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In zoology, copulation is animal sexual behavior in which a male introduces sperm into the female's body, especially directly into her reproductive tract.[1][2] This is an aspect of mating. Many animals that live in water use external fertilization, whereas internal fertilization may have developed from a need to maintain gametes in a liquid medium in the Late Ordovician epoch. Internal fertilization with many vertebrates (such as reptiles, some fish, and most birds) occur via cloacal copulation (see also hemipenis), while mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization.[3][4]

In non-primate mammals (rodents, canines, felines, bovines, and equines), the anatomy of the reproductive organs and some circuits of the nervous system are specifically organized for heterosexual copulation.[5] On the other hand, human sexual intercourse stems from a change in biological factors that controls the copulation of mammals, and is mainly learned.[6]

Contents

In spiders and insectsEdit

Spiders are often confused with insects, but they are not insects; instead, they are arachnids.[7][8] Spiders have separate male and female sexes. Before mating and copulation, the male spider spins a small web and ejaculates on to it. He then stores the sperm in reservoirs on his large pedipalps, from which he transfers sperm to the female's genitals. The females can store sperm indefinitely.[9]

For primitive insects, the male deposits spermatozoa on the substrate, sometimes stored within a special structure; courtship involves inducing the female to take up the sperm package into her genital opening, but there is no actual copulation.[10][11] In groups that have reproduction similar to spiders, such as dragonflies, males extrude sperm into secondary copulatory structures removed from their genital opening, which are then used to inseminate the female. In dragonflies, it is a set of modified sternites on the second abdominal segment.[12] In advanced groups of insects, the male uses its aedeagus, a structure formed from the terminal segments of the abdomen, to deposit sperm directly (though sometimes in a capsule called a spermatophore) into the female's reproductive tract.[13]

In mammalsEdit

Non-primate mammalsEdit

Some scientific studies show that the general neuroanatomic organization of non-primate mammals is specifically designed for heterosexual copulation.[14] By simplifying, there are three major hardwired neurobiological circuits, controlled by hormones: A) The olfactory circuits (red arrows, diagram below), which underlie sexual arousal and sexual orientation; B) The circuits of sexual reflexes (lordosis, erection, ejaculation ... orange arrows), which allow copulation; C) The circuits of sexual rewards (reward system associated with penis / clitoris - blue arrows), which are involved in sexual learning (especially sexual motivation).[15]

 
Simplified diagram of the neurobiological circuits that control reproductive behavior in non-primate female mammals. By simplifying, the hormones control the activity of these innate circuits. They activate the secretion of pheromones and their detection,[16] and disinhibit the lordosis reflex.[17] The pheromones of the male (1) are detected and treated by the olfactory circuits (2 - red arrows). They trigger sexual arousal in the female, stimulate hippocampal neurogenesis,[18] and, via the hypothalamus, facilitate the lordosis reflex.[19] The mount by the male stimulates the rump of the female (3) which triggers the lordosis reflex (4 - orange arrows).[17] The arching of the back induces the presentation of the vagina to the male (5). Then the clitoral sensations during penetration (6) trigger ovulation in some species (and in all ancestral species[20]); activate the reward system (7 - blue arrows), inducing the learning of sexual motivations[21] and to stay close to the copulation partner (attachment).[22]

Particularly in the female, copulation is controlled by several innate neurobiological processes, including the motor sexual reflex of lordosis[17] (see diagram below).

 
Simplified diagram of the neurobiological circuits of the lordosis reflex, specific to female mammals, and indispensable to the realization of copulation. This complex motor sexual reflex is hardwired in the spinal cord and receives modulatory afferents from the forebrain.[17][15][23] Caption: a) Median preoptic nucleus; b) Anterior hypothalamic nucleus; c) Ventromedial hypothalamic nucleus; d) Midbrain reticular formation; e) Vestibulo-spinal tract; f) Reticulo-spinal tract; g) Dorsal roots L1, L2, L5, L6 and S1. NB: The neural circuit is bilateral. The diagram is simplified for greater clarity.

By simplifying, the female can not have any other sexual activity than lordosis.

