Editing Coolidge effect

{{Short description|Sexual phenomenon}}
The '''Coolidge effect''' is a biological phenomenon seen in animals, whereby males exhibit renewed sexual interest whenever a new female of reproductive availability is introduced, even after sex with prior but still available sexual partners.<ref>{{Cite book|last1=Reber|first1=Arthur S.|url=https://archive.org/details/penguindictionar00rebe_0|title=The Penguin dictionary of psychology|last2=Reber|first2=Emily Sarah|last3=Allen|first3=Rhianon|date=2001|publisher=Penguin Books|isbn=978-0-14-051451-3|edition=3rd|series=Penguin reference|location=London |author-link=Arthur S. Reber}}</ref><ref>{{Cite journal|last=Brown|first=Richard E.|date=1974|title=Sexual arousal, the coolidge effect and dominance in the rat (rattus norvegicus)|url=https://linkinghub.elsevier.com/retrieve/pii/S0003347274800096|journal=Animal Behaviour|language=en|volume=22|issue=3|pages=634–637|doi=10.1016/S0003-3472(74)80009-6|url-access=subscription}}</ref><ref name="Lester">{{Cite journal|last1=Lester|first1=Gillian L.L. |author-link=Gillian Lester|last2=Gorzalka|first2=Boris B.|date=1988|title=Effect of novel and familiar mating partners on the duration of sexual receptivity in the female hamster|url=https://linkinghub.elsevier.com/retrieve/pii/S0163104788904189|journal=Behavioral and Neural Biology|language=en|volume=49|issue=3|pages=398–405|doi=10.1016/S0163-1047(88)90418-9|pmid=3408449|url-access=subscription}}</ref><ref name="Biopsych">{{Cite book|last=Pinel|first=John P. J.|title=Biopsychology|date=2007|publisher=Pearson Allyn and Bacon|isbn=978-0-205-42651-5|edition=6th|location=Boston}}</ref> To a lesser extent, the effect is also seen among females with regard to their mates.<ref name="Lester" />

The Coolidge effect can be attributed to an increase in sexual responsiveness, and a shortening of the [[Refractory period (sex)|sexual refractory period]].<ref name="Andrew Colman">{{Cite book|last=Colman|first=Andrew Michael|url=https://www.worldcat.org/oclc/260204714|title=A dictionary of psychology|date=2009|publisher=Oxford University Press|isbn=9780199534067|edition=3rd|location=Oxford|oclc=260204714 |author-link=Andrew Colman}}</ref> The evolutionary benefit to this phenomenon is that a male can fertilize multiple females.<ref name="Tlachi-López" /> The male may be reinvigorated repeatedly for successful insemination of multiple females.<ref>Carlson, N. (2013). Reproductive Behavior. In Physiology of Behavior (11th ed., p. 332). Boston, MA: Pearson Education.</ref> This type of [[mating system]] can be referred to as [[Polygyny in animals|polygyny]], where one male has multiple female mates, but each female mates with only one or a few males.<ref name="Andrew Colman" /> The Coolidge effect has been demonstrated to occur in [[Cross-cultural psychology|humans across cultures]] and in both sexes.<ref>{{cite book|last=Buss|first=David M.|title=The Evolution of Desire: Strategies of Human Mating|title-link=The Evolution of Desire|publisher=[[Basic Books]]|year=2016|isbn=978-0465097760|edition=3rd|place=New York|pages=125–127|author-link=David Buss|orig-date=1994}}</ref>

