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I understand (a little) that there are biological clocks and reason that after a certain amount of time organisms die. I'm wondering if that is something inherent in our DNA or in biology/chemistry in general. EG, is it possible that there could be a complex organism that would not die and would just regenerate it's cells In Perpetuam? I'm specifically interested in mammals and even more specifically interested in humans. But, I would be interested in hearing about other organisms like bugs, fish, plant, algae, etc.
I'm not asking if this practical, do we know how to do this, etc… I just want to know theoretically if living forever is biologically possible, as far as we know. If not, is there an estimated upper limit?
The immortal jellyfish can revert back to its immature polyp stage after reaching maturity, then mature again, over and over. You can read more on the wikipedia page, but this ability means it can potentially avoid senescence altogether.
You have a very interesting question there!
In order to answer, however, we must examine the most widely accepted "reason" for why we age and eventually die. Most scientists agree that it is because of mass cell death. Normally you and I would be able to deal quite well with mass cell death (such as a very large injury), the problem comes in when we are older because we cannot replenish them because we have physically exhausted our own supply of something called stem cells.
Most cells in our bodies actually cannot divide, so they rely on these stem cells (which can divide into any cell; think of them as a wild card) to replenish whatever cells die.
Sounds perfect, right? Not quite, each of us only have a given number of stem cells in our body (even though stem cells can divide into more stem cells, they usually don't). So the reason we age and die is because we "run out", if you will, of these stem cells and our supply of cellular replenishment is slowly cut off.
Back to your question, is it possible to stop this? Well you've probably already come to this conclusion by now, but theoretically if you could somehow supply the body with a constant number of stem cells, theoretically, you could live forever (or at least a really long time). This is evident, as you are aware, in flatworms, who have stem cells constantly circulating their bodies and are practically immortal.
Awesome question! It could use a couple qualifiers, however…
1) How do we define organism?
2) Are we assuming the environment never changes?
CactusWoman mentioned jellyfish that continually revert to an immature stage, essentially remaining young indefinitely. We could also cite colonial organisms. For example, some scientists say the world's biggest known organism is a fungus growing over an area of many acres (in Oregon, I believe). How long could something like that live?
Then there's the environment; as Joshua said, every living thing on Earth will presumably die when the sun dies.
And there's yet another thing to consider - dormancy.
Seeds that are centuries old have been sprouted. So would it be possible for a seed or spore to survive indefinitely?
In this spirit, some have suggested that life on Earth began when the planet was "seeded" by meteorites carrying life forms. A Martian meteorite that crashed into Antarctica created a sensation when it was announced that it might contain evidence of primitive life.
Whether or not the meteorite was "inhabited" is a matter of debate, and if life evolved independently on Mars, why couldn't it do so on Earth?
Nevertheless, to truly live forever - or even for a mere 100 billion years - an organism would presumably have to somehow escape its dying home planet and float in space in a state of dormancy… something that may or may not be possible.
P.S. I just discovered that the environment has already been discussed and pronounced irrelevant to this discussion. But I think it still makes for an interesting side discussion. ;)
Organisms created with synthetic DNA pave way for entirely new life forms
From the moment life gained a foothold on Earth its story has been written in a DNA code of four letters. With G, T, C and A - the molecules that pair up in the DNA helix - the lines between humans and all life on Earth are spelled out.
Now, the first living organisms to thrive with an expanded genetic code have been made by researchers in work that paves the way for the creation and exploitation of entirely new life forms.
Scientists in the US modified common E coli microbes to carry a beefed-up payload of genetic material which, they say, will ultimately allow them to program how the organisms operate and behave.
The work is aimed at making bugs that churn out new kinds of proteins which can be harvested and turned into drugs to treat a range of diseases. But the same technology could also lead to new kinds of materials, the researchers say.
In a report published on Monday, the scientists describe the modified microbes as a starting point for efforts to “create organisms with wholly unnatural attributes and traits not found elsewhere in nature.” The cells constitute a “stable form of semi-synthetic life” and “lay the foundation for achieving the central goal of synthetic biology: the creation of new life forms and functions,” they add.
Floyd Romesberg and his team at the Scripps Research Institute in California expanded the genetic code from four letters to six by adding two new molecules they call X and Y and adding them to the bugs’ genetic makeup. The microbes are modified to absorb the new genetic material which the scientists make separately and then feed to the cells.
The need to supply the bugs with the X and Y molecules is meant to ensure that the cells will die should they somehow get out of the lab. But Romesberg said that despite the protective measure, he still gets asked if he has seen Jurassic Park. In the 1993 movie, Jeff Goldblum questions whether the park’s dinosaurs might breed in the wild despite the failsafes built into their genetic makeup. “What the movie depicted is very different to our failsafe,” Romesberg said. “Our failsafe is based on the availability of X and Y and the cell could never make them.”
“In addition, evolution works by starting with something close and then changing what it can do in small steps. Our X and Y are unlike natural DNA, so nature has nothing close to start with. We have shown many times that when you do not provide X and Y, the cells die, every time,” he added.
It is not the first time Romesberg has made microbes with an expanded genetic alphabet. In 2014, he announced the first such organisms, but these were sickly and soon died out. He compares the situation to having proved he could generate electricity, but not put it to good use. “We demonstrated that you could throw the switch and the light would go on, but then it would quickly go out,” he said.
Over the past two years, his team worked out how to make the microbes hardier and pass on their synthetic genetic bases more faithfully when they divided. If the X and Y are not passed on, the bugs’ DNA quickly reverts to the standard four letter genetic code, he said.
It took three crucial fixes for the microbes to survive and reliably pass on their new genetic material. In one key improvement, Romesberg modified the microbe’s immune system so that it destroyed any DNA that was missing the synthetic X and Y bases. The end result, he says, is that the bugs can hold the new genetic material indefinitely. “Now you throw the switch and the light stays on,” he told the Guardian.
