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Ageing
Measuring our narrow strip of life
In line with previous research, a demographic analysis corroborates the presence of a limit to human lifespan, indicating that increases in life expectancy are likely to slow down or stop over the coming years.
The British author Annie Besant once wrote1: “out of the darkness of the womb, into the darkness of the grave, man passes across his narrow strip of life.” The ration of time allocated to humans is of profound personal and scientific interest. On page 257, Dong et al.2 turn to the demographic literature to analyse whether there is a limit to human lifespan — and find evidence to suggest that there is.
Before discussing the study at hand, we should define some relevant terms. Lifespan describes how long an individual lives. Life expectancy is a population-based estimate of expected duration of life for individuals at any age, based on a statistical 'life table'. And maximum lifespan is the age reached by the longest-lived member of a species.
Human life expectancy has risen fairly steadily and rapidly over the past 150 years3 in most countries. In 1990, colleagues and I predicted that this increase would slow over time4, and this has proved to be the case5. Maximum lifespan also seems to have risen steadily6, but this too might have reached an upper asymptote — no one is known to have lived longer than Jeanne Calment, who died in 1997 at the age of 122. Thus, the debate about life's limits is ongoing.
Some scientists speculate that fixed limits to life are unlikely to exist, because they cannot be observed using the tools of mathematical demography7. Others suggest that unknown technological advances in the future will continue to drive down death rates8, leading to accelerated gains in life expectancy and maximum lifespan. And yet others argue that there is a limit to lifespan9.
Dong and colleagues used demographic data to investigate whether there is a limit to human lifespan and, by implication, life expectancy. They first hypothesized that, if a biological limit does not exist (or is currently unobservable), the age group experiencing the greatest increase in survival should shift to ever-older groups over time. This hypothesis makes perfect sense, and the authors discovered that, in most countries that have reliable data, the greatest improvement in survival in the oldest age groups peaked in about 1980 and has not shifted since.
Next, the researchers investigated whether increases in maximum lifespan had been observed in recent decades. They discovered that, since the death of Calment, maximum lifespan for humans has regressed. This occurred in spite of the increasing size of ageing populations worldwide, which, in itself, should have led to an increase in maximum lifespan. Dong et al. conclude that these two observations represent compelling evidence that human lifespan has a 'natural limit' (Fig. 1).
Alessandro Grassani/The New York Times/Eyevine
At 116, Emma Morano is the oldest known person alive today. Dong et al.2 provide evidence that we are approaching the natural limit to human lifespan.
Scientists who study ageing know that there is considerable variation in the duration of life across species10, but within species there are fixed attributes associated with life history — and longevity determination is one of them. Under protected living conditions in which predation is largely removed, mice tend to live about 1,000 days10, dogs about 5,000 days10 and humans about 29,000 days11. Clearly, there are biological reasons for each species' average lifespan, so why would anyone think that people could live for much longer than we do now?
The answer lies in the historical context within which human longevity has changed. The 30-year rise in life expectancy at birth seen during the past century has nothing to do with a modified rate of ageing12. Instead, it reflects improvements in public health that have drastically reduced early-age mortality, allowing most people in developed nations to reach old age for the first time in history. Death now clusters in people between the ages of 65 and 95 (ref. 11). But, without further biomedical breakthroughs, life expectancy cannot continue to rise by much, and so future longevity gains will diminish. The crucial question is how much more survival time can be gained through medical technology. With fixed life-history traits, it would seem that we are running up against a formidable barrier.
As the authors rightly point out, the idea of a 'natural limit' to life does not imply that such a limit is a direct by-product of some genetically driven program that causes both ageing and death. Fixed genetic programs that directly cause ageing and death cannot exist as a direct product of evolution, because the end result would be death at an age beyond which almost every member of a species would ordinarily live. A genetic time bomb designed to kill us at older ages is equivalent to automobile manufacturers building in an explosive device that is set off only when a car reaches one million miles. Because most cars are never driven that far, such a device would be useless.
How is it possible to have a biological limit to life, yet no genetic program that runs it? There are biological clocks that measure time from conception and birth, but these metronomes are there to transform a fertilized egg into an adult capable of reproducing. These fixed genetic programs for growth, development, maturation and reproduction (collectively known as a life-history strategy) are products of more than 3.7 billion years of evolution. Biological metronomes do not measure the time to age or die; instead, ageing is an inadvertent by-product of these clocks, which are designed to sustain life.
