Sexual coercion

Sexual coercion in animals is the use of violence, threats, harassment, and other tactics to help them forcefully copulate.[1] Such behavior has been compared to sexual assault, including rape, among humans.[2]

In nature, males and females usually differ in reproductive fitness optima.[3] Males generally prefer to maximize their number of offspring, and therefore their number of mates; females, on the other hand, tend to care more for their offspring and have fewer mates.[4] Because of this, there are generally more males available to mate at a given time, making females a limited resource.[4][5] This leads males to evolve aggressive mating behaviors which can help them acquire mates.[5]

Sexual coercion has been observed in many species, including mammals, birds, insects, and fish.[6] While sexual coercion does help increase male fitness, it is very often costly to females.[5] However, in spite of these costs, a possible benefit to the females is a chance to test the stamina of the males, so that only those with "good genes" will father their offspring.[7] Sexual coercion has been observed to have consequences, such as intersexual coevolution, speciation, and sexual dimorphism.[4][8]

Male adaptations

Harassment/aggression

Harassment is a technique used by males of many species to force females to submit to mating.[9] It has been observed in numerous species, including mammals, birds, insects and fish.[6] Aggression and harassment have been documented in the males of guppies (Poecilia reticulata),[4] bottlenose dolphins (Tursiops aduncus), botos (Inia geoffrensis), dusky dolphins (Lagenorhynchus obscurus), Hector's dolphins (Cephalorhynchus hectori), grizzly bears, polar bears, and ungulates.[10] It is also seen in Chinook salmon (Oncorhynchus tshawytscha),[6] red-spotted newts (Notophthalmus viridescens), and seed-eating true bugs (Neacoryphus spp.).[11] Furthermore, it is prevalent in spider monkeys,[1] wild Barbary macaques (Macaca sylvanus) and many other primates.[12]

In basically all major primate taxa, aggression is used by the dominant males when herding females and keeping them away from other males.[1] In hamadryas baboons, the males often bite the females’ necks and threaten them.[13] Wild chimpanzees can charge at females, shake branches, hit, slap, kick, pound, drag, and bite them. Orangutans are among the most forceful of mammals. Bornean orangutans (Pongo pygmaeus) exhibited aggression in almost 90 percent of their copulations, including when the females were not resisting.[14] A possible explanation for aggressive behaviors in primates is that it is a way for males to train females to be afraid of them and be more likely to surrender to future sexual advances.[1]

Intimidation

Males may also use more indirect techniques to mate with females, such as intimidation. While most female water striders (Gerridae) have their genitalia exposed, females of the water strider species Gerris gracilicornis have evolved a shield over their genitals. As a result, males cannot physically coerce females because mating is difficult unless the female exposes her genitalia. Therefore, males intimidate females into mating by attracting predators; they tap on the water’s surface and create ripples that catch the attention of predatory fish. From there, it is in the best interest of the female to mate, and as quickly as possible, to avoid being eaten by predators. Typical mating positions of water striders have the females on the bottom, closer to predators, so the risk of predation is much higher for them. Females succumb to copulation to get males to cease signaling to predators.[15]

Another indirect form of sexual coercion occurs in red-sided garter snakes, Thamnophis sirtalis parietalis. When males "court" females, they line their bodies up to the females' and produce caudocephalic waves, which are a series of muscle contractions that travel through their bodies from tail to head. The exact reason for this behavior is unknown, but some studies show that it relates to stress. Females have nonrespiratory air sacs containing anoxic air, and the waving pushes this air into her lungs. The resulting stress causes her cloaca to open, and aids the male in inserting his hemipenis. The stronger and more frequent the caudocephalic waves and the closer the male’s cloaca to the female’s, the more likely the male is to mate successfully.[16]

Grasping and grappling

Males of certain species have evolved mating behaviors in which they forcefully attempt to mate with and inseminate females, often employing grasping techniques. These male grasping devices exist to increase the duration of copulation and restrict females from mating with other males. They are in some ways a form of mate guarding. While some males have evolved different types of modifications to aid in grasping, others just grab females and attempt to force copulation.

One type of grasping modification is spiny male genitalia. In seed beetles (Coleoptera: Bruchidae), males possess sclerotized spines on their genitalia. These spines are used during copulation to help overcome female resistance and penetrate into their copulatory duct. In addition to aiding penetration, these spines promote the passage of seminal fluids, and act as an anchor to keep the female from fleeing. Furthermore, spiny genitals can injure the females and make them less likely to remate.[8] Sepsidae fly males have modifications on their forelegs to help them grasp onto female wing bases. These modifications include cuticular outgrowths, indentations, and bristles, and males use them to secure themselves onto females after jumping on them. Once the males grab on, a struggle ensues akin to a rodeo, where males try to hold on while females violently shake them off.[7]