What Do Organisms Need to Survive?
All organisms need food, air, water, sunlight, and the right habitat. Organisms need to obtain nutrients from food. Air is the mixture of natural gases in the right proportions for each organism. While animals need oxygen for respiration, plants require carbon dioxide to manufacture food.
All organisms need food because it contains essential nutrients that body cells use for their growth, movement, and reproduction. Water is very important because it is the medium where vital nutrients and minerals enter the body. Without water, the cells and tissues of animals and humans would not function properly. At the same time, water is the natural habitat for such organisms as fish, crocodiles, hippopotamus, octopus, and other marine animals. The heat energy from the sun is perhaps the most important need for most organisms. While plants need sunlight for photosynthesis, animals need it for supply of energy. Every organism needs to be in the right habitat to survive. For example, polar bears only live in very cold areas of the world and cannot survive in hot environments. At the same time, fish only live in water and will die if left on dry land. Organisms can develop adaptive features to survive in their respective habitats. When the basic needs in their habitats are depleted, they move to another habitat or die.
Extinction is the dying out of a species. Extinction plays an important role in the evolution of life because it opens up opportunities for new species to emerge.
Biology, Ecology, Earth Science, Geology, Geography, Physical Geography
Many species have gone extinct throughout history and all that marks their presence on Earth are fossils, such as this one of a dinogorgon.
Photograph by Jonathan Blair
When a species disappears, biologists say that the species has become extinct. By making room for new species, extinction helps drive the evolution of life. Over long periods of time, the number of species becoming extinct can remain fairly constant, meaning that an average number of species go extinct each year, century, or millennium. However, during the history of life on Earth, there have been periods of mass extinction, when large percentages of the planet&rsquos species became extinct in a relatively short amount of time. These extinctions have had widely different causes.
About 541 million years ago, a great expansion occurred in the diversity of multicellular organisms. Paleobiologists, scientists who study the fossils of plants and animals to learn how life evolved, call this event the Cambrian Explosion. Since the Cambrian Explosion, there have been five mass extinctions, each of which is named for the geological period in which it occurred, or for the periods that immediately preceded and followed it.
The first mass extinction is called the Ordovician-Silurian Extinction. It occurred about 440 million years ago, at the end of the period that paleontologists and geologists call the Ordovician, and followed by the start of the Silurian period. In this extinction event, many small organisms of the sea became extinct. The next mass extinction is called Devonian extinction, occurring 365 million years ago during the Devonian period. This extinction also saw the end of numerous sea organisms.
The largest extinction took place around 250 million years ago. Known as the Permian-Triassic extinction, or the Great Dying, this event saw the end of more than 90 percent of the Earth&rsquos species. Although life on Earth was nearly wiped out, the Great Dying made room for new organisms, including the first dinosaurs. About 210 million years ago, between the Triassic and Jurassic periods, came another mass extinction. By eliminating many large animals, this extinction event cleared the way for dinosaurs to flourish. Finally, about 65.5 million years ago, at the end of the Cretaceous period came the fifth mass extinction. This is the famous extinction event that brought the age of the dinosaurs to an end.
In each of these cases, the mass extinction created niches or openings in the Earth&rsquos ecosystems. Those niches allowed for new groups of organisms to thrive and diversify, which produced a range of new species. In the case of the Cretaceous extinction, the demise of the dinosaurs allowed mammals to thrive and grow larger.
Scientists refer to the current time as the Anthropocene period, meaning the period of humanity. They warn that, because of human activities such as pollution, overfishing, and the cutting down of forests, the Earth might be on the verge of&mdashor already in&mdasha sixth mass extinction. If that is true, what new life would rise up to fill the niche that we currently occupy?
Many species have gone extinct throughout history and all that marks their presence on Earth are fossils, such as this one of a dinogorgon.
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The basic and most fundamental component present in every living entity is the cell. Both plants and animals are made up of one to countless number of these units, which carry out different sets of functions. Life before evolution began from a single cell. Similarly even today, life is generated from a single cell, which then divides or multiplies to give rise to a complex living form. After fertilization, once the zygote is formed, the cells start differentiating into their types, and over a certain period of time, give rise to a fully developed, mature living entity.
Plants and animals use various forms of energy for the development of their bodies. The entire amount of chemical energy used by them to carry out their life processes is called metabolism. Plants use solar energy to carry out photosynthesis, which is the process for making their food (glucose). Hence, they are known as ‘autotrophs’. However, animals cannot produce their own food, and are dependent on plants and other animals for their energy source. Hence, they are called ‘heterotrophs’.
One of the rules of nature is growth, which is followed by all life forms. As development is an involuntary process, every cell in a living entity has to age. Growth and change is a part of all living organisms, as cells divide to give rise to new and identical ones. Sometimes due to some genetic defects, during differentiation, some cells mutate to form other types of cells, and result in complex organisms. This process of constant development and growth is also called organogenesis.
All organisms reproduce to continue their species’ life. Plants and animals have a reproductive system, which is completely developed at puberty. There are two types of reproduction prevalent in nature, viz. sexual and asexual. The former involves the combination of genetic material to give rise to a single zygote, which further develops into a bigger organism. The latter type involves splitting of one organism or cell, to form two separate individuals of the same species.
Every living thing is highly organized when it comes to the pattern or structure of the body. Plants as well as animals have very complicated cell structures that are arranged uniquely in different organs. The cells form organelles, which in turn form organs. The organs make up the various parts of the organism. This is a network that is followed by every cell.
Whatever is created has to come to an end. Both plants and animals have limited life spans, during which they go through their life processes like development and reproduction. As the cells age over a particular time period, they start becoming weak and lose their functions. They can’t survive, and this is called death. They all have a particular age they live up to, and then surrender to nature.
These include homeostasis, which is the process to maintain stable internal conditions for survival. These conditions have to be maintained for body temperature, heartbeat, water content, etc. When homeostasis is regulated, the metabolism of the body is also regulated, and the living things stay healthy and fit.
