 Finally, Darwin endorses the view, widely favoured these days, that natural selection need not act on organisms. Rather, natural selection is substrate-neutral. A natural selection process can occur whenever certain abstract conditions—these days often expressed as differential reproduction with inheritance—are met. Darwin explicitly endorses the view that natural selection can act on entities other than organisms in the context of language change, a cultural phenomenon. This position is briefly explored in the Origin of Species, and further expanded in the Descent of Man. In this work, he endorses the opinion of Max Müller: