Most mans in the animal world do little paternity. Their strategy is simple: fertilize as many females as possible and hope for the best. Sometimes, however, a man’s parental investment pays off. The chicks of songbirds are usually cared for by both mother and father. Wolf packs see alpha males and females collaborate to raise cubs. And in human beings the father of children also turns to help in raising children.
Understanding why some men settle in a family with the mother of their children and others do not is usually seen as the prerogative of the social sciences. But biology also has a role to play. And the work has just been published in Proceedings of the National Academy of SciencesLee Hitler, from the University of Notre Dame in Indiana, clarifies how part of this biological mechanism, testosterone, works.
Preliminary studies show that high testosterone levels the main male hormoneharmful to family life. Parents with lower testosterone levels provide more child care and are the best partners for mothers of children. Indeed, parenthood is often associated with a drop in testosterone levels. Conversely, men with high testosterone are less prone to themselves.
Dr. Gettler showed something further. This is what an adult man’s testosterone level seems to correlate with, whether his father was present in his teens. His data come from a survey launched in the city of Cebu in the Philippines in 1983. During the monitoring of health and nutrition 966 men registered as children. Extensive information was also collected on whether the parents of these men were nearby and whether they provided parental care in the families in which they were raised. In addition, it was documented whether the participants were married, had children and, if so, whether they were involved in child care. Importantly, he also measured their testosterone levels at the ages of 21, 26 and 30.
Overall, Dr. Gettler and his colleagues found that by becoming parents, men had lower testosterone levels when their own parents lived with them and practiced them as teenagers. In particular, if this had happened, the testosterone levels in their saliva would have been 16% lower than in men whose parents were not left behind to help their upbringing.
This difference has two possible explanations. One is that it is directly genetic, and parents with high testosterone levels (those who are least likely to stay close) give birth to sons with high testosterone levels. In this case, the correlation with the absence of the father would be a coincidence. Second, adolescent experience actually modulates testosterone levels. This explanation, which Dr. Gettler prefers, could lead to a vicious circle of high-testosterone men who abandon their sons, who in turn become high-testosterone.
Dr. Hitler found that testosterone levels are not entirely determined in matters of parental care. Some of those surveyed whose parents were absent in adolescence and who had high hormone levels nevertheless became caregivers. But they are indicative.
Why this model should apply is an unanswered question. But the zoologist, looking at these data, may be tempted to see in them an example of plasticity of development, in which the same genes in different circumstances bring different but relevant results.
If raising young animals is at the expense of reproductive opportunities lost elsewhere (which is thought to be the case), then evolution would not have contributed to this in times of uncertainty – in times that lead to early death. A dead person cannot take care of his children, and dead children cannot be cared for. It’s best, evolutionarily speaking, to spread your genes far and wide as long as you can. Because the absence of a father could, in turn, mark such uncertain times, as this absence can cause high levels of testosterone in development, which encourages this, even if it is not in line with the modern world.
This is speculation. But whatever the truth, Dr. Hitler’s discovery certainly sheds useful light on the problem of orphans and how to put an end to it. ■