Movement is also one such characteristic. The type of movements depend on each species of plants and animals. Adaptation and defense are also considered as common traits. Every living entity has to adapt to certain conditions for survival, and if it can’t, then it won’t survive. It is their right to protect themselves from predators.
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Evolution is a miracle that has accompanied us for billions of years, and is still in process. Eventually, all living entities complement each other through their characteristics.
Did you know the fact that fungi lack chlorophyll? This type of life form can cause diseases in humans and can also be used to make cheese by the process&hellip
The animals of Phylum Platyhelminthes are worm-like animals with soft and unsegmented bodies. They are characterized by bilateral symmetry, absence of a body cavity, no respiratory and circulatory organs, and&hellip
Have you ever wondered whether any kind of organism exists even in the volcanic vents or lava mud? It's unbelievable, but true. Archaebacteria are such organisms that are the true&hellip
What is apoptosis?
There are two ways that a cell can die: necrosis and apoptosis. Necrosis occurs when a cell is damaged by an external force, such as poison, a bodily injury, an infection or getting cut off from the blood supply (which might occur during a heart attack or stroke). When cells die from necrosis, it's a rather messy affair. The death causes inflammation that can cause further distress or injury within the body.
Apoptosis, on the other hand, is relatively civil, even though it may not sound so at first -- it's when a cell commits suicide. How is that better than necrosis? For one thing, the cleanup is much easier. It's sometimes referred to as programmed cell death, and indeed, the process of apoptosis follows a controlled, predictable routine.
When a cell is compelled to commit suicide (we'll get to the triggers for apoptosis in just a minute), proteins called caspases go into action. They break down the cellular components needed for survival, and they spur production of enzymes known as DNases, which destroy the DNA in the nucleus of the cell. It's like roadies breaking down the stage in an arena after a major band has been through town. The cell shrinks and sends out distress signals, which are answered by vacuum cleaners known as macrophages. The macrophages clean away the shrunken cells, leaving no trace, so these cells have no chance to cause the damage that necrotic cells do.
Apoptosis also differs from necrosis in that it's essential to human development. For example, in the womb, our fingers and toes are connected to one another by a sort of webbing. Apoptosis is what causes that webbing to disappear, leaving us with 10 separate digits. As our brains develop, the body creates millions more cells than it needs the ones that don't form synaptic connections undergo apoptosis so that the remaining cells function well. Programmed cell death is also necessary to start the process of menstruation.
That's not to say that apoptosis is a perfect process. Sometimes, the wrong cells kill themselves off, and sometimes, the ones that should say "auf Wiedersehen" stick around instead. This brings us to our discussion of the triggers of apoptosis. Rather than dying due to injury, cells that go through apoptosis die in response to signals within the body. When cells recognize viruses and gene mutations, they may induce death to prevent the damage from spreading. When cells are under stress, as may happen when free radicals are on the loose or when a person undergoes radiation, apoptosis can occur. But there are also signals within the body that send the message that a cell should continue living. All cells have varying level of sensitivity to the positive and negative triggers, so sometimes the wrong cells live and die.
Scientists are trying to learn how they can modulate apoptosis, so that they can control which cells live and which undergo programmed cell death. Anti-cancer drugs and radiation, for example, work by triggering apoptosis in diseased cells. Many diseases and disorders are linked with the life and death of cells -- increased apoptosis is a characteristic of AIDS, Alzheimer's and Parkinson's disease, while decreased apoptosis can signal lupus or cancer. Understanding how to regulate apoptosis could be the first step to treating these conditions.
2. A Progressive Alternative: The Higher-Brain Approach
According to the higher-brain standard, human death is the irreversible cessation of the capacity for consciousness. &ldquoConsciousness&rdquo here is meant broadly, to include any subjective experience, so that both wakeful and dreaming states count as instances. Reference to the capacity for consciousness indicates that individuals who retain intact the neurological hardware needed for consciousness, including individuals in a dreamless sleep or reversible coma, are alive. One dies on this view upon entering a state in which the brain is incapable of returning to consciousness. This implies, somewhat radically, that a patient in a PVS or irreversible coma is dead despite continued brainstem function that permits spontaneous cardiopulmonary function. Although no jurisdiction has adopted the higher-brain standard, it enjoys the support of many scholars (see, e.g., Veatch 1975 Engelhardt 1975 Green and Wikler 1980 Gervais 1986 Bartlett and Youngner 1988 Puccetti 1988 Rich 1997 and Baker 2000). These scholars conceptualize, or define, human death in different ways&mdashthough in each case as the irreversible loss of some property for which the capacity for consciousness is necessary. This discussion will consider four leading argumentative strategies in support of the higher-brain approach.
2.1 Appeals to the Essence of Human Persons
One strategy for defending the higher-brain approach is to appeal to the essence of human persons on the understanding that this essence requires the capacity for consciousness (see, e.g., Bartlett and Youngner 1988 Veatch 1993 Engelhardt 1996, 248 Rich 1997 and Baker 2000, 5). &ldquoEssence&rdquo here is intended in a strict ontological sense: that property or set of properties of an individual the loss of which would necessarily terminate the individual's existence. From this perspective, we human persons&mdashmore precisely, we individuals who are at any time human persons&mdashare essentially beings with the capacity for consciousness such that we cannot exist at any time without having this capacity at that time. We go out of existence, it is assumed, when we die, so death involves the loss of what is essential to our existence.