Another type of modification is found in male diving beetles (of the family Dytiscidae), who are equipped with suction cup structures on their front legs. They use these to grab passing females and attach to their dorsal surfaces. To get the females to submit, males shake the females violently and keep them submerged underwater (diving beetles cannot go long without atmospheric oxygen). Unable to get air, female diving beetles submit to the male’s advances in order to avoid drowning (and they lose the energy to resist). Once the males attach, copulation can occur.[17]

Male waterfowl have developed another modification; while most male birds have no external genitalia, male waterfowl (Aves: Anatidae) have a phallus (length 1.5–4.0 centimetres [0.59–1.57 in]). Most birds mate with the males balancing on top of the females and touching cloacas in a “cloacal kiss”; this makes forceful insemination very difficult. The phallus that male waterfowl have evolved everts out of their bodies (in a clockwise coil) and aids in inseminating females without their cooperation.[18]

Another such technique is having a "lock-like" mechanism, found in Drosophila montana, dogs, wolves, and pigs. Towards the end of copulation, females struggle to try to dislodge the males, whose genital organs take much longer to deflate than females do; the locking (most commonly known in canids as a "tie") allows the males to copulate for as long as they need to until they are finished. In dogs, the male has a knot in his penis that gets engorged with blood and ties the female, locking them together during copulation, until the act is complete. Male dogs have evolved this mechanism during mating in order to prevent other males from penetration whilst they are and the use of the tie enables them to be more likely to inseminate the female and produce a healthy litter of pups. Breaking this "tie" can be physically harmful to both females and males.[19]

Males of many species simply grab the females and force a mating. Coercive mating is very common in water striders (Gerridae) because in most of the species, the female genitalia are often exposed and easily accessible to males.[3] Without any courtship behavior, males initiate by forcefully trying to mount the females. Carrying the males on their backs is energetically costly to females, so they try to resist and throw off the males. The males fight back even harder and use their forelegs to tightly grasp the female’s thorax and keep them from escaping.[20] The males then forcefully insert their genitalia into the female vulvar opening.[3] In the newt species Notophthalmus viridescens, males carry out a courtship behavior called amplexus. It consists of males capturing females that do not want to mate with them and using their hind limbs to grasp the females by their pectoral regions.[5]

Male guppies (Poecilia reticulata) have been observed to forcefully copulate with females by trying to insert their gonopodium (male sex organ) into female’s genital pores, whether or not they are accepting.[6] Sometimes, male guppies also try to forcefully mate with Skiffia bilineata (goodeid) females, which resemble guppy females and tend to share the same habitat, even when guppy females are available. A possible explanation for this is the deeper genital cavity of S. bilineata, which stimulates the males more than when mating with guppy females.[11]

Males of some species are able to immobilize females and force copulation. In pigs and boars, males grab females and maneuver the pelvis to lift the vaginal opening and facilitate copulation. The stimulation following intromission causes the female to be immobilized. The male can then freely continue copulation without worrying about the female escaping.[21] Immobilization of the female also occurs in muscovy ducks.

Grasping and/or grappling mating situations have also been documented in Calopteryx haemorrhoidalis haemorrhoidalis (Odonata),[22] fallow deer (Dama dama),[6] wild orangutans (Smuts 1993), wild chimpanzees,[1] water voles (semi-aquatic rats) Arvicola amphibius,[21] feral fowl,[23] mallard (Anas platyrhynchos),[24] hamadryas baboons[25] and many other primates,[1] coho salmon (Oncorhynchus kisutch),[6] and others.

Infanticide

In some mammal species, mostly nonhuman primates, it is common for males to commit infanticide to mate with females. This happens often in species that live in groups, such as Old and New World monkeys, apes, prosimians, and hamadryas baboons.[25] There is usually a single breeding male in a group, and when an outside male aggressively takes over, he kills off all of the young offspring. The males kill infants that are not their own to assert their strength and position, and mate with the females.[1] Sometimes, multiple males will invade a troop and gang up on females, killing their offspring and subsequently mating with them. This occurs in spider monkeys, red-backed squirrel monkeys, chimpanzees, and red howlers.[1]

Secretions

In the newt species Notophthalmus viridescens, the males rub off hormonal secretions onto the skin of the females they are courting. These hormones have been shown to make the female more receptive to mating with the male. When the male deposits the secretions, he detaches from the female and releases a spermatophore (containing spermatozoa). It is then the female’s decision to either accept it and pick it up or reject it by running away; these hormones make her more likely to accept it.[5]

Coercive faithfulness

Post-copulatory guarding

Another form of coercion is male mate guarding, used to keep females from mating with other males, and often involves aggression.[9] Guarding allows the males to assure their paternity. A classic example occurs in diving beetles, family Dytiscidae. After copulation, males continue to guard females for up to six hours. They hold them underwater, occasionally tilting them up for air.[17] Guarding also occurs in water striders where, once males complete their sperm transfer, they often remain on top of the females. This guarding duration varies, lasting from several minutes to several weeks. The purpose of such long guarding periods is for the males to see the females lay their eggs and be assured that the offspring are theirs.[20] This behavior also occurs in hamadryas baboons (Papio hamadryas), where the leader males practice intensive mate guarding.[25] In Drosophila Montana, studies have shown that following mate guarding, the chances of a female mating with or being inseminated by another male were greatly diminished. This shows that the mate guarding tactic can be very effective.[19]

