Sex and the Origins of Death | Date: 28 April 2011, 07:11
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Product Description:
Death, for bacteria, is not inevitable. Protect a bacterium from predators, and provide it with adequate food and space to grow, and it would continue living--and reproducing asexually--forever. But a paramecium (a slightly more advanced single-cell organism), under the same ideal conditions, would stop dividing after about 200 generations--and die. Death, for paramecia and their offspring, is inevitable. Unless they have sex. If at any point during that 200 or so generations, two of the progeny of our paramecium have sex, their clock will be reset to zero. They and their progeny are granted another 200 generations. Those who fail to have sex eventually die. Immortality for bacteria is automatic; for all other living beings--including humans--immortality depends on having sex. But why is this so? Why must death be inevitable? And what is the connection between death and sexual reproduction?
In Sex and the Origins of Death, William R. Clark looks at life and death at the level of the cell, as he addresses such profound questions as why we age, why death exists, and why death and sex go hand in hand. Clark reveals that there are in fact two kinds of cell death--accidental death, caused by extreme cold or heat, starvation, or physical destruction, and "programmed cell death," initiated by codes embedded in our DNA. (Bacteria have no such codes.) We learn that every cell in our body has a self-destruct program embedded into it and that cell suicide is in fact a fairly commonplace event. We also discover that virtually every aspect of a cell's life is regulated by its DNA, including its own death, that the span of life is genetically determined (identical twins on average die 36 months apart, randomly selected siblings 106 months apart), that human tissue in culture will divide some 50 times and then die (an important exception being tumor cells, which divide indefinitely). But why do our cells have such programs? Why must we die? To shed light on this question, Clark reaches far back in evolutionary history, to the moment when "inevitable death" (death from aging) first appeared. For cells during the first billion years, death, when it occurred, was accidental; there was nothing programmed into them that said they must die. But fierce competition gradually led to multicellular animals--size being an advantage against predators--and with this change came cell specialization and, most important, germ cells in which reproductive DNA was segregated. When sexual reproduction evolved, it became the dominant form of reproduction on the planet, in part because mixing DNA from two individuals corrects errors that have crept into the code. But this improved DNA made DNA in the other (somatic) cells not only superfluous, but dangerous, because somatic DNA might harbor mutations. Nature's solution to this danger, Clark concludes, was programmed death--the somatic cells must die. Unfortunately, we are the somatic cells. Death is necessary to exploit to the fullest the advantages of sexual reproduction.
In Sex and the Origins of Death, William Clark ranges far and wide over fascinating terrain. Whether describing a 62-year-old man having a major heart attack (and how his myocardial cells rupture and die), or discussing curious life-forms that defy any definition of life (including bacterial spores, which can regenerate after decades of inactivity, and viruses, which are nothing more than DNA or RNA wrapped in protein), this brilliant, profound volume illuminates the miraculous workings of life at its most elemental level and finds in these tiny spaces the answers to some of our largest questions.
Amazon.com:
Despite its provocative title, Sex & the Origins of Death is not as sensationalistic as it sounds. William R. Clark is a professor of immunology at UCLA, and his avowed intention is to enlighten his readers rather than to frighten or titillate. Drawing on his broad knowledge of the cellular systems that make up our bodies and the medical and ethical arguments on the nature of death, he presents a compelling tale of the evolution of sex and death interwoven with a story of a man experiencing a heart attack. This juxtaposition humanizes the discussion and grounds the reader firmly in day-to-day reality, even when considering such bizarre topics as immortal bacteria and Sea Monkey spores.
Clark covers the development of sex in microorganisms and how this novelty may have guaranteed the inevitability of death (though perhaps not that of taxes). From this level of thinking, he changes quickly to 20th-century American law, which has pondered the question of death at great length as our scientific prowess has enabled us to maintain deeply traumatized individuals in persistent vegetative states, presumably free from conscious awareness of any kind. Now that death has become a matter of opinion, Clark insists that we pay careful attention to it, both as scientists and as human beings. Sex & the Origins of Death is a great place to start. --Rob Lightner
Summary: Death - a price worth paying?
Rating: 5
William Clark has done a great job here of explaining the connection in evolution between the origins of sexual reproduction and the origins of death. To know that the original living organisms, and their single-cell descendents today, do not die from aging but are potentially immortal leads to interesting questions about ourselves and particularly the relationship between our soma (body) cells and our gametes ie those cells that can potentially take our DNA into the future beyond the death of the body.
Clark uses the hypothetical case of a man's second major heart attack to explain necrotic cell death. He also covers the problems we are faced with today around determing 'death', brain death and dealing with persistent vegetative state etc. Taking another perspective he looks at the dried cysts and spores of simple organisms in the search for a clearer definition of life at the level of the cell.
The type of cell death of particular interest is programmed cell death that arose along with sexual reproduction and multicellular organisms. Programmed cell death occurs in the developing fetus where excess cells quietly self-destruct. It also continues throughout life in, for example, the immune system. And ultimately body cells themselves are programmed to die once enough time has elapsed for the body's DNA to have passed on to new bodies.
As Clark puts it, the only purpose of somatic cells, from nature's point of view, is to optimize the survival and function of the true guardians of the DNA - the germ cells. In the original living organisms the first somatic DNA was itself germline DNA. But programmed death is apparently necessary in order to realize the full biological advantage of sex as part of reproduction. Our DNA makes a hundred trillion copies of itself to ensure the transmission of just a few copies to the next generation. Then it directs the destruction of the other hundred trillion copies and we die. Death of cells is therefore not an a priori requirement of life but an evolutionary consequence of the way we reproduce ourselves and of our multicellularity.
Perhaps the knowledge of our own mortality can be made more palatable when we see it as a price we all pay for the great and awesome diversity of life on our beautiful planet that has arisen from the evolution of sexual reproduction and multicellularity.
Summary: much misrepresented by reviewers
Rating: 5
I delayed to read this book, put off by a reviewer who warned that it was difficult due to the author's use of scientific jargon. But that reviewer was wrong. There is a lot of jargon in this book: all clearly introduced, defined, and rarely used. In fact, the author presents things a little more simply than he could have!
This is one of the better biology books I've ever read (and I read about a dozen each year) because of the issue it d
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