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143-412: Cowardice is a trait wherein excessive fear prevents an individual from taking a risk or facing danger. It is the opposite of courage . As a label, "cowardice" indicates a failure of character in the face of a challenge. One who succumbs to cowardice is known as a coward . As the opposite of bravery , which many historical and current human societies reward, cowardice is seen as a character flaw that

286-490: A DNA sequence within a chromosome is known as a locus . If the DNA sequence at a locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism. However, while this simple correspondence between an allele and

429-570: A GC-biased E. coli mutator strain in 1967, along with the proposal of the neutral theory , established the plausibility of mutational explanations for molecular patterns, which are now common in the molecular evolution literature. For instance, mutation biases are frequently invoked in models of codon usage. Such models also include effects of selection, following the mutation-selection-drift model, which allows both for mutation biases and differential selection based on effects on translation. Hypotheses of mutation bias have played an important role in

572-458: A Santa Claus mask with white cotton balls in the beard. Fear can be learned by experiencing or watching a frightening traumatic accident. For example, if a child falls into a well and struggles to get out, he or she may develop a fear of wells, heights ( acrophobia ), enclosed spaces ( claustrophobia ), or water ( aquaphobia ). There are studies looking at areas of the brain that are affected in relation to fear. When looking at these areas (such as

715-527: A chemical smelling of banana, and a component of bee alarm pheromone. The experiment also showed that the bees' fear-induced pain tolerance was mediated by an endorphin . By using the forced swimming test in rats as a model of fear-induction, the first mammalian "alarm substance" was found. In 1991, this "alarm substance" was shown to fulfill criteria for pheromones: well-defined behavioral effect, species specificity, minimal influence of experience and control for nonspecific arousal. Rat activity testing with

858-434: A child's psyche development or personality. For example, parents tell their children not to talk to strangers in order to protect them. In school, they would be motivated to not show fear in talking with strangers, but to be assertive and also aware of the risks and the environment in which it takes place. Ambiguous and mixed messages like this can affect their self-esteem and self-confidence. Researchers say talking to strangers

1001-514: A chromosome becoming duplicated (usually by genetic recombination ), which can introduce extra copies of a gene into a genome. Extra copies of genes are a major source of the raw material needed for new genes to evolve. This is important because most new genes evolve within gene families from pre-existing genes that share common ancestors. For example, the human eye uses four genes to make structures that sense light: three for colour vision and one for night vision ; all four are descended from

1144-400: A cold person warmer or a frightened animal look more impressive), sweating, increased blood glucose ( hyperglycemia ), increased serum calcium, increase in white blood cells called neutrophilic leukocytes, alertness leading to sleep disturbance and "butterflies in the stomach" ( dyspepsia ). This primitive mechanism may help an organism survive by either running away or fighting the danger. With

1287-415: A comparably strong emotional response in both females and males, stress-induced sweat from females produced markedly stronger arousal in women than in men. Statistical tests pinpointed this gender-specificity to the right amygdala and strongest in the superficial nuclei. Since no significant differences were found in the olfactory bulb , the response to female fear-induced signals is likely based on processing

1430-418: A creature, species, or situations that should be avoided. SSDRs are an evolutionary adaptation that has been seen in many species throughout the world including rats, chimpanzees , prairie dogs , and even humans , an adaptation created to help individual creatures survive in a hostile world. Fear learning changes across the lifetime due to natural developmental changes in the brain. This includes changes in

1573-424: A fear-provoking situation. This suggests that fear can develop in both conditions, not just simply from personal history. Fear is affected by cultural and historical context. For example, in the early 20th century, many Americans feared polio , a disease that can lead to paralysis. There are consistent cross-cultural differences in how people respond to fear. Display rules affect how likely people are to express

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1716-460: A genetic effect that is the result of natural selection . From an evolutionary psychology perspective, different fears may be different adaptations that have been useful in our evolutionary past. They may have developed during different time periods. Some fears, such as fear of heights, may be common to all mammals and developed during the mesozoic period. Other fears, such as fear of snakes, may be common to all simians and developed during

1859-524: A high testosterone level related to unhappiness in response to androstenone in men, and a high estradiol level related to disliking of androstenone in women. A German study from 2006 showed when anxiety-induced versus exercise-induced human sweat from a dozen people was pooled and offered to seven study participants, of five able to olfactorily distinguish exercise-induced sweat from room air, three could also distinguish exercise-induced sweat from anxiety induced sweat. The acoustic startle reflex response to

2002-404: A higher level of fear. Pathogens can suppress amygdala activity. Rats infected with the toxoplasmosis parasite become less fearful of cats, sometimes even seeking out their urine-marked areas. This behavior often leads to them being eaten by cats. The parasite then reproduces within the body of the cat. There is evidence that the parasite concentrates itself in the amygdala of infected rats. In

2145-402: A manner similar to a sequence of letters spelling out a sentence. Before a cell divides, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. Portions of a DNA molecule that specify a single functional unit are called genes; different genes have different sequences of bases. Within cells, each long strand of DNA is called a chromosome . The specific location of

2288-399: A natural pheromone-containing solution, it has been shown that the impairment was associated with defective detection of related pheromones, and with changes in their inborn preference for pheromones related to sexual and reproductive activities. Lastly, alleviation of an acute fear response because a friendly peer (or in biological language: an affiliative conspecific ) tends and befriends

2431-405: A nutrient in a long-term laboratory experiment , Flavobacterium evolving a novel enzyme that allows these bacteria to grow on the by-products of nylon manufacturing, and the soil bacterium Sphingobium evolving an entirely new metabolic pathway that degrades the synthetic pesticide pentachlorophenol . An interesting but still controversial idea is that some adaptations might increase

2574-611: A phenomenon termed de novo gene birth . The generation of new genes can also involve small parts of several genes being duplicated, with these fragments then recombining to form new combinations with new functions ( exon shuffling ). When new genes are assembled from shuffling pre-existing parts, domains act as modules with simple independent functions, which can be mixed together to produce new combinations with new and complex functions. For example, polyketide synthases are large enzymes that make antibiotics ; they contain up to 100 independent domains that each catalyse one step in

