 In its seventeenth-century context, the issue of species origins also involved debates over the possibility of the spontaneous generation of forms (Roger 1963 [1997: chp. 2]). The experimental refutations by Francesco Redi (1626–67) of theories of origin relying on abiogenesis, such as those proposed by Thomas Burnet, weakened, but did not destroy, the belief in spontaneous generation. Evidence for spontaneous generation could always be explained by appeal to Augustine’s theory of the pre-existent “seeds” or “germs”.