Secretions/ejaculations

Males of some species use bodily fluids, such as seminal fluid from their ejaculate, to aid in the coercion of females. Seminal fluid in males of Drosophila melanogaster may contain chemicals that increase the amount of time it takes for females to remate, decrease the length of successive matings, or keep her from remating at all. The less a female mates with other males after copulation with a male, the more likely it is for him to ensure his paternity. These chemicals may also serve to increase the female’s reproductive success, but at the cost of decreased longevity and immune response.[19]

In many species, seminal fluid can be used as a sort of mating plug. Males of these species transfer their sperm at the beginning of copulation and use the rest of copulation to transfer substances that help build up the mating plugs. These plugs are effective in ensuring that the female does not mate with any other males and that the male’s paternity is secured.[19]

Costs to females

Direct

A major direct cost of sexual coercion is physical injury.[6] Male seed beetles (Coleoptera: Bruchidae) have sclerotized spine on their genitalia, which penetrate the female and leave melanized scars. Females can be physically injured from just one mating, and the more a female mates, the more scarring forms in the copulatory duct.[8] In guppies, the male’s gonopodium can cause damage when forcefully inserted, causing cloacal damage to the females.[11] In fowl, females can be physically injured during forceful copulations. Also, semen transferred from the males can contain pathogens and fecal matter, which can lead to disease and decrease female fitness.[23] In elephant seals, physical injury happens very often. In fact, mating leads to 1 in every 1,000 female elephant seals getting killed.[21] Other species in which the females (and/or their offspring) are injured or even killed include lions, rodents, farm cats, crabeater seals, elephant seals, sea lions,[1] wild Trinidadian guppies (Poecilia reticulata),[10] red-sided garter snakes (Thamnophis sirtalis parietalis),[16] and newts (N. viridescens).[5]

Another cost is the excess energy and time expenditure that comes with mating. For example, female water striders, Gerridae,[20] and marine snails of the genus Littorina 24 have to carry the males on their backs while they mate. First of all, this is a great loss of energy.[20] Second, both the male and the female are at a much greater risk of predation in this position.[6] Furthermore, the time spent mating interferes with the time that could have been spent foraging[6] and feeding.[26]

In addition, sexual coercion can lower body condition and immunity in ways other than physical damage. Harassment can lead to stress, which can result in weight loss, decreased immune function and energy stores, and less feeding, which has been seen in red-spotted newts.[5] Furthermore, when females are constantly moving around to avoid violent males, they are not able to form female social ties (for example, Grévy's zebra/Equus grevyi).[26] This also happens in species where herding males sometimes do not permit females to join their family in different groups, like in hamadryas baboons.[1]

Indirect

Indirect costs are those that affect females in the future. One such cost happens because sexual coercion does not allow females to choose the males they want to mate with, which are usually males that are higher quality, compatible, and/or have good genes that will increase their offspring’s survival and fitness. Coercion decreases this choice and can lead to their offspring having lower genetic quality. Studies of the rose bitterling (Rhodeus ocellatus), have shown that offspring of females with mate choice had higher survival rates than offspring of females that did not.[6] Another ultimate cost comes from when males commit infanticide to obtain mating access. This loss of offspring leads to a decrease in fitness of females.[1]

Female counter-adaptations

Anatomical protection

As a response to sexual coercion and the costs that females face, one of their counter-adaptations is the evolution of anatomical protection.[3] Females of some species, such as the water striders, developed morphological shields to protect their genitalia from males that want to forcefully copulate.[15] Some Gerridae females have also evolved abdominal spines and altered the shapes of their abdomens to make them less accessible to males.[3]

Waterfowl males of the family Aves: Anatidae have evolved a phallus to aid in coercion. This phallus everts out of the male body (when it’s time to mate) in a counter-clockwise coil. As a response, females have developed vaginal structures called dead end sacs and clockwise coils to protect themselves from forceful intromission.[18] Waterfowl females have evolved these “convoluted vaginal morphologies” to make it harder for males to insert themselves without the female’s consent.[27]

Male avoidance/habitat change

Another female tactic to counter coercion is to try to avoid males that may cause them harm. To do this, females often change their habitats to get away from aggressive males, as is seen in wild Trinidadian guppies (Poecilia reticulata).[10] Female bottlenose dolphins behave in similar ways by moving into shallow waters where there are not too many males.[10] Other species that practice mate avoidance are Calopteryx haemorrhoidalis, a species of damselfly, who often try to hide from large groups of males to avoid harassment.[22]

Females of the marine intertidal periwinkle species (genus Littorina) have another way to avoid males. Males usually recognize female snails by cues in their mucous trails. However, females try to mask their gender by altering these cues.[28] In damselflies, females also try to mask their gender by mimicking male colors, which make them less attractive to males.[28]

