Sex and Death promote diversity, the basis of life.
A woman in her 60s brought in her mother with frequent falls. Her mom was increasingly debilitated and not able to walk without falling and was confused in her thinking and verbal expression. Drilling down on the history, the patient had stereotypical epileptic seizures preceded by automatic lip smacking and the seizures caused some of her falls. Her daughter would not agree to additional medicine to control seizures or even accept tiny doses of medicine carefully introduced, insisting her mother was lethargic. Eventually the doctors threw up their hands and seizure medicine was abandoned. This protectiveness, right or wrong, made it difficult for the physician intervene in a meaningful way in this elderly lady’s medical care. The daughter’s reactions were ambivalent in the sense that while soliciting care she would not accept any. She was of divided mind about whether there is any help yet unable to accept the inevitable. Ambivalence at the end of life is magnified by unresolved conflicts festering from earlier relations. If your daughter is unsure whether she wants you to live or die that conflict will slow medical decision making.
At the other end of this spectrum is an active garrulous 90 year old woman living alone shopping driving keeping house mowing lawns and cleaning windows. She is admitted with stroke like symptoms and she has atrial fibrillation that runs strongly in her family. She has been aware of at least since her 40s. Paroxysmal atrial fibrillation increases the risk of stroke about 5 fold and anticoagulation to stop the formation of clot is generally recommended therapy. Heretofore her cardiologists decided against anticoagulation as she went for over 50 years having atrial fibrillation but never a stroke. Now having had a stroke demonstrated increased risk of doing nothing. Her doctors decided to give her warfarin anticoagulation. She gladly accepted therapy to diminish her chances of having a serious stroke. One month later she returned to the hospital with increased sudden weakness on both her right and her left sides still garrulous and in high spirits. Her CT scan that found subdural hematomas, bleeding on both outer surfaces of the brain induced by her warfarin anticoagulant. Being elderly her brain was shrunken and this increased chances of developing these pancakes of blood accumulating between brain and skull.. Brain atrophy expands this potential space. It goes to show you that even robust appearing elderly are most likely to suffer from the consequences of aggressive medical interventions. Very often the best medical therapies given with the best of intentions only seem to make things worse – what may be called geri-iatrogenics.
Advances in medical technology permit more elderly people to live into old age. Even so, we are all destined to die. Death and senescence are inevitable for humans. At the present time in the United States we have very high-tech therapies such as advanced intensive care, antibiotics and interventions through arteries to retrieve clots and place stents and even replace heart valves. We use these high-tech options extensively on the oldest old patients. While this saves a few of them, the therapies also cause illness and may accelerate death. It is well-known that low tech interventions applied widely and to younger patients, especially interventions that prevent disease and even non-medical interventions, such as decent housing and plumbing, will affect life expectancies and health a great deal more. Countries lacking very high-tech interventions and widespread intensive care have life expectancies comparable to the USA. Well done blinded studies show the ineffectiveness of many of our high-tech therapies in extending life.
The expectation of death is something that we have to live with for the foreseeable future even if so many more of us live into advanced old age. We experience the deterioration of aging in our parents and ourselves. It is fair to ask whether senescence and death are experienced by all living creatures. If there are some animals that don’t get old and die, they may teach us about ourselves. Conversely if senescence and death are universal, our struggles to find a fountain of youth or eternal life are bound to fail.
All known biological entities use the same genetic code. The same trinucleotide sequence codes for the same amino acid. This is strong evidence not necessarily that life evolved just once on earth, but that all life over the whole planet, comes from the same progenitor a biological Eve. The first formers of concatenation of nucleic acids or amino acids may well have existed along with other chemical codes. They appear to have outcompeted chemical adversaries in that all of life uses this same genetic code. (There is another much less probable explanation and that is this particular code or language, translating chains of nucleotides into chains of amino acids, is the only translation that works or works best.)
