of our own planet. Man and all his achievements will one day be obliterated like a child's sand-castle when the next tide comes in. Lucretius, who gave us the word progress, has told us our ultimate fate in sonorous lines:
'Quorum naturam triplicem, tria corpora, Memmi,
tres species tam dissimiles, tria talia texta,
una dies dabit exitio, multosque per annos
sustentata ruet moles et machina mundi'.
The racial life of the species to which we happen to belong is a brief episode even in the brief life of the planet. And what we call civilization or culture, though much older than we used to suppose, is a brief episode in the life of our race. For tens of thousands of years the changes in our habits must have been very slight, and chiefly those which were forced upon our rude ancestors by changes of climate. Then in certain districts man began, as Samuel Butler says, to wish to live beyond his income. This was the beginning of the vast series of inventions which have made our life so complex. And, we used to be told, the 'law of all progress is the same, the evolution of the simple into the complex by successive differentiations'. This is the gospel according to Herbert Spencer. As a universal law of nature, it is ludicrously untrue. Some species have survived by becoming more complex, others, like the whole tribe of parasites, by becoming more simple. On the whole, perhaps the parasites have had the best of it. The progressive species have in many cases flourished for a while and then paid the supreme penalty. The living dreadnoughts of the Saurian age have left us their bones, but no progeny. But the microbes, one of which had the honour of killing Alexander the Great at the age of thirty-two, and so changing the whole course
