'When we revolve in our minds,' says the eighteenth century prophet of evolution, 'the great similarity of structure which obtains in all the warm-blooded animals, as well quadrupeds, birds, and amphibious animals, as in mankind; from the mouse and bat to the elephant and whale; one is led to conclude that they have alike been produced from a similar living filament. In some this filament in its advance to maturity has acquired hands and fingers with a fine sense of touch, as in mankind. In others it has acquired claws or talons, as in tigers and eagles. In others, toes with an intervening web or membrane, as in seals and geese. In others it has acquired cloven hoofs, as in cows and swine; and whole hoofs in others, as in the horse: while in the bird kind this original living filament has put forth wings instead of arms or legs, and feathers instead of hair.' This is a very crude form of evolutionism indeed, but it is leading up by gradual stages to the finished and all-sided philosophy of physical life, which at last definitely formulates itself through the mouth of Charles Darwin. We shall see hereafter wherein Erasmus Darwin's conception of development chiefly failed--in attributing evolution for the most part to the exertions and endeavours of the animal itself, rather than to inevitable survival of the fittest among innumerable spontaneous variations--but we must at least conclude our glimpse of his pregnant and suggestive work by quoting its great fundamental _aperçu_:--'As the earth and ocean were probably peopled with vegetable productions long before the existence of animals, and many families of these animals long before other families of them, shall we conjecture that one and the same kind of living filament is and has been the cause of all organic life?'
A few lines from the 'Temple of Nature,' one of Erasmus Darwin's poetic rhapsodies, containing his fully matured views on the origin of living creatures, may be worth reproduction in further elucidation of his philosophical position:--
'Organic life beneath the shoreless waves Was born, and nursed in ocean's pearly caves; First forms minute, unseen by spheric glass. Move on the mud, or pierce the watery mass; These, as successive generations bloom, New powers acquire, and larger limbs assume; Whence countless groups of vegetation spring, And breathing realms of fin and feet and wing.'