Protection/alliances

An effective female strategy is the employment of protection and alliances. Some females, such as wild Trinidadian guppies (Poecilia reticulate) associate themselves with protective males who come to their rescue.[29] This also occurs in hamadryas, savanna, and olive baboons, where males and females form friendships where the female gets male protection.[25] In northern elephant seals, the females give loud cries when mounted by undesirable or subordinate males, which attract dominant males to help. A similar phenomenon occurs in elephants, bighorn sheep, and fallow deer, where the females stay close to dominant males for protection.[1]

Females can also form alliances with other females for protection against aggressive males.[1] In African vervet monkeys, related females often form groups and “gang up” on males. Females of high rank create networks of female alliances; together, they fight away persistent suitors.[1]

Resistance/fighting back

Resisting males and fighting back are important tactics some species use to counter male coercion. Many females try to vigorously shake off males to dislodge them and flee; this is seen in females sepsid flies[7] and diving beetles.[17] Sepsids also try to bend their abdomen in such a way that males cannot copulate forcefully.[7] Females are especially likely to fight back when they are protecting their offspring. This is seen in mountain gorillas, red howlers, and grey langur females, where males are often infanticidal.[1]

Female resistance has rarely been found to be effective. Male mammals and birds are usually larger than females, and the sheer size and strength difference makes this very difficult.[1] However, it has been observed in some species, such as squirrel monkeys, patas monkeys, vervets, and captive chimpanzees, that females can “gang up” on males when they are being aggressive. They will even try to protect a female in distress. Females have even been observed to kill immigrant males in wild red colobus monkeys.[1]

Acceptance/submission

Sometimes, females choose not to struggle and simply acquiesce to forceful matings. This can happen when they decide that the cost of resisting would be greater than the cost of mating.[22] They use submission to avoid further harassment or aggression, which could end in death or injury.[26] This is often seen in primate species, such as chimpanzees and hamadryas baboons.[1]

Female benefits

Some possible benefits of sexual coercion for females have been hypothesized.

Proximate

A possible proximate benefit for females is that sometimes after a male mates with a female, he becomes her mate. Then, he would defend and protect her.[22] This is seen in many primate species.[1]

Ultimate

A possible benefit of sexual coercion that would come out in the long run is the “good genes” hypothesis.[17] If males can overcome a female’s resistance, then they must possess good genes that would increase the survival, mating success, and ultimately the fitness of her offspring. The hypothesis is that females can use the sexual coercion process to assess the quality of a male.[3]

Consequences

Coevolutionary arms race

Sexual coercion often leads to an intersexual coevolutionary arms race. This consists of females evolving adaptations to male advances and males evolving counter-adaptations as a response.[4] Males persist in violent behavior, which favors the evolution of female resistance to defend themselves.[3][8] In organisms where males have genitalia harmful to females, such as in certain insects, females tend to evolve thicker, less sensitive copulatory tracts.[8] Also, they may evolve shield over their genital openings to prevent intromission.[15] Females of some species of water striders have evolved protection from forceful insemination, such as abdominal spines and downward-bent abdomens to make it harder for males to mate. In response, however, males have counter evolved, also changing the shape of their abdomens to those that would facilitate forceful mating.[3]

The male waterfowl (Aves: Anatidae) evolution of a phallus to forcefully copulate with females has led to counteradaptations in females in the form of vaginal structures called dead end sacs and clockwise coils. These structures make it harder for males to achieve intromission. The clockwise coils are significant because the male phallus everts out of their body in a counter-clockwise spiral; therefore, a clockwise vaginal structure would impede forceful copulation. Studies have shown that the longer a male’s phallus is, the more elaborate the vaginal structures were.[18]

Speciation

Speciation has been observed to be a possible consequence of sexual coercion. In diving beetle species family Dytiscidae, an intersexual arms race occurs between males and females. Males have evolved suction cup structures on their forelegs to help grasp females; females have counter-evolved setose dorsal furrows to impede forceful copulation. This continuous evolution (in both the forward and reverse directions) has led to the recent speciation of A. japonicus and A. kishii, where females of A. kishii have lost their dorsal furrows while those of A. japonicus have not.[17]

Sexual dimorphism

Sexual coercion can lead to sexual dimorphisms, in which males and females have significant morphological differences. For example, in some species, larger males are more successful in forcefully mating/insemination, leading to a higher fitness.[4] In red-sided garter snakes, Thamnophis sirtalis parietalis, it has been shown that heavier-bodied males were better courters and their size gave them an advantage over smaller bodied snakes.[16] This helps lead to an evolution of sexual dimorphism, with males larger than females.[4] In other species, males that are smaller than females have higher fitness. Basically, many sex-specific morphological adaptations (for example, in Dytiscidae diving beetles, females have setose dorsal furrows that males do not and males have suction cups on their forelegs that females do not[17]) are sexual dimorphisms caused by sexual coercion.