By the same token all biological entities die. I suspect that there may have existed species with immortal individuals, but we don’t find any of them now. Paradoxically, any species with short-lived individuals generally will out compete ones with higher longevity, the worst case being immortality. Species with high longevity are largely extinct, the exception rather than the rule. Immortality in the biological sense isn’t the same as being indestructible. An individual that doesn’t age may potentially live forever but doesn’t because some disaster will come along and kill them anyway. As time passes the likelihood of death increases. Cross paths with predators and pathogens enough times and you are that much more likely to meet your end.
Much has been written about a species of Benjamin Button jellyfish which regresses from a mature medusoid form into an immature larval polypoid form to reproduce. Under stress the mature animal reverts to an immature form a little like an adult being able to turn into a child over again. Since in these early developing species, cells have barely learned to specialize, they are capable of changing back between their few different types. In more advanced animals whose cellular specialization is farther along and has diverged along complex pathways, cells lose their ability to de-differentiate as they have ventured so far out on branches of specialization. Liver cells, blood or brain cells can no longer be changed to progenitor cells so are committed specialists. There is no going back.
Hydras are early evolutionary cousins of jellyfish which have just a few types of cells and the most primitive tissues. Some Hydras also appear to be immortal as they continue to grow one part dying off the other end continuing to produce cells seemingly forever so never stop growing unless poisoned or killed. Hydras and some jellyfish, don’t seem to age. They don’t experience the accumulation of decrepitating changes like arthritis and heart disease or Alzheimer’s that we humans do. But in practice, as I say they do die, because although they are immortal, they are not indestructible.
We marvel at long-lived species such as the Sequoia trees some of which have been around for three thousand years or longer. When you go to see Sequoias the experts talk endlessly about fire. We humans view fire as destructive which it obviously is. It took a long time to learn that fires are a part of the cycle of nature what amounts to creative destruction and that the life of the forest depends on fires. Sequoias in particular are adapted to the presence of repeated forest fires. For these magnificent trees fire desiccates and opens their seed cones. Otherwise they would fail to germinate. Sequoias are equipped with thick fire resistant bark so as to thrive and reproduce in fires that burn out their competitors. Meeting these elderly sky scraping trees in Yosemite, so wide you can drive a car through them, changed my view of life and time, I met trees which were alive before the invention of the alphabet and are nearly as old human written history. Those crazy young tree huggers who protected magnificent old trees using their own bodies from the loggers who came to cut them down don’t deserve our disdain, but our gratitude.
Living long is but one strategy for survival of a type. That there are but few species with such long life expectancies. tells us that except under very limited circumstances, long life is disadvantageous for the survival of a species. Other trees such as mangroves with enormous root systems, seem capable of infinite self regeneration single plants forming truly enormous structures, which fascinated Thomas Edison, one of my very early heroes. Edison’s summer home in Ft Myers Florida features giant mangrove trees. Florida is full of mangroves as are other low-lying coastal areas around the world. These trees extend far out into time and space but their expanse is still limited by physiology. Even mangroves will not extend everywhere or last forever. After all mangroves have not taken over the planet, which goes to show you that growth in time and space has limits. The sequoias evolved originally before the uplift of the Sierra Nevada mountain range less than 4 million years ago and now are trapped in relatively small numbers west of the mountain range in California. Their range is limited and they are not all that successful as a group and could easily become extinct, except for the fact that humans, appreciating their magnificence, have planted them all around the world.
Planarians, primitive flatworms we recall from our biology class, can survive being longitudinally split again and again. Bacteria seem to split forever although some say in the case of bacteria, one half has the characteristics of the parent cell and the other the daughter cell so in the instance of direct splits of cells called fission, there is imperfect reproduction of the original cell into the next generation. In very early times one of the strategies for taking advantage of strength in numbers was to form a colony of individual nearly identical cells. Here I include a picture of Volvox which is a colony of Chlamydomonases, single flagellated cells which also contain chloroplasts one reason to classify them as plants though the flagella make them mobile. They are beautiful colonies of like cells.