2717-538: A population are therefore more likely to be replaced by the offspring of parents with favourable characteristics for that environment. In the early 20th century, competing ideas of evolution were refuted and evolution was combined with Mendelian inheritance and population genetics to give rise to modern evolutionary theory. In this synthesis the basis for heredity is in DNA molecules that pass information from generation to generation. The processes that change DNA in

2860-575: A population include natural selection, genetic drift, mutation , and gene flow . All life on Earth—including humanity —shares a last universal common ancestor (LUCA), which lived approximately 3.5–3.8 billion years ago. The fossil record includes a progression from early biogenic graphite to microbial mat fossils to fossilised multicellular organisms . Existing patterns of biodiversity have been shaped by repeated formations of new species ( speciation ), changes within species ( anagenesis ), and loss of species ( extinction ) throughout

3003-430: A population is not critical, but instead a measure known as the effective population size. The effective population is usually smaller than the total population since it takes into account factors such as the level of inbreeding and the stage of the lifecycle in which the population is the smallest. The effective population size may not be the same for every gene in the same population. It is usually difficult to measure

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3146-439: A population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation . The scientific theory of evolution by natural selection was conceived independently by two British naturalists, Charles Darwin and Alfred Russel Wallace , in the mid-19th century as an explanation for why organisms are adapted to their physical and biological environments. The theory

3289-433: A population through neutral transitions due to the principles of excess capacity, presuppression, and ratcheting, and it has been applied in areas ranging from the origins of the spliceosome to the complex interdependence of microbial communities . The time it takes a neutral allele to become fixed by genetic drift depends on population size; fixation is more rapid in smaller populations. The number of individuals in

3432-499: A range of genes from bacteria, fungi and plants. Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains . Large-scale gene transfer has also occurred between the ancestors of eukaryotic cells and bacteria, during the acquisition of chloroplasts and mitochondria . It is possible that eukaryotes themselves originated from horizontal gene transfers between bacteria and archaea . Some heritable changes cannot be explained by changes to

3575-542: A rat perceived alarm pheromones, it increased its defensive and risk assessment behavior, and its acoustic startle reflex was enhanced. It was not until 2011 that a link between severe pain, neuroinflammation and alarm pheromones release in rats was found: real time RT-PCR analysis of rat brain tissues indicated that shocking the footpad of a rat increased its production of proinflammatory cytokines in deep brain structures, namely of IL-1β , heteronuclear Corticotropin-releasing hormone and c-fos mRNA expressions in both

3718-430: A reduction in scope when it was discovered that (1) GC-biased gene conversion makes an important contribution to composition in diploid organisms such as mammals and (2) bacterial genomes frequently have AT-biased mutation. Contemporary thinking about the role of mutation biases reflects a different theory from that of Haldane and Fisher. More recent work showed that the original "pressures" theory assumes that evolution

3861-403: A response to the stimulus in the form of fear or aggression commences, the amygdalae may elicit the release of hormones into the body to put the person into a state of alertness, in which they are ready to move, run, fight, etc. This defensive response is generally referred to in physiology as the fight-or-flight response regulated by the hypothalamus, part of the limbic system . Once the person

4004-414: A result of learning. This has been studied in psychology as fear conditioning , beginning with John B. Watson's Little Albert experiment in 1920, which was inspired after observing a child with an irrational fear of dogs. In this study, an 11-month-old boy was conditioned to fear a white rat in the laboratory. The fear became generalized to include other white, furry objects, such as a rabbit, dog, and even

4147-476: A separate experiment, rats with lesions in the amygdala did not express fear or anxiety towards unwanted stimuli. These rats pulled on levers supplying food that sometimes sent out electrical shocks. While they learned to avoid pressing on them, they did not distance themselves from these shock-inducing levers. Several brain structures other than the amygdalae have also been observed to be activated when individuals are presented with fearful vs. neutral faces, namely

4290-452: A single ancestral gene. New genes can be generated from an ancestral gene when a duplicate copy mutates and acquires a new function. This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function. Other types of mutations can even generate entirely new genes from previously noncoding DNA,

4433-419: A single chromosome compared to expectations , which is called their linkage disequilibrium . A set of alleles that is usually inherited in a group is called a haplotype . This can be important when one allele in a particular haplotype is strongly beneficial: natural selection can drive a selective sweep that will also cause the other alleles in the haplotype to become more common in the population; this effect

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4576-435: A sound when sensing anxiety sweat was larger than when sensing exercise-induced sweat, as measured by electromyography analysis of the orbital muscle, which is responsible for the eyeblink component. This showed for the first time that fear chemosignals can modulate the startle reflex in humans without emotional mediation; fear chemosignals primed the recipient's "defensive behavior" prior to the subjects' conscious attention on

4719-552: A source of feedback or even stimulus change. Intrinsic feedback or information coming from within, muscle twitches, increased heart rate, are seen to be more important in SSDRs than extrinsic feedback, stimuli that comes from the external environment. Dr. Bolles found that most creatures have some intrinsic set of fears, to help assure survival of the species. Rats will run away from any shocking event, and pigeons will flap their wings harder when threatened. The wing flapping in pigeons and

4862-420: A species or population, in particular shifts in allele frequency and adaptation. Macroevolution is the outcome of long periods of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one—the difference is simply the time involved. However, in macroevolution, the traits of the entire species may be important. For instance, a large amount of variation among individuals allows

5005-544: A species to rapidly adapt to new habitats , lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution might involve selection at different levels—with microevolution acting on genes and organisms, versus macroevolutionary processes such as species selection acting on entire species and affecting their rates of speciation and extinction. A common misconception

5148-411: A striking example are people with the inherited trait of albinism , who do not tan at all and are very sensitive to sunburn . Heritable characteristics are passed from one generation to the next via DNA , a molecule that encodes genetic information. DNA is a long biopolymer composed of four types of bases. The sequence of bases along a particular DNA molecule specifies the genetic information, in

5291-472: A system in which organisms interact with every other element, physical as well as biological , in their local environment. Eugene Odum , a founder of ecology, defined an ecosystem as: "Any unit that includes all of the organisms...in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i.e., exchange of materials between living and nonliving parts) within

