The theory which French philosopher Henri Bergson (1859-1941) substituted for the Darwinian mechanism of his day.
Bergson's theory mediated between the mechanism of natural selection and an outright teleological view, appealing to an dan vital ('vital impetus') which guided evolution in a certain direction; not in what he saw as the mechanistic non-explanatory fashion of current ORTHOGENESIS, nor under the influence of a pre-envisaged (and therefore in a sense preexisting) end, which for him is a mere 'inverted mechanism' which excludes invention and the unforeseen.
Part of Bergson's popular appeal was his espousal of a theory of evolution that did not (as Darwin's seemed to) exclude religion.
Bergson uses detailed scientific arguments as well as philosophical ones, but it is unclear that he can say why evolution takes the path that it does (or any coherent path) and is not merely chaotic.
H L Bergson, L'evolution creatrice (1907), trans, as Creative Evolution (1911)