question: Why do animals have an instinct not to die, if they don’t even know what happens after death.
comment: Evolution. A mother bear gives birth to two cubs. One (due to totally random gene combination) is not afraid of death, and dies early on. Second (again, due to totally random gene combination) is afraid of death, and lives a long life, mating with some females and becoming father of more cubs. The first "mutation" was less optimised for survival, and produced less offspring than second "mutation". Thus second version is more likely to appear in future cubs (because it managed to actually produce those cubs). So over many many many many many generations, entities with instinct of self-preservation were more successful at survival, and thus at propagation, and so became dominant.
passages: In mammals, the Virginia opossum is perhaps the best known example of defensive thanatosis. "Playing possum" is an idiomatic phrase which means "pretending to be dead". It comes from a characteristic of the Virginia opossum, which is famous for pretending to be dead when threatened. This instinct does not always pay off in the modern world; for example, opossums scavenging roadkill may use it in response to the threat posed by oncoming traffic, and subsequently end up as roadkill themselves.
   Death feigning may also play a role in reproduction, for example, in the nursery web spider, the male sometimes feigns death to avoid getting eaten by females during mating. In some cases, death feigning is used by a predator. For example, the predatory cichlid "Haplochromis livingstoni" lies on its side on the bottom sediments until approached by scavengers attracted to what appears to be a dead fish, whereupon "H. livingstoni" abandons the pretence, rights itself and attacks the scavenger.
   In beetles, artificial selection experiments have shown that there is heritable variation for length of death-feigning. Those selected for longer death-feigning durations are at a selective advantage to those at shorter durations when a predator is introduced. Birds often feign death to escape predation; for example tonic immobility in quail reduces the probability of attacks by cats.
   BULLET::::- Chimpanzee orphans can die while in the state of grieving. Jane Goodall (1990) followed Flint, a chimpanzee, for a few days after the death of Flint's friend Flo. She noted that Flint "walked along one of the branches, then stopped and stood motionless, staring down at an empty nest". Flint had been lethargic, even refusing food. Per Goodall, Flint was "hollow-eyed, gaunt and utterly depressed".
  
  BULLET::::- Magpies have been seen to mourn over their dead.
   A well-researched form of deception is feigning death, often referred to by non-specialists as "playing dead" or "playing possum", although specialists use the terms "tonic immobility" or "thanatosis". A wide range of animals, e.g. lizards, birds, rodents, and sharks, behave as if dead as an anti-predator adaptation, as predators usually take only live prey.
   Despite appearances, the animal remains conscious throughout tonic immobility. Evidence for this includes the occasional responsive movement, scanning of the environment and animals in TI often taking advantage of escape opportunities.
  
  Section::::Tonic immobility.:In sharks.
   Tonic immobility has been used to show that hens in cages are more fearful than those in pens, hens on the top tier of tiered battery cages are more fearful than those on the lower levels, hens carried by hand are more fearful than hens carried on a mechanical conveyor, and hens undergoing longer transportation times are more fearful than those undergoing transport of a shorter duration.
  
  Tonic immobility as a scientific tool has also been used with mice, gerbils, guinea pigs, rats, rabbits and pigs.
  
  Section::::Thanatosis.
   A case is shown with one named Amos. The day before he died he spent the day in his nest and did not move until a female chimpanzee Daisy went up to him (Safina, 2015). When Amos died, one of the chimpanzees who was more sociable than the rest as well as a “higher rank” than the rest did not want to be with the group for weeks. As shown here it also depends on who passed away on how long an animal can grieve. Though through the time spent mourning many signs can appear of an animals grief and agony of the loss of their companion.
   An example of this is seen in white-tailed deer fawns, which experience a drop in heart rate in response to approaching predators. This response, referred to as "alarm bradycardia", causes the fawn's heart rate to drop from 155 to 38 beats per minute within one beat of the heart. This drop in heart rate can last up to two minutes, causing the fawn to experience a depressed breathing rate and decrease in movement, called tonic immobility. Tonic immobility is a reflex response that causes the fawn to enter a low body position that simulates the position of a dead corpse. Upon discovery of the fawn, the predator loses interest in the "dead" prey. Other symptoms of alarm bradycardia, such as salivation, urination, and defecation, can also cause the predator to lose interest.
   BULLET::::- Elephants have been "observed to stand guard over a stillborn baby for days with their head and ears hanging down". Orphan elephants, who have watched their mothers be killed, have been shown to wake up screaming.
  
