This is a repost from Forbes.

Myth: Biology determines that women live longer than men.

Reality: Longevity depends on economic, social, and biological factors. At age 55, American men in the top 10% of the earnings distribution will live 4.3 years longer than women in the bottom 90% of the earnings distribution.

The false certainty that women live longer than men comes from the enduring finding in human biology research that, on average, women live longer than men do. However, averages hide important differences and extreme variation.

First, let us take a closer look at average female survival superiority. New U.S. government data released in November 2017 predicts that, among babies born in 2015, the average white girl will live 4.8 years longer than the average white boy, and the average black girl will live 6.3 years longer than the average black boy.

However, this longevity gap between the sexes narrows with age. Among 55-year-olds, the average white woman will live 3.3 years longer than the average white man and the average black woman will live 4.2 years longer than the average black man.

Why do women live longer on average? We really do not know. Ironically, despite women having higher survival rates at all ages, women across the world suffer from more health problems throughout their lives than men. But this difference between women’s longevity and morbidity could be a selective factor. For example, in terms of ensuring the reproduction of the species, a woman’s wellness is secondary to her need to survive.

Nevertheless, gender is not destiny. Social and economic factors are crucial. You can see this in the changing gender longevity gaps by country. The gender differential in average life expectancy from birth in the United States is 6.5 years. In the United Kingdom, it’s 5.3 years. In Russia, it’s 12 years. And in India, women live on average only about 6 months longer than men.

Perhaps lab rats can help us determine if longevity is a result of nature or nurture. Male lab rats will live longer than females if they have superior diets and healthier parents and grandparents. However, we need a lot more research on how economic factors determine women’s survival superiority at older ages.

In a surprise finding by economists Kathleen Burke and Barry Bosworth, the gap between expected life spans for women and men at age 55 narrows by class. Specifically, the richest 10% of men will live an average of 34.3 more years compared to 31 years for women in the bottom 90% of the earnings distribution.

What does this mean for women and men who are both in the top 10% of the earnings distribution? Burke and Bosworth’s answer: there is no gap. Both are expected to live an average of 34.3 years after age 55. Additionally, high-income men live longer than 90% of women in the bottom 90% of the earnings distribution.

These results suggest that rich men can protect themselves from threats that affect the longevity of lower-income men and women. Our unequal society may create the same longevity gaps as we see among lab rats.

The gender longevity gap looks different at birth than at older ages, when people have their lives and acquired education, income, and made choices exacerbate the wear and tear of age in certain lives. It all adds up to age 55, when a rich man is expected to live longer than 90% of women his age. Perhaps the well-fed, well-bred man has the same advantage as the well-fed, well-bred male lab rat.

Proven longevity differences by class turns commonplace retirement guidelines and social policy on its head. Now that growing class gaps in health care another form of the American divide, both men and women need to plan for the expenses of living in retirement.