By 1850 it was a familiar idea in Europe, but was not yet universally accepted as obviously true.  The notion of social Progress had been growing in the atmosphere of the notion of biological development, but this development still seemed a highly precarious speculation.  The fixity of species and the creation of man, defended by powerful interests and prejudices, were attacked but were not shaken.  The hypothesis of organic evolution was much in the same position as the Copernican hypothesis in the sixteenth century.  Then in 1859 Darwin intervened, like Galileo.  The appearance of the origin of species changed the situation by disproving definitely the dogma of fixity of species and assigning real causes for “transformism.”  What might be set aside before as a brilliant guess was elevated to the rank of a scientific hypothesis, and the following twenty years were enlivened by the struggle around the evolution of life, against prejudices chiefly theological, resulting in the victory of the theory.

The origin of species led to the third stage of the fortunes of the idea of Progress.  We saw how the heliocentric astronomy, by dethroning man from his privileged position in the universe of space and throwing him back on his own efforts, had helped that idea to compete with the idea of a busy Providence.  He now suffers a new degradation within the compass of his own planet.  Evolution, shearing him of his glory as a rational being specially created to be the lord of the earth, traces a humble pedigree for him.  And this second degradation was the decisive fact which has established the reign of the idea of Progress.

2.

Evolution itself, it must be remembered, does not necessarily mean, applied to society, the movement of man to a desirable goal.  It is a neutral, scientific conception, compatible either with optimism or with pessimism.  According to different estimates it may appear to be a cruel sentence or a guarantee of steady amelioration.  And it has been actually interpreted in both ways.

In order to base Progress on Evolution two distinct arguments are required.  If it could be shown that social life obeys the same general laws of evolution as nature, and also that the process involves an increase of happiness, then Progress would be as valid a hypothesis as the evolution of living forms.  Darwin had concluded his treatise with these words: 

As all the living forms of life are the lineal descendants of those which lived long before the Silurian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world.  Hence we may look with some confidence to a secure future of equally inappreciable length.  And as natural selection works solely by and for the good of each being, all corporeal and mental environments will tend to progress towards perfection.