A "Harvard study on Brain Chemistry" isn't a DEFINITION of gender, it may be a brain study. This is the definition of gender.
Websters 1828 Dictionary
GEN'DER, noun [Latin genus, from geno, gigno; Gr.to beget, or to be born; Eng. kind. Gr. a woman, a wife; Sans. gena, a wife, and genaga, a father. We have begin from the same root. See Begin and Can.]
1. Properly, kind; sort.
2. A sex, male or female. Hence,
3. In grammar, a difference in words to express distinction of sex; usually a difference of termination in nouns, adjectives and participles, to express the distinction of male and female. But although this was the original design of different terminations, yet in the progress of language, other words having no relation to one sex or the other, came to have genders assigned them by custom. Words expressing males are said to be of the masculine gender; those expressing females, of the feminine gender; and in some languages, words expressing things having no sex, are of the neuter or neither gender
GEN'DER, verb transitive To beget; but engender is more generally used.
GEN'DER, verb intransitive To copulate; to breed. Leviticus 19:19.
There is your answer, it isn't a Harvard study but it is the DEFINITION of gender.