The Toxic Sex

Women tend to live longer than men.  We see this trend definitively in birth and death records going back centuries, and the pattern may even stretch into ancient human history.  Of course, the sad fact is that the life expectancy at birth of someone in the first world is longer than someone born in the third world, since life expectancy varies greatly worldwide.  But, if you compare men and women in the same country or region, men tend to have a shorter life expectancy than women.  According to the CIA World Factbook, global life expectancy at birth for 2012 was 66.57 years, with a half-century spread separating Chad’s 49.69 years and Monaco’s 89.68 years.  The breakdown of life expectancy by sex is striking and nearly universal in pattern.  Worldwide, men at birth can expect to live an average of 64.52 years while the average for women is 68.76.  This trend holds for nearly every country (except for a handful in the midst of prolonged insurgency or ravaged by the unchecked AIDS epidemic).  Monaco’s men have an average life expectancy at birth of nearly 86 years, while for women it is almost 94 years.  For Chad, male life expectancy at birth is just under 48 years, and for women it is nearly 50.  In the United States, a baby boy has can expect to live an average of just over 76 years, while the outlook is five years higher for girls.  Thus, wherever you’re born in the world, it appears that being a man comes with hazards.

The root causes for the predicted shorter lifespan in males have been difficult to pin down.  Still, it doesn’t take much mining of birth and death records to begin to see the symptoms.  Early in life, males actually outnumber females, but die early on at a higher rate.  At fertilization, there are an estimated 107 male embryos for every 100 females.  This ratio decreases to 105 boys for every 100 girls at birth, indicating that more male fetuses die before birth.  This ratio of boys-to-girls continues to decrease slowly throughout childhood, teenage years, and into early adulthood, until roughly age 25.  At that age, women begin to outnumber men, and the trend gets more pronounced as the decades drag on.  In the United States, an estimated 85% of centenarians are women.

It's a guy thing?

It’s a guy thing?

There are a number of lifestyle factors that may partially explain this earlier death rate among men.  Men are more likely than women to smoke, drink alcohol, and take illegal drugs.  These and other lifestyle choices that can lead to premature death from causes ranging from drug overdose or diseases such as cancer or liver cirrhosis.  Compared to women, men are also more likely to die from accidents or suicide, as well as conditions such as heart disease.  While these grim statistics may explain why women start out life with a longer life expectancy than men, they don’t really explain why men are more likely to engage in these behaviors.  There could be genetic or physiological causes, sociocultural influences, or some mixture of both.

There is some evidence that genes might be to blame.  Specifically, genes in males that are responsible for the production of male hormones, including infamous testosterone.  The evidence implicating testosterone and other male hormones comes from an invasive procedure carried out by many human societies for millennia: castration.  The techniques used to castrate males range from gruesome and inhumane practices of history to today’s minimally-invasive surgical castration or non-surgical chemical castration.  But in all these cases, the primary results are the same: in castrated males the gonads, the testes (testicles), no longer produce male hormones.  If the castration procedure removes the testicles entirely, he will be sterile.  Depending on the age at which a male is castrated, the effects can be profound.  Castrated pre-pubescent boys retain the small genitals and low muscular build of their youth, as well as the high-pitched voices that made castrati singers popular starting with the ancient Byzantine court.  They develop little or no sexual desire.  Men castrated after puberty report a decreased (or absent) sex drive, though other post-pubescent changes to anatomy and appearance (including a deeper voice and body hair) remain.

Boys and men were castrated for a variety of purposes throughout human history, from punishment for crimes to government service as a eunuch.  But, regardless of the technique used, bits of demographic data collected over the centuries indicates that castrated men (assuming they survived the often harsh castration process) appeared to live longer lives than their intact male counterparts.  This observation, which comes to us from multiple sources and cultures, might indicate that male hormones contribute to the shorter male life expectancy.  However, the history of castration has not provided us with a definitive study of the longevity of castrated and intact men.  The observations from historical data are correlational, spotty, and vague in many cases.  Many scientists have rightly pointed out that the comparisons between castrated and intact men in historical records did not rule out many confounding factors when comparing two groups, such as lifestyle and livelihood.  It is not useful, for example, to compare the lifespan of a castrated, mentally-ill man in an institution to an intact, non-institutionalized man, since their lifespans are likely affected by so many other factors that differ between them (mental state, freedom) that the effect of castration would be difficult or impossible to discern.

