Monday, November 3, 2014

The Longevity Deception (part 1 of 5)

1. The Longevity Deception

Have you ever heard people saying how good we have it because in the recent past "a forty-year old was an old man," or something like that? Have you ever heard someone denigrate the hunter-gatherer lifestyle by saying "well, you know, they were all dead by age thirty-five." Do you know someone who avoids the Paleo diet because no one in the Paloelithic Era ever lived past age 40, the implication being that if you avoid sugar, salt, grains, dairy, legumes and processed foods then you too will not live past forty? What's with that? Well, read on.

What if I told you that the average hunter-gatherer lived to be zero?

That might seem absurd, and indeed it is. Part of the confusion stems from the way we use the English language, and how that interacts with the more precise mathematical concepts of mean, median, and mode.

The above statement is in fact true if am using the term average in its standard use in English meaning “normal” or “typical.” But this usage is imprecise. Mathematically we are using the term “average” to mean the mode, which is simply the number that occurs most often in a data set. As the BBC recently pointed out, as recently as 1964, the most common age of death in England and Wales was zero years, as it had been throughout most of human history. The reason is that for most of human history, there has been a very high infant mortality rate. In many past societies, up to a quarter of infants died (0 years). Consider the data set from a hypothetical tribe below:

5 0 0 35 0 75 0 68 0 25 0 0 0 0 0 3 0 50 58 72 85 0 65 56 0 42 0 0 0 0 66 0 12 0 0 76 0 0 57 0 75 0 0 0 47.

So if I gather all the dates of death of the tribe, the most common number (the mode) I find will be zero. Thus the “average” hunter-gatherer lived to be zero. Note that most people in the tribe who did not die at zero lived to be well past fifty. If a hunter-gatherer made it past 15, the odds would be heavily in his favor to live to a decent age. Yet the average (mode) age of death in this tribe is zero years. Hence the statement above.

However, if we throw out these zeroes and take the modal adult life span, we get something closer to what we typically mean when we say “the average hunter gatherer lived to be X.” In their paper, Longevity Among Hunter Gatherers A Cross Cultural Examination, Michael Gurven and Hillard Kaplan conclude:
Post reproductive longevity is a robust feature of hunter-gatherers and the life-cycle of Homo sapiens. Survivorship to grandparental age is achieved by over two-thirds of people who reach sexual maturity and can last an average of 20 years.

[M]odal age refers to a peak in the distribution of deaths...The average modal age of adult death for hunter-gatherers is 72 with a range of 68-78 years. This range appears to be the closest functional equivalent of an “adaptive” human life span.

Departures from this general pattern in published estimates of life expectancy in past populations (e.g., low child and high adult mortality) are most likely due to a combination of high levels of contact-related infectious disease, excessive violence or homicide, an methodological problems that lead to poor age estimates of older individuals and inappropriate use of model life tables for deriving demographic estimates.
The median number is simply the middle of the distribution - with half the numbers being higher, and half being lower. We usually report incomes in terms of median rather than mean because a small number of super-rich billionaires (the "one percent") would distort the statistics and make the average person seem richer than they are. Most people don't die at the median age. Median ages are usually a measure of how "young" a society is, since half of the people are younger than that age. Places with high mortality rates tend to have higher birth rates and proportionately less older people, hence a low median age. Median ages average hover around 30, with median ages in the 40's for Europe and Japan and in the teens for much of Central Africa, which is quite low.

Now consider this statement:

The average age of death for hunter-gatherers was 25.

This sentence uses "average" in the sense of arithmetic mean. The mean is simply a mathematical formula arrived at by adding up all the numbers and dividing by the number of numbers. If a hunter-gatherer died at 45, but his brother died of infection at age 5, the mean of their ages is:

(45 + 5)/2 = 25.

Notice that 25 is nowhere near the ages either of them died! As we saw above, if there are a lot of zeros in the data set, the mean is even more distorted. Imagine if you lived to age 75 (a decent life expectancy by modern standards), but you had two brothers who died at birth. The mean age of death in your family would be:

(75 + 0 + 0)/3 = 25

The same number. Our hunter-gatherer lived to be 75, but the average (mean) age of death in his family is 25 years old! A lot of people think that if the “average” age of death is 25, then that’s when most people died. Not true. Life expectancy at birth, and life expectancy at age 15 are two different things. What is usually reported for some reason is life expectancy at birth.