  BULLET::::- A wolf "sniffed [her dead companion], then sat back and gave the most soulful and heart-wrenching howl I've ever heard!"; After a pack member died, the wolves let their tails and heads hang low while walking slowly.
   Sudden prolonged immobility or faked death is an adaptive response exhibited by many mammalian species. Hofer(1970) demonstrated that several rodent species when threatened exhibited an immobility that was accompanied by a very low heart rate. For some of the rodents that heart rate reached below 50% of the baseline. Hofer distinguished between prolonged immobility and faked death phenomenon. Unlike the behavior of "hopelessness" described by Richter, the death-faking occurred with a sudden motor collapse during active struggling. Hofer interpreted the fear-inducing slowing of heart rate as a vagal phenomenon.
   Even the most simple of living organisms (for example, the single-celled bacteria) are typically under intense selective pressure to evolve a response that would help avoid a damaging environment, if such an environment exists. Organisms also evolve while adapting - even thriving - in a benign environment (for example, a marine sponge modifies its structure in response to current changes, in order to better absorb and process nutrients). Self-preservation is therefore an almost universal hallmark of life. However, when introduced to a novel threat, many species will have a self-preservation response either too specialised, or not specialised enough, to cope with that particular threat. An example is the dodo, which evolved in the absence of natural predators and hence lacked an appropriate, general self-preservation response to heavy predation by humans and rats, showing no fear of them.
   Section::::Marc Bekoff's Recent Research on Animal Grief.
  
  Marc Bekoff is a professor of ecology and evolutionary biology at the University of Colorado-Boulder. He has spent his life studying animals and their emotions, finding that animals grieve quite frequently. Such examples of grieving animals are:
  
  BULLET::::- Bekoff found that sea lion mothers squeal eerily when they watch their babies be eaten by killer whales.
  
  BULLET::::- Even after their calves have died, dolphin mothers have been seen to save them and grieve when they confirm the death.
   Mortality salience engages the conflict that humans have to face both their instinct to avoid death completely, and their intellectual knowledge that avoiding death is ultimately futile. According to terror management theory, when human beings begin to contemplate their mortality and their vulnerability to death, feelings of terror emerge because of the simple fact that humans want to avoid their inevitable death. Mortality salience comes into effect, because humans contribute all of their actions to either avoiding death or distracting themselves from the contemplation of it. Thus, terror management theory asserts that almost all human activity is driven by the fear of death.
   Tonic immobility is considered to be a fear-potentiated response induced by physical restraint and characterised by reduced responsiveness to external stimulation. It has been used as a measure in the assessment of animal welfare, particularly hens, since 1970. The rationale for the TI test is that the experimenter simulates a predator thereby eliciting the anti-predator response. The precept is that the prey animal 'pretends' to be dead to be able to escape when/if the predator relaxes its concentration. Death-feigning birds often take advantage of escape opportunities; TI in quail reduces the probability of the birds being predated by cats.
   Mammals have demonstrated grief-like states, especially between a mother and her offspring. She will often stay close to her dead offspring for short periods of time and may investigate the reasons for the baby's non-response. For example, some deer will often sniff, poke, and look at its lifeless fawn before realising it is dead and leaving it to rejoin the herd shortly afterwards. Other animals, such as a lioness, will pick up its cub in its mouth and place it somewhere else before abandoning it.
   In 1879, Arthur E. Brown studied how a male chimpanzee reacted after the death of his female counterpart. He saw the male chimpanzee display grief and "a cry which the keeper of the animals assures [Brown] he had never heard before"). Continuing to the next day, the chimpanzee sulked and barely moved. Brown deciphered that the male chimpanzee was depressed after the female chimpanzee died. However, Brown concluded that any permanent grief is only found in man, as the chimpanzee seemed fine after a couple of days.
   Attention to the dead is not unique to elephants or chimpanzees. Dolphins have been known to stay with recently deceased members of their pod for several days, preventing divers from getting close. However, the reasons for this remain obscure. While scientists can observe their actions, the thought processes that motivate them are beyond current study.
  
