Joseph J
California School of Professional Psychology, Alameda, USA.
Genet Soc Gen Psychol Monogr. 2001 Feb;127(1):27-57.
In 1960, Don Jackson published "A Critique of the Literature on the Genetics of Schizophrenia." Jackson's critique nearly relegated the classical twin method to obscurity as being hopelessly confounded by environmental factors. Jackson noted several trends in the schizophrenia twin data that were difficult to explain on genetic grounds. In fact, none of Jackson's 12 major points, examined in this article, have been satisfactorily answered by proponents of the twin method. The evidence in support of Jackson's most controversial claim-that the psychology of twinship itself might lead to a greater rate of schizophrenia among twins when compared with the single-born population--is inconclusive. However, although several leading twin researchers have dismissed Jackson's entire thesis on the basis of the inconclusiveness of this one claim, this idea was not central to Jackson's basic argument. The research undertaken for this article appears to confirm the validity of the most important points of Jackson's analysis and that therefore the classical twin method is of doubtful value as an indicator of genetic influences on schizophrenia and other diagnoses or psychological trait differences. Jackson's article demonstrated the implausibility of what came to be known as the MZ/DZ "equal environment assumption" of the twin method, implying that the twin method records nothing more than environmental differences between monozygotic and dizygotic twins.
1960年，唐·杰克逊发表了《对精神分裂症遗传学文献的批判》。杰克逊的批判几乎使经典双胞胎研究方法被弃用，因为它被环境因素严重混淆，毫无希望。杰克逊指出了精神分裂症双胞胎数据中的几个趋势，这些趋势从遗传学角度很难解释。事实上，本文所探讨的杰克逊的12个主要观点，双胞胎研究方法的支持者都未能给出令人满意的答案。支持杰克逊最具争议性观点（即双胞胎关系本身的心理因素可能导致双胞胎患精神分裂症的比例高于单胎出生人群）的证据尚无定论。然而，尽管几位顶尖的双胞胎研究人员基于这一观点的不确定性驳回了杰克逊的整个论点，但这一观点并非杰克逊基本论点的核心。本文所进行的研究似乎证实了杰克逊分析中最重要观点的正确性，因此经典双胞胎研究方法作为遗传因素对精神分裂症及其他诊断或心理特质差异影响指标的价值值得怀疑。杰克逊的文章证明了后来被称为双胞胎研究方法的MZ/DZ“等同环境假设”的不合理性，这意味着双胞胎研究方法所记录的不过是同卵双胞胎和异卵双胞胎之间的环境差异。
