When nearly a dozen scientists, all in some way associated with research on biotechnology, die within a year of the 9/11 attacks, can it be coincidence? Yes, says Lisa Belkin, author of this excellent article on one of the constants of pseudoscience, the attribution of "cause" to random events. In a class of 23 students, there is a 50% chance that two of them have the same birthday, much higher than most people would predict. What are the chances that two elderly Finnish twin brothers would be killed in separate bicycle accidents within two hours on March 5 of this year? That actually happened, and investigations revealed no reason other than chance. The human mind seems programmed to recognize and to attribute significance to patterns in nature, but they are not always the result of nonrandom causes. Ms. Belkin has written a perceptive and provocative essay.