Next and last, and only with the appearance of _Man_, another entirely different and far higher factor was introduced, viz., _conscious, voluntary co-operation_ in the work of his own evolution--a conscious, voluntary striving to _attain an ideal_. We have called this a factor, but it is much more than a mere factor, co-ordinate with other factors. It is, rather, a different kind of evolution. It is evolution on a higher plane and by another nature. As _physical_ Nature works _unconsciously_, using certain factors, so _spiritual_ nature works _consciously_, co-operating and using the same factors. At first this factor, if we still call it so, was extremely feeble. In the early stages of his progress, man, like other animals, was largely urged on by forces of organic evolution, unknowing and uncaring whither he tended. But more and more, as civilization advances, this higher and distinctively human factor becomes more and more dominant, until now, in civilized communities, it takes control of evolution. Reason, instead of Nature, now assumes control, though still using the methods and factors of Nature. This _free_, self-determined evolution of the race, in order to distinguish it from the _necessary_ evolution of the organic kingdom, we call progress. Now, in this whole process we observe two striking stages. The one is the introduction of sex, the other is the introduction of reason.[19] They may be compared to two equally striking stages in the development of the _individual_. As the _ontogenic_ evolution receives fresh impulse at the moment of fertilization, so the evolution of the organic kingdom receives fresh impulse at the moment of introduction of sex. As in ontogenic evolution the individual at birth enters upon a new and higher plane, in which it co-operates in its own _physical_ growth, so the organic kingdom, with the introduction of man, enters upon a new and higher plane, in which man co-operates in the physical and _spiritual_ growth of the race. With sex three new and higher factors were introduced, and these immediately assumed control and quickened the rate of evolution. With reason another and infinitely higher factor is introduced, which, in its turn, assumes control, and not only again quickens the rate, but elevates the whole plane of evolution. Moreover, this voluntary, rational factor not only takes control itself, but transforms all other factors and uses them in a new way and for its own higher purposes.