Darwin's theory of evolution predicts that men will take more care of children that look like them. A team at the Institut des sciences de l'évolution (CNRS / Université de Montpellier 2) verified this prediction in a study published online in the pre-print issue of the journal Animal Behaviour.
The investment of a father in the care and education of a child is a decisive factor for the child's development, growth and even survival, particularly in countries with high infant mortality. As this behavior is transmitted from generation to generation, it can evolve by natural selection. Evolutionary theory predicts that men should have developed the capacity to recognise their biological children. This recognition of paternity can be made on the basis of physical resemblance.
The study by the ISEM(1) team has shown for the first time that paternal investment is partly influenced by genetically based similarities.
The study was conducted in several villages in Senegal, where the researchers used a method that simultaneously quantified investment made by fathers and their resemblance to their children. A total of thirty families, each with two children, took part in the study. To quantify paternal investment, mothers answered a questionnaire in which they had to estimate the time that the father spent looking after the child, his attention, affection and even the money he provided.
According to their answers, each father was assigned an investment index. A separate group of people, who did not know these families, were chosen as relatedness 'raters' to evaluate facial and olfactory resemblance between children and fathers. For the faces, a photograph of each child was shown to the raters, together with those of three men including the father. For odor, the evaluator had to compare the odors of a tee-shirt worn by the child with those of two men. Each time that the father was recognized, a point was attributed and these results were collated to build a resemblance index.
A correlation was found between these resemblance indices and the paternal investment as calculated from the questionnaire results. The study also clearly confirmed the positive impact of a father's presence on the nutrition and growth of the child. In this region, children who benefit from the presence of their father clearly have better living conditions.
From the point of view of Darwinian theory, very few studies have been made on the link between paternal investment and genetically based resemblance, and none have been done with real families. Today, these results represent an important step in the study of the evolution of paternal investment. The ISEM team has also conducted a study on paternal investment in France from which results will be published in the coming months.
1) Institut des sciences de l'évolution de Montpellier (CNRS / Université de Montpellier)
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