I used to believe that the ethos of science, the very nature of science, guaranteed the ethical behavior of its practitioners. As a student and a young researcher, I could not conceive of cheating, claiming credit for the work of others, or fabricating data. Among my mentors and my colleagues, I saw no evidence that anyone else believed otherwise. And I didn't know enough of the history of my own subject to be aware of ethical lapses by earlier scientists. There was, I sensed, a wonderful purity to science. Looking back, I have to count naiveté as among my virtues as a scientist.
Now I have changed my mind, and I have changed it because of evidence, which is what we scientists are supposed to do. Various examples of cheating, some of them quite serious, have come to light in the last few decades, and misbehaviors in earlier times have been reported as well. Scientists are, as the saying goes, "only human," which, in my opinion, is neither an excuse nor an adequate explanation. Unfortunately, scientists are now subjected to greater competitive pressures, financial and otherwise, than was typical when I was starting out. Some — a few — succumb.
We do need to teach ethics as essential to the conduct of science, and we need to teach the simple lesson that in science crime doesn't pay. But above all, we need to demonstrate by example that the highest ethical standards should, and often do, come naturally.