I assume that the poster is referring to undergraduate science education in universities in the USA. I am a British scientist, but from reading general science news in journals like Nature I am not aware of a historic event involving “guidelines… written by a major academic body” on the use of ‘he/she’. I imagine that in today’s climate this would be covered by general sexual discrimination guidelines and, in any case, there is probably widespread cultural conformism or self-censoring. I, for one, would regard an edict on what words I or my students were allowed to use as an assault on academic freedom.
However, the question can be interpreted in a more general sense as:
“When did the change of attitude against the use of ‘he’ to cover individuals of both sexes appear in English-speaking academic science?”
The answer is, of course,
I have a cutting in my possession, taken from Nature 309, 387 (1984) which accompanied a piece on the (British) Dunstan Committee Report on artificial insemination etc. As this is not freely available, I reproduce an edited version below:
The introduction to the Dunstan report by Professor John Ziman… includes the following explanation of a now-unfashionable usage:
“The report is written in English, a language which has a common gender
for statements applying to masculine and feminine, male and female,
without distinction. Sometimes the grammatical form of the common
gender and masculine coincide, but that is no impediment to its use.
We have employed this grammatical facility because it yields a prose
less cluttered and more elegant, and as readable.”