Development proceeds as a stereotypical sequence of landmarking events conserved among different vertebrate species. However, the pace of development varies greatly among species and is, more importantly, species-specific. For instance, human embryogenesis follows the same developmental events but occurs 2-3 times more slowly than mouse embryogenesis. Historically, the species-specific pace of development has been hypothesized to scale with various parameters such as body weight, gestation period, metabolic rate, or biochemical reaction rate. This paper compared the periodic expression of segmentation clock genes, which represent the pace of somitic development, in cells differentiated from pluripotent stem cells prepared from six different mammalian species.