This distinction is important — it means that there is no fixed limit beyond which humans cannot live, but that there are, nevertheless, limits on the duration of life that are imposed by other genetically determined life-history traits. Think of constraints on running speed as an analogy. No genetic program specifically limits how fast humans can run, but biomechanical constraints on running speed are imposed by a fixed body design that evolved for other purposes. The absence of ageing and death programs opens the door to non-genetic interventions that extend health and length of life, just as new training methods enable us to run incrementally faster. This is precisely why modifying behavioural risk factors such as diet and exercise does extend the period of healthy life, but yields diminishing gains in life expectancy.
Dong and colleagues remind us that humanity is approaching a natural limit to life. This limit is now apparent in national vital statistics. Humanity is working hard to manufacture more survival time, with some degree of success, but we should acknowledge that a genetically determined fixed life-history strategy for our species stands in the way of radical life extension.1
Xi’s Power Trip Could Change China
"Truths are illusions which we have forgotten are illusions — they are metaphors that have become worn out and have been drained of sensuous force, coins which have lost their embossing and are now considered as metal and no longer as coins."
--from "On Truth and Lie in an Extra-Moral Sense" (1873)
Android Phones Take a Power Trip
By DAVID POGUE
In a world crammed with Android phones, HTC, Samsung and Motorola introduce three new models, each of them Verizon 4Gs.
power trip
Definition of power trip
: : an activity or way of behaving that makes a person feel powerful : something that a person does for the pleasure of using power to control other people
- She's been on a power trip since she was promoted to manager.
n. Slang
An action undertaken chiefly for the gratification associated with the exercise of power over another or others: "He was giving orders, and people were taking them. He was on a power trip" (Nelson DeMille).
pow
er-trip
(pou
r-tr
p) v.
er-trip (pour-trp) v.
power tripper n.
Urban Dictionary: power trip
https://www.urbandictionary.com/define.php?term=power%20trip
Someone, typically at work, who has higher powers over most people they work with. This higher power (usually a manager or someone's boss) tends to go to their head causing them to "Power trip" and abuse their rights as a manager/bossThe Container Store Recalls Brightly-Colored Power Strips Due to Fire Hazard
WASHINGTON, D.C. - The U.S. Consumer Product Safety Commission, in cooperation with the firm named below, today announced a voluntary recall of the following consumer product. Consumers should stop using recalled products immediately unless otherwise instructed. It is illegal to resell or attempt to resell a recalled consumer product.Name of Product: Lush Life® power strips
Units: About 7,200
Importer: The Container Store Inc., of Coppell, Texas
Hazard: The power strips have undersized wiring, and the wiring and plastic strip fail to meet the requirements for fire resistance, posing a fire hazard.
Incidents/Injuries: None reported
Description: This recall involves three designs of brightly-colored, six-outlet power strips with model number 8001-6 embossed on the back. Power strip designs include Pop Power Strip in Scroll (black with white scroll), Dot (blue with orange, white and lime green dots and a lime green cord), and Zebra (black and white zebra stripes). The power strips have three-foot power cords. “Lush Life® power strips by design” is printed on the product’s packaging.
Sold at: The Container Stores nationwide and on the firm’s website www.containerstore.com from October 2011 through December 2011 for about $15.
Manufactured in: China
Remedy: Consumers should stop using the recalled power strips immediately and return them to any of The Container Store locations for a full refund plus a $15 merchandise card.
Consumer Contact: For additional information, consumers should contact The Container Store toll-free at (888) 266-8246 between 8 a.m. and 8 p.m. CT Monday through Saturday, and between 9 a.m. and 7 p.m. CT on Sunday, or visit the firm’s website at www.containerstore.com
comb
(kōm)
n.
- A thin toothed strip, as of plastic, used to smooth, arrange, or fasten the hair.
- An implement, such as a card for dressing and cleansing wool or other fiber, that resembles a hair comb in shape or use.
- A currycomb.
- The fleshy crest or ridge that grows on the crown of the head of domestic fowl and other birds and is most prominent in the male.
- Something suggesting a fowl's comb in appearance or position.
- A honeycomb.
v., combed, comb·ing, combs. v.tr.
- To move a comb through (the hair) so as to arrange or groom: combed her hair with a comb; combed his hair with his fingers.
- To move though or pass across with a raking action: The wind combed the wheatfields.
- To card (wool or other fiber).
- To search thoroughly; look through: combed the dresser drawers for a lost bracelet.
- To eliminate with or as with a comb: combed the snarls out of his hair.
- To roll and break. Used of waves.
- To make a thorough search: combed through the file for the contract.
[Middle English, from Old English.]
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