5434-669: A tail", which may conjure an image of an animal displaying its tail in flight of fear ("turning tail"), or a dog 's habit of putting its tail between its legs when it is afraid. Like many other English words of French origin, this word was introduced in the English language by the French-speaking Normans , after the Norman conquest of England in 1066. The English surname Coward (as in Noël Coward ), however, has

5577-494: A term coined in analogy to keystone species . Pheromones may determine species compositions and affect rates of energy and material exchange in an ecological community . Thus pheromones generate structure in a food web and play critical roles in maintaining natural systems . Evidence of chemosensory alarm signals in humans has emerged slowly: Although alarm pheromones have not been physically isolated and their chemical structures have not been identified in humans so far, there

5720-428: A trait works in some cases, most traits are influenced by multiple genes in a quantitative or epistatic manner. Evolution can occur if there is genetic variation within a population. Variation comes from mutations in the genome, reshuffling of genes through sexual reproduction and migration between populations ( gene flow ). Despite the constant introduction of new variation through mutation and gene flow, most of

5863-658: A variety of translational animal models. These models are particularly important for research that would be too invasive for human studies. Rodents such as mice and rats are common animal models, but other species are used. Certain aspects of fear research still requires more research such as sex, gender, and age differences. Evolution Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within

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6006-454: Is directional selection , which is a shift in the average value of a trait over time—for example, organisms slowly getting taller. Secondly, disruptive selection is selection for extreme trait values and often results in two different values becoming most common, with selection against the average value. This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilising selection there

6149-442: Is more noticeable . Indeed, the evolution of microorganisms is particularly important to evolutionary research since their rapid reproduction allows the study of experimental evolution and the observation of evolution and adaptation in real time. Adaptation is the process that makes organisms better suited to their habitat. Also, the term adaptation may refer to a trait that is important for an organism's survival. For example,

6292-427: Is a byproduct of this process that may sometimes be adaptively beneficial. Gene flow is the exchange of genes between populations and between species. It can therefore be a source of variation that is new to a population or to a species. Gene flow can be caused by the movement of individuals between separate populations of organisms, as might be caused by the movement of mice between inland and coastal populations, or

6435-417: Is an inherited characteristic and an individual might inherit the "brown-eye trait" from one of their parents. Inherited traits are controlled by genes and the complete set of genes within an organism's genome (genetic material) is called its genotype . The complete set of observable traits that make up the structure and behaviour of an organism is called its phenotype . Some of these traits come from

6578-464: Is based on standing variation: when evolution depends on events of mutation that introduce new alleles, mutational and developmental biases in the introduction of variation (arrival biases) can impose biases on evolution without requiring neutral evolution or high mutation rates. Several studies report that the mutations implicated in adaptation reflect common mutation biases though others dispute this interpretation. Recombination allows alleles on

6721-407: Is called deep homology . During evolution, some structures may lose their original function and become vestigial structures. Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely related species. Examples include pseudogenes , the non-functional remains of eyes in blind cave-dwelling fish, wings in flightless birds,

6864-401: Is called " social buffering ". The term is in analogy to the 1985 "buffering" hypothesis in psychology, where social support has been proven to mitigate the negative health effects of alarm pheromone mediated distress. The role of a "social pheromone" is suggested by the recent discovery that olfactory signals are responsible in mediating the "social buffering" in male rats. "Social buffering"

7007-692: Is called genetic hitchhiking or genetic draft. Genetic draft caused by the fact that some neutral genes are genetically linked to others that are under selection can be partially captured by an appropriate effective population size. A special case of natural selection is sexual selection, which is selection for any trait that increases mating success by increasing the attractiveness of an organism to potential mates. Traits that evolved through sexual selection are particularly prominent among males of several animal species. Although sexually favoured, traits such as cumbersome antlers, mating calls, large body size and bright colours often attract predation, which compromises

7150-478: Is determined by the level of fear as well as the specific context, such as environmental characteristics (escape route present, distance to refuge), the presence of a discrete and localized threat, the distance between threat and subject, threat characteristics (speed, size, directness of approach), the characteristics of the subject under threat (size, physical condition, speed, degree of crypsis , protective morphological structures), social conditions (group size), and

7293-546: Is detrimental to society and thus the failure to face one's fear is often stigmatized or punished. According to the Online Etymology Dictionary , the word coward came into English from the Old French word coart (modern French couard ), which is a combination of the word for "tail" (Modern French queue , Latin cauda ) and an agent noun suffix . It would therefore have meant "one with

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7436-428: Is evidence for their presence. Androstadienone , for example, a steroidal, endogenous odorant, is a pheromone candidate found in human sweat, axillary hair and plasma. The closely related compound androstenone is involved in communicating dominance, aggression or competition; sex hormone influences on androstenone perception in humans showed a high testosterone level related to heightened androstenone sensitivity in men,

7579-432: Is how animals survive in the wild. Humans and animals both share these species-specific defense reactions, such as the flight-or-fight, which also include pseudo-aggression, fake or intimidating aggression and freeze response to threats, which is controlled by the sympathetic nervous system . These SSDRs are learned very quickly through social interactions between others of the same species, other species, and interaction with

7722-524: Is in safe mode, meaning that there are no longer any potential threats surrounding them, the amygdalae will send this information to the medial prefrontal cortex (mPFC) where it is stored for similar future situations, which is known as memory consolidation . Some of the hormones involved during the state of fight-or-flight include epinephrine , which regulates heart rate and metabolism as well as dilating blood vessels and air passages, norepinephrine increasing heart rate, blood flow to skeletal muscles and

7865-420: Is increased, which activates processes with the expected consequence of increasing consistency and decreasing arousal." In this context, it has been proposed that fear behavior is caused by an inconsistency between a preferred, or expected, situation and the actually perceived situation, and functions to remove the inconsistent stimulus from the perceptual field, for instance by fleeing or hiding, thereby resolving

8008-594: Is measured by an organism's ability to survive and reproduce, which determines the size of its genetic contribution to the next generation. However, fitness is not the same as the total number of offspring: instead fitness is indicated by the proportion of subsequent generations that carry an organism's genes. For example, if an organism could survive well and reproduce rapidly, but its offspring were all too small and weak to survive, this organism would make little genetic contribution to future generations and would thus have low fitness. If an allele increases fitness more than

