Sex Has a Meaning and Sex Differences Are Real

In 1871, Charles R. Darwin published his book, The Descent of Man and Selection in Relation to Sex (Darwin 1899). He discussed his ideas on the origins of dimorphic features of anatomy, citing examples of insects, crustaceans, birds, and mammals. Although he did not include behavior in his exhaustive coverage, it was indirectly discussed, because he suggested that male weaponry existed because it had the potential to give specific males an advantage in intrasexual combat. Females were not involved in such agonistic battles and so would not benefit from the burdensome and unused antlers, horns, or tusks. Since these contests were being exhibited by one sex and not by the other, they could certainly qualify as “sexually dimorphic behaviors” even if never presented and discussed by Darwin as such. Mating behavior for species with internal fertilization would also obviously reflect a sexual dimorphism. However, its causal foundations could possibly be attributed to differing internal hormonal environments rather than differing central nervous system organization. Frank Beach (1974) focused upon prepubertal development of urination patterns in dogs as being an example of a sexually dimorphic behavior pattern that is exhibited in the absence of the activational action of gonadal hormones. Field observations on a wide variety of primates have confirmed a wide variety of sexually dimorphic behaviors (Bernstein 1978). Harry Harlow’s work with surrogatereared rhesus monkeys (Macaca mulatta) established that these behavioral differences did not require exposure to adult models for their development and display and since these young rhesus monkeys were all prepubertal, there was confirmation of the independence of these behaviors from circulating hormones (Harlow 1971). Harlow’s work provided the appropriate backdrop for the experimental work with rhesus carried out by Charles Phoenix, Arnold Gerall, Robert Goy, and William C. Young that confirmed the organizational action of gonadal hormone exposure in utero (Goy 1968). The extension of this to humans is more problematic because ethics prevent direct manipulation, and a necessary reliance on clinical conditions is in some respects less than ideal, although congenital adrenal hyperplasia has been a disorder which has allowed for appropriate examination. For a great many people, the validity of sex differences is well-established and beyond question at the level of behavior and the central nervous system. However, the field is experiencing an inappropriate shift where the term “gender” is being substituted for the word “sex” even in situations where it is clearly inappropriate. For example, a 2015 work by Haynh et al. (2015) was published as a paper entitled “Forensic Identification of Gender from Fingerprints.” The very first table in the paper is headed “Average amino acid concentration (mM) values for males and females derived from sweat” and the very first figure has reference to “males” and “females.”Although the terms “man” and “woman” never appear in the article, these terms might have been appropriate under the article’s title. The first thing I want to commend Geary for is his sensitivity to the appropriate use of terminology; the term “gender” does not even appear in the book’s index. I doubt, however, that this was much of an effort for a man who has published an approximately 400-page book with the title Male, Female: the Evolution of Human Sex Differences (Geary 2005). In this reviewed book, the conceptual model which Geary sets up to examine is a simple and straightforward one: “traits that have been elaborated through sexual or social selection * Craig Bielert Craig.Bielert@oneonta.edu