Resumen

FERRARINI, Stella Ofelia  y  MENDEZ, Marta Graciela. (Girl or boy: birth intervals and children sex among wichi). Cuad. Fac. Humanid. Cienc. Soc., Univ. Nac. Jujuy [online]. 2014, n.45, pp.137-154. ISSN 1668-8104.

Birth interval is, from an evolutionary perspective, measure of parental investment in a child. Parents make active decisions with respect to the length of the birth intervals, even in societies without access to artificial methods of contraconception. This parental investment can vary according to the child's sex. The sexual preferences differ with the ecological limitations the societies face. The traditional societies based on the subsistence, exhibit fertility levels near to the natural one and they have low levels access at modern health care. Birth intervals are investigated among the Wichí mothers to estimate the time that maternal effort invest in each offspring and if there are sexual differences in the timing of the births. Mothers spaced their childbirths in mean intervals of 38.05 months. 60.8% completed intervals smaller than 36 months. The sex-ratio was biased toward women. However, the intervals opened by male were significantly longer that those open by woman. Sexual effect was not detected for the closing. Wichí reproductive strategy is directed to assure a bigger maternal investment in the male children. Either because they look for the survival of the scarcest sex that, exactly for this reason, increases their reproductive value, or because the birth interval is biologically adjusted and the mothers take more time in recovering some level of necessary physiologic condition for a next pregnancy. These mechanisms are not mutually exclusive and they can both to be operating at the same time.

Palabras clave : Birth Interval; Parental Investment; Sex-ratio; Wichí.

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