In chapter 6, titled "Thinking About Homosexuality," of her book Sex/Gender: Biology in a Social World, Anne Fausto-Sterling argues that the Victorians' role in constructing the concept of "homosexuality" actually first stemmed from the roles of earlier periods.
In the beginning of her chapter, Fausto-Sterling points out that lots of historians identify the 1600s and 1700s as "periods of great change in our concepts of sex and sexuality" (p. 70). In particular, historian Michel Foucault identifies the transition from feudalism to the beginnings of industrialization in the 1700s as a time when society needed to develop "new methods to control" people who were becoming progressively controlled by machinery used in mass production. The need for finding new ways to control people in the 1700s led the first scientists of the 1800s, especially the first social scientists, to find new ways to classify people in terms of "births and mortality, life expectancy and longevity" (p. 70). The need to classify gave rise to new scientific fields, including "embryology, endocrinology, surgery, psychology, and biochemistry," and all of these scientific fields have "encouraged physicians to attempt to control the very gender of the body by making categories" (pp. 71 - 72).
It was then in the Victorian era (1837 - 1901) that the terms and definitions of "homosexuality" and "heterosexuality" began to emerge. A German devoted to legalizing sodomy first used the term "homosexuality" in 1869. It was also at this time that psychiatrists and other behavioral specialists started to publish reports on homosexual behavior, which helped to categorize the behavior as a mental illness. However, Fausto-Sterling points to the Victorians' "two-sex model of masculinity and femininity" as the basis for our current "definitions of homo- and heterosexuality" (p. 73). The Victorians defined "masculine" behavior as "sexually aggressive" and "feminine" behavior as "sexually indifferent" (p. 73). But these two definitions failed to explain women's sexual interest in other women, because how can two "sexually indifferent" women feel any attraction for each other? To remedy the problem, the Victorians also developed the idea that at least one of the women had to be "different"; she "had to be an invert, someone with markedly masculine attributes" (p. 73). Similarly, homosexual males had to display feminine characteristics.
Hence, the scientific categorizations of gender and sexuality in the 1800s was a product of the the Industrial Age of the 1700s, but, in the last half of the 1800s, the Victorians contributed to our categorizations and definitions of homosexual behavior due to their own "two-sex model."