The role of lactic acid (lactate) in cell metabolism has been significantly revised in recent dec-ades. Initially, lactic acid was attributed to the role of a toxic end product of metabolism, which accumulation in the cell and extracellular space leads to acidosis, muscle pain and other adverse effects. However, it has now become obvious that lactate is not only a universal fuel molecule and the main substrate for gluconeogenesis, but also one of the most ancient metabolites with signaling function, which has a wide range of regulatory activity. The Warburg effect described 100 years ago (that means intensification of glycolysis associated with high lactate production), which is characteristic of many malignant tumors, confirms the key role of lactate not only in physiological conditions, but also in pathologies. The study of lactate’s role in the malignant transformation becomes more relevant in the light of the “atavistic theory of carcinogenesis,” which suggests that tumor cells return to a more primitive hereditary phenotype during micro-evolution. In this review, we attempted to summarize the accumulated knowledges about the functions of lactate in cell metabolism and its role in the process of carcinogenesis, and to con-sider the possible evolutionary significance of the Warburg effect.