The pendulum of scientific explanation swings from reductionism to superordination, from explaining too little to explaining too much. In the 1920s, psychology appealed to the biological sciences for help. By the '30s, political changes favored reliance on the more social sciences. An aversion to biological determinism persisted into the '60s. In more recent years, I think there is a decided swing back to biology. As a developmental psychologist concerned with genetic differences in behavior, I hardly despise the shift; in fact, I feel better understood with each passing year. But I am also concerned about the excessive zeal with which biological notions are being received in psychology today, and, more painfully, with sane of the misconceptions that uncritical adoption can bring.