References

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  2. ^ Stamos, David N., Evolution and the Big Questions: Sex, Race, Religion, and Other Matters, John Wiley & Sons, 2011; Alcock, John, The Triumph of Sociobiology, Oxford University Press, 2003, p.207-9.
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  4. ^ a b c d e f g Gage, M. J. G., Parker, G. a, Nylin, S. & Wiklund, C. Sexual selection and speciation in mammals, butterflies and spiders. Proceedings: Biological Sciences 269, 2309–16 (2002).
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  6. ^ a b c d e f g h i j Garner, S. R., Bortoluzzi, R. N., Heath, D. D. & Neff, B. D. Sexual conflict inhibits female mate choice for major histocompatibility complex dissimilarity in Chinook salmon. Proceedings: Biological Sciences 277, 885–94 (2010).
  7. ^ a b c d Puniamoorthy, N., Su, K. F.-Y. & Meier, R. Bending for love: losses and gains of sexual dimorphisms are strictly correlated with changes in the mounting position of sepsid flies (Sepsidae: Diptera). BMC Evolutionary Biology 8, 155 (2008).
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  9. ^ a b Muller, M. N., Kahlenberg, S. M., Emery Thompson, M. & Wrangham, R. W. Male coercion and the costs of promiscuous mating for female chimpanzees. Proceedings: Biological Sciences 274, 1009–14 (2007).
  10. ^ a b c d Fury, C. A., Ruckstuhl, K. E. & Harrison, P. L. Spatial and social sexual segregation patterns in indo-pacific bottlenose dolphins (Tursiops aduncus). PLoS ONE 8, e52987 (2013).
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  12. ^ McFarland, R. & Majolo, B. Grooming coercion and the post-conflict trading of social services in wild Barbary macaque s. PLoS ONE 6, e26893 (2011).
  13. ^ Nitsch, F., Stueckle, S., Stahl, D. & Zinner, D. Copulation patterns in captive hamadryas baboons: a quantitative analysis. Primates; journal of primatology 52, 373–83 (2011).
  14. ^ Knott, C. D., Emery Thompson, M., Stumpf, R. M. & McIntyre, M. H. Female reproductive strategies in orangutans, evidence for female choice and counterstrategies to infanticide in a species with frequent sexual coercion. Proceedings: Biological Sciences 277, 105–13 (2010).
  15. ^ a b c Han, C. S. & Jablonski, P. G. Male water striders attract predators to intimidate females into copulation. Nature Communications 1, 52 (2010).
  16. ^ a b c Shine, R., Langkilde, T. & Mason, R. T. Courtship tactics in garter snakes: how do a male’s morphology and behaviour influence his mating success? Animal Behaviour 67, 477–483 (2004)
  17. ^ a b c d e f Bergsten, J. & Miller, K. B. Phylogeny of diving beetles reveals a coevolutionary arms race between the sexes. PLoS ONE 2, e522 (2007).
  18. ^ a b c Brennan, P. L. R. et al. Coevolution of male and female genital morphology in waterfowl. PLoS ONE 2, e418 (2007).
  19. ^ a b c d Mazzi, D., Kesäniemi, J., Hoikkala, A. & Klappert, K. Sexual conflict over the duration of copulation in Drosophila montana: why is longer better? BMC Evolutionary Biology 9, 132 (2009).
  20. ^ a b c d Han, C. S., Jablonski, P. G., Kim, B. & Park, F. C. Size-assortative mating and sexual size dimorphism are predictable from simple mechanics of mate-grasping behavior. BMC Evolutionary Biology 10, 359 (2010).
  21. ^ a b c Zehr, J. L. NIH Public Access. 41, 101–112 (2005).
  22. ^ a b c d Rivera, a C. & Andrés, J. a Male coercion and convenience polyandry in a calopterygid damselfly. Journal of insect science (Online) 2, 14 (2002).
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  24. ^ Cunningham, E. J. A. & Cheng, K. M. Biases in sperm use in the mallard : no evidence for selection by females based on sperm genotype. (1999).
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  27. ^ Brennan, P. L. R., Clark, C. J. & Prum, R. O. Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitalia. Proceedings: Biological Sciences 277, 1309–14 (2010).
  28. ^ a b Johannesson, K., Saltin, S. H., Duranovic, I., Havenhand, J. N. & Jonsson, P. R. Indiscriminate males: mating behaviour of a marine snail compromised by a sexual conflict? PLoS ONE 5, e12005 (2010).
  29. ^ Darden, S. K. & Croft, D. P. Male harassment drives females to alter habitat use and leads to segregation of the sexes. Biology letters 4, 449–51 (2008).
A Natural History of Rape

A Natural History of Rape: Biological Bases of Sexual Coercion is a 2000 book by the biologist Randy Thornhill and the anthropologist Craig T. Palmer, in which the authors criticize the idea, popularized by the feminist author Susan Brownmiller in Against Our Will (1975), that rape is an expression of male domination and is not sexually motivated. The authors argue that evolutionary psychology can account for rape among human beings, and maintain that rape is either a behavioral adaptation or a byproduct of adaptive traits such as sexual desire and aggressiveness. The authors also make proposals for preventing rape, and criticize as the "naturalistic fallacy" the assumption that there is a connection between what is naturally selected and what is morally right or wrong.