==Origin of the term==
In a 1974 letter,<ref>{{cite book|last1=Kimble|first1=Gregory Adams|url=https://www.worldcat.org/title/5565027?oclcNum=5565027|title=Principles of General Psychology|last2=Garmezy|first2=Norman|last3=Zigler|first3=Edward Frank|publisher=Ronald Press Company|year=1974|isbn=9780721651606|edition=4th|page=249 |author-link=Gregory Kimble |author-link2=Norman Garmezy |author-link3=Edward Zigler}}</ref> behavioral endocrinologist [[Frank A. Beach]] claims to have introduced the term "Coolidge effect" in either 1958 or 1959.<ref>{{Cite web|date=2018-03-30|title=Coolidge Effect – Quote Investigator®|url=https://quoteinvestigator.com/2018/03/30/coolidge/ |access-date=2023-06-08|language=en-US}}</ref> He attributed the [[neologism]] to an old joke about [[Calvin Coolidge]] when he was [[President of the United States]].<ref name="Dewsbury">{{cite journal|last1=Dewsbury|first1=Donald Allen |author-link=Donald Dewsbury|last2=Kimble|first2=Gregory Adams |author-link2=Gregory Kimble|last3=Wertheimer|first3=Michael Matthew |editor-first1=Gregory A. |editor-first2=Michael |editor-last1=Kimble |editor-last2=Wertheimer |author-link3=Michael Wertheimer (psychologist)|year=2000|title=Frank A. Beach, Master Teacher|url=https://www.worldcat.org/title/868976337|journal=Portraits of Pioneers in Psychology|volume=4|pages=269–281|doi=10.4324/9781410607638|isbn=9781410603876|oclc=868976337|url-access=subscription}}</ref>

{{quote|The President and [[Grace Coolidge|Mrs. Coolidge]] were being shown [separately] around an experimental government farm. When [Mrs. Coolidge] came to the chicken yard she noticed that a rooster was mating very frequently. She asked the attendant how often that happened and was told, "Dozens of times each day." Mrs. Coolidge said, "Tell that to the President when he comes by." Upon being told, the President asked, "Same hen every time?" The reply was, "Oh, no, Mr. President, a different hen every time." President: "Tell that to Mrs. Coolidge."}}

The joke appears in a 1972 book (''Aggression in Man and Animals'', by Roger N. Johnson, p.&nbsp;94).<ref>{{cite book|last=Johnson|first=Roger N.|url=https://www.worldcat.org/title/341023|title=Aggression in Man and Animals|publisher=Saunders|year=1972|isbn=9780721651606|edition=3rd|page=94|oclc=341023}}</ref>

== Empirical evidence ==
The original experiments with [[Brown rat|rats]] applied the following protocol: A male rat was placed into an enclosed large box with four or five female rats [[estrus|in heat]].<ref name="Beach Jordan">{{Cite journal|last1=Beach|first1=Frank Ambrose |author-link=Frank A. Beach|last2=Jordan|first2=Lisbeth|date=1956|title=Sexual Exhaustion and Recovery in the Male Rat|url=http://journals.sagepub.com/doi/10.1080/17470215608416811|journal=Quarterly Journal of Experimental Psychology|language=en|volume=8|issue=3|pages=121–133|doi=10.1080/17470215608416811|issn=0033-555X|s2cid=144834469|url-access=subscription}}</ref> He immediately began to mate with all the female rats repeatedly until he eventually became exhausted.<ref name="Beach Jordan" /> The females continued nudging and licking him, yet he did not respond.<ref name="Beach Jordan" /> When a novel female was introduced into the box, he became alert and began to mate once again with the new female.<ref name="Beach Jordan" /> This phenomenon is not limited to [[Rattus norvegicus|common rats]].<ref>{{Cite journal|last1=Wilson|first1=James R.|last2=Kuehn|first2=Robert E.|last3=Beach|first3=Frank Ambrose |author-link3=Frank A. Beach|date=1963|title=Modification in the sexual behavior of male rats produced by changing the stimulus female.|url=http://doi.apa.org/getdoi.cfm?doi=10.1037/h0042469|journal=Journal of Comparative and Physiological Psychology|language=en|volume=56|issue=3|pages=636–644|doi=10.1037/h0042469|issn=0021-9940|pmid=14001051|url-access=subscription}}</ref>

