第92页 Chapter 5: The Active Germ-Line Replicator

“趋势比现状重要”（https://www.zhihu.com/question/53520699/answer/135897865）
这里 Dawkins 对 difference between two alleles 的强调是另一个例证：
It is a fundamental truth, though it is not always realized, that whenever a geneticist studies a gene 'for' any phenotypic character, he is always referring to a difference between two alleles. This is a recurring theme throughout this book.