We are the mammals that take the longest to reach mature and adult body development. It takes more than a dozen years, three or four times longer than the species closest to us.
At four years old, for example, while our chimpanzee “cousins” are already in their reproductive age, the human species is in a defenseless state and very dependent on adults for its survival.
Why is this so? Why do we need such a prolonged childhood? An answer, sought for many years by anthropologists and other scientists, has now been published in the US journal Proceedings of the National Academy of Sciences.
In a detailed study published in the advanced edition of that journalNorthwestern University scientists present the results obtained by studying the consumption of glucose by the brain throughout childhood. The investigation was carried out using brain imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging.
Scientists measured the consumption of glucose (the main food of neurons that are cells in nervous tissue) in relation to brain volume at different ages. Thus, they were able to determine whether the stages of development in which the brain consumes more glucose proportionally coincide with the periods in which the growth of the rest of the organism is slower.
The results show that between four and five years of age is when the brain's voracity for glucose is at a maximum, which retards the proportional growth of the rest of the body. At this stage of child growth, the brain burns 66% of the energy that the entire body consumes at rest! With glucose being primarily consumed by the brain, the rest of the organism can only develop at a much slower pace than that seen in other primates.
The study now published also contradicts the hypothesis that suggested that newborn brains needed proportionally more resources. It diverts this higher consumption to the five-year-olds. According to the first author of the article, the anthropologist Christopher Kuzawa, “the results suggest that it is between the ages of four and five that a greater number of synapses (connections between neurons) are produced in the brain, and that is also when we learn many of the things we need to acquire to be human”.
Thus, we can say that long childhood is an evolutionary price that the human species “pays” so that the intelligence and other cognitive abilities that characterize it can be acquired and developed. The rest of the body can wait.
Author Antonio Piedade
Science in the Regional Press – Ciência Viva
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