The suggestion is certainly occasionly made that Newton was homosexual, but I suspect that in each instance they’re, at best, based on reading biographies that themselves don’t propose this.
Indeed I suspect that all such claims ultimately derive from Frank Manuel’s - rather more cautious - interpretation of Newton’s mental life and character. He’s written a number of important books on aspects of the man, but the best known is his A Portrait of Isaac Newton (1968; Da Capo, 1990). This is a Freudian biography, in the manner for which there was something of a fashion for at the time; Manuel specifically acknowledges his dept to Erik Erikson.
At the heart of Manuel’s interpretation is, inevitably, Newton’s relationship with his mother. His father died during her pregnancy and so he never knew him. The mother then quickly remarried and Manuel suggests that Newton saw this as a betrayal, with the result that his childhood becomes Hamlet relocated to Lincolnshire. The fraught relationship with his mother then screws up Newton’s feelings about sex and women, so that he never forms an adult relationship with any. There are also few close friendships with men. Basically, in Manuel’s view, the guy needed therapy. Lots of it.
Enter Nicolas Fatio de Duillier, a Swiss would-be scientist who arrives in London in 1687. The subsequent friendship between Fatio and Newton was certainly close, at least while it lasted, and it’s invariably what people, knowingly or otherwise, have in mind when suggesting that Newton was a homosexual. Amongst the biographers, while everybody sees it as one of the most important friendships in Newton’s life, Manuel stands out for the particular importance he places on it, notably seeing it end as a crucial trigger for the breakdown he suffers in 1693. For a Freudian biographer, this is great material and hence Manuel makes the most of it.
But even he rules out a physical relationship between them.
And on the specific friendship with Fatio:
Thus, as elsewhere in the book, Manuel raises the possibility of homosexuality as an interpretation, without regarding it as the best one.
Manuel also explicity begins his chapter on Fatio by accepting the story that, late in life, Newton confided to a relative that he had been chaste throughout his life. Whatever happened with Fatio, it wasn’t physical. (Other Newtonian specialists have been slightly more cagey about this story, though all accept that it’s plausible.)
But Manuel’s book seems to be where the notion that Newton was possibly homosexual entered public conciousness. Of course, we aren’t bound to follow Manuel’s interpretations and conclusions, but what I’ve read of the correspondence between Fatio and Newton certainly seems consistent with just a close friendship. In fact, the letters are entirely unremarkable in terms of their intimacy compared to those between other close friends in the period. They’re only unusual when compared to most of the rest of Newton’s.
Incidentally, on the general question of Newton’s celibacy, Patricia Fara has an interesting discussion in her Newton: The Making of Genius (2002; Picador, 2003, p211-13) about how the notion has been used in different images of him over the centuries.
I tend to be skeptical of most claims of this sort. We’ve almost reached a point where being gay is assumed by default in the absence of a publicly detailed active heterosexual life. Sad to say, sexual fulfillment is not like air, water, and food. One can live without it for protracted periods, as I’m sure many here are aware. The absence of heterosexual relationships doesn’t mean that he had homosexual ones. Maybe inventing calculus took every bit of spare energy he had to spare.
It seems that any and every Long-Dead Famous Person is claimed by someone to be gay. Leaving aside social customs that may have been very different from modern ones, the continuous claims of homosexuality leave me with a ‘Boy Who Cried Wolf’ feel.
Eh, who cares? Really, does anyone think that it would diminish his contributions to math/science if he were? The only thing that I can think of that would happen is that the Gay People would add him to the list of Famous Gay People.