Volvox
Watching cells divide it seems they form 2 identical cells but looks can deceive. It is more common to see identical appearing cells increasingly diverge in type over successive generations. That is best appreciated in the embryo. The original zygote, whose genetic material is a combination of the egg and sperm, starts to divide, ostensibly into identical cells, and divide again into what embryologists recognize as blastula, morula, gastrula stages. It seems as if the cells are exact reproductions of their progenitors and brother and sisters but obviously they are not, as slowly through generations of what at first seem to be simple divisions, the cells begin to change into cells of specific tissues and organs, committing themselves through repeated divisions into all the different types of cells found in that particular animal or plant. This brings up the important point that reproduction in biology is not producing exact copies. Reproduction is inexact and is a means of creating all important variation. In that sense cloning is abiological. Cloning, forming exact reproductions of one’s self is closer to the dream in science fiction of robots reproducing on distant planets and eventually colonizing the whole universe. This is mechanical, like making factory widgets, but is on a basic level, antagonistic to what is known about life.
It seemed at first watching the process of cell division that a particular cell line ought to be able to keep dividing forever as long as you provide it with the essentials of life. That was accepted dogma until recently. Cell divisions shorten ends of chromosomes, the telomeres. Telomere length is a means of counting each cell division by shortening each time a cell divides. When the telomere reaches a minimal length the cell will stop dividing. When I was young I learned about an immortal line of cells called HeLa cells which reproduced forever. Now we know HeLa cells came equipped with a telomerase enzyme restoring the telomere lengths allowing cells to continue to reproduce but this is distinctly unusual and was part of what defined this cell line as cancerous, unable to limit its own reproductive potential.
If scientists could somehow teach our cells to reproduce forever that could be key to the fountain of youth, so say some authorities. Our older or non functioning cells could replace themselves ad infinitum. I don’t think so. Some cell groups do best to divide extensively throughout an animal’s life such as in the digestive system and the skin. In other instances you have to have cell division stop at a certain point as in the nervous system. In most instances regulation of cell division is all important. To allow cells to keep dividing would introduce chaos in embryological development of the a body plan and might even cause cancers which are best conceived as loss of restraint against suppressors of continued cell division. Many cancers are known to be caused by mutations in tumor suppressing genes. In the embryo we see not only limited controlled cell division, but extensive pruning and cell death which help to sculpt the perfect animal or plant. Therefore the cessation and control of cell division are all important. Uncontrolled cell division is likely to cause disease, malformations and tumors. Organisms have evolved elaborate chemical signals to control this process.
Sequoias, mangroves, jellyfish, Hydras, bacteria weigh in on one side of the spectrum as long livers. Many other organisms particularly insects such as mayflies are at the other end. Mayflies and similar insects have learned to capitalize on extremely short life spans. They live at most hours as adults, desperately trying in their short mature lives to mate. Typically these insects have very long sometimes multiyear dormancies at which time they mature through larval stages. Then all at once and over a very short time frame millions and billions of mature adults seeking quick sex are born into the environment. In the space of a few hours they get the sexual deed done and a long cycle of reproduction is again begun, leading you to ask why they go to all this trouble to reproduce in this way, why does anyone, why are we so desperate to find some mate and reproduce?
And how will this relate to the necessity of death? Sex and death are necessary for the same reason. Cell division, like all biological processes, needs a brake, some form of regulation. Mangroves, Sequoias, embryos and bacteria have to stop growing at some point so as not to overgrow their nutritional supplies. And growth in embryos depends on control of cell divisions and cannot go on forever either in order to sculpt their subtle and beautiful natural forms. One of the goals of researchers is to define these chemical brakes on growth and the messengers of cell death governing the emergence of form in living things.
Even if there were once immortal species, we know of none today. Paradoxically that proves the strategy of having the individual living forever or even for a very long time, leads to the demise of the species. Otherwise we would have organisms that live forever which we do not. Why are there not species that live for any length of time approaching geological timeframes? It is because long life is inimical to adaptation to a changing environment.
Suppose you have a species whose members live forever or even a very long time. The elderly remain alive well adapted to their environment. Moreover elderlies would have two characteristics: They will fail to decrepitate with advancing age. Secondly they will stay very much the same, well adapted to their current environment where they will happily be able to survive forever or at least a very long time.
