Van Valen L M
J Morphol. 1982 Sep;173(3):305-12. doi: 10.1002/jmor.1051730307.
Homology is resemblance caused by a continuity of information. In biology it is a unified developmental phenomenon. Homologies among and within individuals intergrade in several ways, so historical homology cannot be separated sharply from repetitive homology. Nevertheless, the consequences of historical and repetitive homologies can be mutually contradictory. A detailed discussion of the rise and fall of the "premolar-analogy" theory of homologies of mammalian molar-tooth cusps exemplifies such a contradiction. All other hypotheses of historical homology which are based on repetitive homology, such as the foliar theory of the flower considered phyletically, are suspect.
同源性是由信息连续性导致的相似性。在生物学中，它是一种统一的发育现象。个体之间以及个体内部的同源性以多种方式渐变，因此历史同源性无法与重复同源性截然分开。然而，历史同源性和重复同源性的结果可能相互矛盾。对哺乳动物臼齿尖同源性的“前磨牙类比”理论的兴衰进行详细讨论，就例证了这样一种矛盾。所有其他基于重复同源性的历史同源性假说，比如从系统发育角度考虑的花的叶性理论，都是可疑的。