8151-774: Is modulated by the process of cognition and learning. Thus, fear is judged as rational and appropriate, or irrational and inappropriate (or unconscious). An irrational fear is called a phobia . Fear is closely related to the emotion anxiety , which occurs as the result of often future threats that are perceived to be uncontrollable or unavoidable. The fear response serves survival by engendering appropriate behavioral responses, so it has been preserved throughout evolution . Sociological and organizational research also suggests that individuals' fears are not solely dependent on their nature but are also shaped by their social relations and culture, which guide their understanding of when and how much fear to feel. Many physiological changes in

8294-451: Is not something to be thwarted but allowed in a parent's presence if required. Developing a sense of equanimity to handle various situations is often advocated as an antidote to irrational fear and as an essential skill by a number of ancient philosophies. Fear of the unknown (FOTU) "may be a, or possibly the, fundamental fear" from early times when there were many threats to life. Although fear behavior varies from species to species, it

8437-489: Is often divided into two main categories; namely, avoidance/flight and immobility. To these, different researchers have added different categories, such as threat display and attack, protective responses (including startle and looming responses), defensive burying, and social responses (including alarm vocalizations and submission). Finally, immobility is often divided into freezing and tonic immobility . The decision as to which particular fear behavior to perform

8580-421: Is selection against extreme trait values on both ends, which causes a decrease in variance around the average value and less diversity. This would, for example, cause organisms to eventually have a similar height. Natural selection most generally makes nature the measure against which individuals and individual traits, are more or less likely to survive. "Nature" in this sense refers to an ecosystem , that is,

8723-429: Is that evolution has goals, long-term plans, or an innate tendency for "progress", as expressed in beliefs such as orthogenesis and evolutionism; realistically, however, evolution has no long-term goal and does not necessarily produce greater complexity. Although complex species have evolved, they occur as a side effect of the overall number of organisms increasing, and simple forms of life still remain more common in

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8866-447: Is the nearly neutral theory , according to which a mutation that would be effectively neutral in a small population is not necessarily neutral in a large population. Other theories propose that genetic drift is dwarfed by other stochastic forces in evolution, such as genetic hitchhiking, also known as genetic draft. Another concept is constructive neutral evolution (CNE), which explains that complex systems can emerge and spread into

9009-495: Is the more common means of reproduction among eukaryotes and multicellular organisms. The Red Queen hypothesis has been used to explain the significance of sexual reproduction as a means to enable continual evolution and adaptation in response to coevolution with other species in an ever-changing environment. Another hypothesis is that sexual reproduction is primarily an adaptation for promoting accurate recombinational repair of damage in germline DNA, and that increased diversity

9152-439: Is the process by which traits that enhance survival and reproduction become more common in successive generations of a population. It embodies three principles: More offspring are produced than can possibly survive, and these conditions produce competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors are more likely to pass on their traits to

9295-522: Is to defend themselves and at the same time to inform members of the same species of danger and leads to observable behavior change like freezing, defensive behavior, or dispersion depending on circumstances and species. For example, stressed rats release odorant cues that cause other rats to move away from the source of the signal. After the discovery of pheromones in 1959, alarm pheromones were first described in 1968 in ants and earthworms, and four years later also found in mammals, both mice and rats. Over

9438-619: Is typically severe, ranging from corporal punishment to the death sentence . The United States military codes of justice define cowardice in combat as a crime punishable by death . Generally, cowardice was punishable by execution during World War I , and those who were caught were often court-martialed and, in many cases, executed by firing squad . British soldiers executed for cowardice were often not commemorated on war memorials, and their families often did not receive benefits and had to endure social stigma . However, many decades later, those soldiers all received posthumous pardons in

9581-459: The amygdala ), it was proposed that a person learns to fear regardless of whether they themselves have experienced trauma, or if they have observed the fear in others. In a study completed by Andreas Olsson, Katherine I. Nearing and Elizabeth A. Phelps, the amygdala were affected both when subjects observed someone else being submitted to an aversive event, knowing that the same treatment awaited themselves, and when subjects were subsequently placed in

9724-417: The cenozoic time period (the still-ongoing geological era encompassing the last 66 million of history). Still others, such as fear of mice and insects, may be unique to humans and developed during the paleolithic and neolithic time periods (when mice and insects become important carriers of infectious diseases and harmful for crops and stored foods). Nonhuman animals and humans innovate specific fears as

9867-425: The neutral theory of molecular evolution most evolutionary changes are the result of the fixation of neutral mutations by genetic drift. In this model, most genetic changes in a population are thus the result of constant mutation pressure and genetic drift. This form of the neutral theory has been debated since it does not seem to fit some genetic variation seen in nature. A better-supported version of this model

10010-407: The paraventricular nucleus and the bed nucleus of the stria terminalis , and it increased stress hormone levels in plasma ( corticosterone ). The neurocircuit for how rats perceive alarm pheromones was shown to be related to the hypothalamus , brainstem , and amygdalae , all of which are evolutionary ancient structures deep inside or in the case of the brainstem underneath the brain away from

10153-615: The prefrontal cortex and the amygdala . The visual exploration of an emotional face does not follow a fixed pattern but modulated by the emotional content of the face. Scheller et al. found that participants paid more attention to the eyes when recognising fearful or neutral faces, while the mouth was fixated on when happy faces are presented, irrespective of task demands and spatial locations of face stimuli. These findings were replicated when fearful eyes are presented and when canonical face configurations are distorted for fearful, neutral and happy expressions. The brain structures that are

10296-454: The product of a gene , or prevent the gene from functioning, or have no effect. About half of the mutations in the coding regions of protein-coding genes are deleterious — the other half are neutral. A small percentage of the total mutations in this region confer a fitness benefit. Some of the mutations in other parts of the genome are deleterious but the vast majority are neutral. A few are beneficial. Mutations can involve large sections of

10439-402: The "recipient" rat (the rat perceiving the pheromone) depending which body region they were released from: Pheromone production from the face modified behavior in the recipient rat, e.g. caused sniffing or movement, whereas pheromone secreted from the rat's anal area induced autonomic nervous system stress responses, like an increase in core body temperature. Further experiments showed that when

