If I were called upon to exhibit the chief determinants of human life as a single chain of causes and effects—­a simplification of the historical problem, I may say at once, which I should never dream of putting forward except as a convenient fiction, a device for making research easier by providing it with a central line—­I should do it thus.  Working backwards, I should say that culture depends on social organization; social organization on numbers; numbers on food; and food on invention.  Here both ends of the series are represented by spiritual factors—­namely, culture at the one end, and invention at the other.  Amongst the intermediate links, food and numbers may be reckoned as physical factors.  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.  But, given the needful inventions, superior weapons for instance, you need never allow yourselves to be shoved away into such an inhospitable region; to which you presumably do not retire voluntarily, unless, indeed, the state of your arts—­for instance, your skill in hunting or taming the reindeer—­inclines you to make a paradise of the tundra.

Suppose it granted, then, that a given people’s arts and inventions, whether directly or indirectly productive, are capable of a certain average yield of food, it is certain, as Malthus and Darwin would remind us, that human fertility can be reckoned on to bring the numbers up to a limit bearing a more or less constant ratio to the means of subsistence.