Boys are wilder and more aggressive; girls are calmer and more affectionate. That’s what most people seem to believe.

Boys are wilder and more aggressive; girls are calmer and more affectionate. That’s what most people seem to believe. But what are these clichés hiding about the behaviour and character of boys and girls? Are these differences present at birth?

From conception, the embryo is already destined to be either a girl or a boy. If it carries the XX pair of chromosomes, it will be a girl, and if it carries the XY pair, then it will be a boy. However, until about 7 weeks after conception, the embryo is neither male nor female. It even has everything it needs to develop the reproductive system of either a girl or a boy. It’s only towards the eighth week of pregnancy that the sex chromosomes come into play and sexual differentiation begins. And at 12 weeks, the fetus’ reproductive organs and internal and external genital structures are fully differentiated.

Moreover, as surprising as it may seem, there are no sexual hormones that are specific to either girls or boys. Both genders produce hormones (e.g.: testosterone, estrogen, progesterone), which are often incorrectly qualified as either male or female. The difference lies in the quantity: boys have higher levels of testosterone, and girls have more estrogen and progesterone. Before puberty, however, the secretion of these sexual hormones is still weak in both boys and girls.

During the second half of pregnancy, hormones contribute to differentiating the reproductive system’s organs and form neural networks in the brain that will be responsible for reproductive functions at puberty. The brain will then continue to develop until adulthood. Your child is born with billions of neurons that need to interconnect in order to function. The neural junctions, called synapses, develop through learning and experience. In other words, the brain is malleable and creates signals based on the information and stimuli it receives. We’ll take a closer look at how this plays an important role in relation to the differences between the genders later.

Your child’s brain can be altered by her environment and experiences.

It’s been proven that, in the womb, boys develop faster than girls. That’s why, at birth, they are bigger, heavier and have a stronger grip than girls when they grab an object. However, while girls’ bodies don’t grow as quickly, they mature faster. Similarly, even though girls generally weigh less at birth, it is boys who are more fragile. According to the Institut de la statistique du Québec, in 2011 the infant mortality rate in Quebec was 4.7 deaths per 1,000 live births among boys, as opposed to 3.9 among girls. There are also more miscarriages of boys, and they are more likely to be born prematurely and suffer ensuing health problems. “Premature boys have more respiratory and neurological problems than girls, and their survival rate is lower,” says Ahmed Moussa, neonatologist at CHU Sainte-Justine. “They also end up with more cognitive sequelae, including intellectual disabilities.”

Why this difference? Studies have shown that premature boys show more signs of chronic inflammation than girls and that their lung development is not as advanced. We also know that sexual hormones play a role in pulmonary development. But to date, we still don’t know why boys are more vulnerable before and after birth.


Photo: Maxim Morin


Naitre et

Source: Naître et grandir magazine, September 2013
Research and copywriting: Nathalie Vallerand
Scientific review: Sylvie Richard-Bessette, psychologist