Two things will happen. They may be able to reproduce but not for long. Failing to die their numbers will increase. In that case their growth will exhaust resources. If they need nutrients, eventually their numbers will increase until they simply starve. This is like the growth of bacteria in a petri dish which has limited agar. Living forever puts the kibosh on reproduction as you eventually outrun your supplies. More importantly, the environment is certain to change, The one thing we can count on as the saying goes, is change. We know that the climate and conditions have changed drastically over geological time. Plate tectonics alone has moved and turned the continents so that what were once dense seas and tropical forests are now deserts. Even if you don’t age, over long timeframes an environment that you are permanently adapted to will change enough to kill you.
Not only does the environment change over time but over space. Like organisms will be adapted to small areas but types that are diverse will be able to radiate more so as to compete less with their conspecifics for resources, and the more different they are than their brothers, the better they will be at taking advantage of related but slightly different environments. Some areas will have more or less water, will be hotter or colder and your species will be able to take on these slight gradual changes. Species that are more diverse have many different types of individuals and it will be then be advantageous to have a shorter generation time, perhaps a shorter lifespan with as huge as possible a number of different individuals who will be able to work in slightly different environments. Over time slight environmental shifts are less likely to lead to the demise of the species or type as well as long as individuals will maintain diversity. Diversity then would seem to be necessary to the survival of a type, those species that are most diverse being able to most successfully compete then less diverse species. An environmental perturbation of any type is much less likely to knock off all the members of a given species as long as that species is more diverse. All the advantages go to the short lived diverse types, the mayflies in other words, not the Sequoias.
In fact many insects in particular have evolved a way of life that involves production of huge numbers of diverse individuals with short generation times to allow for rapid adaptation. Insects seem to be far more successful that vertebrates especially our own animal group for example the primates, as far as number so species and type adaptational radiation and ought to be far more resistant to environmental change on account of adaptational speed and diversity. Noting water beetles in my pool, I discovered to my amazement over 2000 species of them adapted to all sorts of things even the specialized chlorinated water found in pools and skimmers. Are there 2000 species of primates?
When you view every individual organism as a separate experiment which is more or less suited to its environment it is easy to see that a species able to generate more diversity, an increased number of strategies to handle changing contingencies, is one that will prevail against the competition. The worst case scenario is a species whose members live forever. If any such species did ever exist, it is easy to see why it is no longer with us. Within certain limits species with short generation times and more diverse individuals will last longer for these species will have more adaptive capacity. We die due to the fact that the alternative of living forever, or even a very long time, is not feasible in a changing world of the survival of the fittest.
We die to promote diversity, as It is grist for the mill of adaptation. We die for the same reason we have sex. Organisms do not reproduce in order to make exact replicas of themselves. One of the most successful strategies ever developed ensuring the inexactness of replication is the is sexual reproduction with its amazing process of producing haploid gametes that occurs with gene shuffling during meiosis. This ensures goodly supply of diversity in offspring, each of which is a separate biological trial or experiment in survival in the environment to come. The concept of organisms adapting to their environment is a fallacy. Each generation or iteration of a particular species is sufficiently different from his cohorts so as to be either pre-adapted or pre-maladapted to his own environmental contingencies. True, he may be slaughtered due to problems totally unrelated to his adaptational fit, such as by a volcanic eruption or sudden meteorite strike, fire or some similar environmental catastrophe. Strikingly many animals create terrible struggles of their own making, so as to ensure that life is hard and that only the strongest minorities survive. In many species only a very few males enjoy the vast majority of matings for example and other species design special struggles, such as salmon swimming upstream or birds or butterflies flying thousands of miles merely to reward small ultra-fit minorities of the next generation.
The strategy of sexual reproduction where there are only two sexes seems to have evolved as the most successful of all among animals and plants as the mechanism of choice to ensure continued diversity. I know of no organisms with three or four sexes, so that having two sexes seems to be optimal. I am sure there is some mathematical reason for the existence of just two sexes for that is the system that is obviously prevalent but I have not seen this worked out.
