Well, I just looked up Shaw's version (gutenberg.org/ebooks/13084). It's Shaw's usual epater the English, contrasting their immaturity with everyone else, including Scots. The character who wants to 'save' the white race, is one of its rare long-lived mutants, who is proposing marriage to another long-living one, to produce long-living children -- who will live long enough to develop some maturity of their own, thus improving the English race toward the level of all the other races.

I'm not sure I could handle the disconcertingness of what c. 2000 probably made of this.