Unfortunately, the use of terminology in these arguments can be confusing because the same term may be used in different ways and terms are frequently used without precise definition. It is sometimes claimed, for example, that we are essentially persons. But what, exactly, is a person? Some authors (e.g., Engelhardt 1996, Baker 2000) use the term to refer to beings with relatively complex psychological capacities such as self-awareness over time, reason, and moral agency. Then the claim that we are essentially persons implies that we die upon losing such advanced capacities. But this means that at some point during the normal course of progressive dementia the demented individual dies&mdashupon losing complex psychological capacities, however these are defined&mdashdespite the fact that a patient remains, clearly alive, with the capacity for (basic) consciousness. This view is extraordinarily radical and appears inconsistent with the higher-brain approach, which equates death with the irreversible loss of the capacity for (any) consciousness. A proponent of the view that we are essentially persons in the present sense, however, may hold that practical considerations&mdashsuch as the impossibility of drawing a clear line between sentient persons and sentient nonpersons, and the potential for abuse of the elderly&mdashrecommend the capacity for consciousness as the only safe line to draw, thereby vindicating the higher-brain view (Engelhardt 1996, 250). Meanwhile, other proponents of the view that we are essentially persons (e.g., Bartlett and Youngner 1988) apparently hold that any member of our species who retains the capacity for consciousness qualifies as a person. This view, unlike the previous one, straightforwardly supports the higher-brain standard. Still other authors (e.g., Veatch 1993) hold that we are essentially human beings where this term refers not to all members of our species but just to those judged to be persons by the previous group of authors: members of our species who have the capacity for consciousness. And some authors who defend the higher-brain standard (e.g., McMahan 2002) assert that we are essentially minds or minded beings, which is to say beings with the capacity for consciousness. In each case, an appeal to our essence is advanced to support the higher-brain standard.
Taking this collection of arguments together, the reasoning might be reconstructed as follows:
- For humans, the irreversible loss of the capacity for consciousness entails (is sufficient for) the loss of what is essential to their existence
- For humans, loss of what is essential to their existence is (is necessary and sufficient for) death
- For humans, irreversible loss of the capacity for consciousness entails (is sufficient for) death.
We have noted that various commentators who advance this reasoning hold that we are essentially persons in a sense requiring complex psychological capacities. We have noted that this implies that for those of us who become progressively demented, we die&mdashgo out of existence&mdashat some point during the gradual slide to permanent unconsciousness. Even if practical considerations recommend safely drawing a line at irreversible loss of the capacity of consciousness for policy purposes, the implication that, strictly speaking, we go out of existence during progressive dementia will strike many as incredible. At the other end of life there is another problematic implication. For if we are essentially persons (in this sense), then inasmuch as human newborns lack the capacities that constitute personhood, each of us came into existence after what is ordinarily described as his or her birth.
For those attracted to the general approach of understanding our essence in terms of psychological capacities, a promising alternative thesis is that we are essentially beings with the capacity for at least some form of consciousness who die upon irreversibly losing that very basic capacity. Stated more simply, we are essentially minded beings, or minds, and we die when we completely &ldquolose our minds.&rdquo (Note that this thesis is consistent with the claim that we are also essentially embodied.)
What, then, about the human organism associated with one of us minded beings? Surely the fetus that gradually developed prior to the emergence of sentience or the capacity for consciousness&mdashthat is, prior to the emergence of a mind&mdashwas alive. On the other end of life, a patient in a PVS who is spontaneously breathing, circulating blood, and exhibiting a full range of brainstem reflexes appears to be alive. Consider also anencephalic infants, who are born without cerebral hemispheres and never have the capacity for consciousness: They, too, seem to be living organisms, their grim prognosis notwithstanding. In response to this challenge, a proponent of the higher-brain approach may either (1) assert that the presentient fetus, PVS patient, and anencephalic infant are not alive despite appearances (Puccetti 1988) or (2) allow that these organisms are alive but are not of the same fundamental kind as we are: minded beings (McMahan 2002, 423&ndash6). Insofar as life is a biological concept, and the organisms in question satisfy commonly accepted criteria for life, option (1) seems at best hyperbolic. At best, the claim is really that these organisms, though alive, are not alive in any state that matters much, so we may count them as dead or nonliving for our purposes. This claim, in turn, may be understood as depending on option (2), on which we may focus. This option implies that for each of us minded beings, there is a second, closely associated being: a human organism. The prospects of the present strategy for defending the higher-brain approach turn significantly on its ability to make sense of this picture of two closely associated beings: (1) the organism, which comes into existence at conception or shortly thereafter (perhaps after twinning is no longer possible) and dies when organismic functioning radically breaks down, and (2) the minded being, who comes into existence when sentience emerges and might&mdashin the event of PVS or irreversible coma&mdashdie before the organism does. (For doubts on this score, see DeGrazia 2005, ch. 2).
Appealing to the authority of biologists and common sense, some philosophers (e.g., Olson 1997) charge as indefensible the claim that we (who are now) human persons were never presentient fetuses. One might also find puzzling the thesis that there is one definition of death, appealing to the capacity for consciousness, for human beings or persons and another definition, appealing to organismic functioning, for nonhuman animals and the human organisms associated with persons. It is open to the higher-brain theorist, however, to allow that there are also two closely associated beings in the case of sentient nonhuman animals&mdashthe minded being and the organism&mdashwith the death of, say, Lassie (the minded dog) occurring at her irreversible loss of consciousness (McMahan 2002, ch. 1). But some will find unattractive the failure to furnish a single conception of death that applies to all living things. To be sure, not everyone finds these objections compelling.
One of the most significant challenges confronting the present approach is to characterize cogently the relationship between one of us and the associated human organism. The relationship is clearly not identity&mdashthat is, being one and the same thing&mdashbecause the organism originates before the mind, might outlive the mind, and therefore has different persistence conditions. This strongly suggests, perhaps surprisingly, that we human persons are not animals. If you are not identical to the human organism associated with you, then since there is at most one animal sitting in your chair, you are not she and are therefore not an animal (Olson 1997). Yet many consider it part of educated common sense that we are animals.