In the male, the realization of copulation is more complex, because some learning is necessary. Nevertheless, the innate processes (retrocontrol of penis intromission in the vagina, rhythmic movement of the pelvis, detection of female pheromones ...) are specific to copulation. These innate processes direct learning to heterosexual copulation.[24]

Thus, through the coordination of hormones, pheromones and sexual reflexes, there is a true reproductive behavior in non-primate mammals.

Evolution of copulation control in hominidsEdit

 
Evolution of the main neurobiological factors that control the sexual behavior of mammals.[15]

In the case of mammals with a highly developed brain (chimpanzee, bonobo, Orangutans, and dolphins), the cerebral structure has evolved. As a result of these evolved differences, the human intercourse depends on another type of neurobiological control:[6]

  • Female lordosis behaviour became secondary in hominidae and is apparently non-functional in humans.[25] Sexual stimuli no longer trigger immobilization or reflex arching of the back. If a woman gets onto all fours, curves her back and remains still, it is no longer a reflex movement triggered by sexual stimuli, but a voluntary movement.[15]
  • Pheromones become secondary. 90% of sex pheromone receptor genes become pseudogens,[26] and the vomeronasal organ is altered.[27]
  • The sexual activities are gradually dissociated from the hormonal cycles,[25] especially in pan paniscus[28] and humans.
  • Sexual learning, induced by sexual rewards and the reward system, become a major factor in hominids.[14][29]
  • The major development of the cortex in hominids leads to the gradual emergence of complex cognitive abilities, which have enabled the human species to develop culture.[30]

Thus, the functional dynamics of the copulation behavior has been modified in hominids: the reproductive behavior becomes an erotic behavior.[6] Vaginal coitus is still practiced in humans, but it is no longer a reflex motor activity, guided by pheromones and controlled by hormones. It is rather an erotic activity, among others, carried out voluntarily to obtain cerebral reward (sexual pleasure [29]).[15]

