Ages and cranial capacity data: C. De Miguel and M. Henneberg (2001). "Variation in hominid brain size: How much is due to method?" Homo 52(1), pp. 3-58.

Cranial capacity of modern humans: McHenry et al. (1994). "Tempo and mode in human evolution." Proceedings of the National Academy of Sciences, 91:6780-6.

Graphic by Nick Matzke, National Center for Science Education. May be freely reproduced for nonprofit educational purposes.