Animal suicide is when an animal intentionally ends its own life through its actions. [1] It implies a wide range of higher cognitive capacities that experts have been wary to ascribe to nonhuman animals such as a concept of self, death, and future intention. There is currently not enough empirical data on the subject for there to be a consensus among experts. [2] For these reasons, the occurrence of animal suicide is controversial among academics. [3]
While it has not been proven that non-human animals do, or even can, die by suicide, many animals behave in ways that may seem suicidal. There are anecdotes of animals refusing to eat in periods of grief or stress. [4] [5] Some social insects have been known to defend their colony by sacrificing themselves. [6] Other animals are victims of parasites that are known to alter the behavior of their host to complete their lifecycle, which result in the host's death. [7]
There are yet to be definitive, unanimously agreed upon, instances of non-human animal suicide. This is due to the many components of suicide which are difficult to empirically observe without interpretation bias. [3] An animal would need to be aware of its own existence as distinct from other individuals. It would need to have an understanding of mortality and sufficient for it to realize that it is a possibility. To choose death for itself, the animal has to know about itself and that it can die. It would also need some concept of the future in order to intend to die. Each of these requisites have been studied independently, and there is some evidence of some animals being capable of each. The mirror test is currently used to determine whether an animal has a concept of self. Some animals, such as some species of cetaceans and primates, are believed to grasp the concept of death enough to mourn conspecifics. [8]
Some animals, such as octopuses, stop eating food and waste away after reproducing, seemingly losing any desire to live. As this is a genetically programmed behavior that all individuals of the species engage in, it is not intentional and therefore cannot be considered suicide.
Several risk-factors for suicide, such as addiction, depression, and PTSD, have already been modeled independently in animals. [9] [10] These animal models allow scientists to study the neuroscience behind these disorders as well as explore potential treatments. While demonstrating animal suicide itself in a lab is believed to be possible by some, [11] the ethics of driving an animal to kill itself are debated. [10] [12] In the field, it can be difficult to not only find examples of suicide, but to be certain that the death was intentional, not accidental.
Many animals that appear to be depressed or grieving begin to exhibit self-destructive behavior that sometimes ends in death, but this is not considered suicide, as the achieving of death was not necessarily the purpose or objective of the behaviors. [13]
In 1845, the Illustrated London News reported that a Newfoundland dog had been acting less lively over a period of days before being seen "to throw himself in the water and endeavor to sink by preserving perfect stillness of the legs and feet". [14] Every time he was rescued he attempted to do this again before he finally held his head underwater until death. [14] The newspaper ran stories on other dogs, as well as ducks, that had also allegedly drowned themselves, although the veracity or certainty of these cases is disputed. [15] In one of the alleged cases, one duck did so after the death of its mate. [16]
Another example of an alleged case of animal suicide is the case of the dolphin which most often portrayed Flipper on the 1960s television show Flipper . According to trainer Ric O'Barry in the film The Cove, Kathy, the dolphin, suffocated herself before him. The veracity or accuracy of this case has not been established in rigorous, scientific or objective terms. [17] [18] Similarly, a male bottle nose dolphin named Peter who was a subject in a series of experiments led by John C. Lilly, a neuroscientist, and Margaret Howe Lovatt, a volunteer naturalist, apparently stopped breathing after it was moved to a lab in a different location and separated from Lovatt. [19] [20]
Some dogs will refuse food from some unknown person after the death of their owner, a behavior that might lead to disease or death in severe cases. [16] The death of mourning animals is likely to be caused by depression leading to starvation or drowning, instead of the intent of suicide.