  Section::::Relevance to the study of early modern humans.
   Section::::Implications of Research.
   Death feigning behaviour can be deliberately induced by humans, a prominent example being the "hypnosis" of chickens or pigeons. For example, if a pigeon is grasped firmly, quickly inverted and held briefly on its back on a table, it often remains immobile for a minute or two. According to Gilman et al. the investigation of 'animal hypnosis' dates back to the year 1646 in a report by Kircher. It has been shown that the intensity and duration of death feigning is related to the intensity of fear prior to the feigning state being induced. This has been used to show that hens in cages are more fearful than those in pens, hens on the top tier of battery cages are more fearful than those on the lower levels, hens carried by hand are more fearful than hens carried on a mechanical conveyor, and hens undergoing longer transportation times are more fearful than those undergoing transport of a shorter duration.
   Elephant researcher Martin Meredith recalls in his book an occurrence of a typical elephant death ritual as witnessed by Anthony Hall-Martin, a South African biologist who had studied elephants in Addo, South Africa, for over eight years. The entire family of a dead matriarch, including her young calf, were all gently touching her body with their trunks, trying to lift her. The elephant herd were all rumbling loudly. The calf was observed to be weeping and made sounds that sounded like a scream, but then the entire herd fell silent. They then began to throw leaves and dirt over the body and broke off tree branches to cover her. They spent the next two days quietly standing over her body. They sometimes left to get water or food, but they would always return.
   With mortality salience, humans who have encountered near-death experiences develop a greater sense of self and meaning to life. It has been shown that individuals who face these experiences tend to invest more into relationships, political beliefs, religious beliefs, and other beliefs over material things. As a patient with AIDS shared, "Because of my illness I have nothing to hide. It has freed me because now I am completely honest". Developing a cultural worldview provides humans with comfort from the thought of their own inevitable death. This coping mechanism has shown to highly improve the self-worth of humans and highly alleviates existential anxiety.
   Death feigning as a way to attract prey is another form of deception. In Lake Malawi, the predatory cichlid "Nimbochromis livingstonii" have been seen first remaining stationary with their abdomen on or near sand and that then dropping onto their sides. In a variant behaviour, some "N. livingstonii" fell through the water column and landed onto their side. The fish then remained immobile for several minutes. Their colour pattern was blotchy and suggested a rotting carcass. Small inquisitive cichlids of other species often came near and they were suddenly attacked by the predator. About a third of the death-feigning performances led to an attack, and about one-sixth of the attacks were successful. Another African cichlid, "Lamprologus lemairii", from Lake Tanganyika, has been reported to do the same thing. A South American cichlid, the yellowjacket cichlid "Parachromis friedrichsthalii", also uses death feigning. They turn over onto their sides at the bottom of the sinkholes they inhabit and remain immobile for as long as 15 minutes, during which they attack the small mollies that come too close to them. The comb grouper "Mycteroperca acutirostris" may also be an actor, though in this case the behaviour should be called dying or illness feigning, rather than death feigning, because while lying on its side the fish occasionally undulates its body. In 1999, off the coast of southeastern Brazil, one juvenile comb grouper was observed using this tactic to catch five small prey in 15 minutes.
   Though Bekoff is the face of recent research on animal grief, other scientists are starting to look more into it. Some studies have looked at depression in animals, with Paul Willner finding that there are eighteen animal models of depression. Peter J. Fashing & Nga Nguyen (2012) found that a group of chimpanzees groomed and caressed a grieving, older chimpanzee. They also found that "the dying female [elephant] was approached by the matriarch of another group who repeatedly attempted to bring her to her feet using her tusks". Even otters grieve, where members of a group caught fish for months and brought them to the matriarch who had failing vision and poor mobility.
   It is generally considered that humans are the only known beings to use weapons when putting an end to their own life. Some species might be driven to engage in suicidal behavior for the sake of others, which is an example of altruism in animals. These actions are performed when the reproductive fitness of others outweighs the reproductive fitness of the individual. There are examples of animals dying in defense of their family or colony, such as the case of pea aphids increasing their chances of death as a response to parasitism. Vervet monkeys will alert others when a predator is near, consequently drawing attention to itself and increasing their likelihood of being attacked.
  
raw_presuppositions: Animals shouldn't have an instinct not to die because they don't know what happens after death. Animals that don't know what happens after death shouldn't fear death.
raw_corrections: Preventing death is evolutionarily advantagous. Animals feat death because of evolutionary instincts.