Haeckel constructed the first of the now commonplace ancestral trees, depicting the evolution of life from the simplest organisms through 21 stages of development to modern man – the 22nd and final stage. Within this general scheme he created the concept of the Phylum (i.e. stem) to accommodate all organisms descended from a common form, and created the word Phylogeny to describe their evolutionary development from common form to distinct species. He suggested that within each species the term Ontogeny should describe the development of the individual from conception to maturity. From this he proposed his famous biogenetic law, “Ontogeny recapitulated Phylogeny”. English translation, 2 vols., London, 1876. Darwin wrote in The Descent of man (No. 227) “if [the English translation of] this work had appeared before my essay [Descent…] had been written, I should probably never have completed it. Almost all the conclusions at which I have arrived I find confirmed by this naturalist, whose knowledge on many points is much fuller than mine”. 

Haeckel differed from Darwin in advocating a polygenist theory of human evolution. He traced human lineage back to a hypothetical ancestral form, intermediate between humans and apes, that he named Pithecanthropus. “It was from the ‘Pithecanthropoi,’ Haeckel contended, that primeval humanity (which he termed Homo primigenius) was derived.... The various human races were considered to have been derived from Homo primigenius by natural selection, resulting in the formation of two quite divergent forms of humanity: (i) ‘the wooly-haired men’ (Ulotrichi); and (ii) ‘the straight-haired men’ (Lisotrichi). The Ulotrichi, Haeckel said, initially spread south from their primeval homeland, and then east and west. The remnants of the eastern branch being the peoples of New Guinea and Melanesia, while the negroes of Africa were considered representatives of the western branch. The remainder of modern humanity, the Lisotrichi, consisted of several divergent branches of what he called the ‘primeval Malays, or Promalays.’ The ‘Indo-Germanic race’ was a branch of the Lisotrichi, which he considered to have deviated furthest from the common ancestry. The chief representatives of this group were the Germans and English, who he said ‘are in the present age laying the foundation for a new period of higher mental development’” (Spencer, Ecce Homo [1986] 156.)