The Coolidge effect is attributed to an increase in [[dopamine]] levels and the subsequent effect upon an animal's [[limbic system]].<ref name="Fiorino">{{Cite journal|last1=Fiorino|first1=Dennis F.|last2=Coury|first2=Ariane|last3=Phillips|first3=Anthony G.|date=1997-06-15|title=Dynamic Changes in Nucleus Accumbens Dopamine Efflux During the Coolidge Effect in Male Rats|journal=The Journal of Neuroscience|language=en|volume=17|issue=12|pages=4849–4855|doi=10.1523/JNEUROSCI.17-12-04849.1997|issn=0270-6474|pmc=6573325|pmid=9169543}}</ref> In a study conducted by Fiorino et al., male rats were used to study the role of the [[Mesolimbic pathway|mesolimbic]] dopamine system on their sexual behaviour.<ref name="Fiorino" /> In their experiment, [[microdialysis]] was used to monitor dopamine efflux from the [[nucleus accumbens]] during three stages of sexual behaviour, these included: [[copulation (zoology)|copulation]], sexual satiety, and the reinitiation of sexual behaviour.<ref name="Fiorino" /> Behavioural testing for the Coolidge effect consisted of several phases including, copulation with a female, reintroduction to the same female, access to the same female, introduction to a novel female, and copulation with the novel female.<ref name="Fiorino" /> During these phases, dopamine and its metabolites were monitored.<ref name="Fiorino" /> Results from this study found that overall there was a significant increase in dopamine efflux in response to both the first female and the second female.<ref name="Fiorino" /> During copulation with the first female, concentrations of dopamine in these male rats showed a significant increase, however, when the same female was presented again, a significant increase in dopamine was not observed.<ref name="Fiorino" /> When a novel female was presented, initially, there was a small increase in the levels of dopamine, however, after continued copulation with the novel female, a significant increase in dopamine levels was observed.<ref name="Fiorino" /> From these results, they concluded that an increase in mesolimbic dopamine efflux is associated with the appetitive and consummatory stages of sexual behaviour in male rats.<ref name="Fiorino" /> Their data also suggest that stimuli associated with a novel female may increase dopamine transmission in a rat that is sexually satiated, and hence have a role in the reinitiation of sexual behaviour.<ref name="Fiorino" />

Additional studies have also provided further evidence for the role of the nucleus accumbens on sexual behaviour in rats.<ref name="Wood Kosobud Rebec">{{Cite journal|last1=Wood|first1=David A.|last2=Kosobud|first2=Ann E.K.|last3=Rebec|first3=George V.|year=2004|title=Nucleus accumbens single-unit activity in freely behaving male rats during approach to novel and non-novel estrus|url=https://linkinghub.elsevier.com/retrieve/pii/S0304394004007918|journal=Neuroscience Letters|volume=368|issue=1|pages=29–32|doi=10.1016/j.neulet.2004.06.051|pmid=15342128|s2cid=23866210|url-access=subscription}}</ref> In a study conducted by Wood et al., male rats were divided into three conditions, and were presented with a cotton ball laden in either saline (control group), estrous vaginal smear of a familiar female (experimental group), and estrous vaginal smear of a novel female (experimental group).<ref name="Wood Kosobud Rebec" /> In this experiment, the role of the nucleus accumbens was characterized through recording neuronal activity of single cells in this area of the brain.<ref name="Wood Kosobud Rebec" /> Results from this study showed a greater proportion of neuronal activation when initially presented with a novel estrus stimulus in comparison to familiar estrus stimulus.<ref name="Wood Kosobud Rebec" /> Subsequent presentations of the novel estrus stimulus did not show an increase in neuronal activity.<ref name="Wood Kosobud Rebec" />

