More likely to survive from egg to senior citizen.
Males start out in the lead, with perhaps 33% more male embryos than female.
By the time of birth, the lead is closer to 3%.
Infant mortality is almost 30% greater for males.
Now culture kicks in, and males start playing more dangerous games, taking more risks, either as a matter of course, as males are given more dangerous jobs, or just on dares.
Next the male's sickly body starts giving out on him. We all know males are more prone to heart attacks and stroke, among other ailments. All in all, males live an average of 6 years less than females.
Males also have the disadvantage of getting one X chromosome and one Y chromosome. The X chromosome is bigger, and therefore has some genes that the Y doesn't. Males may therefore get a 'bad' gene in their single X chromosome without having a corresponding 'good' gene to counteract it -- one that a female would get in her second X chromosome. Recessive genes, such as the ones for hemophilia, colorblindness, and baldness, can wreak havoc in those poor males.