Aristotle described an unverified story involving one of the King of Scythia's horses dying by suicide after having been made to unwittingly impregnate its mother in his History of Animals. [21]
Some species of social insects will die by suicide in an act of altruism through autothysis. These insects will sacrifice themselves if the colony is in danger, to alert the colony of danger, or if they become diseased they will sacrifice themselves to prevent the colony from becoming diseased. [6] Carpenter ants and some species of termite will rupture glands and expel a sticky toxic substance thought to be an aliphatic compound in a process called autothysis . Termites will use autothysis to defend their colony, as the ruptured gland produces a sticky harmful secretion that leads to a tar baby effect in defense. [22] [23] When threatened by a ladybug, the pea aphid will explode itself, protecting other aphids and sometimes killing the ladybug. [14] Another example is the Camponotus saundersi, or Malaysian worker ant, which is capable of dying by suicide by exploding. [24]
Honeybees use their stinger to deliver poisonous chemicals to their attacker, effectively both injuring the predator and killing the insect in the colony's defense. [25] This self-destructive and often altruistic defense is known as sting autonomy. The stinger is easily torn from the animal's body, allowing the hazardous stinger to be left stuck in the predator. [6] Honey bees are the only bees to die after stinging. [26]
Lemmings are known to migrate when the population in their area becomes too large for its food supply. During these migrations, some will swim to cross bodies of water, but not all of them will make it back to land alive. This unfortunate consequence of migration has sometimes been perceived as an act of mass suicide. This myth has been popularized in various media. [27]
Certain types of parasites will cause their hosts to engage in suicidal behavior, through altering how the intermediate host acts, but this is not considered suicide (at least not considered suicide in a psychological or ethological sense). The change in the host's actions often benefit the parasite's search for a final host. [28] A main example is the phylum Acanthocephala, which will direct its host to a predator so as to be eaten by the predator, their new definitive host. The parasitic worm Spinochordodes tellinii will develop in grasshoppers and crickets until it is grown, at which time it will cause its host to leap into water to its death so that the worm can reproduce in water. [29] However, S. tellinii only causes its host to drown when the host is already close to water as opposed to seeking it out over large distances. [30]
Infection with Toxoplasma gondii has been shown to alter the behavior of mice and rats in ways thought to increase the rodents’ chances of being preyed upon by cats. [31] [32] Infected rodents show a reduction in their innate aversion to cat odors; while uninfected mice and rats will generally avoid areas marked with cat urine or with cat body odor, this avoidance is reduced or eliminated in infected animals. [33] Moreover, some evidence suggests this loss of aversion may be specific to feline odors: when given a choice between two predator odors (cat or mink), infected rodents show a significantly stronger preference to cat odors than do uninfected controls.
Suicide induction in intermediate hosts has been shown to help disperse the parasites to their final hosts. [34] The intermediate host of Parvatrema affinis is the bivalve mollusc, Macoma balthica . [35] The clams feed when in the sublittoral and tidal flat muds, and usually leave no conspicuous marks in the mud that could indicate their presence. However, infected clams are concentrated in the higher parts of the tidal flats, closer to shore, and leave conspicuous zig-zag markings in the sand. Visual and tactile cues have shown to be used by oyster catchers and other shore birds, the definitive hosts of the parasite.
One of the most clear examples of animal suicide would most likely be the suicidal behavior of tarsiers that are kept in captivity. Tarsiers are nervous and shy by nature, and do not do well in captivity. Many activities associated with captivity, such as camera flashes, being touched, and being kept in an enclosure, can stress the tarsiers. This stress can lead to sore eyes, which is an indication of a poor diet, and the lighting usually used in captivity can cause long-lasting damage to the eyes. When they feel too stressed out, they start beating their heads against hard surfaces, which leads to death. [36] [37] [38] [39] [40]
A popular misconception is that the lemming will die by mass suicide during reproduction. This misconception was first popularized by media in the 1960s, such as a mention in the Cyril M. Kornbluth short story "The Marching Morons" in 1951 and the 1955 comic "The Lemming with the Locket", inspired by a 1953 American Mercury article. [41] [42] Perhaps one of the most influential factors in this misconception was the 1958 Academy Award-winning Disney film White Wilderness , which showed staged footage of lemmings jumping off a cliff during reproduction. [43]
Werner Herzog's 2007 Academy Award-nominated documentary film Encounters at the End of the World features footage of a penguin marching away from the sea, going inland to its certain death. [44] National Geographic dubbed the penguin "suicidal". [45]
Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or months of mild, flu-like illness such as muscle aches and tender lymph nodes. In a small number of people, eye problems may develop. In those with a weak immune system, severe symptoms such as seizures and poor coordination may occur. If a person becomes infected during pregnancy, a condition known as congenital toxoplasmosis may affect the child.
Toxoplasma gondii is a parasitic protozoan that causes toxoplasmosis. Found worldwide, T. gondii is capable of infecting virtually all warm-blooded animals, but felids are the only known definitive hosts in which the parasite may undergo sexual reproduction.
Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is known as a bud. Since the reproduction is asexual, the newly created organism is a clone and excepting mutations is genetically identical to the parent organism. Organisms such as hydra use regenerative cells for reproduction in the process of budding.
Coccidia (Coccidiasina) are a subclass of microscopic, spore-forming, single-celled obligate intracellular parasites belonging to the apicomplexan class Conoidasida. As obligate intracellular parasites, they must live and reproduce within an animal cell. Coccidian parasites infect the intestinal tracts of animals, and are the largest group of apicomplexan protozoa.