== Allocating sperm ==
It has been observed that in certain species, males allocate sperm differently due to the Coolidge effect.<ref name="Spence 82–88" /> The allocation is usually according to level of [[sperm competition]], female novelty, and female reproductive quality.<ref name="Spence 82–88">{{Cite journal|last1=Spence|first1=Rowena|last2=Reichard|first2=Martin|last3=Smith|first3=Carl|date=2013-01-01|title=Strategic sperm allocation and a Coolidge effect in an externally fertilizing species|journal=Behavioral Ecology|language=en|volume=24|issue=1|pages=82–88|doi=10.1093/beheco/ars138|issn=1045-2249|doi-access=free}}</ref> An experiment performed on an external fertilizing fish called ''[[European bitterling|Rhodeus amarus]]'', also known as the European bitterling, was used to show that sperm can be allocated differently if a novel partner is around, but that it also happens if there is male-male competition.<ref name="Spence 82–88" /> It is important to know that the European bitterling mating system works by females depositing their eggs into the gill filaments of freshwater mussels by her long ovipositor and then males proceed by ejecting their sperm into the gills of the mussel hosting the eggs.<ref name="Spence 82–88" /> This means fertilization and development of the offspring relies on the quality and survival of the mussel.<ref name="Spence 82–88" /> When the Coolidge effect was applied to this system, the experiment showed that it is the mussels, or the site of fertilization, that the males prefer to be novel.<ref name="Spence 82–88" /> However, the takeaway from the experiment performed was that in male-male competition of the ''[[European bitterling|Rhodeus amarus]],'' the dominant male will allocate more sperm when a novel mussel is present, while the subordinate male conserved its sperm until a proper opportunity came where it had a better chance of fertilization.<ref name="Spence 82–88"/> A similar result was found in fowls, ''[[Red junglefowl|Gallus gallus]]'', where the male showed a sperm allocation due to the Coolidge effect.<ref name="Sophisticated" /> The experiment found that male fowls reduce sperm investment in particular females they've encountered already, but increase sperm investment instantaneously if they encountered a new female.<ref name="Sophisticated">{{Cite journal|last1=Pizzari|first1=Tommaso|last2=Cornwallis|first2=Charles K.|last3=Løvlie|first3=Hanne|last4=Jakobsson|first4=Sven|last5=Birkhead|first5=Tim Robert |author-link5=Tim Birkhead|date=2003-11-06|title=Sophisticated sperm allocation in male fowl|url=http://eprints.whiterose.ac.uk/73/1/pizzarit1.pdf|journal=Nature|language=en|volume=426|issue=6962|pages=70–74|bibcode=2003Natur.426...70P|doi=10.1038/nature02004|issn=0028-0836|pmid=14603319|s2cid=4313252}}</ref>

Wedell et al. suggest a theory that when a male allocates sperm so that he can save sperm for novel partners, he limits himself and the mate by possibly investing too little sperm to their partners which in return can inseminate only a few eggs therefore making reproduction less successful.<ref name=":0">{{Cite journal|last1=Wedell|first1=Nina|last2=Gage|first2=Matthew J.G.|last3=Parker|first3=Geoffrey A.|date=2002|title=Sperm competition, male prudence and sperm-limited females|url=https://linkinghub.elsevier.com/retrieve/pii/S0169534702025338|journal=Trends in Ecology & Evolution|language=en|volume=17|issue=7|pages=313–320|doi=10.1016/S0169-5347(02)02533-8|url-access=subscription}}</ref> This could even possibly force females to seek more copulation to ensure successful reproduction.<ref>{{Cite journal|last=Pizzari|first=Tommaso|year=2002|title=Sperm allocation, the Coolidge effect and female polyandry|url=http://www.cell.com/trends/ecology-evolution/abstract/S0169-5347(02)02591-0|journal=Trends in Ecology & Evolution|volume=17|issue=10|pages=456|doi=10.1016/s0169-5347(02)02591-0|bibcode=2002TEcoE..17..456P |url-access=subscription}}</ref> These types of evidence of sperm allocation would suggest that Coolidge effect will determine how much sperm is invested into females, and if possible, sperm will be allocated so that sperm can be evenly distributed for multiple mates.<ref name=":0" /><ref>{{Cite journal|last1=Scharf|first1=Inon|last2=Peter|first2=Franziska|last3=Martin|first3=Oliver Y.|date=2013-06-01|title=Reproductive Trade-Offs and Direct Costs for Males in Arthropods|url=http://link.springer.com/10.1007/s11692-012-9213-4|journal=Evolutionary Biology|language=en|volume=40|issue=2|pages=169–184|doi=10.1007/s11692-012-9213-4|bibcode=2013EvBio..40..169S |issn=0071-3260|s2cid=14120264|url-access=subscription}}</ref> Overall, it is typically seen that allocation changes due to male-male competition and whether a novel partner is encountered or not.<ref>{{Cite journal|last=Parker|first=Geoffrey Alan |author-link=Geoff Parker|date=1970-11-01|title=Sperm Competition and Its Evolutionary Consequences in the Insects|url=https://onlinelibrary.wiley.com/doi/10.1111/j.1469-185X.1970.tb01176.x|journal=Biological Reviews|language=en|volume=45|issue=4|pages=525–567|doi=10.1111/j.1469-185x.1970.tb01176.x|issn=1469-185X|s2cid=85156929|url-access=subscription}}</ref><ref>{{Cite book|last1=Birkhead|first1=Timothy Robert|url=https://www.worldcat.org/oclc/162128897|title=Sperm competition and sexual selection|last2=Møller|first2=Anders Pape|date=1998|publisher=Academic Press|isbn=978-0121005436|location=San Diego|oclc=162128897 |author-link=Tim Birkhead}}</ref><ref>{{Cite book|last=Simmons|first=Leigh W.|url=https://www.worldcat.org/title/45804827|title=Sperm competition and its evolutionary consequences in the insects|date=2001|publisher=Princeton University Press|isbn=978-0691059877|location=|oclc=45804827}}</ref>

