“Everything that exists in the Universe
is the result of chance and necessity
(Jacques Monod, 1970
quoting Democritus)
“The sociobiology review
the biological basis
social behavior
in all types
organisms ”
(Edward. O. Wilson)
An article published in the April number of this year in a prestigious scientific journal, the Proceedings of the Royal Society of Biological Sciences, has had an impact on the daily headlines that could be described as global. The conclusion of a rigorous epidemiological study, conducted in a population of mothers in the UK universities of Exeter and Oxford, is that the fetal sex is associated with the characteristics of the diet consumed by the mother immediately before and after the time at which it occurs conception when a sperm fertilizes the egg: the more calories it is rich in the diet (and especially when consuming cereal at breakfast) is more likely to conceive a male fetus. As a result of this finding, the authors believe to be low calorie diets, prevalent today in young women in industrialized countries, which would explain the slow decline in the number of births of sons.
This finding may be read, no doubt, as an argument for the influence of the biological behaviors in humans, in the context of evolutionary biology, rooted in Darwinian evolution, and also the kind of sociobiology, as define, in 1975, the American zoologist and entomologist Edward O. Wilson, a discipline on the borderline between anthropology, life sciences and sociology, which studies the interaction between biological systems and the evolution of social behavior, and how and to what extent these social behaviors are listed in the genes, even in humans (Wilson, EO Sociobiology: The New Synthesis, 25 Anniversary Edition, Harvard University Press, 2000).
One of the most active areas of sociobiology is that studies in nonhuman mammals, the biological basis of the ratio between males and females in offspring, seen as the set of children who have a birth animals. ” The hypotheses that have attempted to answer this question, the best known and controversial is the proposal published in the journal Science, in 1973, two scientists from Harvard, Robert sociobiólogo. L. Trivers and mathematician Dan Willard.
The Trivers-Willard hypothesis suggests that the physiological condition of the mother influences the sex of their offspring: mothers whose physiological condition is good, because they live in areas with ample food resources, gestarían more male offspring, whereas mothers whose physiological is poor, because they live in areas short of food, females have more offspring.
This theory, from the perspective of evolutionary biology, predicts that mothers with different physiological conditions with biologically in their pregnancies, the proportion of male offspring / female (sex ratio “or ratio between the sexes in the offspring) in connection with future reproductive benefits of the flock in the environment in which they live: if the environment is favorable, with abundant food that allow mothers to maintain good physiological condition, males predominate in the offspring, as they can reproduce more (andalusia inseminate more and females have more offspring), but if the environment is poor in resources, and physiological condition of the mother is poor, the pups are females, mostly.
The application of the Trivers-Willard hypothesis to humans has been and is controversial because theoretical, empirical and ideological. New Zealand’s Elissa Cameron, an evolutionary biologist who has worked in Australia and South Africa, currently at the University of Nevada at Reno, has recently contributed to the analysis of the Trivers-Willard hypothesis by analyzing nearly 1,000 studies that had subjected to experimental verification. In his review (Proceedings of the Royal Society of London, 2004) found that 34% of the published studies had data that favored the Trivers-Willard hypothesis, at 8.5% did not favor the data, while in the rest found no evidence for or against.
In a previous study in this review, conducted by the Elissa Cameron with wild horses in Australia, concluded that the physical condition of the mother when the concept is associated, significantly, with the birth of a male or a female. In his view, body fat and diet might affect glucose levels in maternal circulation, thus suggesting that these glucose levels at the time of conception could influence the sex of the animal conceived, so excess glucose that favor males.
Working at the University of Pretoria in South Africa, Cameron set out to prove through experiments in mice, the theory of the influence of maternal diet on the sex of the offspring. The experimental method used was adding dexamethasone, which reduces levels of blood glucose, water to drink to be 20 female mice, using as many females who do not drink this water as controls. During three days in cages made for male mice copulate with females with the following results: females with low levels of blood glucose, because they had drunk water with dexamethasone, gave birth to litters with 42% of males, compared with females that had not been drunk, with high levels of blood glucose, with 52% of males in their litters.
That is, under certain conditions, Darwinian natural selection would favor deviations in either direction, which is considered typical division of the sex of the offspring, half female, half male sex andalusia encourage better reproduced in poor physical condition, which is the feminine, and that mothers in poor physiological condition still can find some male insemination while the male weakened more difficult to find a female to mate.
“Would you like a child? Take cereal for breakfast” is the title of a commentary on the magazine’s ScienceNOW Daily News 23 April 2008, which analyzes the findings of researchers from Exeter and Oxford, and their relationships with the hypothesis sociobiológica of Trivers and Willard, in which, even accepting that these results are the first to appear in favor of this hypothesis, however, not clear that the nutrition of the mother is the most important cause of progressive decline in the number of children in developed countries, and is likely to coexist with other factors have also been implicated as environmental pollution.
Anyway, what can not be overlooked is the unfathomable complexity of the biological background of certain human behaviors, so partial to findings, although relevant from the standpoint of sociobiology, it must avoid any temptation too reductionist, understood here as an oversimplification of what is, in itself, is very complicated.