The Olmecs are sometimes referred to as the mother culture of Mesoamerica, as they were the first Mesoamerican civilization and laid many of the foundations for the civilizations that followed. However, the causes and degree of Olmec influences on Mesoamerican cultures has been a subject of debate over many decades. Practices introduced by the Olmec include ritual bloodletting and the Mesoamerican ballgame; hallmarks of subsequent Mesoamerican societies such as the Maya and Aztec. Although the Mesoamerican writing system would fully develop later, early Olmec ceramics show representations that may be interpreted as codices.