Fans of Douglas Hofstadter, Daniel Bennet, and Richard Dawkins (as well as science buffs and readers of “Wired Magazine”) will revel in Aaron Lynch’s groundbreaking examination of memetics–the new study of how ideas and beliefs spread. What characterizes a meme is its capacity for displacing rival ideas and beliefs in an evolutionary drama that determines and changes the way people think. Exactly how do ideas spread, and what are the factors that make them genuine thought contagions? Why, for instance, do some beliefs spread throughout society, while others dwindle to extinction? What drives those intensely held beliefs that spawn ideological and political debates such as views on abortion and opinions about sex and sexuality?By drawing on examples from everyday life, Lynch develops a conceptual basis for understanding memetics. Memes evolve by natural selection in a process similar to that of Genes in evolutionary biology. What makes an idea a potent meme is how effectively it out-propagates other ideas. In memetic evolution, the “fittest ideas” are not always the truest or the most helpful, but the ones best at self replication.Thus, crash diets spread not because of lasting benefit, but by alternating episodes of dramatic weight loss and slow regain. Each sudden thinning provokes onlookers to ask, “How did you do it?” thereby manipulating them to experiment with the diet and in turn, spread it again. The faster the pounds return, the more often these people enter that disseminating phase, all of which favors outbreaks of the most pathogenic diets. Like a software virus traveling on the Internet or a flu strain passing through a city, thought contagions proliferate by programming for their own propagation. Lynch argues that certain beliefs spread like viruses and evolve like microbes, as mutant strains vie for more adherents and more hosts. In its most revolutionary aspect, memetics asks not how people accumulate ideas, but how ideas accumulate people. Readers of this intriguing theory will be amazed to discover that many popular beliefs about family, sex, politics, religion, health, and war have succeeded by their “fitness” as thought contagions.