Language evolution remains contentious and to some extent speculative. While most writers agree that language depends to some extent on some degree of biological infrastructure, the extent and nature of the biological contribution is still controversial. One much-debated issue concerns whether (or to what extent) language shows continuity with other species’ communication. Possible contributions from primate behaviors and capacities have received intense study, fostering neglect of nonprimate species that show some degree of language readiness; moreover, too little attention is paid to contrasting ecologies of great apes and human ancestors. While social intelligence constitutes the most popular selective pressure, specific proposals face formidable problems. Another controversial issue concerns the nature of the earliest stages of language. For later stages, estimates of the role of natural selection vary from 100% to 0. Yet despite continuing disagreements, knowledge in relevant sciences is accumulating fast enough for the issues to be resolved this century.