Does the maternal instinct really exist? In an article published on June 1 on its website, France Inter explains that it would actually be a “vast deception”, a “social construction”, even a “useful invention”. To support this information, which goes against all the research in this field, the most listened to radio station in the country quotes… a comic book author, as well as columnists and producers of various shows that the media has produced on the parental instinct. But without scientific sources bearing directly on the subject.
Seen more than 2 million times on Twitter, the article conveys however many untruths. We read there in particular that in prehistory men and women would have had the same size. A reminiscence of the theory of the “steak patriarchy”, of the anthropologist Priscille Touraille. According to this researcher, women are smaller than men, because the latter have deprived them of meat since prehistoric times. Never published in a scientific journal, the idea is however regularly relayed as a truth in many media.
Contrary to what France Inter suggests, the concept of maternal instinct is not a sexist creation – even though it has regularly been used to justify male dominance and confine women to the margins of society. “What is written is completely false, it is an assemblage of beliefs without any foundation, which denies the biological differences between the sexes”, castigates Claudine Junien, professor emeritus of genetics at the University of Versailles, former director of unit researcher at Inserm and co-author, with Nicole Priollaud, of It’s your sex that makes the difference, published in February by Plon.
Behind this “instinct”, no baby bottles or nappies, but a paradox: almost all female mammals, a class of animals to which Homo sapiens, flee, ignore or attack the young when they have never had one. A phenomenon documented many times, as recalled by a review of the literature on the question, published in Science in 2014. Conversely, a large majority of females who have already given birth cannot resist the cries or the smell of the young, even when they are not their own.
Before having procreated, the females flee the young
During gestation, therefore, something favors the attention of most females, helps them to attach themselves to the young and to react to their stimuli. This is what the maternal instinct is: a trigger, an impulse, a biological, natural nudge, which encourages interest in the fate of one’s offspring, just as there are survival or sexual instincts which lead to to sustain life or to procreate. Nothing more, and certainly not an “ability […] to know how to take care of your child”, as France Inter tries to define it. No “knowledge” in there: if you transfuse blood from pregnant rats to never fertilized rats, the latter end up adopting the same behaviours.
Further examinations make it possible to clarify the phenomenon: at the time of fertilization, immense hormonal changes take place in mammals. They allow the development of the embryo, the expulsion of the young and the production of milk. But the estrogens, progesterone, oxytocin and prolactin released modify the neuron circuits in passing, in a profound and lasting way. The brain transforms and prepares to ensure the survival of the offspring even before they are born.
This remodeling promotes brain activity in the areas involved in the maternal bond. It has been observed several times in the human species, thanks to brain imaging. During human pregnancy, which generally shares the same characteristics as that of other mammals, the female brain seems to undergo “further maturation”, a “better specialization” of the neural network involved in “social cognition”, described in particular a study published in 2016 in Nature, the first of its kind, conducted on 25 women, before and after their first pregnancy.
Pregnancy changes the neural circuits of women
Could it be, however, that these cues, neurological and hormonal, are misinterpreted because of gender stereotypes? After all, the woman has long been seen as a mothering machine by many men. To guard against such risks, but above all to clarify our knowledge, researchers continue to study the brains of pregnant women from other aspects. A study published in 2022 in Nature alwaysthis time carried out on 40 women pregnant with their first child, confirmed that the changes observed were indeed due to their pregnancy, thanks in particular to the addition of examinations at different stages of the pregnancy.
The modern woman therefore has a “maternal instinct”. No offense to France Inter, or even to Elisabeth Badinter, who in 1980 claimed that there was nothing like it. Still, the word is often misunderstood, interpreted as proof that the attachment to the child would be irresistible and systematic. “Because it is hereditary, it would be obligatory, present in all individuals. These are common errors. Sometimes the click does not occur, or it occurs but is then masked by other phenomena”, illustrates Ghislain Nicaise, biologist, professor emeritus at the University of the Côte d’Azur.
By dint of controversy and media misinterpretation, the semantics is evolving: “Many scientists now prefer to speak of maternal adaptations, to better account for the diversity of parental strategies within each species, and their permeability to other phenomena. For example, to living conditions, the number of children or mating strategies and, in humans, to societal fashions and customs”, explains David Buss, researcher at the University of Texas , a specialist in human mating strategies.
And with fathers?
Especially since there is also a paternal instinct, that is to say biological mechanisms favoring the protection of the offspring, although these are much rarer in mammals. “It would also be the same groups of neurons that would act in both sexes, but they produce different effects, due to the biological differences between the two sexes”, explains geneticist Claudine Junien. What, once again, to invalidate the extrapolations which mix innate and acquired, according to which the existence of transformations in the brain of the woman would justify, for example, that the men disengage from parental tasks.
The brain of men evolves, him, in contact with the child, according to several studies, including one carried out in particular on homosexual parents, published in 2014 in PNAS, the journal of the American Academy of Sciences. Spending time with offspring would increase levels of oxytocin, the bonding hormone par excellence, and drop testosterone levels. These changes would also allow, but in another way, a reorganization of the brain, which would facilitate the establishment of parental behaviors, and therefore the father’s commitment to his child.
A relatively singular characteristic in mammals, as pointed out in particular by a literature review published in 2014 in Science, which is explained by different selection processes that occurred during evolution. “In the human species, childhood is so long and fragile that it takes the cooperation of several people to optimize the chances of survival. The saying is true: ‘It takes a whole village to make a child.’ We call it alloparenting”, popularizes the biologist Ghislain Nicaise. Thus the man can acquire a paternal instinct, thanks to these faculties of socialization.
If these different phenomena are the subject of consensus, research on the parental instinct has been bubbling in recent years, thanks to progress in brain imaging and genetics. A Franco-American woman is notably at the forefront of this field: in 2020, biologist Catherine Dulac, who officiates at Harvard, was rewarded with the prestigious Breakthrough Prize for his groundbreaking work on the neural circuits behind the specification of parental behaviors in mice.
The discoveries of Catherine Dulac should put an end to the polemics about the different parental instincts. They show that while female and male rats have specialized neural circuits responsible for parenting, that is to say different according to their sex, they are also very dependent on their life experiences. Thus a behavior hitherto attributed only to the mother can occur in the father depending on the context and his environment… Proof that innate and acquired always go hand in hand.