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The old Palaeolithic race had never reached Ireland, which seems to have been cut oft from the Continent during the Ice-Age, and most of the authorities still believe in spite of some recent claims that it never reached Scotland. England itself was well populated, and the remains found in the caves of Derbyshire show that even the artist or his art had reached that district.
As regards the ice-age, Mr. Laing is professedly interested in putting it as far back as possible, since "a short date for that period shortens that for which we have positive proof of the existence of man, and ... a very short date ... brings us back to the old theories of repeated and recent acts of supernatural interference."
The backbone of our present system of determining the series of pre-historic epochs is the geological theory of an ice-age comprising a succession of periods of extreme glaciation punctuated by milder intervals.
And were the air of Mentone not unpropitious to the composition of anything save a kind of literary omelette soufflee, one might like to expatiate on Sergi's remarkable book, and devise thereto an incongruous footnote dealing with the African origin of sundry Greek gods, and another one referring to the extinction of these splendid races of men; how they came to perish so utterly, and what might be said in favour of that novel theory of the influence of an ice-age on the germplasm producing mutations new races which breed true ... enough!
The chief ice-age was some hundreds of thousands of years ago, that is all we can say with any confidence. In dismissing the question of climate, however, we should note that a very serious problem remains unsolved. As far as present evidence goes we seem to be free to hold that the ice-ages which have at long intervals invaded the chronicle of the earth were due to rises of the land.
The effect would be to prolong the winter and shorten the summer of each hemisphere in turn. The total amount of heat received would not alter, but there would be a long winter with less heat per hour, and a short summer with more heat. The short summer would not suffice to melt the enormous winter accumulations of ice and snow, and an ice-age would result.
Wood, observing my interest in this relic of the ice-age, gave it to me on the spot. "No granite in situ hereabouts, the living rock is mountain limestone, but no end of granite boulders, which are blasted to the tune of half-a-ton of tonite per week."
The last great selection, the northern Ice-Age, will give the last touches of modernisation. We have reserved for a closer inquiry that order of the placental mammals to which we ourselves belong, and on which zoologists have bestowed the very proper and distinguishing name of the Primates.
We do not know the causes of this climatic evolution the point will be considered more closely in connection with the last Ice-Age but we see that it throws a flood of light on the evolution of organisms. It is one of the chief incarnations of natural selection.
Once more I do not wish to enfeeble the general soundness of this account of the evolution of life by relying on any controverted theory, and we shall find it possible to avoid taking sides. I have not referred to the climate of the earth in earlier ages, except to mention that there are traces of a local "ice-age" about the middle of the Archaean and the beginning of the Cambrian.
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