== Absence ==
The Coolidge effect is typically found in most animals; however, there are instances where the Coolidge effect is absent.<ref name="Gershman, Sakaluk" /><ref name="Pisaura Mirabilis" /><ref name="Koene, Maat" /><ref name="Biomphalaria" /> A study in decorated crickets, ''[[Tropical house cricket|Gryllodes sigillatus]]'', showed that even though females do display the Coolidge effect, the males in this species have no preference for novel mates.<ref name="Gershman, Sakaluk">{{Cite journal|last1=Gershman|first1=Susan N.|last2=Sakaluk|first2=Scott K.|date=2009-08-01|title=No Coolidge Effect in Decorated Crickets|url=https://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2009.01663.x|journal=Ethology|language=en|volume=115|issue=8|pages=774–780|doi=10.1111/j.1439-0310.2009.01663.x|bibcode=2009Ethol.115..774G |issn=1439-0310|url-access=subscription}}</ref> Because the females in this species control copulation, to test the Coolidge effect in males, two dead females were used.<ref name="Gershman, Sakaluk" /> One female was already previously mated and the other was a novel female.<ref name="Gershman, Sakaluk" /> To measure the Coolidge effect, the variables examined were the amount of courtship for the preferred mate and the size of the spermatophore transferred to the female.<ref name="Gershman, Sakaluk" /> The size of the spermatophore was measured by weighing the mass after it was transferred to the female.<ref name="Gershman, Sakaluk" /> The outcome of the experiment showed that there was no difference in the latency to re-mating of males confined with novel females and those paired with previous mates.<ref name="Gershman, Sakaluk" /> There also was no difference in mass of the spermatophore.<ref name="Gershman, Sakaluk" /> This experiment would suggest that the Coolidge effect is not applicable since the males of the ''[[Tropical house cricket|Gryllodes sigillatus]]'' do not prefer novel females.<ref name="Gershman, Sakaluk" /> Further research done on spiders also supports the possibility of absence of the Coolidge effect in certain species.<ref name="Pisaura Mirabilis">{{Cite journal|last1=Tuni|first1=Cristina|last2=Bilde|first2=Trine|date=2010-09-01|title=No preference for novel mating partners in the polyandrous nuptial-feeding spider Pisaura mirabilis (Araneae: Pisauridae)|url=https://www.sciencedirect.com/science/article/pii/S0003347210002198|journal=Animal Behaviour|language=en|volume=80|issue=3|pages=435–442|doi=10.1016/j.anbehav.2010.05.029|s2cid=53151908|issn=0003-3472|url-access=subscription}}</ref> Another study that focused on the Coolidge effect in simultaneously [[hermaphrodite|hermaphroditic]] species confirmed the validity of the Coolidge effect in freshwater snail ''[[Lymnaea stagnalis]]''.<ref name="Koene, Maat">{{cite journal|last1=Koene|first1=Joris M.|last2=Maat|first2=Andries Ter|year=2007|title=Coolidge effect in pond snails: male motivation in a simultaneous hermaphrodite|journal=[[BMC Evolutionary Biology]]|volume=7|issue=1 |page=212|doi=10.1186/1471-2148-7-212|pmc=2186336|pmid=17986351 |doi-access=free|bibcode=2007BMCEE...7..212K }}</ref> ''[[Biomphalaria glabrata]]'', another simultaneous hermaphrodite freshwater snail, does not exhibit sex-specific effects of partner novelty, and thus there is either no Coolidge effect in the species or no difference between the degrees to which the effect is expressed in the respective sexes.<ref name="Biomphalaria">{{cite journal|last1=Häderer|first1=Ines K.|last2=Werminghausen|first2=Johanna|last3=Michiels|first3=Nico K.|last4=Timmermeyer|first4=Nadine|last5=Anthes|first5=Nils|year=2009|title=No effect of mate novelty on sexual motivation in the freshwater snail ''Biomphalaria glabrata''|journal=[[Frontiers in Zoology]]|volume=66|page=23|doi=10.1186/1742-9994-6-23|pmc=2766376|pmid=19818155 |doi-access=free }}</ref>

