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The Biology of Death: Origins of Mortality
Why do we die? Do all living creatures share this fate? Is the body's slow degradation with the passage of time unavoidable, or can the secrets of longevity be unlocked? Over the past two decades, scientists studying the workings of genes and cells have uncovered some of the clues necessary to solve these mysteries. In this fascinating and accessible book, two neurobiologists share the often-surprising findings from that research, including the possibility that aging and natural death may not be forever a certainty for most living beings. André Klarsfeld and Frédéric Revah discuss in detail the latest scientific findings and views on death and longevity. They challenge many popular assumptions, such as the idea that the death of individual organisms serves to rejuvenate species or that death and sexual reproduction are necessarily linked. Finally, they describe current experimental approaches to postpone natural death in lower organisms as well as in mammals. Are all organisms that survive until late in life condemned to a "natural" death, as a consequence of aging, even if they live in a well-protected, supportive environment? The variability of the adult life span—from a few hours for some insects to more than a millennium for the sequoia and thirteen times that for certain wild berry bushes—challenges the notion that death is unavoidable. Evolutionary theory helps explain why and how some species have achieved biological mechanisms that seemingly allow them to resist time. Death cannot be understood without looking into cells—the essential building blocks of life. Intriguingly, at the level of cells, death is not always an accident; it is often programmed as an indispensable aspect of life, which benefits the organism as a whole.
- GenresDeathNonfiction
211 pages, Hardcover
First published October 16, 2003
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August 13, 2019
Why we die, technically explained
It may come as a surprise for you to learn (I know it did for me) that science is not quite certain as to why we die. I mean generally. In each specific case a cause of death is usually made: heart attack, cancer, gunshot wound, etc. But as far as why human beings in general die rather than go on living indefinitely, the answer is murky.
It used to be the case (and perhaps still is) that coroners would cite "natural causes" as the cause of the death of certain old people. However in some places this is no longer allowed since science has established that there is no such thing as the nebulous "natural causes." If the medical examiner looks closely enough it will always be found that some part or parts of the body failed for one reason or another and should be cited as the cause of death.
Some people think we die (theoretically) because it is good for the species. Some people think we die because it is programmed into our cells to die. Others think we die because our bodies wear out. These are proximate reasons perhaps, but they do not explain why the evolutionary mechanism does not allow us to be immortal. The authors recall the idea that death is a byproduct of sexuality, noting that dividing nonsexual bacteria, for example, are theoretically immortal (as are cancer cells). They also point out that many species (salmon, for example) die immediately after reproduction. They cite studies showing that such species may go on living if they do not reproduce. Furthermore, they note that natural selection works most effectively when the organism is at or near sexual maturity. The further the organism gets from the onset of sexual maturity, the less effect natural selection has on making it adaptive; that is, making it healthy and effective in warding off dangers from the environment.
This is really a fine explanation for why we die, and one that is cited by all the authorities I have read. Put another way, what it means is that the evolutionary mechanism "cares" less about older organisms that are no longer sexually reproductive than it does about younger ones that are. Or put still another way, the harmful mutations that would be selected against in younger organisms are not selected against in older individuals because those individuals are so few in number, relatively speaking; (and more generally), because they produce so few offspring, the effect of their genes is small in the overall gene pool. I think it can be added that the young are better adapted (if only slightly, and in general) to the environment and therefore should be expected to out-reproduce the old.
If this is not clear, let me say that I did not understand these subtle points for a long time. Furthermore, they seem to beg the question of why the evolutionary mechanism does not allow organisms to continue to reproduce as they get older. In lobsters, the authors point out, their reproductive capability actually increases with age, and indeed this is understood as being one reason they live relatively long lives.
A more profound way of looking at this conundrum was suggested by G.C. Williams who explains that a flying fish always falls back into the water and that natural selection does nothing and needs to do nothing to return the fish to the water. (Gravity does it!--and note that gravity is in this example analogous to the natural forces--accident, predation, disease, etc.--that will eventually kill an organism.) What natural selection works on is making the fish more effective at staying in the air longer. Eventually however the fish must return to the water. The authors explain, "Natural selection gives the organism the means...to remain alive longer than if it were abandoned only to physical forces...these means are inevitably limited. Again, they can only delay the final outcome." (p. 188)
The authors further explain that "natural death has no value in and of itself [giving the lie to the good-for-the-species argument]; its existence is simply the result of a central biological pointlessness to repair systems that would prevent aging. All...organisms...are doomed to exist temporarily...and the time they have to procreate cannot be extended indefinitely. Natural selection 'judges' each organism by the yardstick of procreation... The goal is successful reproduction...[even if it leads to a shortened lifespan]." Consequently, "[w]ithout going to the extreme examples of mayflies or salmon, this arrangement leads the organism to neglect itself just enough so that aging and natural death occur." (pp. 182-183)
Another point is that programmed cell death (apoptosis) is NOT the cause of the death of the organism. In fact, apoptosis works in exactly the opposite direction: the death of certain cells is for the betterment of the organism, as the authors argue in Chapter Six.
