces, less-developed musculature, and little if any libido. Such pre-pubertal castrates were often considered beautiful as young men (they were at times equated with angels, and some women even pretended to be male eunuchs to enjoy a freedom of mobility normally denied to their own sex), but they also tended to age prematurely and die young.