 Darwin’s theory of natural selection explains adaptation by appealing to what we now call vertical transmission—the inheritance of parental traits by offspring. As we have seen, cultural processes such as learning might, in principle, underpin this form of inheritance. But we do not learn only from our parents—we also learn from peers, authority-figures and so forth. This is known as oblique transmission. Once we acknowledge the possibility that learning can underpin natural selection, we also acknowledge that a theory of evolution—a theory which seeks to explain change, including adaptive change in a population—may also need to be further expanded to encompass oblique transmission. The admittance of oblique transmission into evolutionary theory necessitates far more radical revisions to traditional Darwinian models of evolution. This is because oblique transmission opens up the possibility that some traits may spread through a population in spite of the fact that they reduce the fitness of the individuals who bear them.