Many cultures used castrated men as eunuchs for service in royal courts, harems, or bureaucratic offices.  They often had better access to food, shelter, and other benefits of a relatively high social position.  In fact, some eunuchs volunteered to be castrated and trained in these roles in order to improve their social standing and ensure a more comfortable life for themselves.  Yet even in these cases from history, a palace eunuch led a much different lifestyle to his intact brethren out among the general populace.  History did not design an ideal experiment where we could compare the lifespans of eunuchs and intact men who had similar social standings, lifestyles, and livelihoods.

That is, until a group of scientists and historians from South Korea delved into historical and demographic records concerning a unique group of eunuchs from Korea’s Chosun Dynasty (1392-1910).  Chosun-era eunuchs lived relatively privileged lives in government service.  Unlike eunuchs in many other cultures, they could have homes outside of the royal palace, and were encouraged to marry and adopt children (usually castrated boys and intact girls).  While these eunuchs performed diverse roles at the royal palace and within the government’s civil service bureaucracy, the Chosun Dynasty also saw many intact men perform similar duties and lead similar private lives with marriages, children, and homes outside of the palace.  Critically, both eunuchs and intact men meticulously documented demographic details of their lives and families for generations.  A eunuch would pass along family records to their oldest adopted (usually castrated) son, who would marry and adopt his own children.  In studying the eunuch family records, the Yang-Se-Gye-Bo, and checking its accuracy by cross-referencing its entries with other historical documents from the Chosun era, scientists were able to calculate the lifespans of government eunuchs and compare them to the lifespans of intact men from the same socio-economic level who also had families.  While eunuchs lived to an average age of 70, intact men died at an average age of 51 to 56.  In addition, 3 of the 81 eunuchs with verifiable birth and death dates lived at least a century, a rate of centenarian achievement that is 130 times greater than the frequency of male centenarians in the Western world today.  One eunuch even made it to 109 years.  Thus, it appears that castration and removal of the male hormones helped these eunuchs live longer lives than their intact brethren, even though both groups had similar social and political power, as well as similar home lives.

This is a compelling line of evidence linking to testosterone and other male hormones a lower life expectancy among men.  Scientists do not completely understand why testosterone could have such an effect.  There is evidence that testosterone interferes with the immune response, and it most certainly affects behavior.  But, biologists have not yet woven together testosterone’s many effects into a comprehensive tapestry for the role this sex hormone plays in the human condition.  Thus, it will be some time before we completely understand why and how testosterone contributes to a decreased male life expectancy.  However, as others have recently pointed out, testosterone isn’t all bad.  Men couldn’t have children without it, and many scientists also think men couldn’t attract mates without it.

Brainless?  Or should we blame the hormones?

Brainless? Or should we blame the hormones?

Testosterone is not the sole cause of decreased male life expectancy.  For example, by some quirk of mammalian genetics, there are between 1,000 and 2,000 genes for which human males (but not females) lack a spare copy; if a man’s cells have a mutation in one of these genes, he has no extra copy to prevent trouble brewing.  There are also likely other factors that depress male life expectancy at birth, though they have not been well studied.  But while this phenomenon is fascinating to explore from a biological and sociological standpoint, it is critical to remember that life expectancy is not lifespan.  Life expectancy is a prediction, while lifespan is reality.  Any person’s lifespan is affected by a myriad of genetic and environmental factors.  For most, lifestyle choices have a tremendous impact on whether or not a person’s life expectancy is at all close to his or her lifespan… perhaps as great an impact as the hormones flowing from the gonads.

Further reading:

About James Urton

I went to school to become a molecular biologist.  At some point in this long education, I discovered that I love communicating science to the general public: talks, writing, at a pub, on the street corner...  Whatever venue will let me hold your attention for a few moments.  Unfortunately, I can't do this for a living, since no one will pay me.  So, I have a job as a molecular biologist at the University of Washington, where I get to work with great scientists on some really awesome projects, and I'll blog about science here at Muller's Ratchet in my spare time. Why should the general public want to know anything about science? Here's my explanation (which also explains why I chose the name Muller's Ratchet for this site). Briefly as a graduate student (before I had to devote all of my time to graduating), I blogged at Adaptive Radiation.
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2 Responses to The Toxic Sex

  1. A says:

    …but I still find myself looking down at my manhood and can’t help but say “neither can live while the other survives.”

  2. Eric says:

    The Art of Manliness blog is doing a whole week of posts on testosterone, if you’re interested:

    http://artofmanliness.com/2013/01/13/testosterone-week-intro/

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