The book received extensive media coverage following the publication of an extract in The Sciences. It became controversial, received many negative reviews, and was denounced by feminists. Thornhill and Palmer were criticized for suggesting that rape is a reproductive adaptation, misrepresenting Brownmiller, making questionable comparisons between humans and non-human animals such as insects, their treatment of the naturalistic fallacy, and their proposals for preventing rape. In response to their suggestion that rape is a reproductive adaptation, critics observed that many rapes, such as those involving young children, the elderly, or persons of the same sex, cannot lead to reproduction. They also characterized A Natural History of Rape as poorly written, and suggested it was part of a trend to blame social problems on biological causes and had received unwarranted attention due to its controversial subject matter.

However, some reviewers commended the book's discussion of evolutionary theory, offered a mitigated defense of the view that rape has an evolutionary basis, or argued that the view that rape is sexually motivated is partially correct, while suggesting that rape might also involve a desire for violence and domination. Defenders of the book, including its authors, argued that much of the criticism it had received was misinformed and misrepresented what it actually argued. Commentators compared the controversy surrounding A Natural History of Rape to that provoked by the psychologist Richard Herrnstein and the political scientist Charles Murray's The Bell Curve (1994), and suggested that it was partly a result of larger controversies surrounding evolutionary psychology.

Causes of sexual violence

Causes of sexual violence are debated and explanations of the cause include military conquest, socioeconomics, anger, power, sadism, sexual pleasure, psychopathy, ethical standards, laws, attitudes toward the victims, and evolutionary pressures.

Clasper

In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating.

Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve as intromittent organs used to channel semen into the female's cloaca during mating. The act of mating in some fish including sharks usually includes one of the claspers raised to allow water into the siphon through a specific orifice. The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. The siphon then begins to contract, expelling water and sperm. Male chimaeras have cephalic claspers (tenacula) on their heads, which are thought to aid in holding the female during mating.

In entomology, it is a structure in male insects that is used to hold the female during copulation (see Lepidoptera genitalia for more).

Conflict tactics scale

The conflict tactics scale (CTS), created by Murray A. Straus in 1979, is the "most widely used instrument in research on family violence." There are two versions of the CTS; the CTS2 (an expanded and modified version of the original CTS) and the CTSPC (CTS Parent-Child). As of 2005, the CTS has been used in about 600 peer reviewed scientific or scholarly papers, including longitudinal birth-cohort studies. National surveys conducted in the USA include two National Family Violence Surveys (1975 and 1985), the National Violence Against Women Survey (1998), which, according to Straus, used a "feminist version" of the CTS in order to minimize data on female perpetration of intimate partner violence (IPV), and the National Survey of Child and Adolescent Well-Being. A major international survey to use the CTS was the 2006 International Dating Violence Study, which investigated IPV amongst 13,601 college students across thirty-two different countries.In a 2005 article in the Journal of Interpersonal Violence, Jennifer Langhinrichsen-Rohling listed the CTS amongst the most important advances in the field of IPV research, stating it "was revolutionary because it allowed researchers to quantitatively study events that had often been ignored culturally and typically took place in private."However, the CTS is one of the most widely criticized domestic violence measurement instruments due to its exclusion of context variables and motivational factors in understanding acts of violence. The National Institute of Justice cautions that the CTS may not be appropriate for IPV research "because it does not measure control, coercion, or the motives for conflict tactics."

Domestic violence in Kenya

Domestic violence in Kenya constitutes any harmful behavior against a family member or partner, including rape, assault, physical abuse, and forced prostitution. Domestic violence in Kenya reflects worldwide statistics in that women are the overwhelming majority of victims. Over 40% of married women in Kenya have reported being victims of either domestic violence or sexual abuse. Worldwide, over 30% of "ever-partnered women" aged 15 and older have experienced physical or sexual partner violence. The distinct factors and causes of this high percentage have often not been studied due to lack of data.Factors such as low levels of education, religion, and socioeconomic status all are relevant when looking at the causes of domestic violence in Kenya. Sexual coercion is prevalent in Kenya and often leads to abuse as well. Pregnant women are more likely to be victims of domestic abuse because they are more likely to be in a relationship. Pregnant women are often also economically or socially vulnerable, putting them at a higher risk for domestic violence due to the patriarchal dominance. Unwanted pregnancies are often seen as the fault of the woman, leading to more abuse. The gender roles in Kenya contribute to the acceptance of domestic abuse.Domestic violence also contributes to negative mental and physical health effects. Negative outcomes of domestic violence include pregnancy loss and complications, hypertension, physical injuries, and stress. In addition, victims of domestic violence are more likely to contract HIV/AIDS and other sexually transmitted diseases. Responses to domestic violence in Kenya include legal mandates and programs set in place by social organizations. Underreporting of domestic violence in developing countries is due to many reasons, including shame, financial barriers, lack of awareness and access to services, and distrust of healthcare workers.

