 Weismann’s theory postulated the existence of several levels of hypothetical units. By the 1890s, it was agreed that individuals begin as cells, those cells contain nuclei, and that nuclei contain chromosomes. The chromosomes are the material of heredity, Weismann postulated, and they consist of a string of determinants, correlated with characters in the organism. Each determinant consisted of a number of material particles called biophores, inherited from both parents. These biophores compete with each other and some prevail, which then determines the character of the determinant, which in turn determines the character of the organism. During each cell division, the original whole chromosomal material is divided up, so that the effect is like a mosaic. Each cell becomes the right type just because of the action of the determinants distributed to it. As Weismann put it,