George Bernard Shaw's Life Force is the vital energy that strives to attain ever-higher levels of achievement and evolution. Through Creative Evolution, the Life Force bursts forth to create life forms superior to those already developed. This superiority will manifest in the Supermen, an advanced race of humans which will evolve in the future because the most vital and energetic women will mate with the most creative and intelligent men. Shaw based this theory of eugenics on the work of such thinkers Henri Bergson, Samuel Butler, Charles Darwin, and Friedrich Nietzsche.
In his "Epistle Dedicatory" to Man and Superman, Shaw writes that:
Man is no longer, like Don Juan, victor in the duel of sex. Whether he has ever really been may be doubted: at all events the enormous superiority of Woman's natural position in this matter is telling with greater and greater force.
The play shows, in action, Shaw's theory that the woman is the great and aggressive pursuer of the man and that this will lead to a higher evolutionary state, as the best women seek out and conquer the smartest and most creative men by persuading them to marry and procreate. Ann Whitefield, with her "ensnaring eyes and hair" and high degree of vital energy, is an example of this kind of woman, as she overcomes the highly intelligent John Tanner's reluctance to marry. Pairings like this will inevitably improve the human race, according to Shaw.
Of course, today we find theories of creating a race of supermen repugnant, but Shaw was writing before experiences in the middle of the twentieth century warned society that it is dangerous to try to create a 'superior' caste.