Thus, in technical terms, the average age of death for our hunter-gatherer tribe could very well be 25, but almost nobody is dropping dead at age 25! If you made it past childhood, you had a reasonable expectation of living to a decent age. If you make it to 15, your chances are good to making it past 60. By the way, the mean for my data set above is only 32 thanks to all the zeros.

One comprehensive study divided hunter-gatherer groups into “untouched” hunter-gatherers, forager-horticulturalists who practiced some sort of cultivation, and “acculturated” hunter-gatherers who had extensive regular contact with modern societies. They found that 57 percent of untouched hunter-gathers, 64 percent of forager-horticulturalists, and 79 percent of acculturated hunter-gatherers made it to 15 years old. The last number is probably related to better access to food and medicine.

If you made it 15 your odds were 64%, 61% and 79% or hunter-gatherers, forager-horticulturalists, and acculturated hunter-gatherers, respectively, of making it to age 40. From age 45, the mean number of expected remaining years of life is 20.7, 19.8, and 24.6.

Life expectancy at 15 was about 48 additional years among the Australian Aborigines (63) and 51 additional years for the !Kung Bushmen (66). And, of course, many people lived longer than that. A study of the Inuit between 1822-1866 showed that the most common age of death besides 0-4 years was 43.5 years, but a quarter of the population lived past age 60. This was probably not much different than the Russians who were studying them. Gurven and Kaplan write:
For groups living without access to modern health care, public sanitation, immunizations, or adequate and predictable food supply, it seems that still at least one-fourth of the population is likely to live as grandparents for 15-20 years.
Even thousands of years ago in Biblical times, many people lived to age seventy, as illustrated by Psalm 90:10:

The days of our years are threescore years and ten; and if by reason of strength they be fourscore years, yet is their strength labour and sorrow; for it is soon cut off, and we fly away.

This is summarized by science writer Maggie Koerth-Baker writing in The New York Times (emphasis mine):
A Swedish baby born in 1800 had a life expectancy of just 32 years. We know this because Sweden was one of the first countries to keep extensive records of births and deaths and, by 1800, had a reliable national system that allowed this morbid statistic to be calculated. That baby’s life may sound nasty, brutish and short, especially for a nation advanced enough to keep such detailed records, but before you imagine 19th-century Swedish teenagers suffering the regret and ennui of midlife crises, consider this: that same year, a 20-year-old Swede could reasonably expect to live another 37 years.
Life expectancy is an average, and it fluctuates with age as the risks we face change throughout our lifetimes. Both those facts make it a frequently misunderstood statistic. High infant-mortality rates depress the figure substantially. This can lead contemporary observers to the false conclusion that most humans died quite young, even in the not-so-distant past. (Were you ever told, as a petulant teenager, that you’d have been considered middle-aged in medieval Europe?)

“ ‘Life expectancy’ is this term that entered public lingo without public understanding of what it really means,” says Andrew Noymer, associate professor of public health and sociology at the University of California, Irvine. Our hypothetical Swedish baby’s 1832 expiration date is, of course, nothing of the sort. It’s a way of expressing, statistically, that lots of babies and small children were dying in 19th-century Sweden. By simply surviving childhood, a young Swede could expect a relatively long life — and if he was lucky, a proper midlife crisis.

But so could Fred Flintstone. In the last decade, scientists have concluded that humans have lived into older adulthood since 30,000 years ago, during the Upper Paleolithic (part of the era more commonly known as the Stone Age). Michael Gurven, a professor of anthropology at U.C. Santa Barbara who has studied modern hunter-gatherer and horticultural tribes, found that people in these societies who survived childhood lived about as long as 19th-century Swedes did — into their 50s and beyond. His work is one clue that suggests Enlightenment Age Europeans could have had the same longevity as our ancestors who painted caves and hunted the woolly mammoth.
Imagine if you went to find the "average" height of a tribe without factoring out newborns and children. The "average" height might turn out to be something like 3-4 feet tall, since in a tribe most people are children, teenagers, and newborn babies. Babies are very short indeed! Arriving at our tribe, we expect to find a race of Pygmies, yet find most people of average height (in fact, hunter-gatherers were taller than people who lived in pre-industrial agricultural civilizations).

We recognize the absurdity of this - average heights reported are always those of adults only, but when it comes to mortality rates, everyone including children is lumped in, which is why reported averages are so low. It's almost like someone wants to distort the statistics for some reason.

