The quotation is from Ch. 4 of Wells' novella, The Time Machine. The Time Traveler, arriving in the "year Eight Hundred and Two Thousand odd," speculates about the evolution of mankind in an effort to account for the fragile, child-like Eloi:

'So watching, I began to put my interpretation upon the things I had seen, and as it shaped itself to me that evening, my interpretation was something in this way. (Afterwards I found I had got only a half-truth—or only a glimpse of one facet of the truth.)

'It seemed to me that I had happened upon humanity upon the wane. The ruddy sunset set me thinking of the sunset of mankind. For the first time I began to realize an odd consequence of the social effort in which we are at present engaged. And yet, come to think, it is a logical consequence enough. Strength is the outcome of need; security sets a premium on feebleness. The work of ameliorating the conditions of life—the true civilizing process that makes life more and more secure—had gone steadily on to a climax. One triumph of a united humanity over Nature had followed another. Things that are now mere dreams had become projects deliberately put in hand and carried forward. And the harvest was what I saw!"

...

By the end of the chapter The Time Traveler concludes:

"'As I stood there in the gathering dark I thought that in this simple explanation I had mastered the problem of the world—mastered the whole secret of these delicious people. Possibly the checks they had devised for the increase of population had succeeded too well, and their numbers had rather diminished than kept stationary. That would account for the abandoned ruins. Very simple was my explanation, and plausible enough—as most wrong theories are!"

(http://www.gutenberg.org/cache/epub/35/pg35.html)

Cheap enough for the wealth of the Time Machine.

>> Wells readily agreed, and was paid £100 (equal to about £9,000 today) on its publication by Heinemann in 1895.