Might you be part of the organism associated with you&mdashnamely, the brain (more precisely, the portions of the brain associated with consciousness) (McMahan 2002, ch. 1)? But the brain seems capable of surviving death, when you are supposed to go out of existence. Are you then a functioning brain, which goes out of existence at the irreversible loss of consciousness? But it seems odd to identify the functioning brain&mdashas distinct from the brain&mdashas you. How could you be some organ only when it functions? Presumably you are a substance (see the entry on substance), a bearer of properties, not a substance only when it has certain properties. One might reply that the functioning brain is itself a substance, a substance distinct from the brain, but that, too, strains credibility. Might you instead be not the brain, but the mind understood as the conscious properties of the brain? That would imply that you are a set of properties, rather than a substance, which is no less counterintuitive. Note that the charge of incredibility is not directed at the assertion that the mind is the functioning brain, or is a set of brain properties, and not a distinct substance&mdasha thesis in good standing in the philosophy of mind (see the entries on identity theory of mind and functionalism). The charge of incredibility is directed at the assertion that you are a set of properties and not a substance. 
Another possibility regarding the person/organism relationship is that the human organism constitutes the person it eventually comes to support (Baker 2000). One might even claim the legitimacy of saying&mdashemploying an &ldquois&rdquo of constitution&mdashthat we are animals (or organisms), just as we can say that a statue constituted by a hunk of bronze, shaped in a particular way, is a hunk of bronze (ibid). Challenges to this reasoning includes doubts that we may legitimately speak of an &ldquois&rdquo of constitution if not, then the constitution view implies that we are not animals after all. Another challenge, which applies equally to the view that we minds are parts of organisms, concerns the counting of conscious beings. On either the constitution view or the part-whole view, you are essentially a being with the capacity for consciousness. Closely associated with you&mdashwithout being (identical to) you, due to different persistence conditions&mdashis a particular animal. But that animal, having a functioning brain, would also seem to be a conscious being. Either of these views, then, apparently suggests that for each of us there are two conscious beings, seemingly one too many. Despite such difficulties as these, the thesis that we are essentially minded beings remains a significant basis for the higher-brain approach to human death.
2.2 Appeals to Personal Identity
A second argumentative strategy in defense of the higher-brain approach claims to appeal to our personal identity while remaining agnostic on the question of our essence (Green and Wikler 1980). The fundamental claim is that, whatever we are essentially, it is clear that one of us has gone out of existence once the capacity for consciousness has been irreversibly lost, supporting the higher-brain standard of death. Clearly, though, any view of our numerical identity over time&mdashour persistence conditions&mdashis conceptually dependent on a view of what we essentially are (DeGrazia 1999 DeGrazia 2005, ch. 4). If we are essentially human animals, and not essentially beings with psychological capacities, then, contrary to the above argument, it is not clear&mdashindeed, it is false&mdashthat we go out of existence upon irreversible loss of the capacity for consciousness rather, we die upon the collapse of organismic functioning. The appeal to personal identity in support of the higher-brain standard depends on the thesis that we are essentially minded beings and therefore inherits the challenges facing this view, as discussed in the previous subsection. Nevertheless, the appeal to personal identity, construed as a distinct argumentative strategy, was somewhat influential in early discussions of the definition of death (see, e.g., President's Commission 1981, 38&ndash9).
2.3 The Claim that the Definition of Death is a Moral Issue
Another prominent argumentative strategy in support of the higher-brain approach contends that the definition of death is a moral issue and that confronting it as such vindicates the higher-brain approach (see, e.g., Veatch 1975, 1993 Gervais 1986, ch. 6). In asking how to determine that a human has died, according to this argument, what we are really asking is when we ought to discontinue certain activities such as life-support efforts and initiate certain other activities such as organ donation, burial or cremation, grieving, change of a survivor's marital status, and transfer of property. The question, in other words, is when &ldquodeath behaviors&rdquo are appropriate. This, the argument continues, is a moral question, so an answer to this question should be moral as well. Understood thus, the issue of defining human death is best addressed with the recognition that irreversible loss of the capacity for consciousness marks the time at which it is appropriate to commence death behaviors.
Is the definition of death really a moral issue? To say that someone has died does seem tantamount to saying that certain behaviors are now appropriate while certain others are no longer appropriate. But it hardly follows that the assertion of death is itself a moral claim. An alternative hypothesis is that the sense of moral import derives from the fact that certain moral premises&mdashfor example, that we shouldn't bury or cremate prior to death&mdashare shared by virtually everyone. Moreover, the concept of death is (at least originally) at home in biology, which offers many instances in which a determination of death&mdashsay, of a gnat or a clover&mdashseems morally unimportant. Rather than asserting that death itself is a moral concept, it might be more plausible to assert that death, a biological phenomenon, is generally assumed to be morally important&mdashat least in the case of human beings&mdashgiven a relatively stable background of social institutions and attitudes about &ldquodeath behaviors.&rdquo Furthermore, due to the moral salience of human death, discussions about its determination are often prompted by a moral or pragmatic agenda such as interest in organ transplantation or concerns about expensive, futile treatment. But these observations do not imply that death is itself a moral concept.
Even if it were, it would hardly follow that the higher-brain standard is preferable to other standards. A person with relatively conservative instincts might hold that death behaviors are morally appropriate only when the whole-brain or cardiopulmonary standard has been met. We need to ask, therefore, what grounds exist for the claim&mdashadvanced by proponents of the higher-brain standard&mdashthat death behaviors are appropriate as soon as someone has irreversibly lost the capacity for consciousness. Perhaps the best possible grounds are that irreversible loss of consciousness entails an existence lacking in value for the unconscious individual herself. It appears, then, that the strongest specification of the present line of reasoning actually relies upon the next (and final) argumentative strategy to be considered&mdashand might, as we will see, lead to the conclusion that we should permit individuals to select among several standards of death.