Here are some ages of various historical figures:
  • Ramesses II (1303BC – 1213BC ): 96
  • Plato (428 BC-348 BC): 80
  • Aristotle (384 BC-322 BC): 62
  • Caesar Augustus (63BC - 14AD): 75
  • Seneca the Younger (4BC - 65AD): 68
  • Cicero (106BC – 43BC): 63
  • St. Augustine (354-430): 75
  • Charlemagne (742(?) – 814): 71
  • Frederick Barbarossa (1122-1190): 68
  • Michelangelo (1475 - 1564): 88
  • Voltaire (1694-1788) : 83
  • Thomas Jefferson (1743-1826): 83
  • Benjamin Franklin (1706-1790): 84
  • Immanuel Kant (1724-1804): 79
  • Giacomo Casanova (1725-1798): 73
If "40 was old" than what were these guys? It’s true that these were elites and not typical of the entire population; by definition they lived long enough to do enough things to be remembered by posterity. But it puts to rest the idea that no one before the Industrial Revolution ever lived to an old age. A hunter-gatherer dying at 35 – the same age as Mozart -- was not typical either. If you opened a newspaper today to the obituaries, you would see similar ages.

Maria Lucimar Pereira, an indigenous Amazonian belonging to the Kaxinaw√° tribe of western Brazil in a remote corner of the Amazon, is not typical either. In 2011 she celebrated her 121st birthday.
Pereira credits her long-life to an active, healthy lifestyle, in addition to a diet rich in locally grown meats, fruits, and vegetables gathered in the forests around her home -- free of the extra salt, sugar, and preservatives so commonly found in foods around the world. Her all-natural diet, along with frequent walks around town, has allowed Pereira to thrive while others, many years her junior, do not.
Averages can be deceiving in another way too. Hunter-gatherers lived in egalitarian societies. Americans, with their highly unequal society and expensive health care, have among the worst outcomes in the developed world in both life expectancy and infant mortality. And lifespans are only increasing for the wealthiest Americans, while they are actually declining for the rest of us. Maggie Koerth-Baker:
The most recent rapid increase in human life expectancy started around 1880 in Europe, North America and Japan. Now we might be approaching another age of great technological upheaval, as stem cells and gene therapy offer the potential to extend lives to unprecedented lengths. But life expectancy measures only gains that refer to a whole population, and in the United States, rising inequality has become a drag on this most basic measure of human progress.
Currently, life expectancy at birth in the United States is roughly 79 years, and it’s the same at age 25, but our gains have slowed considerably. The U.S. ranks 51st in the world for life expectancy at birth. Around 1950, we were ninth. Furthermore, what improvements we do see are not spread evenly across the population. For example, between 1990 and 2008, white women with college degrees picked up three and a half years of life expectancy, while those without a high-school diploma lost five years.

Perhaps one day there will be a stem-cell treatment that can double one’s life expectancy by slowing the aging process, making a centenarian as spry as a quinquagenarian. But if such a serum benefits only the few who can afford it, our national life expectancy will hardly budge — it’s an average, after all. In 19th-century Sweden, the figure was dragged down by infant mortality. Today in the United States, it grows slowly because of the premature deaths of the less fortunate. Thanks to this vast inequality, even a high-tech fountain of youth would hardly move the needle.

“Look at the countries with the highest average life expectancy,” says Denney, referring to places like Japan, Australia, Canada and, yes, Sweden — nations that distribute their health resources more evenly. “Ultimately,” he says, “life expectancy is a measure of quality of life.”
So you're more likely to see a forty-year old with gray hair, a cane, or a walker in your local supermarket than a hunter-gatherer tribe.


Small Data: When the average age of death was zero (BBC News)
Who Lives Longest? (New York Times)
World's Oldest Person Found Thriving in the Amazon (Treehugger)
Nasty, Brutish, But Not That Short (West Hunter)
Just How Long Did Grok Live, Really? – Part 2 (Mark's Daily Apple)
These 8 Maps Show the Median Age of Every Country on Earth (The Week)
Why Cavemen Didn’t Actually Die Young (Paleo Leap)
Mortality and Lifespan of the Inuit (Whole Health Source)
Longevity Among Hunter Gatherers A Cross Cultural Examination (PDF)

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.