 Modern evolutionary theory equates inheritance with the transmission of genes from parents to offspring and as such focuses only on genetic inheritance (which will be further described in section 3.3.1). Nevertheless, biologists have long known of patterns of inheritance, and eventually of inheritance mechanisms, that go beyond genetic inheritance (Jablonka &amp; Lamb 2005; Sapp 1987). Two fundamental types of arguments led to this conclusion: arguments based on observations regarding patterns of inheritance, and arguments concerned with the localization of hereditary factors inside cells. Arguments of the first kind were based on hereditary relations and inheritance patterns that fail to conform to the rules of Mendelian inheritance (e.g., maternal inheritance). If Mendelian inheritance patterns are the result of the way the chromosomes in the eukaryotic cell nucleus behave, non-Mendelian heredity must depend on separate inheritance processes, mechanisms, or systems (Beale 1966; Sager 1966). Second, there were observations of hereditary phenomena that seemed to depend on factors residing in the cytoplasm of cells, rather than their nucleus, where the genetic material is localized. The interpretation of these observations was highly contested (Darlington 1944; Sapp 1987).