Further readingEdit

ReferencesEdit

  1. ^ Michael Kent (2000). Advanced biology. Oxford University Press. pp. 250–253. ISBN 0199141959. Retrieved 2015-10-21. 
  2. ^ "Copulation". Dorland's Medical Dictionary for Health Consumers, 2007/TheFreeDictionary.com for various dictionary definitions. Retrieved September 6, 2012. 
  3. ^ Cecie Starr; Christine Evers; Lisa Starr (2010). Cengage Advantage Books: Biology: A Human Emphasis. Cengage Learning. pp. 630–631. ISBN 1133170056. Retrieved December 9, 2010. 
  4. ^ Edward J. Denecke Jr. (2006). New York State Grade 8 Intermediate Level Science Test. Barron's Educational Series. p. 105. ISBN 0764134337. Retrieved December 9, 2014. 
  5. ^ Knobil E., Neill J.D. (Eds). The physiology of reproduction. Academic Press, 3nd edition, 2005
  6. ^ a b c Wunsch S. Phylogenesis of mammal sexuality. Analysis of the evolution of proximal factors. Sexologies 26(1):e1-e10, 2017
  7. ^ Donna M. Jackson (2004). The Bug Scientists. Houghton Mifflin Harcourt. p. 13. ISBN 0618432329. Retrieved March 7, 2017. 
  8. ^ Fred F. Ferri (2016). Ferri's Clinical Advisor 2017: 5 Books in 1. Elsevier Health Sciences. p. 178. ISBN 0323448380. Retrieved March 7, 2017. 
  9. ^ Ruppert, E.E.; Fox, R.S. & Barnes, R.D. (2004). "Chelicerata: Araneae". Invertebrate Zoology (7th ed.). Brooks/Cole. pp. 571–584. ISBN 0-03-025982-7. 
  10. ^ M. Yadav (2003). Breeding in Insects. Discovery Publishing House. p. 59. ISBN 817141737X. Retrieved December 9, 2014. 
  11. ^ Franz Engelmann (2013). The Physiology of Insect Reproduction: International Series of Monographs in Pure and Applied Biology: Zoology. Elsevier. pp. 58–59. ISBN 1483186539. Retrieved December 9, 2014. 
  12. ^ Janet Leonard; Alex Cordoba-Aguilar (2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. p. 334. ISBN 0199717036. Retrieved December 9, 2014. 
  13. ^ P. J. Gullan; P. S. Cranston (2009). The Insects: An Outline of Entomology. John Wiley & Sons. p. 124. ISBN 1405144572. Retrieved December 9, 2014. 
  14. ^ a b Agmo A. Functional and dysfunctional sexual behavior.
  15. ^ a b c d e (in French) Wunsch S. (2014) To understand the origins of human sexuality. Neurosciences, ethology, anthropology. Comprendre les origines de la sexualité humaine. Neurosciences, éthologie, anthropologie. L'Esprit du Temps.
  16. ^ Lin H.H., Cao D.S., Sethi S., Zeng Z., Chin J.S., Chakraborty T.S., Shepherd A.K., Nguyen C.A., Yew J.Y., Su C.Y., Wang J.W. Hormonal modulation of pheromone detection enhances male courtship success. Neuron, 90(6):1272-1285, 2016
  17. ^ a b c d PFAFF Donald W. , SCHWARTZ-GIBLIN Susan, MACCARTHY Margareth M. , KOW Lee-Ming : Cellular and molecular mechanisms of female reproductive behaviors, in KNOBIL Ernest, NEILL Jimmy D. : The physiology of reproduction, Raven Press, 2nd edition, 1994
  18. ^ Hoffman E., Pickavance L., Thippeswamy T., Beynon R.J., Hurst J.L. The male sex pheromone darcin stimulates hippocampal neurogenesis and cell proliferation in the subventricular zone in female mice. Front Behav. Neurosci., 9:106, 2015.
  19. ^ Haga S., Hattori T., Sato T., Sato K., Matsuda S., Kobayakawa R., Sakano H., Yoshihara Y., Kikusui T., Touhara K. The male mouse pheromone ESP1 enhances female sexual receptive behaviour through a specific vomeronasal receptor. Nature, 466(7302):118-122, 2010
  20. ^ Pavlicev M., Wagner G. The evolutionary origin of female orgasm. J. Exp. Zool. B Mol. Dev. Evol., 2016
  21. ^ Cibrian-Llanderal T., Tecamachaltzi-Silvaran M., Triana-Del R.R., Pfaus J.G., Manzo J., Coria-Avila G.A. Clitoral stimulation modulates appetitive sexual behavior and facilitates reproduction in rats. Physiology & Behavior, 100(2):148-153, 2010
  22. ^ Roberts S.A., Simpson D.M., Armstrong S.D., Davidson A.J., Robertson D.H., McLean L., Beynon R.J., Hurst J.L. Darcin: a male pheromone that stimulates female memory and sexual attraction to an individual male's odour. BMC. Biol., 8(1):75, 2010
  23. ^ Kow L.M., Florea C., Schwanzel-Fukuda M., Devidze N., Kami K.H., Lee A., Zhou J., Maclaughlin D., Donahoe P., Pfaff D. Development of a sexually differentiated behavior [lordosis] and its underlying CNS arousal functions. Curr. Top. Dev. Biol., 79:37-59, 2007
  24. ^ MEISEL Robert L. , SACHS Benjamin D. : The physiology of male sexual behavior. in KNOBIL Ernest, NEILL Jimmy D. The physiology of reproduction, Raven Press, 2nd edition, 1994
  25. ^ a b Dixson A.F. Primate sexuality: Comparative studies of the Prosimians, Monkeys, Apes, and Human Beings. Oxford University Press, 2nd edition, 2012.
  26. ^ Nei M., Niimura Y., Nozawa M. (2008) The evolution of animal chemosensory receptor gene repertoires: roles of chance and necessity. Nat. Rev. Genet., 9(12):951-963.
  27. ^ Zhang J., Webb D.M. Evolutionary deterioration of the vomeronasal pheromone transduction pathway in catarrhine primates. Proceedings of the National Academy of Sciences of the United States of America, 100(14):8337-8341, 2003.
  28. ^ Furuichi T. Female contributions to the peaceful nature of bonobo society. Evolutionary Anthropology, 20(4):131-142, 2011.
  29. ^ a b Georgiadis J.R., Kringelbach M.L., Pfaus J.G. (2012) Sex for fun: a synthesis of human and animal neurobiology. Nat. Rev. Urol., 9(9):486-498.
  30. ^ Gazzaniga M.S., Ivry R.B., Mangun G.R. Cognitive neuroscience. The biology of the mind. W.W. Norton & Company, 2e edition, 2002.