8. Parental Investment, Discriminative Childcare
- Parental psychology has been shaped by selection to make adaptive decisions about the timing and amount of investment in offspring. The probability of future reproduction is expected to be higher when the resources available for a mother would have greater fitness returns if they have been consumed for the subsequent offspring, rather than for a present one. Low birth weight and the infant's health status are expected to strongly influence the child's reproductive value and, thus, the maternal decisions on the amount and timing of investment. In accordance with the theoretical expectations, mothers have been found to breastfeed their healthy infant of normal birth weight for a longer period of time and give birth to the next child later. Those with a low birth weight and/or unhealthy infant terminate lactation earlier and shorten birth spacing. Socioeconomic status, in itself, had also a positive effect on maternal care but it did not change the basic pattern of diminishing maternal care as a function of the infants' low reproductive value. As a result of the combination of these factors, a cumulative effect on maternal investment has been found among mothers with handicapped children at various levels of risk. An attempt has been made to answer the questions of why women decrease the length of breastfeeding in the case of high-risk children, instead of increasing parental care in order to improve these infants' survival ability, and why they make an exception with unhealthy infants without birth weight deficit (Bereczkei 2001)
- In a subsequent study we have made an attempt to clarify the possible adaptive consequences of low weight delivery (Bereczkei et al. 2000). We aimed at revealing the cost and benefit components of bearing small children, estimating the chance of the infants' survival and calculating the mothers' reproductive success. According to the life-history theory, under certain circumstances mothers can enhance their lifetime fitness by lowering the rate of investment in an infant and/or enhancing the rate of the subsequent births. We assumed that living in a risky environment and giving birth to an infant with low weight may involve a shift from a qualitative to a quantitative production of offspring. Given the high infant mortality rates, parents will have a reproductive interest in producing a relatively large number of children with a smaller amount of prenatal investment. This hypothesis was tested among 650 Gypsy and 717 non-Gypsy Hungarian mothers. Our study has revealed that 23.8 % of the Gypsy mothers gave birth to low weight (<2500 g) children, whose mortality rate is very high. These mothers also had more spontaneous abortions and stillbirths than those with normal weight children. As a possible response to these reproductive failures, they shortened birth spacing, gaining 2-4 years for having additional children. Due to the relatively short interbirth intervals, by the end of their fertility period, Gypsy mothers with one or two low birth weight infants had significantly more children than their counterparts. They appeared to level off handicaps associated with low birth delivery by having a larger number of closely spaced children following the birth of one or more infants with a reduced probability of survival.
- Bereczkei T. Evolúciós pszichológia. Osiris Kiadó, Bp., 2003.
- Bereczkei T. (2007) Parental impact on development: how proximate factors mediate adaptive plans. In: Oxford Handbook of Evolutionary Psychology (Eds. R. Dunbar and L. Barrett. Oxford: Oxford University Press, pp. 255-272.
- Bereczkei, T. and Dunbar, R. (2002) Helping-at-the-nest and reproduction in a Hungarian Gypsy population. Current Anthropology 43: 804-809.
- Bereczkei T. (2001) Maternal trade-off in treating high-risk children. Evolution and Human Behavior 22: 197-212.
- Bereczkei, T., Hofer, A., Ivan, Zs (2000). Low birth weight maternal birth-spacing decisions, and future reproduction. A cost-benefit analysis. Human Nature 11: 183-205.
- Bereczkei, T. and Dunbar, R.I.M. (1997) Female-biased reproductive strategies in two Gipsy populations. The Royal Society Proceedings 264: 17-22.
- Berteczkei T. Maternal care of high-risk children. XIV. Human Behavior and Evolution Society Conference, Amherst, USA, 2000.
- Bereczkei T. Sex-ratio at birth among Hungarian Gipsies. XIX. European Sociobiological Conference Conference, Cambridge, 1996.