Origins of the nucleate organisms.

A theory regarding the early evolution of the eukaryotes is presented. It is proposed that the eukaryotes evolved through the successive stages: amoeba, flagellate, sexual flagellate. It postulated that sexuality emerged only once. A scheme relating evolution of the whiplash and tinsel forms of the flagellum to the evolution of sexuality is presented. It is suggested that sexuality first appeared in organisms capable of producing both forms of the flagellum. The phylogeny supports the hypotheses that the flagellum developed from the spindle system, and that the nucleate algae evolved from protozao through symbiosis with photosynthetic organisms related to the blue-green bacteria. It is consistent with the hypothesis that the mitochondrion was acquired by symbiosis. The phylogeny provides clearer definitions for kingdoms, and indicates the separation into seven kingdoms, as follows: Monera, Protozoa, Algae, Fungi, Porifera, Plantae, Animalia.