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In the trenches with the corpus callosum: Some redux of redux

My interest in sex differences in the brain stems from my earlier articles (e.g., Holloway, 1967, 1996, 2008), which suggested that much of human brain evolution involved social behavior. In particular, this involved complementary selection for patterns of male/female social behavior, the main goal of which was to provide nurturance for offspring with prolonged periods of dependence and concomitant increases in brain growth. (I wish I had called it the “social brain”). I accepted Dr. Cahill’s invitation to detail some of my experiences on the corpus callosum (CC) battlefield instead of providing an update on the totality of brain differences between the sexes, which will surely be more than adequately expressed in the various chapters of this volume. In 1982, my student, Christine De LacosteUtamsing, and I published a paper in Science that described a sexually dimorphic aspect of the CC in modern humans. We tried to show that the relative size of the CC was greater in females than in males, and we further suggested that the splenial portion appeared more bulbous in the female CC. Our sample was very small (14 males, five females). We were requested to submit our findings so that Science could independently check our statistics because the P value of significance between male and female CC area was a paltry 0.08. This started what has amounted to a “cottage industry” of sorts, sparking dozens of articles, some of which confirmed some of our findings and others not. The arguments continue to the present. Indeed, that was the purpose of our article, to generate replication or rebuttal. Little did we expect that we would be cast as villains engaging in a veritable “reenactment” of the sexist and racist studies of Spitzka and Bean of 1905–1909 vintage, although Mall (1909) had written against such views. (In fact, we were ignorant of those articles.) The criticisms of our findings by Fausto-Sterling (1985, 1987,1992) were particularly harsh, in that we got tarred by the earlier racial brush: “. . . and there the matter rested until 1982.” Referring to the articles by Spitka (1907), Bean (1906), and Mall mentioned above: “The modern reenactment came from physical anthropologist Ralph Holloway and cell biologist Christine De LacosteUtamsing in a paper published in Science magazine” (p. 229). On page 232 we read that “. . . De LacosteUtamsing and Holloway made some remarkable claims. First they said that the shape of the splenium differed so dramatically between the sexes . . . that complete novices could using this feature to distinguish male from female brains. They argued, in fact, that the width of the splenium had a bimodal distribution, meaning that, save for reproductive organs, this would be the strongest known sex difference. . . .” (Fausto-Sterling, 1992, 2nd ed.). This certainly came as news to us, since our paper was simply fact-based, without claims about novices, and contained simple speculation regarding the possible evolutionary significance of our findings. Fausto-Sterling’s chapter then goes on to assess in a score-card fashion the multitude of articles published, some agreeing with our findings but mostly not. Her critique was in the most acerbic and sarcastic style and always cast our and other similar work as attempts to prove male superiority in one task or another. It seemed pointless to respond to her misreading of our intentions and studies. In fact, at the time, our first article grew out of my insistence that Christine’s work on determining origins and terminations of fibers in different parts of the CC should include as much information as possible on variability within and between the sexes. We were unaware of the earlier literature and were not initially trying to show sex differences in the brain or behavior. It was a vexing time, I admit, because almost all of the articles disagreeing with our findings did not appear to understand our claim of “relative,” and many so-called refutations simply never took brain size into account. Most authors seemed to find that either the male CC area was slightly larger than that in females, or there was no significant difference in the CC areas, or that the female CC was just slightly larger. In no case, when the brain