== Means of sexual recognition for mates ==
Though there is not just a single reason why males will choose a novel partner, there have been experiments that show that the major determining factor for detecting a novel partner is olfactory preference.<ref name="Carr Hirsch Balazs">{{Cite journal|last1=Carr|first1=William J.|last2=Hirsch|first2=Jay T.|last3=Balazs|first3=Joann M.|date=1980-07-01|title=Responses of male rats to odors from familiar vs novel females|url=https://linkinghub.elsevier.com/retrieve/pii/S0163104780902216|journal=Behavioral and Neural Biology|volume=29|issue=3|pages=331–337|doi=10.1016/S0163-1047(80)90221-6|pmid=7417195|url-access=subscription}}</ref> An experiment using [[Laboratory rat|Long-Evans rats]], showed that odor played a major role in distinguishing the difference between a novel partner and familiar partner.<ref name="Carr Hirsch Balazs" /> In their experiment, Carr et al. paired each male rat with a female rat and allowed them to mate. Male rats were then tested for preference through the use of an apparatus that had two cylinders that were attached to their home cage and contained the familiar female and the novel female in each cylinder.<ref name="Carr Hirsch Balazs" /> Caps at the end of these cylinders prevented access to the females but had a hole in them to allow their odors to pass through to the male's cage.<ref name="Carr Hirsch Balazs" /> Before the testing phase, the females were removed, and then the caps were removed to allow the male to explore both cylinders.<ref name="Carr Hirsch Balazs" /> From this experiment, they found that males preferred the scent of the novel female.<ref name="Carr Hirsch Balazs" /> While these males did not have access to these females to demonstrate mating preferences, this odor preference is believed to reflect promiscuous behavior, and therefore be important to the male mating strategy.<ref name="Carr Hirsch Balazs" /> 

In an earlier experiment, also conducted by Carr et al., they found that, unlike male rats, female rats preferred the odor of a familiar partner rather than the odor of a novel partner.<ref>{{Cite journal|last1=Carr|first1=Williaw J.|last2=Demesquita-Wander|first2=Marla|last3=Sachs|first3=Sandra Rodde|last4=Maconi|first4=Pamela|date=1979-08-01|title=Responses of female rats to odors from familiar vs. novel males|journal=Bulletin of the Psychonomic Society|language=en|volume=14|issue=2|pages=118–120|doi=10.3758/BF03329417|issn=0090-5054 |doi-access=free}}</ref> 

