Although genetics is all about inheritance, inheritance is certainly not all about genetics. Nearly all inherited characteristics more complicated than a single change in the DNA involve gene and environment acting together. It is impossible to sort them into convenient compartments. An attribute such as intelligence is often seen as a cake which can be sliced into so much “gene” and so much “environment.” In fact, the two are so closely blended that trying to separate them is more like trying to unbake the cake. Failure to understand this simple biological fact leads to confusion and worse. Not far from Herbert Spencer's (and his neighbor Karl Marx's) tomb, in Hampstead―a notably affluent part of London―is a large red-brick house. It was occupied by Sigmund Freud after he fled Austria to avoid racial policies which descended from the Galtonian ideal. On his desk is a collection of stone axes and ancient figurines. Freud's interest in these lay in his belief that behavior is controlled by biological history. Everyone, he thought, recapitulates during childhood the phases which humans experienced during evolution. Freud saw unhappiness as a sort of living fossil, the emergence of ancient behavior which was inappropriate today. Like Galton he viewed the human condition as formed by inheritance. Freud hoped that once he had uncovered the inherited fault which underlies mental illness, he might be able to cure it.    Today's Freudians have moved away from their master's Galtonizing of behavior. 太字は造語です。フランシス・ガルトンはダーウィンの従兄弟で、遺伝学者。人間の才能は遺伝によるという考えで、「優生学」という言葉を創り、優れた遺伝子を持つ人間同士を交配することで、人間の品種改良を提唱。フロイト同様、「遺伝」に重点を置いた。上の文は、今日のフロイト派はその師匠の（遺伝に重きを置く）ガルトン的考え方とは反対の非遺伝的要素、つまり育ちや環境に重点を移している、ということ。

They feel that nurture is more important. Analysis looks for childhood events rather than race-memories. In so doing it is in as much danger as was Freud of trying to unbake the cake of human nature. Any attempt to do so is likely to prove futile. The Siamese cat shows how futile the task may be. Siamese have black fur on the tips of the ears, the tail and the feet, but are white or light brown elsewhere. The cats carry the “Himalayan” mutation, which is also found in rabbits and guinea pigs (but not, unfortunately, in humans). Breeding experiments show that a single gene inherited according to Mendel's laws is involved. At first sight, then, the Siamese cat fur is set in its nature: if coat color is controlled by just one gene then surely there is no room for nurture to play a part. However, the Himalayan mutation is odd. The damaged gene cannot produce pigment at normal body temperature but works perfectly if it is kept cool. This is why the colder parts of the cat's body, its ears, nose, and tail (and, for a male, its testicles) are darker than the rest. An unusually dark cat can be produced by keeping a typical Siamese in the cold and a light one by bringing it up in a warm room. It is meaningless to ask whether its pattern is due to gene or environment. It is due to both. What the Siamese cat―and every living creature―inherits is an ability to respond to the environment in which it is placed.

文頭の Although genetics is all about inheritance, inheritance is certainly not all about genetics.　　の説明。 これまで読んだように、ある生物（人でもシャムネコでも何でも）の外形や性質を決定するのは遺伝だけでなく、環境も大事である。Geneticsといううものは親などから受け継ぐものである。しかし、受継ぐのは遺伝子が環境と相互作用する「仕組み」であり、遺伝（子）単体ではないということ。