Boys exist because they get a Y chromosome from their fathers instead of an X chromosome like they get from their mothers.
A girl is formed if the baby gets an X chromosome from each parent. That one chromosome makes boy babies more susceptible to a variety of diseases.
If girls have a defective copy of a gene on one of their two X chromosomes, they usually have a non-defective copy on the other one that will work just fine.
Because boys have only one X chromosome, any defective genes on it can cause diseases usually not seen in girls.
These “X-linked” diseases include hemophilia, red-green color blindness, and some types of muscular dystrophy.
For a variety of reasons, boys tend to more commonly develop a whole host of disorders.
These include autism spectrum disorders, Tourette’s syndrome, reading delay, conduct disorders, oppositional-defiant disorder and stuttering.
Many of these ailments are genetic or have a strong genetic component.
In the U.S., there are 105 male infants born to every 100 female infants. Because of genetic defects seen in the boy babies, girls are 10% more likely to survive infancy.
Even though male infants are born larger on average than female infants, they are less developed physically.
In fact, a newborn female infant is about as developed as a 4- to 6-week-old male infant. This can make a big difference if a baby is born prematurely.
Testosterone is the hormone that boys secrete even while developing inside their mothers – it is what makes them male.
The hormone makes males more aggressive, more active and more likely to take risks. Unfortunately, it makes males more injury-prone.
The larger amounts of testosterone that boys secrete during and after puberty suppress their immune systems.
This decreases the incidence of asthma and allergies seen in them, but it also makes them more susceptible to infection.
The estrogen that helps girls develop into women actually makes their immune systems stronger.
Some of the causes of increased disease seen in males are cultural.
Men have traditionally spent more time outside of the house doing dangerous tasks (ex. lumberjacking, warfare, etc.).
They also tended to get more exposure to dangerous substances (ex. coal dust, automotive fluids, etc.).
Boys tend to be larger and physically stronger than girls. In other ways, though, they are weaker. This definitely includes their susceptibility to disease.