2.4 The Appeal to Prudential Value
The idea here is to defend the higher-brain approach on the basis of claims about prudential value (for a discussion, see DeGrazia 2005, 134&ndash8). Conscious life, it is argued, is a precondition for virtually everything that we value in our lives. We have an enormous stake in continuing our lives as persons and little or no stake in continuing them when we are permanently unconscious. The capacity for consciousness is therefore essential not in a metaphysical sense connected to our persistence conditions, but in the evaluative sense of indispensable to us. One need not claim that the capacity for consciousness underlies everything of prudential value, just that it underlies the overwhelmingly greater part of what matters to us prudentially. And although, for many people, consciousness may not be sufficient for what matters prudentially&mdashinsofar as they find indispensable, say, some degree of self-awareness and meaningful interaction with others&mdashit is certainly necessary and the basic capacity for consciousness (as opposed to self-consciousness or personhood) is the only safe place to demarcate death for policy and social purposes. We should therefore regard irreversible loss of the capacity for consciousness as a human being's death&mdasheven if the original concept of death is biological and biological considerations favor some less progressive standard.
How persuasive is this case for the higher-brain approach? One might challenge the assumption that prudential, as opposed to moral, considerations ought to be decisive in adopting a standard for human death. On the other hand, as suggested in our discussion of the previous argumentative strategy, moral considerations may not favor a particular standard of death except insofar as they rest on prudential considerations&mdashour present concern. But even if we accept the claim that human death should be understood on the basis of prudential values, we confront the prospect of reasonable pluralism about prudential value. While supporters of the higher-brain approach (who tend to be liberal intellectuals) are likely to have prudential values in line with this approach, many other people do not. If a patient has a stake in his family's need for closure should he enter a PVS&mdashan interest that may be self-regarding as well as other-regarding&mdashthis fact would count against allowing the PVS to constitute death in his case. If an Orthodox Jew or conservative Christian believes that (biological) life is inherently precious to its possessor, even if the individual cannot appreciate its value at a given time, this would count against the higher-brain standard in the case of the individual in question. Perhaps, then, the appeal to prudential value favors not the higher-brain standard for everyone but a pro-choice view about standards of death. A jurisdiction might, for example, have one default standard of death but permit conscientious exemption from that standard and selection of a different one within some reasonable range of options (Veatch 2019).
In reply to this argument, a proponent of the appeal to prudential value might contend that it is simply irrational to value biological existence without the possibility of returning to consciousness. But this reply assumes the experience requirement: that only states of affairs that affect one's experience can affect one's well-being (for a discussion, see Griffin 1986, 16&ndash19). The experience requirement is not self-evident. Some people believe that they are worse off for being slandered even if they never learn of the slander and its repercussions never affect their experience. Some even believe, following Aristotle's suggestion, that the quality of one's life as a whole can be affected by posthumous states of affairs such as tragedy befalling a loved one. Although the intelligibility of this belief in posthumous interests might be challenged, the following is surely intelligible: States of affairs that don't affect one's experience but connect importantly with one's values can affect one's interests at least while one exists. Desire-based accounts of well-being (see, e.g., Hare 1981) standardly accept this principle, for what is desired may occur without one's awareness of its occurrence and without affecting one's experience. These considerations illuminate the intelligibility of one's prudential values extending to a period of time when one is alive but irreversibly unconscious.
In view of apparently reasonable pluralism regarding prudential values, including reasonable disagreement about the experience requirement, it seems doubtful that appeal to prudential value alone can support the higher-brain standard for everyone. At the same time, and more generally, the higher-brain approach remains an important contender in the debate over the definition of death.
Do all organisms have to die? - Biology
Have you ever wondered why we can't seem to feed the world's hungry? It's a complex issue, but it might surprise you to learn that it's not because there isn't enough food current agricultural capacity, based on current technology, exists to feed as many as 10 billion people. The Earth's population is "only" about 7 billion. The big question really is: If we want to feed everyone, what would everyone need to eat? To answer that question, download this excel spreadsheet and try plugging in some numbers.
Example : One acre of a grain crop could be used to feed cattle, and then the cattle could be used to feed people. If 50% of the energy is lost to the cattle, you could feed twice as many people if you fed them the grain directly. Another way of looking at it is that it would only take a half acre of land to feed the people grain, but a whole acre if you feed the grain to the cattle and the cattle to the people. A common practice to grow cattle faster is to feed them ground up animal protein. This means that when we eat the meat from the cow, we're at the tertiary level or higher. The loss of energy between trophic levels may also be even higher. Recent studies suggest that only
10% of energy is converted to biomass from one trophic level to the next!
The Food Chain: The answer has to do with trophic levels. As you probably know, the organisms at the base of the food chain are photosynthetic plants on land and phytoplankton (algae) in the oceans. These organisms are called the producers, and they get their energy directly from sunlight and inorganic nutrients. The organisms that eat the producers are the primary consumers. They tend to be small in size and there are many of them. The primary consumers are herbivores (vegetarians). The organisms that eat the primary consumers are meat eaters (carnivores) and are called the secondary consumers. The secondary consumers tend to be larger and fewer in number. This continues on, all the way up to the top of the food chain. About 50% of the energy (possibly as much as 90%) in food is lost at each trophic level when an organism is eaten, so it is less efficient to be a higher order consumer than a primary consumer. Therefore, the energy transfer from one trophic level to the next, up the food chain, is like a pyramid wider at the base and narrower at the top. Because of this inefficiency, there is only enough food for a few top level consumers, but there is lots of food for herbivores lower down on the food chain. There are fewer consumers than producers.
