'Sir - I ask for a portion of your space to say something about a lecture, 'On some of the Conditions of Mental Development,' which I delivered at the Royal Institution in March last. 

In that lecture I attempted to state and partially answer the question, 'What is that attitude of mind which is most likely to change for the better?' I proposed to do this by applying the hjrpothesis of the variability of species to the present condition of the human race. I put forward also for this purpose a certain biological law, viz. that permanent advantageous changes in an organism are due to its spontaneous activity, and not to the direct action of the environment. 

In the short account of the evolution-hypothesis which I prefixed, I followed Mr. Herbert Spencers Principles of Biology, not knowing, at the time, how much of the theory was due to him personally... I was also ignorant of the developments and applications of the theory which he has made in his other works, in which a great portion of my remarks had been anticipated. These omissions I desire now to rectify. 

Mr. Spencer's theory is to the ideas which preceded it even more than the theory of gravitation was to the guesses of Hooke and the facts of Kepler. 

... even if the two points which I put forward as my own - viz. the formal application of the biological method to a certain special problem, and the biological law which serves as a partial solution of it - have not before been explicitly developed (and of this I am not sure), yet they are consequences so immediate of the general theory that in any case the credit of them should entirely belong to the philosopher on whose domains I have unwittingly trespassed. The mistake, of course, affects me only, and could in no way injure the fame of one whose philosophical position is so high and so assured. 

I may perhaps be excused for anticipating here what I hope to say more at length at another time, that in my belief the further deductions to be made from this theory, with reference to modem controversies, will lead to results at once more conservative, and in a certain sense more progressive, than is commonly supposed.' (72-73)