Life expectancy in the U.S. is at an all-time high, according to a report released last week by the Centers for Disease Control and Prevention (CDC). And while the news that we’re living, on average, to the ripe old age of 78 years and 9 ½ months isn’t that surprising, there is one stat that is: A girl born in 2012 can expect to live to 81.2 years—almost 5 years longer than a boy baby born the same year, who’s likely live to age 76.4. Weaker sex, indeed.

“Men are biologically and sociologically at a disadvantage from the time they’re conceived to the time they die,” said Dr. Marianne Legato, professor emerita of clinical medicine at Columbia University College of Physicians and Surgeons and founder and director of the Foundation for Gender-Specific Medicine. Here’s why:

Females are tougher in utero
Two and a half as many boys are conceived as girls, Legato said, but they’re so much more likely to succumb to prenatal infection or other issues in the womb that by the time they’re born, the ratio is close to one to one.

“They’re also slower to develop physically than girls prenatally, which means they’re more likely to die if they are preemies due to underdeveloped lung or brain development,” Legato explained.

RELATED: 10 Biggest Myths About the Flu

Women are less likely to be daredevils
Unintentional injuries are the third leading cause of death in men, according to the CDC; for women it’s only the sixth. Again, you can blame it on biology: The frontal lobes of the brain—which deal with responsibility and risk calculation—develop much more slowly in males than females, Legato said.

The result: Guys often take many more risks (which you probably already realize if your small son has taken one too many spins off his bike handlebars).

“Almost inevitably, a male will take risks that a woman of his same age wouldn’t take,” Legato said.

Women succumb to heart disease later
Heart disease is the leading killer of both men and women, but men are more likely to develop it—and die from it—as early as their 30s and 40s. Women, on the other hand, typically develop heart disease 10 years later than men. They’re protected from it until menopause, since their bodies churn out estrogen, which helps keep arteries strong and flexible, said Legato.

RELATED: 15 Weird Things Linked to Heart Attacks

Women have stronger social networks
Friends make good medicine: People with strong social connections have a 50 percent lower chance of dying than those with few social ties, according to a 2010 study at Brigham Young University.

“Most men tend to hold their stress and worries close to their chest, while women tend to reach out and talk to others,” Legato explained.

The one exception: married men, which also explains why so many studies show that they’re likely to be healthier and live longer.

RELATED: How Friends Make You Healthier

Women take better care of their health
Men are 24 percent less likely than women to have visited a doctor within the past year and are 22 percent more likely to skip out on cholesterol testing, according to the Agency for Healthcare Research and Quality. In fact more than a quarter (28 percent) of men don’t have a regular physician and about one in five didn’t have health insurance in 2012, according to the Kaiser Family Foundation.

You can blame it on the so-called John Wayne syndrome: “Men often deny illness; they minimize symptoms because they don’t want to go to a doctor and find out something is wrong,” Legato noted.

RELATED: 10 Worst States for Women’s Health

This article originally appeared on Health.com.