NATURE AND NURTURE, SEX AND GENDER
The terms “sex” and “gender” merit clarification because both are used inconsistently and interchangeably in research on health. Sex refers to the biological distinctions between males and females, most often in connection with reproductive functions.
8 Gender, by contrast, emphasizes the socially constructed differences between men and women that give rise to masculinity and femininity.
9 The term gender can be applied to individual difference, as well as to cultural, institutional, and structural difference. In the 1970s, feminist scholars promoted use of the term gender to draw attention to the reality that not all differences between men and women could be explained by biology. This distinction allowed scholars to counter academic and popular portrayals of the differences between men and women as natural, and by extension, immutable.
Sex, with its emphasis on sex-specific variation in biology, includes sex-specific variation in chromosomes. In addition to 22 pairs of autosomal chromosomes, humans have an additional pair of what have come to be known as the sex chromosomes. Most females have 2 X chromosomes and most males have an X and Y chromosome. With males and females sharing all 22 autosomal chromosome pairs and an X chromosome, sex-specific variation among the roughly 20 000 protein-coding genes is small. Relatively few genes, estimated around 75, are located on the Y chromosome, including those linked to the development of the testes.
10,11 Although a quick reading of such numbers might suggest sex-specific variation in genes of about 0.5%, estimating functionally relevant variation is complex. Recent estimates suggest that protein-coding genes account for only about 3% of the human genome.
12 Not all genes code for unique proteins; noncoding DNA is relevant to biological function and phenotypic expression, and methylation patterns, expression levels, and other factors may shape meaningful sex-specific genomic variation.
10,12,13Furthermore, despite the binary that is suggested by human reproduction, both sex and gender are fluid. Variations in chromosomes, hormone levels, and reproductive organs result in more than 2 sexes, reflecting complex processes of sex development across multiple levels, and suggesting that sex itself is culturally constructed.
14,15 Likewise, individuals transgress normative gender boundaries in everyday life, recasting gender as more than a simple dichotomy of men and women.
16 Gender is created and recreated through social interaction that takes place in dynamic cultural and institutional contexts.
7Much as there is not a neat dichotomy represented within sex or gender, the supposed dichotomy between sex-as-biology (within the body) and gender-as-society (outside the body) masks considerable complexity. More recent scholarship recognizes that gender is not disembodied, and that physiological differences, including sex differences, can contribute to gendered realities. The observation that gender contributes to biological expression is much less prevalent, but is emerging, especially with regard to health and disease.
17 In a study of bones, biologist Fausto-Sterling illustrates the myriad pathways through which culture and lived experience can affect biology. For example, Fausto-Sterling explains how culture, which might include gender-specific ideas and opportunities regarding diet or physical activity, can interweave with biology to shape group differences in bone characteristics.
18 Others suggest that gender structures in society can constrain individual choices, which can, in turn, have an effect on health, including longevity.
19 Moreover, gender contexts in society can shape our very understanding of sex differences, as illustrated by Jordan-Young using the example of brain organization.
20Thus, as our science recognizes that individual attributes reflect the combination of biological and social factors that work in concert over time to shape one another, and that physiological difference can reflect social experience, scholars have called both for greater precision in use of the terms sex and gender, and for abandonment of the false sex and gender dichotomy.
18,21,22 Just as the oversimplification represented in a nature–nurture distinction is inadequate, so too is the oversimplification reproduced in the sex–gender distinction. These issues come to the fore in the arena of gender, genetics, and health.
We use the phrase “gender differences in health” to refer to differences between men and women. Because health itself refers to the body, we understand that gender differences in health reflect social and biological factors. We use the terms sex and “sex differences” when referring more narrowly to physiological differences associated with male and female bodies, and reporting on literatures that primarily use the term sex. Although we recognize that these differences also reflect social factors, and the very argument of this article is to more fully represent this integration, we adopt what we understand to be the conventional interpretation of sex in public health and medical research for the purposes of this article, rather than the term “sex/gender” as is sometimes used by gender scholars and social scientists.
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