10582-447: The "unknown". The irrational fear can branch out to many areas such as the hereafter, the next ten years or even tomorrow. Chronic irrational fear has deleterious effects since the elicitor stimulus is commonly absent or perceived from delusions. Such fear can create comorbidity with the anxiety disorder umbrella. Being scared may cause people to experience anticipatory fear of what may lie ahead rather than planning and evaluating for

10725-666: The UK Armed Forces Act 2006 and have been commemorated with the Shot at Dawn Memorial . Unlike British, Canadian, French, German, and Russian forces, the U.S. military tried soldiers for cowardice, but never followed through with execution while German commanders were less inclined to use execution as a form of punishment. Considerable controversy was generated by military historian S.L.A. Marshall , who claimed that 75% of U.S. combat troops in World War II never fired at

10868-519: The ability of organisms to generate genetic diversity and adapt by natural selection (increasing organisms' evolvability). Adaptation occurs through the gradual modification of existing structures. Consequently, structures with similar internal organisation may have different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are very similar to those in mice feet and primate hands, due to

11011-608: The acoustic startle reflex level. In analogy to the social buffering of rats and honeybees in response to chemosignals, induction of empathy by "smelling anxiety" of another person has been found in humans. A study from 2013 provided brain imaging evidence that human responses to fear chemosignals may be gender-specific . Researchers collected alarm-induced sweat and exercise-induced sweat from donors extracted it, pooled it and presented it to 16 unrelated people undergoing functional brain MRI . While stress-induced sweat from males produced

11154-402: The adaptation of horses' teeth to the grinding of grass. By using the term adaptation for the evolutionary process and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection. The following definitions are due to Theodosius Dobzhansky: Adaptation may cause either the gain of a new feature, or

11297-446: The alarm pheromone, and their preference/avoidance for odors from cylinders containing the pheromone, showed that the pheromone had very low volatility . In 1993 a connection between alarm chemosignals in mice and their immune response was found. Pheromone production in mice was found to be associated with or mediated by the pituitary gland in 1994. In 2004, it was demonstrated that rats' alarm pheromones had different effects on

11440-507: The alleles are subject to sampling error . This drift halts when an allele eventually becomes fixed, either by disappearing from the population or by replacing the other alleles entirely. Genetic drift may therefore eliminate some alleles from a population due to chance alone. Even in the absence of selective forces, genetic drift can cause two separate populations that begin with the same genetic structure to drift apart into two divergent populations with different sets of alleles. According to

11583-447: The amount of experience with the type of the threat. Often laboratory studies with rats are conducted to examine the acquisition and extinction of conditioned fear responses. In 2004, researchers conditioned rats ( Rattus norvegicus ) to fear a certain stimulus, through electric shock. The researchers were able to then cause an extinction of this conditioned fear, to a point that no medications or drugs were able to further aid in

11726-487: The amygdala are generated by activation of the neurons in the region. Experimental data supports the notion that synaptic plasticity of the neurons leading to the lateral amygdalae occurs with fear conditioning. In some cases, this forms permanent fear responses such as post-traumatic stress disorder (PTSD) or a phobia . MRI and fMRI scans have shown that the amygdalae in individuals diagnosed with such disorders including bipolar or panic disorder are larger and wired for

11869-441: The biosphere. For example, the overwhelming majority of species are microscopic prokaryotes , which form about half the world's biomass despite their small size and constitute the vast majority of Earth's biodiversity. Simple organisms have therefore been the dominant form of life on Earth throughout its history and continue to be the main form of life up to the present day, with complex life only appearing more diverse because it

12012-457: The body are associated with fear, summarized as the fight-or-flight response . An innate response for coping with danger, it works by accelerating the breathing rate ( hyperventilation ), heart rate, vasoconstriction of the peripheral blood vessels leading to blood pooling, dilating the pupils, increasing muscle tension including the muscles attached to each hair follicle to contract and causing "goosebumps", or more clinically, piloerection (making

12155-520: The brain, there are various regions of the brain involved in deciphering fear in humans and other nonhuman species. The amygdala communicates both directions between the prefrontal cortex , hypothalamus , the sensory cortex , the hippocampus , thalamus , septum , and the brainstem . The amygdala plays an important role in SSDR, such as the ventral amygdalofugal, which is essential for associative learning , and SSDRs are learned through interaction with

12298-414: The capacity to fear is part of human nature . Many studies have found that certain fears (e.g. animals, heights) are much more common than others (e.g. flowers, clouds). These fears are also easier to induce in the laboratory. This phenomenon is known as preparedness . Because early humans that were quick to fear dangerous situations were more likely to survive and reproduce; preparedness is theorized to be

12441-418: The center of most neurobiological events associated with fear are the two amygdalae , located behind the pituitary gland. Each amygdala is part of a circuitry of fear learning. They are essential for proper adaptation to stress and specific modulation of emotional learning memory. In the presence of a threatening stimulus, the amygdalae generate the secretion of hormones that influence fear and aggression. Once

12584-488: The change over time in this genetic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene. Variation disappears when a new allele reaches the point of fixation —when it either disappears from the population or replaces the ancestral allele entirely. Mutations are changes in the DNA sequence of a cell's genome and are the ultimate source of genetic variation in all organisms. When mutations occur, they may alter

12727-449: The cortex, and involved in the fight-or-flight response , as is the case in humans. Alarm pheromone-induced anxiety in rats has been used to evaluate the degree to which anxiolytics can alleviate anxiety in humans. For this, the change in the acoustic startle reflex of rats with alarm pheromone-induced anxiety (i.e. reduction of defensiveness) has been measured. Pretreatment of rats with one of five anxiolytics used in clinical medicine

12870-403: The descent of all these structures from a common mammalian ancestor. However, since all living organisms are related to some extent, even organs that appear to have little or no structural similarity, such as arthropod , squid and vertebrate eyes, or the limbs and wings of arthropods and vertebrates, can depend on a common set of homologous genes that control their assembly and function; this

13013-559: The development of the olfactory bulb and odor discrimination and it is highly expressed in developing rat brains, but absent in most regions of adult rat brains. Conditional deletion of the MAPK7gene in mouse neural stem cells impairs several pheromone-mediated behaviors, including aggression and mating in male mice. These behavior impairments were not caused by a reduction in the level of testosterone, by physical immobility, by heightened fear or anxiety or by depression. Using mouse urine as