Genetic cloning is making rafts of ideal perfect replicants such as waves of grain, all the exact same genotype. They may have some ideal genes implanted for good taste, resistance to insects and pathogens, quick growth, and for a while, seem to be the ideal crop for a certain limited circumstance and time frame. But lacking diversity sure as shootin some weakness will emerge capable wiping all of them out. As long as your at it, making the perfect plant, why not keep alive forever single perfect specimens putting out bushels of corn calculated to grow forever. Why waste valuable time sewing new generations of plant? Within the certain limited space-time frame of the farmer, that might be a working goal, only fundamentally the elimination of diversity is abiological. The road is ruin is paved with good intentions.
How does this apply to humans? Most people I know are unfriendly to people who they see as different. Differences may be our saving grace. The enlightened admire diversity. Personally I’m entertained observing the wide spectrum of human behaviors, wide variations of anxiety for example and sexual habits. The diverse supply of behaviors not only improves the chances for our species but the likelihood of survival of our group. We are taught that we should be tolerant to others of a diverse types. Far from tolerating diversity, we should absolutely love it, as it leads to the survival of our group. Diversity is a toolbox to reach into whenever necessary to promote the survival of our general type. For example I have commented on this blog how the very same metabolic characteristics that were adaptive as hunter gatherers, the efficient storage of calories during afeast to promote survival in famine, might be the ones that diminish survival where the supply of calories is always plentiful. The fat type II diabetics of today were the svelte survivors of in hunter gatherer societies of yesteryear.
It has become accepted medical practice to keep the elderly alive and to provide heroic high tech care including intensive care without regard to debility and dementia. It was not like that until relatively recently. In keeping the elderly alive, we would like to think we are preserving function and quality but even then we have diminishing returns as the elderly have few years left. Better to focus care on pediatrics but that is a neglected area of endeavor. As more of the oldest old survive, they are sure to adversely affect the lives of younger individuals, consuming wealth and resources and saddling those able with their extensive care needs. Societies accumulating elderly persons will be less able to compete with younger demographic even if one day robots are employed to care for the old. Advanced first world societies like Japan and Italy, as they accumulate elderly persons, will fall behind others composed of younger educated members. Mothers are diverting care to their elderly mothers and grandmothers that would more profitably be consigned to their children. Everyone was betting on China with its enormous yearly growth in GNP and population of 1.3 billion as opposed to US’s population of only 300 million, But the US has an ace in the pocket. The saving grace for the US is immigration. With so many immigrants including Chinese clamoring to come to the US, the best evidence is that American hegemony is going to be with us for a long time. Hegemony of type is supported by youth and diversity. In our rush to keep the elderly from dying, we will need to be careful what we wish for.
From the biological perspective the strategy of extending life far past reproductive age makes little sense except under limited circumstances. In the human’s case, the elderly may still be productive in society. For example we have many persons in the their 70s and 80s doing advanced cognitive work as musicians, political leaders, and in teaching and handing down tradition, taking care of children and great grandchildren in extended families. Elderlies have what we normally call wisdom and judgment. When the elderly cease in these activities and require total care as many of them do, they will detract from the lives of younger members of society who may be otherwise productively employed. The strategy of extending life will then be most disadvantageous from the biological perspective in preserving the species or of a particular society.
Though long life is not encouraged from the purely biological perspective, long life is advantageous in certain limited situations. Longevity past reproductive age is tenable whenever the environment is remains stable for long periods, something that is rare. It may also work our if the elderly play a specific adaptational role say as repositories of wisdom and cultural mores or as decision makers as the elderly do in some societies. Humans are unique among animals in that do not depend on biological adaptation alone. Sensing the need humans, use their ingenuity to modify themselves and adjust to contingency. For us, advances of thought processes and imagination and creativity allow rapid resonse to environmental contingencies.
Thus some of us dream of one day superseding biological endowments, developing the ourselves further and improving human condition and intelligence and, who knows, even living forever.