Land and aquatic energy pyramids
|Trophic Level||Desert Biome||Grassland Biome||Pond Biome||Ocean Biome|
|Primary Consumer (Herbivore)||Butterfly||Grasshopper||Insect Larva||Zooplankton|
|Secondary Consumer (Carnivore)||Lizard||Mouse||Minnow||Fish|
|Tertiary Consumer (Carnivore)||Snake||Snake||Frog||Seal|
|Quaternary Consumer (Carnivore)||Roadrunner||Hawk||Raccoon||Shark|
Food Web: At each trophic level, there may be many more species than indicated in the table above. Food webs can be very complex. Food availability may vary seasonally or by time of day. An organism like a mouse might play two roles, eating insects on occasion (making it a secondary consumer), but also dining directly on plants (making it a primary consumer). A food web of who eats who in the southwest American desert biome might look something like this:
Keystone Species: In some food webs, there is one critical "keystone species" upon which the entire system depends. In the same way that an arch collapses when the keystone is removed, an entire food chain can collapse if there is a decline in a keystone species. Often, the keystone species is a predator that keeps the herbivores in check, and prevents them from overconsuming the plants, leading to a massive die off. When we remove top predators like grizzly bears, orca whales, or wolves, for example, there is evidence that it affects not just the prey species, but even the physical environment.
Apex Predators: These species are at the top of the food chain and the healthy adults have no natural predators. The young and old may in some cases be preyed upon, but they typically succumb to disease, hunger, the effects of aging, or some combination of them. The also suffer from competition with humans, who often eliminate the top predators in order to have exclusive access to the prey species, or through habitat destruction, which is an indirect form of competition.
Decomposers: When organisms die, they are sometimes eaten by scavengers but the remaining tissues are broken down by fungi and bacteria. In this way, the nutrients that were part of the body are returned to the bottom of the trophic pyramid.
Bioaccumulation: In addition to being less energy efficient, eating higher up the food chain has its risks. Pesticides and heavy metals like mercury, arsenic, and lead tend to be consumed in small quantities by the primary consumers. These toxins get stored in the fats of the animal. When this animal is eaten by a secondary consumer, these toxins become more concentrated because secondary consumers eat lots of primary consumers, and often live longer too. Swordfish and tuna are near the top of the aquatic food chain and, when we eat them, we are consuming all of the toxins that they have accumulated over a lifetime. For this reason, pregnant women are advised against eating these foods. Solve the following problems mathematically.
1. Given: 10 billion people can be fed a basic vegetarian diet that is nutritionally complete. How many people could we feed at the American standard-a tertiary level of consumption (3rd order consumers?). 50% of the energy is lost by each higher level.
2. If there are 250 million people in the United States most of them eating at the Tertiary (3rd) level of consumption, how many people could we feed at the Primary level?
3. Some animals like sharks are 5th order consumers! Sharks eat tuna that eat mackerel that eat herring that eat copepods that eat diatoms. If we were to make the reasonable assumption that each of these animals eats 2 of its prey each day, how many organisms died to feed the shark in one day?
An ecosystem and its components (plants, animals, their interactions, and their surroundings) are all topics prone to misconceptions. Students may give human characteristics to, or anthropomorphize, plants and animals. They may struggle with ideas like predation, believe that only certain animals get eaten, or think that all organisms within an ecosystem “get along.” They may assume certain characteristics about groups of organisms such as carnivores based on a few examples or they may simplify the complex set of relationships represented by a food web. Finally, students may not understand that ecosystems are dynamic and change as a result of natural and human-influenced processes.
Another topic prone to misconception is adaptation. Students (and adults) often misinterpret or misuse this word to indicate that individual organisms intentionally change in response to changes in their environment. Many children’s books and web sites present some variation of this misleading notion in an attempt to simplify the concept or the reading level of material. As a result, adaptation is an extremely misunderstood scientific concept.
We’ve highlighted some common misconceptions about plants, food chains and webs, predator/prey relationships, ecosystems, and ecological adaptations that might be encountered in the elementary classroom. A more complete list can be found at the Overcoming Ecological Misconceptions web site. We’ve also included tools for formative assessment as well as lessons and suggestions for teaching correct scientific concepts.
|Students may think…||Instead of thinking…|
|Plants are dependent on humans.||Humans (and all other animals) are dependent on plants.|
|Plants cannot defend themselves against herbivores.||Plants have a range of defenses including external structures (sap, hairs, thorns, wax) and chemicals that either reduce digestibility or are toxic.|
Students may have many other misconceptions about plants. For more information, please see “Common Misconceptions about Plants” in our March 2009 issue.
Food Chains and Webs
|Students may think…||Instead of thinking…|
|Food webs are interpreted as simple food chains.||Food webs most accurately depict the flow of energy within an ecosystem. They depict a complex set of relationships that is not easily simplified to a food chain.|
|Organisms higher in a food web eat everything that is lower in the food web.||Organisms higher in a food chain eat some, but not necessarily all, of the organisms below them in the food web.|
|There are more herbivores than carnivores because people keep and breed herbivores.||There are more herbivores than carnivores because of the decreasing amount of energy available at each level of the food web.|
|Food chains involve predator and prey, but not producers.||Producers are an essential part of all food chains and webs.|
|Decomposers release some energy that is cycled back to plants.||Decomposers break down dead organisms, returning nutrients to the soil so they can be used by plants. Some decomposers are eaten by carnivores.|
|Carnivores have more energy or power than herbivores do.||While some carnivores may be larger and require more food than some herbivores, they do not have more energy or power.|
|Carnivores are big or ferocious, or both. Herbivores are small and passive.||Although some carnivores may be big and ferocious and some herbivores small and passive, there is a great diversity among each group of organisms.|
Predator/Prey Populations and Relationships
|Students may think…||Instead of thinking…|
|Predator and prey populations are similar in size.||Prey populations tend to be larger than predator populations.|
|The relative sizes of predator and prey populations have no bearing on the size of the other.||The sizes of predator and prey populations influence each other.|
|Students may think…||Instead of thinking…|
|Varying the population size of a species may not affect an ecosystem because some organisms are not important.||All organisms are important within an ecosystem. Varying a species’ population size may not affect all other species equally, but it will affect the ecosystem as a whole.|
|Ecosystems are not a functioning whole but simply a collection of organisms.||Ecosystems include not just the organisms but also the interactions between organisms and between the organisms and their physical environment.|
|Ecosystems change little over time.||Ecosystems change as a result of natural hazards, environmental changes, and human activity.|
|Species coexist in ecosystems because of their compatible needs and behaviors they need to get along.||Within an ecosystem, species compete for resources and feed on one another. Species live in the same ecosystem because of similar adaptations and environmental needs.|
|Students may think…||Instead of thinking…|
|Traits are developed by individuals in response to the needs of the individual.||Traits are developed across generations in response to environmental demands.|
PROBING FOR STUDENT UNDERSTANDING
What do your students think? Formative assessment can provide insight into the ideas (correct and incorrect) that your students have before and during instruction. Teachers should note, however, that simply conducting formative assessment is not enough. Instead, teachers should reflect on the data and use it to plan and refine instruction.
