N. . Wolański, A. . Rojas, G. . Valentin, and A. Siniarska, “Each child and each of its features has a specific pace of development, modified by the living conditions in a given period. (Report 2 of a Biennial Monthly Survey in Yucatan, Mexico)”, seb, vol. 2, no. 1, pp. 47–74, Dec. 2004.