13156-400: The development of thinking about the evolution of genome composition, including isochores. Different insertion vs. deletion biases in different taxa can lead to the evolution of different genome sizes. The hypothesis of Lynch regarding genome size relies on mutational biases toward increase or decrease in genome size. However, mutational hypotheses for the evolution of composition suffered

13299-490: The direct control of genes include the inheritance of cultural traits and symbiogenesis . From a neo-Darwinian perspective, evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms, for example, the allele for black colour in a population of moths becoming more common. Mechanisms that can lead to changes in allele frequencies include natural selection, genetic drift, and mutation bias. Evolution by natural selection

13442-479: The enemy for the purpose of killing, even while under direct threat. Author Dave Grossman attempted to explain these findings in his book On Killing: The Psychological Cost of Learning to Kill in War and Society . Marshall's findings were later challenged as mistaken or even fabricated, and were not replicated in a more rigorous study of Canadian troops in World War II. Fear In humans and other animals, fear

13585-454: The environment and others of the same species. An emotional response is created only after the signals have been relayed between the different regions of the brain, and activating the sympathetic nervous systems; which controls the flight, fight, freeze, fright, and faint response . Often a damaged amygdala can cause impairment in the recognition of fear (like the human case of patient S.M. ). This impairment can cause different species to lack

13728-416: The environment. These acquired sets of reactions or responses are not easily forgotten. The animal that survives is the animal that already knows what to fear and how to avoid this threat. An example in humans is the reaction to the sight of a snake, many jump backwards before cognitively realizing what they are jumping away from, and in some cases, it is a stick rather than a snake. As with many functions of

13871-489: The evolutionary history of life on Earth. Morphological and biochemical traits tend to be more similar among species that share a more recent common ancestor , which historically was used to reconstruct phylogenetic trees , although direct comparison of genetic sequences is a more common method today. Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from

14014-442: The extinction process. The rats showed signs of avoidance learning, not fear, but simply avoiding the area that brought pain to the test rats. The avoidance learning of rats is seen as a conditioned response , and therefore the behavior can be unconditioned, as supported by the earlier research. Species-specific defense reactions (SSDRs) or avoidance learning in nature is the specific tendency to avoid certain threats or stimuli, it

14157-559: The facial expression of fear and other emotions. Fear of victimization is a function of perceived risk and seriousness of potential harm. According to surveys, some of the most common fears are of demons and ghosts , the existence of evil powers, cockroaches , spiders , snakes , heights , water , enclosed spaces , tunnels , bridges , needles , social rejection , failure , examinations , and public speaking . Regionally some may more so fear terrorist attacks , death , war , criminal or gang violence , being alone ,

14300-414: The field or laboratory and on data generated by the methods of mathematical and theoretical biology . Their discoveries have influenced not just the development of biology but also other fields including agriculture, medicine, and computer science . Evolution in organisms occurs through changes in heritable characteristics—the inherited characteristics of an organism. In humans, for example, eye colour

14443-427: The fitness of an allele is not a fixed characteristic; if the environment changes, previously neutral or harmful traits may become beneficial and previously beneficial traits become harmful. However, even if the direction of selection does reverse in this way, traits that were lost in the past may not re-evolve in an identical form. However, a re-activation of dormant genes, as long as they have not been eliminated from

14586-453: The future, nuclear war , flying , clowns , intimacy , people , and driving . Fear of the unknown or irrational fear is caused by negative thinking ( worry ) which arises from anxiety accompanied by a subjective sense of apprehension or dread. Irrational fear shares a common neural pathway with other fears, a pathway that engages the nervous system to mobilize bodily resources in the face of danger or threat. Many people are scared of

14729-448: The gene stathmin show no avoidance learning, or a lack of fear, and will often walk directly up to cats and be eaten. Animals use these SSDRs to continue living, to help increase their chance of fitness , by surviving long enough to procreate. Humans and animals alike have created fear to know what should be avoided, and this fear can be learned through association with others in the community, or learned through personal experience with

14872-472: The genome and were only suppressed perhaps for hundreds of generations, can lead to the re-occurrence of traits thought to be lost like hindlegs in dolphins, teeth in chickens, wings in wingless stick insects, tails and additional nipples in humans etc. "Throwbacks" such as these are known as atavisms . Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorised into three different types. The first

15015-479: The genome of a species is very similar among all individuals of that species. However, discoveries in the field of evolutionary developmental biology have demonstrated that even relatively small differences in genotype can lead to dramatic differences in phenotype both within and between species. An individual organism's phenotype results from both its genotype and the influence of the environment it has lived in. The modern evolutionary synthesis defines evolution as

15158-640: The idea of developmental bias . Haldane and Fisher argued that, because mutation is a weak pressure easily overcome by selection, tendencies of mutation would be ineffectual except under conditions of neutral evolution or extraordinarily high mutation rates. This opposing-pressures argument was long used to dismiss the possibility of internal tendencies in evolution, until the molecular era prompted renewed interest in neutral evolution. Noboru Sueoka and Ernst Freese proposed that systematic biases in mutation might be responsible for systematic differences in genomic GC composition between species. The identification of

15301-434: The inconsistency. This approach puts fear in a broader perspective, also involving aggression and curiosity . When the inconsistency between perception and expectancy is small, learning as a result of curiosity reduces inconsistency by updating expectancy to match perception. If the inconsistency is larger, fear or aggressive behavior may be employed to alter the perception in order to make it match expectancy, depending on

15444-450: The interaction of its genotype with the environment while others are neutral. Some observable characteristics are not inherited. For example, suntanned skin comes from the interaction between a person's genotype and sunlight; thus, suntans are not passed on to people's children. The phenotype is the ability of the skin to tan when exposed to sunlight. However, some people tan more easily than others, due to differences in genotypic variation;

15587-512: The level of the individual organism are genes called transposons , which can replicate and spread throughout a genome. Selection at a level above the individual, such as group selection , may allow the evolution of cooperation. Genetic drift is the random fluctuation of allele frequencies within a population from one generation to the next. When selective forces are absent or relatively weak, allele frequencies are equally likely to drift upward or downward in each successive generation because