One useful set of resources is a collection of formative assessment probes from NSTA Press. Volumes 1, 2, and 3 of Uncovering Student Ideas in Science contain 25 formative assessment probes each to help teachers identify misconceptions. Volumes 2 and 3 contain several probes that relate to biomes and ecosystems.
Related formative assessment probes in Volume 2 of Uncovering Student Ideas in Science:
“Habitat Change” asks students to predict what will happen to an animal population if its habitat changes. It can be used to elicit student ideas about adaptation specifically whether individuals intentionally change their physical characteristics or behaviors in response to an environmental change.
Related formative assessment probes in Volume 3 of Uncovering Student Ideas in Science:
“Rotting Apple” asks students to think about why an apple eventually rots and disappears. It can be used to elicit student ideas about decay and the role of decomposers in an ecosystem.
“Earth’s Mass” asks students to decide if or how the mass of the Earth changes as organisms eliminate waste and die. It can be used to elicit student ideas about the cycling of matter through ecosystems.
TEACHING THE SCIENCE
While teachers will need to tailor their instruction based on student needs and formative assessment data, there are some general suggestions and lessons for teaching correct scientific concepts about biomes and ecosystems.
Teachers should devote time to producers when teaching about ecosystems and food webs, including a discussion of the ways in which plants defend themselves against herbivores. For other ideas about teaching correct scientific concepts about plants, please see “Common Misconceptions about Plants” in our March 2009 issue.
Food Chains and Webs
Teachers should help students go beyond a basic understanding of food chains and webs by asking them to predict what would happen if various organisms were removed from the ecosystem. Teachers can also use these lessons to discuss the impact of pollution at all levels of a food web.
Cycle of Life 1: Food Chain
This lesson gives students the opportunity to learn about a variety of food chains in various environments.
Cycle of Life 2: Food Webs
Students will explore how various organisms satisfy their needs in the environments in which they are typically found. In addition, they will examine the survival needs of different organisms and consider how the conditions in particular habitats can limit what kinds of living things can survive.
Predator/Prey Populations and Relationships
Teachers can help students understand the relative population sizes and balance between predators and their prey by varying the numbers of predators and prey in the activity below. Students can observe what happens with fewer prey, fewer predators, and equal numbers of predators and prey.
The Wolf and the Moose
Students role play a predator/prey relationship. This activity could be modified to focus on any predator/prey pair found in the tundra.
Teachers can help promote correct scientific thinking by focusing on the relationships between organisms and by asking students to predict what might happen if an organism was removed from the ecosystem or if the environmental conditions changed.
Investigating Local Ecosystems
Students in grades K-2 learn about ecosystems and relationships by observing their local environment.
Pond 1: Pond Life
Students explore how various organisms satisfy their needs within their environments and the kinds of relationships that exist between organisms within an environment.
Pond 2: Life in a Drop of Pond Water
Students continue to develop an understanding of a pond ecosystem by observing microscopic life and by discussing how single-celled living things might satisfy their needs for food, water, and air.
Making the Forest and Tundra Wildlife Connection
Students create tundra and boreal forest food webs using Alaska Ecology cards (pdf provided) and string. Teachers may want to use masking tape to tape down the web once it has been formed.
Teachers should take care to use language and select books that describe the concept of adaptation correctly. Elementary students may be more successful thinking about adaptations (traits and behaviors that help plants and animals survive) than about animals adapting to their environment. Students need to have a basic understanding of heredity and genetics to truly understand how species adapt, so this concept may be best left for the middle and high school years.
Students analyze how the traits and behaviors of real and fictional animals reflect adaptations to their environment.
National Science Education Standards
Assessing and targeting student misconceptions about biomes and ecosystems meets the Life Science Content Standard for grades K-4 and 5-8 of the National Science Education Standards. The entire National Science Education Standards document can be read online or downloaded for free from the National Academies Press web site. Science Content Standards can be found in Chapter 6.
This article was written by Jessica Fries-Gaither. For more information, see the Contributors page. Email Kimberly Lightle, Principal Investigator, with any questions about the content of this site.
Copyright April 2009 – The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0733024. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. This work is licensed under an Attribution-ShareAlike 3.0 Unported Creative Commons license.
Organisms have common & scientific name -all organisms have only 1 scientific name
-usually Latin or Greek
-developed by Carolus Linnaeus
This two-word naming system is called…..
-written in italics (or underlined)
-1st word is Capitalized –Genus
-2nd word is lowercase —species
Examples: Felis concolor, Ursus arctos, Homo sapiens, Panthera leo , Panthera tigris. These can also be abbreviated as (P. tigris or P. leo)
Linneaus also devised the system we use to organize animals. This system uses large groups divided into subgroups (like the way you organize folders on your computer)
Kingdom — Phylum — Class — Order — Family — Genus — Species
Each organism has a group and subgroups. The organisms with the most similar groups will be most closely related. Note that both the lion and the tiger are in the same genus, but are considered to be separate species.
There are currently 6 kingdoms – organisms are placed into the kingdoms based on the number and type of cells they have, and their nutritional needs.