POSTERIOR

figure g. і: A three-dimensional rendering of the entire corpus callosum cleanly dissected from the rest of the brain. (Source: Alyce Santoro, for the author)

first tame it—turn it into a tractable, observable, discrete laboratory object. This challenge itself is nothing new. Pasteur had to bring his microbes into the laboratory before he could study them;29 Morgan had to domesticate the fruit fly before he could create modern Mendelian genetics.30 But it is crucial to remember that this process fundamentally alters the object of study. Does the alteration render the research invalid? Not necessarily. But the processes researchers use to gain access to their objects of study—processes often ig­nored in popular reporting of scientific studies—reveal a great deal about the assumptions behind the research.31

Scientists began to tame the CC before the turn of the century. Then, great hopes were pinned on using it to understand racial differences (with a little gender thrown in to boot). In 1906 Robert Bennet Bean, working in the anatomical laboratory at Johns Hopkins University, published a paper entitled ‘‘Some Racial Peculiarities of the Negro Brain.’’32 Bean’s methods seemed un­assailable. He carefully divided the CC into subsections, paid careful attention to specimen preparation, provided the reader with large numbers of CC trac­ings,33 made extensive use of charts and tables, and acquired a large study sample (103 American Negroes and 49 American Caucasians). So useful were his results that some of the participants in the late-twentieth-century debate not only refer to his work but have reanalyzed his data.34 Indeed, despite some modernist flourishes (like the use of sophisticated statistics and computers), the methods used to measure the size and shape of the corpus callosum in cadavers has not changed during the ninety odd years since the publication of Bean’s account. I do not want to tar modern scientists with the brush of earlier research that most now find racist. My point is that, once freed from the body and domesticated for laboratory observation, the CC can serve different mas­ters. In a period of preoccupation with racial difference, the CC, for a time, was thought to hold the key to racial difference. Now, the very same structure serves at gender’s beck and call.35

Bean’s initial measurements confirmed earlier studies purporting to show that Negroes* have smaller frontal lobes but larger parietal lobes than Cauca­sians. Furthermore, he found that Negroes had larger left frontal but smaller left parietal lobes, while the left/right asymmetry was reversed for Cauca­sians. These differences he felt to be completely consistent with knowledge about racial characteristics. That the posterior portion of the Negro brain was large and the anterior small, Bean felt, seemed to explain the self-evident truth that Negroes exhibited ‘‘an undeveloped artistic power and taste. . . an instability of character incident to lack of self-control, especially in connec­tion with the sexual relation.’’ This of course contrasted with Caucasians who were clearly ‘‘dominant. . . and possessed primarily with determination, will power, self-control, self-government. . . and with a high development of the ethical and aesthetic faculties.’’ Bean continues: ‘‘The one is subjective, the other objective; the one frontal, the other occipital or parietal; the one a great reasoner, the other emotional; the one domineering but having great self­control, the other meek and submissive, but violent and lacking self — control.’’36 He found also that the anterior (genu) and posterior (splenium) ends of the corpus callosum were larger in men than in women. Nevertheless, he focused primarily on race. He reasoned that the middle portions (called the body and the isthmus) contained fibers responsible for motor activity, which he thought to be more similar between the races than other brain regions.37

I use the word Negro because it is used in Bean’s paper.

Indeed, he found the greatest racial differences outside the motor areas. Pre­vailing beliefs about race led Bean to expect the splenium, which presumably contained fibers linking more posterior parts of the left and right brain halves—areas thought to be more responsible for the governance of primitive functions—to be larger in nonwhites than whites. And the measurements confirmed it. Similarly, he predicted that the genu, connecting the more ante­rior parts of the brain, would be larger in Caucasians, a prediction again con­firmed by his numbers.38

Then, as now, such work stimulated both scientific and public challenges. In 1909 Dr. Franklin P. Mall, Chairman of the Anatomy Department at Johns Hopkins, disputed Bean’s findings of racial and sexual differences in the brain.39 Mall’s objections have a familiar ring: extensive individual variation swamped group differences. No differences were great enough to be obvious on casual inspection, and Bean and others did not normalize their results by taking into account differences in brain weight. Furthermore, Mall thought his own measurements were more accurate because he used a better instru­ment, and he did his studies blind in order to eliminate ‘‘my own personal equation.’’40 In conclusion, he wrote: ‘‘Arguments for difference due to race, sex and genius will henceforward need to be based upon new data, really scientifically treated and not on the older statements.’’41 At the same time that

Mall engaged Bean in the scientific arena, Bean and the anthropologist Franz Boas tangoed in the popular media.42 The social context may change, but the weapons of scientific battle can be transferred from one era to the next.