15730-452: The longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that cannot or will not interbreed. These outcomes of evolution are distinguished based on time scale as macroevolution versus microevolution. Macroevolution refers to evolution that occurs at or above the level of species, in particular speciation and extinction, whereas microevolution refers to smaller evolutionary changes within

15873-405: The loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to antibiotic selection, with genetic changes causing antibiotic resistance by both modifying the target of the drug, or increasing the activity of transporters that pump the drug out of the cell. Other striking examples are the bacteria Escherichia coli evolving the ability to use citric acid as

16016-477: The meaning, i.e. on the emotional level, rather than the strength of chemosensory cues from each gender, i.e. the perceptual level. An approach-avoidance task was set up where volunteers seeing either an angry or a happy cartoon face on a computer screen pushed away or pulled toward them a joystick as fast as possible. Volunteers smelling androstadienone, masked with clove oil scent responded faster, especially to angry faces than those smelling clove oil only, which

16159-458: The mechanics in developmental plasticity and canalisation . Heritability may also occur at even larger scales. For example, ecological inheritance through the process of niche construction is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effects that modify and feed back into the selection regime of subsequent generations. Other examples of heritability in evolution that are not under

16302-408: The movement of pollen between heavy-metal-tolerant and heavy-metal-sensitive populations of grasses. Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer . Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria. In medicine, this contributes to

16445-457: The natural world. He theorized the species-specific defense reaction (SSDR). There are three forms of SSDRs: flight, fight (pseudo-aggression), or freeze. Even domesticated animals have SSDRs, and in those moments it is seen that animals revert to atavistic standards and become "wild" again. Dr. Bolles states that responses are often dependent on the reinforcement of a safety signal, and not the aversive conditioned stimuli. This safety signal can be

16588-427: The next generation than those with traits that do not confer an advantage. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are seemingly fitted for the functional roles they perform. Consequences of selection include nonrandom mating and genetic hitchhiking . The central concept of natural selection is the evolutionary fitness of an organism. Fitness

16731-530: The next two decades, identification and characterization of these pheromones proceeded in all manner of insects and sea animals, including fish, but it was not until 1990 that more insight into mammalian alarm pheromones was gleaned. In 1985, a link between odors released by stressed rats and pain perception was discovered: unstressed rats exposed to these odors developed opioid-mediated analgesia. In 1997, researchers found that bees became less responsive to pain after they had been stimulated with isoamyl acetate ,

16874-545: The occipito cerebellar regions including the fusiform gyrus and the inferior parietal / superior temporal gyri. Fearful eyes, brows and mouth seem to separately reproduce these brain responses. Scientists from Zurich studies show that the hormone oxytocin related to stress and sex reduces activity in your brain fear center. In threatening situations, insects, aquatic organisms, birds, reptiles, and mammals emit odorant substances, initially called alarm substances, which are chemical signals now called alarm pheromones . This

17017-499: The offspring of sexual organisms contain random mixtures of their parents' chromosomes that are produced through independent assortment. In a related process called homologous recombination , sexual organisms exchange DNA between two matching chromosomes. Recombination and reassortment do not alter allele frequencies, but instead change which alleles are associated with each other, producing offspring with new combinations of alleles. Sex usually increases genetic variation and may increase

17160-456: The other alleles of that gene, then with each generation this allele has a higher probability of becoming common within the population. These traits are said to be "selected for ." Examples of traits that can increase fitness are enhanced survival and increased fecundity . Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele likely becoming rarer—they are "selected against ." Importantly,

17303-578: The overall process, like a step in an assembly line. One example of mutation is wild boar piglets. They are camouflage coloured and show a characteristic pattern of dark and light longitudinal stripes. However, mutations in the melanocortin 1 receptor ( MC1R ) disrupt the pattern. The majority of pig breeds carry MC1R mutations disrupting wild-type colour and different mutations causing dominant black colouring. In asexual organisms, genes are inherited together, or linked , as they cannot mix with genes of other organisms during reproduction. In contrast,

17446-527: The presence of hip bones in whales and snakes, and sexual traits in organisms that reproduce via asexual reproduction. Examples of vestigial structures in humans include wisdom teeth , the coccyx , the vermiform appendix , and other behavioural vestiges such as goose bumps and primitive reflexes . However, many traits that appear to be simple adaptations are in fact exaptations : structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in

17589-469: The process. One example is the African lizard Holaspis guentheri , which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree—an exaptation. Within cells, molecular machines such as the bacterial flagella and protein sorting machinery evolved by

17732-494: The rate of evolution. The two-fold cost of sex was first described by John Maynard Smith . The first cost is that in sexually dimorphic species only one of the two sexes can bear young. This cost does not apply to hermaphroditic species, like most plants and many invertebrates . The second cost is that any individual who reproduces sexually can only pass on 50% of its genes to any individual offspring, with even less passed on as each new generation passes. Yet sexual reproduction

17875-408: The relative importance of selection and neutral processes, including drift. The comparative importance of adaptive and non-adaptive forces in driving evolutionary change is an area of current research . Mutation bias is usually conceived as a difference in expected rates for two different kinds of mutation, e.g., transition-transversion bias, GC-AT bias, deletion-insertion bias. This is related to

18018-442: The release of glucose from energy stores, and cortisol which increases blood sugar, increases circulating neutrophilic leukocytes, calcium amongst other things. After a situation which incites fear occurs, the amygdalae and hippocampus record the event through synaptic plasticity . The stimulation to the hippocampus will cause the individual to remember many details surrounding the situation. Plasticity and memory formation in

18161-406: The same origin and meaning as the word "cowherd". In German, the word translates into "Feigling" and "Weichei", the latter of which translates back to "soft egg" in literal. Acts of cowardice have long been punishable by military law, which defines a wide range of cowardly offenses, including desertion in face of the enemy and surrendering to the enemy against orders. The punishment for such acts

18304-417: The same strand of DNA to become separated. However, the rate of recombination is low (approximately two events per chromosome per generation). As a result, genes close together on a chromosome may not always be shuffled away from each other and genes that are close together tend to be inherited together, a phenomenon known as linkage . This tendency is measured by finding how often two alleles occur together on