Estimates of sexual violence

Surveys of victims of crime have been undertaken in many cities and countries, using a common methodology to aid comparability, and have generally included questions on sexual violence. The United Nations has conducted extensive surveys to determine the level of sexual violence in different societies. According to these studies, the percentage of women reporting having been a victim of sexual assault ranges from less than 2% in places such as La Paz, Bolivia (1.4%), Gaborone, Botswana (0.8%), Beijing, China (1.6%), and Manila, Philippines (0.3%), to 5% or more in Istanbul, Turkey (6.0%), Buenos Aires, Argentina (5.8%), Rio de Janeiro, Brazil (8.0%), and Bogota, Colombia (5.0%).No distinction has been made in these figures between rape by strangers and that by intimate partners. Surveys that fail to make this distinction or those that only examine rape by strangers usually underestimate substantially the prevalence of sexual violence.Apart from crime surveys, there have been a small number of surveys, with representative samples, that have asked women about sexual violence. For instance, in a national survey conducted in the United States of America, 14.8% of women over 17 years of age reported having been raped in their lifetime (with an additional 2.8% having experienced attempted rape) and 0.3% of the sample reported having been raped in the previous year. A survey of a representative sample of women aged 18– 49 years in three provinces of South Africa found that in the previous year 1.3% of women had been forced, physically or by means of verbal threats, to have non-consensual sex. In a survey of a representative sample of the general population over 15 years of age in the Czech Republic, 11.6% of women reported forced sexual contact in their lifetime, 3.4% reporting that this had occurred more than once. The most common form of contact was forced vaginal intercourse.

Human male sexuality

Human male sexuality covers physiological, psychological, social, cultural, and political aspects of the human male sexual response and related phenomena. It encompasses a broad range of topics involving male sexual desires and behavior that have also been addressed by ethics, morality, and religion.

Human sperm competition

Sperm competition is a form of post-copulatory sexual selection whereby male ejaculates simultaneously physically compete to fertilize a single ovum. Sperm competition occurs between sperm from two or more rival males when they make an attempt to fertilize a female within a sufficiently short period of time. This results primarily as a consequence of polyandrous mating systems, or due to extra-pair copulations of females, which increases the chance of cuckoldry, in which the male mate raises a child that is not genetically related to him. Sperm competition among males has resulted in numerous physiological and psychological adaptations, including the relative size of testes, the size of the sperm midpiece, prudent sperm allocation, and behaviors relating to sexual coercion, however this is not without consequences: the production of large amounts of sperm is costly and therefore, researchers have predicted that males will produce larger amounts of semen when there is a perceived or known increase in sperm competition risk. Sperm competition is not exclusive to humans, and has been studied extensively in other primates, as well as throughout much of the animal kingdom. The differing rates of sperm competition among other primates indicates that sperm competition is highest in primates with multi-male breeding systems, and lowest in primates with single-male breeding systems. Compared to other animals, and primates in particular, humans show low-to-intermediate levels of sperm competition, suggesting that humans have a history of little selection pressure for sperm competition.

John-Roger Hinkins

John-Roger Hinkins (born Roger Delano Hinkins) (September 24, 1934 – October 22, 2014) was an American author, public speaker, and founder of the Movement of Spiritual Inner Awareness (MSIA), as well as several other New Age, spiritual, and self-help organizations.

Margo Wilson

Margo Wilson (1942 – 2009) was a Canadian professor of psychology.

National Women's Liberation Conference

The National Women's Liberation Conference (or National Women's Liberation Movement Conference) was a United Kingdom initiative organised to bring together activists in the Women's Liberation Movement with an aim to developing a shared political outlook. Ten UK conferences took place between 1970 and 1978. There was a Welsh conference in 1974 and a Scottish conference in 1977. During these conferences the seven demands of the UK Women' Liberation Movement were formulated:

Equal pay

Equal educational and job opportunities

Free contraception and abortion on demand

Free 24-hour nurseries

Legal and financial independence for all women

The right to a self-defined sexuality. An end to discrimination against lesbians

Freedom for all women from intimidation by the threat or use of violence or sexual coercion regardless of marital status; and an end to the laws, assumptions and institutions which perpetuate male dominance and aggression to women.

Obsessive relational intrusion

Obsessive relational intrusion (ORI) occurs when someone knowingly and repeatedly invades another person's privacy boundaries by using intrusive tactics to try to get closer to that person. It includes behaviors such as repeated calls and texts, malicious contact, spreading rumors, stalking, and violence (kidnapping and assault).

