If identical twins are more similar to each other with respect to an ailment than fraternal twins are, then vulnerability to the disease must be rooted at least in part in heredity.

如果同卵双胞胎彼此在疾病方面比异卵双胞胎更相似，那么这种疾病的易感性至少在一定程度上是由遗传造成的。