Is the reduction of birth intervals an efficient reproductive strategy in traditional Morocco?

Birth interval lengths are analysed from reproductive life histories of 517 Berber peasant women of the region of Marrakesh (Southern Morocco), whose fertility developed in a full traditional context. The high mortality rates associated with short birth intervals indicate that a rapid succession of births is detrimental to the progeny. The reproductive efficiency of the traditional propensity to a large family size is therefore examined by means of two different evaluations of reproductive success: the 'absolute' reproductive success (the absolute number of offspring surviving to maturity) and the 'relative' reproductive success (the proportion of live born surviving to maturity). The first shows that close pregnancies increase the fertility rate to such an extent that the associate higher number of deaths is more than compensated for, so that the women practising short birth intervals produce more surviving offspring than the others by the end of their reproductive life. The second shows that the probability of survival is directly associated with birth interval length, the efficiency of the reproductive process being therefore greater as birth intervals grow. It is suggested that these two behaviours are not contradictory, and that they represent two successive steps of the same reproductive adjustment to evolving environmental conditions.