According to Stephen Hawking in A Brief History of Time, "a theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model which contains only a few arbitrary elements, and it must make definite predictions about the results of future observations". He goes on to state, "any physical theory is always provisional, in the sense that it is only a hypothesis; you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single repeatable observation which disagrees with the predictions of the theory".
算了，多說點要不說不明白。Genome（DNA）里有一種特殊的序列叫transposon,是一種有趣的DNA序列(The lady who discovered it won Nobel prize)。它們能不斷複製自己，然後把複製的copy插入genome里。而且這種插入的位點是隨機的。每次這一事件發生，就會產生一個unique pattern在genome(DNA)上保留下來。如果這一隨機事件發生在生殖細胞里，這一隨機事件在DNA里的記錄會被忠實的遺傳到後代中去。只有從同一祖先繼承下來這一pattern的個體會share這一相同點。
狗仔卡
