Plomin R, Willerman L, Loehlin J C
Behav Genet. 1976 Jan;6(1):43-52. doi: 10.1007/BF01065677.
The equal environments hypothesis of twin methodology was examined for the variable of similarity of appearance as it affects the personality ratings of young twins. There were two separate samples, the first with 95 pairs of same-sex twins and the second with 111 pairs. The average age of the twins in both samples was 3-1/2 years. Mothers rated their twins on four personality traits and on confusability of appearance. Not surprisingly, identical twins were markedly more similar in appearance than fraternal twins. The effect of this inequality on the personality ratings of the two types of twins was examined by correlating ratings of similarity of appearance with the absolute difference on the four personality traits for each pair of twins. None of the correlations was significant for the identical twins, suggesting that greater resemblance in appearance in identical twins does not make them more similar in personality. Indeed, the data suggested a contrast effect in which identical twins who were easily mistaken in appearance tended to be rated as less similar in personality. Thus, although similarity of appearance may create unequal environments for the two types of twins, it does not appear to bias twin studies in the direction of inflated heritabilities, at least for rating studies of the personality of young twins.
针对双胞胎研究方法中的等环境假设，我们考察了外貌相似性这一变量，因为它会影响年幼双胞胎的人格评分。我们使用了两个独立样本，第一个样本包含95对同性双胞胎，第二个样本包含111对。两个样本中双胞胎的平均年龄均为3.5岁。母亲们对她们的双胞胎在四种人格特质以及外貌易混淆程度方面进行了评分。不出所料，同卵双胞胎在外貌上的相似程度明显高于异卵双胞胎。通过将外貌相似性评分与每对双胞胎在四种人格特质上的绝对差异进行关联，我们考察了这种差异对两类双胞胎人格评分的影响。对于同卵双胞胎而言，这些关联均不显著，这表明同卵双胞胎在外貌上更高的相似性并未使他们在人格上更相似。实际上，数据显示出一种对比效应，即在外貌上容易被认错的同卵双胞胎在人格上往往被评为相似度较低。因此，尽管外貌相似性可能会为两类双胞胎创造不平等的环境，但至少对于年幼双胞胎人格的评分研究而言，它似乎并不会使双胞胎研究朝着高估遗传率的方向产生偏差。
