Google's wonderful little Ngram Viewer lets you plot variations in the number of published references to a term over time.
Its results are not perfect but usually strongly suggestive.
It says it could find no references to the use of the term "gene pool" until the early 1950s (but does find scientist L C Dunn using it in a 1946 book).
This confirms my sense that the term was very rare before Auschwitz because the concept behind the term was viewed negatively until then.
Viewed negatively by almost all, except for a few old fashioned fundy-duddys like GK Chesterton.
Certainly viewed negatively by almost every 'with it' 'up to date' modern progressive educated member of the middle class.
They assumed we be much better off if we sharply decreased the variety of genes within the human gene pool, while at the same time increasing the absolute numbers of the people holding the few - 'the right' - remaining genes.
Popular Eugenics, whatever the setbacks among the leading genetics research centres scientific eugenic research was currently experiencing,was becoming more and more popular (not less and less) right up to at least 1943.
Segregating the genes, not pooling them, was the progressive mantra in those besotted pre-Auschwitz days.
Only a few boldly claimed that greater diversity led to greater productivity and creativity - that only with the help from all, could there be hope for all in times of global crisis.
The global middle class mind, circa 1939, was like a close parachute, preparing to jump out of a plane : little wonder then for the six years of disasters that followed....