Our study aims to assess the determinants and the frequency of low birth weight (LBW) in the health district of Monastir (Tunisia). The study was carried out over a three-year period, beginning in January 1995 and ending in December 1997. According to the Monastir district's childbirth register, 1,194 of the 21,393 newborns delivered were babies born with a low birth weight (LBW rate of 5.6%). Common characteristics among the LBW infants were the following: females are more often affected than males (sex ratio of 1.25); 22% of cases were twins; one-third were premature births (< 37 weeks). This study of the determinants of LBW demonstrates that there are several factors linked to the occurrence of LBW such as the mother's age, the number of times she has given birth, an interval between pregnancies of less than 24 months, lack of prenatal care, and the female sex of the baby.

No abstract

Humans have colonized and adapted to extremely diverse environments, and the genetic basis of some such adaptations, for example to high altitude, is understood. In some cases, local or regional variation in selection pressure could also cause behavioural adaptations. Numerous genes influence behaviour, such as alleles at the dopamine receptor locus D4 (DRD4), which are associated with attitude toward risk in experimental settings. We demonstrate genetic differentiation for this gene, but not for five unlinked microsatellite loci, between high- and low risk environments around Mount Merapi, an active volcano in Java, Indonesia. Using a behavioural experiment, we further show that people inhabiting the high risk environment are significantly more risk averse. We provide evidence of a genetic basis for this difference, showing that heterozygotes at the DRD4 locus are more risk averse than either homozygotes. In the high risk environment, allele frequencies are equilibrated, generating a high frequency of heterozygotes. Thus it appears that overdominance (i.e. selective advantage of heterozygotes) generates negative frequency dependent selection, favouring the rarer allele at this locus. Our results therefore provide evidence for adaptation to a marginal habitat through the selection of a neurocognitive trait with a genetic basis.

No abstract

De nombreux pays en développement se sont engagés dans un processus de décentralisation de la gestion de leurs périmètres irrigués. Désormais, les agriculteurs sont eux-mêmes responsables de leur périmètre. Dans ce nouveau contexte, les actions collectives naissantes sont confrontées au défi de la coopération inhérent à la production de biens collectifs. L'objectif de ce travail est d'étudier le comportement de ces agriculteurs participant à l'autogestion des périmètres irrigués. À cet effet, nous mettons en place une expérience de contribution à un jeu de bien public. Ces jeux sont utilisés en économie expérimentale pour étudier le comportement coopératif des individus. La prédiction de la théorie des jeux par rapport à ce jeu consiste en l'adoption de la stratégie du passager clandestin. L'individu maximise son bien être en profitant de l'effort fourni par le groupe. L'expérience en laboratoire montre que les sujets sont plus coopératifs que ce que la théorie prédit mais qu'ils apprennent au fur et à mesure du jeu le choix de la stratégie du passager clandestin. Plusieurs critiques ont été formulées à ces expériences en laboratoire notamment en ce qui concerne la validité externe des résultats. Ce travail rapporte une expérience conduite directement avec des agriculteurs irrigants afin de comparer leur comportement coopératif avec celui obtenu en laboratoire. L'expérience montre que les agriculteurs atteignent un niveau de coopération élevé et que ce dernier se maintient dans le temps. AbstractWhat cooperative behaviour for farmers? Challenging experimental economics with field investigation Many developing countries are committed to a decentralization process of their irrigation system. Farmers have to self-govern their productive activities. Such developments raise the usual challenges of cooperation in collective action providing collective goods. The aim of this investigation is to examine farmers' cooperative behavior. For this purpose, we set up a public good experiment. Public good games are relevant to investigate cooperative behavior. Game theory predicts a free riding strategy as a best reply to the strategic issue of the game. The player maximizes his welfare by benefiting from the effort provided by other members of his group. Experimentation shows that subjects are more cooperative than the theoretical prediction. However, they learn to free ride during the experiment. Several critics are addressed to such experiments, especially concerning the issue of external validity of the results.