18447-572: The same. For example, "continuation of scholarly education" is perceived by many educators as a risk that may cause them fear and stress, and they would rather teach things they've been taught than go and do research. The ambiguity of situations that tend to be uncertain and unpredictable can cause anxiety in addition to other psychological and physical problems in some populations; especially those who engage it constantly, for example, in war-ridden places or in places of conflict, terrorism, abuse, etc. Poor parenting that instills fear can also debilitate

18590-645: The scattered running of rats are considered species-specific defense reactions or behaviors. Bolles believed that SSDRs are conditioned through Pavlovian conditioning, and not operant conditioning; SSDRs arise from the association between the environmental stimuli and adverse events. Michael S. Fanselow conducted an experiment, to test some specific defense reactions, he observed that rats in two different shock situations responded differently, based on instinct or defensive topography, rather than contextual information. Species-specific defense responses are created out of fear, and are essential for survival. Rats that lack

18733-417: The sensation of fear, and often can become overly confident, confronting larger peers, or walking up to predatory creatures. Robert C. Bolles (1970), a researcher at University of Washington, wanted to understand species-specific defense reactions and avoidance learning among animals, but found that the theories of avoidance learning and the tools that were used to measure this tendency were out of touch with

18876-552: The sequence of nucleotides in the DNA. These phenomena are classed as epigenetic inheritance systems. DNA methylation marking chromatin , self-sustaining metabolic loops, gene silencing by RNA interference and the three-dimensional conformation of proteins (such as prions ) are areas where epigenetic inheritance systems have been discovered at the organismic level. Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlay some of

19019-470: The series of physiological changes, the consciousness realizes an emotion of fear. There are observable physical reactions in individuals who experience fear. An individual might experience a feeling of dizziness, lightheaded, like they are being choked, sweating, shortness of breath, vomiting or nausea, numbness or shaking and any other like symptoms. These bodily reactions informs the individual that they are afraid and should proceed to remove or get away from

19162-435: The size of the inconsistency as well as the specific context. Aggressive behavior is assumed to alter perception by forcefully manipulating it into matching the expected situation, while in some cases thwarted escape may also trigger aggressive behavior in an attempt to remove the thwarting stimulus. In order to improve our understanding of the neural and behavioral mechanisms of adaptive and maladaptive fear, investigators use

19305-406: The spread of antibiotic resistance , as when one bacteria acquires resistance genes it can rapidly transfer them to other species. Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean weevil Callosobruchus chinensis has occurred. An example of larger-scale transfers are the eukaryotic bdelloid rotifers , which have received

19448-586: The stimulus that is causing that fear. An influential categorization of stimuli causing fear was proposed by psychologist Jeffrey Alan Gray ; namely, intensity , novelty , special evolutionary dangers, stimuli arising during social interaction, and conditioned stimuli. Another categorization was proposed by Archer, who, besides conditioned fear stimuli, categorized fear-evoking (as well as aggression -evoking) stimuli into three groups; namely, pain , novelty, and frustration , although he also described " looming ", which refers to an object rapidly moving towards

19591-640: The survival of individual males. This survival disadvantage is balanced by higher reproductive success in males that show these hard-to-fake , sexually selected traits. Evolution influences every aspect of the form and behaviour of organisms. Most prominent are the specific behavioural and physical adaptations that are the outcome of natural selection. These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by cooperating with each other, usually by aiding their relatives or engaging in mutually beneficial symbiosis . In

19734-642: The system...." Each population within an ecosystem occupies a distinct niche , or position, with distinct relationships to other parts of the system. These relationships involve the life history of the organism, its position in the food chain and its geographic range. This broad understanding of nature enables scientists to delineate specific forces which, together, comprise natural selection. Natural selection can act at different levels of organisation , such as genes, cells, individual organisms, groups of organisms and species. Selection can act at multiple levels simultaneously. An example of selection occurring below

19877-831: The visual sensors of a subject, and can be categorized as "intensity". Russell described a more functional categorization of fear-evoking stimuli, in which for instance novelty is a variable affecting more than one category: 1) Predator stimuli (including movement, suddenness, proximity, but also learned and innate predator stimuli); 2) Physical environmental dangers (including intensity and heights); 3) Stimuli associated with increased risk of predation and other dangers (including novelty, openness, illumination, and being alone); 4) Stimuli stemming from conspecifics (including novelty, movement, and spacing behavior); 5) Species-predictable fear stimuli and experience (special evolutionary dangers); and 6) Fear stimuli that are not species predictable (conditioned fear stimuli). Although many fears are learned,

20020-532: Was able to reduce their anxiety: namely midazolam , phenelzine (a nonselective monoamine oxidase (MAO) inhibitor), propranolol , a nonselective beta blocker , clonidine , an alpha 2 adrenergic agonist or CP-154,526 , a corticotropin-releasing hormone antagonist . Faulty development of odor discrimination impairs the perception of pheromones and pheromone-related behavior, like aggressive behavior and mating in male rats: The enzyme Mitogen-activated protein kinase 7 (MAPK7) has been implicated in regulating

20163-508: Was also observed to mitigate the conditioned fear responses of honeybees. A bee colony exposed to an environment of high threat of predation did not show increased aggression and aggressive-like gene expression patterns in individual bees, but decreased aggression. That the bees did not simply habituate to threats is suggested by the fact that the disturbed colonies also decreased their foraging. Biologists have proposed in 2012 that fear pheromones evolved as molecules of "keystone significance",

20306-663: Was first set out in detail in Darwin's book On the Origin of Species . Evolution by natural selection is established by observable facts about living organisms: (1) more offspring are often produced than can possibly survive; (2) traits vary among individuals with respect to their morphology , physiology , and behaviour; (3) different traits confer different rates of survival and reproduction (differential fitness ); and (4) traits can be passed from generation to generation ( heritability of fitness). In successive generations, members of

20449-434: Was interpreted as androstadienone-related activation of the fear system. A potential mechanism of action is, that androstadienone alters the "emotional face processing". Androstadienone is known to influence the activity of the fusiform gyrus which is relevant for face recognition . Cognitive-consistency theories assume that "when two or more simultaneously active cognitive structures are logically inconsistent, arousal

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