Social organization, however, seems to face in both directions at once, and to be something half-way between a spiritual and a physical manifestation.
In placing invention at the bottom of the scale of conditions, I definitely break with the opinion that human evolution is throughout a purely "natural" process.

Of course, you can use the word "natural" so widely and vaguely as to cover everything that was, or is, or could be.

If it be used, however, so as to exclude the "artificial," then I am prepared to say that human life is preeminently an artificial construction, or, in other words, a work of art; the distinguishing mark of man consisting precisely in the fact that he alone of the animals is capable of art.
It is well known how the invention of machinery in the middle of the eighteenth century brought about that industrial revolution, the social and political effects of which are still developing at this hour.

Well, I venture to put it forward as a proposition which applies to human evolution, so far back as our evidence goes, that history is the history of great inventions.

Of course, it is true that climate and geographical conditions in general help to determine the nature and quantity of the food-supply; so that, for instance, however much versed you may be in the art of agriculture, you cannot get corn to grow on the shores of the Arctic sea.