This is real. Girls learn to read before boys, get better marks in college, and even their brain contains more gray matter. Moreover, boys are medically clearly weaker than girls, as showed by a new research carried out by a team at the University of Pennsylvania and University of Southern California, and published in PNAS: newborn males in developed nations are more likely to die than their female counterparts.

The team analyzed the situation in 15 countries (Sweden, France, Denmark, England/Wales, Norway, The Netherlands, Italy, Switzerland, Finland, the United States, Spain, Australia, Canada, Belgium and Japan) and used data as old as several centuries.

No earlier than 1970, the infant mortality gap between the sexes was as high as 30%. The team found that following this peak, this has decreased due to medical advancements allowing the survival of more newborn boys, like the popularization of cesarean sections and intensive care units for premature babies.

"The marked reversal of historical trends indicates that at an age when males and females experience very similar lives, they are very different in their biological vulnerability, but how different depends on environmental and medical conditions," said corresponding author Eileen Crimmins, associate dean and professor at the USC Davis School of Gerontology.

In the first part of the 20th century, the main cause of infant death was infections, like diarrhea. Now, the main causes of infant death are congenital diseases, birth complications and premature delivery.

Boys have a 60% higher risk of premature birth, which is accompanied by potentially lethal conditions, like respiratory distress syndrome. The larger body and head of the boys make them more vulnerable to birth injury and mortality.

The now common intensive care units for infants have boosted the survival of premature newborn boys. Also, the percentage of c-section births has boosted from 5% in 1970 to over 20% in the present; they are also 20% more commonly practiced for male fetuses.