Coccidiosis is a parasitic disease of the intestinal tract of animals caused by coccidian protozoa. The disease spreads from one animal to another by contact with infected feces or ingestion of infected tissue. Diarrhea, which may become bloody in severe cases, is the primary symptom. Most animals infected with coccidia are asymptomatic, but young or immunocompromised animals may suffer severe symptoms and death.
A rhoptry is a specialized secretory organelle. They are club-shaped organelles connected by thin necks to the extreme apical pole of the parasite. These organelles, like micronemes, are characteristic of the motile stages of Apicomplexa protozoans. They can vary in number and shape and contain numerous enzymes that are released during the process of host penetration. The proteins they contain are important in the interaction between the host and the parasite, including the formation of the parasitophorous vacuole (PV).
An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce. This is opposed to a facultative parasite, which can act as a parasite but does not rely on its host to continue its life-cycle. Obligate parasites have evolved a variety of parasitic strategies to exploit their hosts. Holoparasites and some hemiparasites are obligate.
Toll-like receptor 11 (TLR11) is a protein that in mice and rats is encoded by the gene TLR11, whereas in humans it is represented by a pseudogene. TLR11 belongs to the toll-like receptor (TLR) family and the interleukin-1 receptor/toll-like receptor superfamily. In mice, TLR11 has been shown to recognise (bacterial) flagellin and (eukaryotic) profilin present on certain microbes, it helps propagate a host immune response. TLR11 plays a fundamental role in both the innate and adaptive immune responses, through the activation of Tumor necrosis factor-alpha, the Interleukin 12 (IL-12) response, and Interferon-gamma (IFN-gamma) secretion. TLR11 mounts an immune response to multiple microbes, including Toxoplasma gondii, Salmonella species, and uropathogenic E. coli, and likely many other species due to the highly conserved nature of flagellin and profilin.
Fish fulfill several criteria proposed as indicating that non-human animals experience pain. These fulfilled criteria include a suitable nervous system and sensory receptors, opioid receptors and reduced responses to noxious stimuli when given analgesics and local anaesthetics, physiological changes to noxious stimuli, displaying protective motor reactions, exhibiting avoidance learning and making trade-offs between noxious stimulus avoidance and other motivational requirements.
Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is typified by a cellular variety with a distinct morphology and biochemistry.
Hammondia is a genus of parasitic alveolates in the phylum Apicomplexa.
Cats are a popular pet in New Zealand. Cat ownership is occasionally raised as a controversial conservation issue due to the predation of endangered species, such as birds and lizards, by feral cats.
Behavior-altering parasites are parasites with two or more hosts, capable of causing changes in the behavior of one of their hosts to enhance their transmission, sometimes directly affecting the hosts' decision-making and behavior control mechanisms. They do this by making the intermediate host, where they may reproduce asexually, more likely to be eaten by a predator at a higher trophic level which becomes the definitive host where the parasite reproduces sexually; the mechanism is therefore sometimes called parasite increased trophic facilitation or parasite increased trophic transmission. Examples can be found in bacteria, protozoa, viruses, and animals. Parasites may also alter the host behaviour to increase protection of the parasites or their offspring; the term bodyguard manipulation is used for such mechanisms.
Hammondia hammondi is a species of obligate heteroxenous parasitic alveolates of domestic cats. Intracellular cysts develop mainly in striated muscle. After the ingestion of cysts by cats, a multiplicative cycle precedes the development of gametocytes in the epithelium of the small intestine. Oocyst shedding persists for 10 to 28 days followed by immunity. Cysts in skeletal muscle measure between 100 and 340 μm in length and 40 and 95 μm in width. Some of the intermediate hosts develop low levels of antibody and some cross-immunity against Toxoplasma.
Welfare biology is a proposed cross-disciplinary field of research to study the positive and negative well-being of sentient individuals in relation to their environment. Yew-Kwang Ng first advanced the field in 1995. Since then, its establishment has been advocated for by a number of writers, including philosophers, who have argued for the importance of creating the research field, particularly in relation to wild animal suffering. Some researchers have put forward examples of existing research that welfare biology could draw upon and suggested specific applications for the research's findings.
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Catia Faria is a Portuguese moral philosopher and activist for animal rights and feminism. She is assistant professor in Applied Ethics at the Complutense University of Madrid, and is a board member of the UPF-Centre for Animal Ethics. Faria specialises in normative and applied ethics, especially focusing on how they apply to the moral consideration of non-human animals. In 2022, she published her first book, Animal Ethics in the Wild: Wild Animal Suffering and Intervention in Nature.
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