To answer this question, one first needs to understand what pathos is. Pathos is a quality one possess (or that is depicted in a text) which evokes sadness.
Stephen Jay Gould, in Women's Brains, is able to appeal to a person's pathos by beginning his essay with a quote by George Eliot. This use of Eliot's words provides two specific ways to appeal to a reader's pathos. First, George Eliot was a woman. She used a male pen name in order to insure that her words were heard and that readers would take her ideologies seriously (given women simply were not looked at as scholarly, educated, or having anything important to say). Second, the fact that a woman is showing her sadness about the fact that women are simply seen as nothing to be taken seriously.
Throughout the essay, Gould discusses the fact that women simply were not being measured fairly, if they were being measured at all. Many times throughout the essay, Gould admits that women simply were ignored.
Therefore, Gould is able to appeal to pathos given that a certain group of mankind was simply being ignored. He repeatedly states that women have been ignored throughout time and this fact alone evokes sadness in a person.
Perhaps Gould's last line can speaks most prominently to his appeal to ethos:
Woman was always the custodian of the human sentiment, morality and honor.
The fact that Gould realizes that this fact has been ignored is especially saddening.
I'm not so sure that the Elliot quotations are the best example of Pathos in the piece. The one section that stood out to me was the section where Gould quote Le Bon. Le Bon said rash and harsh things that completely attack women. I think that this quotation provokes far more of an emotional response than the Elliot quotes. Le Bon's words do not make the reader feel sad but rather infuriated.
Thats just what I think. Hope it Helps.