Drs. Brian Spitzberg and William Cupach, the creators of the term, define ORI as "repeated and unwanted pursuit and invasion of one's sense of physical or symbolic privacy by another person, either stranger or acquaintance, who desires and/or presumes an intimate relationship". Some victims of ORI have no preexisting relationship with or interest in their pursuers; others know their pursuers, but are less interested in making an existing relationship more intimate.

Otto Mainzer

Otto Mainzer (26 November 1903 in Frankfurt am Main – 28 June 1995 in New York City) was a German-American writer. He was unconventional, and wrote about issues such as free love.

Mainzer was the son of Bertha Loeb. He graduated in Law in 1928 and received his doctorate in law. He then worked as a lawyer at the Berlin Court of Appeal. When he removed in 1933 because of his Jewish origin, he emigrated to Paris. There he made the acquaintance of André Gide, Heinrich Mann, Arnold Zweig and Erwin Piscator, who supported him financially. At the time of his Paris exile, Mainzer became acquainted with the writings of psychoanalyst Wilhelm Reich. Under the influence of Reich's ideas about sex-economy, Mainzer produced some major works on sexual coercion. In 1941 Mainz continued his emigration, and went to the USA. There he met his girlfriend Ilse Wunsch and lived for 25 years, "unmarried, in two different apartments, but in an intimate love relationship" until they married. After his death in 1995 his wife established the Otto-Mainzer-Preis in New York for the science of love, worth 5,000 U.S. dollars. The last prize was awarded in 2015.

Pinegrove (band)

Pinegrove is an American indie rock band from Montclair, New Jersey. The band name is an allusion to the Brown Family Environmental Center at Kenyon College, where lyricist Evan Stephens Hall and former keyboardist Nandi Plunkett attended.

Polyandry in nature

In behavioral ecology, polyandry is a class of mating system where one female mates with several males in a breeding season. Polyandry is often compared to the polygyny system based on the cost and benefits incurred by members of each sex. Polygyny is where one male mates with several females in a breeding season (e.g., lions, deer, some primates, and many systems where there is an alpha male).

A common example of polyandrous mating can be found in the field cricket (Gryllus bimaculatus) of the invertebrate order Orthoptera (containing crickets, grasshoppers, and groundhoppers). Polyandrous behavior is also prominent in many other insect species, including the red flour beetle and the species of spider Stegodyphus lineatus. Polyandry also occurs in some primates such as marmosets, mammal groups, the marsupial genus' Antechinus and bandicoots, around 1% of all bird species, such as jacanas and dunnocks, insects such as honeybees, and fish such as pipefish.

Rape by gender

Rape by gender classifies types of rape by the sex or gender of both the rapist and the victim. This scope includes both rape and sexual assault more generally. Most research indicates that rape affects women disproportionately, with the majority of people convicted being men; however, since the broadening of the definition of rape in 2012 by the FBI, more attention is being given to male rape, including females raping males.

Since only a small percentage of acts of sexual violence are brought to the attention of the authorities, it is difficult to compile accurate rape statistics. Conviction rates differ by the gender of both the perpetrator and victim. Various studies argue that male-male and female-female prison rape are quite common and may be the least reported form of rape. Furthermore, a large number of rape cases take place when the victims are below the age of consent, bringing in the issue of child sexual abuse or statutory rape.

Richard Wrangham

Richard Walter Wrangham (born 1948) is a British primatologist. His research and writing have involved ape behavior, human evolution, violence, and cooking.

Sexual selection in amphibians

Sexual selection in amphibians involves sexual selection processes in amphibians, including frogs, salamanders and newts. Prolonged breeders, the majority of frog species, have breeding seasons at regular intervals where male-male competition occurs with males arriving at the waters edge first in large number and producing a wide range of vocalizations, with variations in depth of calls the speed of calls and other complex behaviours to attract mates. The fittest males will have the deepest croaks and the best territories, with females known to make their mate choices at least partly based on the males depth of croaking. This has led to sexual dimorphism, with females being larger than males in 90% of species, males in 10% and males fighting for groups of females.

There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the females attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm.

Skylight (Pinegrove album)

Skylight is the third studio album by Pinegrove, self-released on September 28, 2018. The album was produced by the band's frontman, singer-songwriter Evan Stephens Hall, as well as guitarist Sam Skinner. It was recorded at a home the band lived in in upstate New York in mid-2017. Pinegrove had risen to fame on the heels of its sophomore record, Cardinal, released on independent label Run for Cover. In November 2017, Hall posted a statement on the band's Facebook detailing accusations of "sexual coercion" against him. In response, the band canceled a tour and the planned release of Skylight, entering a hiatus.

The album eventually saw release with little promotion in September 2018 on Bandcamp. It was self-released by the band as they had split from Run for Cover during the interim. Skylight received positive reviews from contemporary music critics. Though initially exclusive to streaming platforms, the album was released physically in February 2019. Its LP release was bundled with an additional disc containing an acoustic rendition of the album, dubbed Skylight II.

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