This is the fourth book I have read on this subject. The other three books are: Austad, Steven N. Why We Age: What Science Is Discovering about the Body's Journey Through Life [1997)]; Clark, William R. A Means to an End: The Biological Basis of Aging and Death [1999]; and Hayflick, Leonard. How and Why We Age [1994]. This book is more technical than the others and is more clearly aimed at the professional scientist. I would recommend it least except for the fact that it is the most current. For those interested in what is going on at the cellular and molecular levels in research, this book is perhaps the best choice.
--Dennis Littrell, author of “Understanding Evolution and Ourselves”
It may come as a surprise for you to learn (I know it did for me) that science is not quite certain as to why we die. I mean generally. In each specific case a cause of death is usually made: heart attack, cancer, gunshot wound, etc. But as far as why human beings in general die rather than go on living indefinitely, the answer is murky.
It used to be the case (and perhaps still is) that coroners would cite "natural causes" as the cause of the death of certain old people. However in some places this is no longer allowed since science has established that there is no such thing as the nebulous "natural causes." If the medical examiner looks closely enough it will always be found that some part or parts of the body failed for one reason or another and should be cited as the cause of death.
Some people think we die (theoretically) because it is good for the species. Some people think we die because it is programmed into our cells to die. Others think we die because our bodies wear out. These are proximate reasons perhaps, but they do not explain why the evolutionary mechanism does not allow us to be immortal. The authors recall the idea that death is a byproduct of sexuality, noting that dividing nonsexual bacteria, for example, are theoretically immortal (as are cancer cells). They also point out that many species (salmon, for example) die immediately after reproduction. They cite studies showing that such species may go on living if they do not reproduce. Furthermore, they note that natural selection works most effectively when the organism is at or near sexual maturity. The further the organism gets from the onset of sexual maturity, the less effect natural selection has on making it adaptive; that is, making it healthy and effective in warding off dangers from the environment.
This is really a fine explanation for why we die, and one that is cited by all the authorities I have read. Put another way, what it means is that the evolutionary mechanism "cares" less about older organisms that are no longer sexually reproductive than it does about younger ones that are. Or put still another way, the harmful mutations that would be selected against in younger organisms are not selected against in older individuals because those individuals are so few in number, relatively speaking; (and more generally), because they produce so few offspring, the effect of their genes is small in the overall gene pool. I think it can be added that the young are better adapted (if only slightly, and in general) to the environment and therefore should be expected to out-reproduce the old.
If this is not clear, let me say that I did not understand these subtle points for a long time. Furthermore, they seem to beg the question of why the evolutionary mechanism does not allow organisms to continue to reproduce as they get older. In lobsters, the authors point out, their reproductive capability actually increases with age, and indeed this is understood as being one reason they live relatively long lives.
A more profound way of looking at this conundrum was suggested by G.C. Williams who explains that a flying fish always falls back into the water and that natural selection does nothing and needs to do nothing to return the fish to the water. (Gravity does it!--and note that gravity is in this example analogous to the natural forces--accident, predation, disease, etc.--that will eventually kill an organism.) What natural selection works on is making the fish more effective at staying in the air longer. Eventually however the fish must return to the water. The authors explain, "Natural selection gives the organism the means...to remain alive longer than if it were abandoned only to physical forces...these means are inevitably limited. Again, they can only delay the final outcome." (p. 188)
The authors further explain that "natural death has no value in and of itself [giving the lie to the good-for-the-species argument]; its existence is simply the result of a central biological pointlessness to repair systems that would prevent aging. All...organisms...are doomed to exist temporarily...and the time they have to procreate cannot be extended indefinitely. Natural selection 'judges' each organism by the yardstick of procreation... The goal is successful reproduction...[even if it leads to a shortened lifespan]." Consequently, "[w]ithout going to the extreme examples of mayflies or salmon, this arrangement leads the organism to neglect itself just enough so that aging and natural death occur." (pp. 182-183)
Another point is that programmed cell death (apoptosis) is NOT the cause of the death of the organism. In fact, apoptosis works in exactly the opposite direction: the death of certain cells is for the betterment of the organism, as the authors argue in Chapter Six.
This is the fourth book I have read on this subject. The other three books are: Austad, Steven N. Why We Age: What Science Is Discovering about the Body's Journey Through Life [1997)]; Clark, William R. A Means to an End: The Biological Basis of Aging and Death [1999]; and Hayflick, Leonard. How and Why We Age [1994]. This book is more technical than the others and is more clearly aimed at the professional scientist. I would recommend it least except for the fact that it is the most current. For those interested in what is going on at the cellular and molecular levels in research, this book is perhaps the best choice.
--Dennis Littrell, author of “Understanding Evolution and Ourselves”
August 12, 2011
Actually very good, but requiring a lot of attentive line by line reading. Explanation from cell biology, biochemistry and holistic body functioning.
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