Another study also examined not only olfactory preference but also what part of the brain targeted the olfactory preference.<ref name="Petrulis Eichenbaum" /> In this study, male hamsters were given lesions to either the [[hippocampus]] or the perirhinal-entorhinal cortex or received a sham treatment. Then the hamsters were allowed to mate with a female hamster until they became satiated. All subjects were then presented with two anesthetized females, one of whom was the female they had previously copulated with, while the other was a novel female.<ref name="Petrulis Eichenbaum" /> Hamsters with sham and hippocampal lesions investigated the anogenital region of the novel females for a significantly longer period in comparison to the familiar females.<ref name="Petrulis Eichenbaum" /> Males with lesions to the perirhinal-entorhinal cortex did not show a preference for either a familiar or novel female and spent a similar amount of time investigating the anogenital region of both females.<ref name="Petrulis Eichenbaum" /> The results from this study revealed that the perirhinal-entorhinal cortex region of the brain in golden hamsters is crucial for the recognition of familiar conspecifics and certain social behaviors.<ref name="Petrulis Eichenbaum">{{Cite journal|last1=Petrulis|first1=Aras|last2=Eichenbaum|first2=Howard B.|date=2003-01-01|title=The perirhinal–entorhinal cortex, but not the hippocampus, is critical for expression of individual recognition in the context of the Coolidge effect|url=https://www.sciencedirect.com/science/article/abs/pii/S0306452203006420|journal=Neuroscience|volume=122|issue=3|pages=599–607|doi=10.1016/j.neuroscience.2003.08.009|pmid=14622903|s2cid=24836670|url-access=subscription}}</ref> The conclusion from this experiment was also consistent in rats and monkeys, since damage to this region of the brain impaired standard recognition memory, which would suggest that the hippocampal region of the brain is not crucial in social behavior memory, but rather, the perirhinal-entorhinal cortex.<ref name="Petrulis Eichenbaum" /><ref>{{Cite journal|last1=Bannerman|first1=David M.|last2=Lemaire|first2=Martine|last3=Beggs|first3=Simon|last4=Rawlins|first4=John Nick P.|last5=Iversen|first5=Susan D.|date=2001-05-01|title=Cytotoxic lesions of the hippocampus increase social investigation but do not impair social-recognition memory|url=http://link.springer.com/10.1007/s002210100687|journal=Experimental Brain Research|volume=138|issue=1|pages=100–109|doi=10.1007/s002210100687|issn=0014-4819|pmid=11374076|s2cid=30186280|url-access=subscription}}</ref>

This effect of olfaction has also been observed in invertebrates such as flies.<ref name="olfaction Tan et al">{{Cite journal|last1=Tan|first1=Cedric K. W.|last2=Løvlie|first2=Hanne|last3=Greenway|first3=Elisabeth|last4=Goodwin|first4=Stephen F.|last5=Pizzari|first5=Tommaso|last6=Wigby|first6=Stuart|date=2013-11-22|title=Sex-specific responses to sexual familiarity, and the role of olfaction in Drosophila|journal=Proc. R. Soc. B|language=en|volume=280|issue=1771|pages=20131691|doi=10.1098/rspb.2013.1691|issn=0962-8452|pmid=24068355|pmc=3790479}}</ref> In a study conducted by Tan and colleagues, the role of olfaction in species recognition was examined using flies, ''Drosophila melanogaster,'' which processed a mutated ''Orco'' gene, which codes for a co-receptor that is important for olfaction.<ref name="olfaction Tan et al" /> The result of this type of mutation renders these flies unable to discriminate between phenotypically familiar (i.e., from the same family and/or environment) and phenotypically novel (i.e., unrelated and from a different environment) females.<ref name="olfaction Tan et al" /> When presented with a phenotypically familiar and phenotypically novel female, mutant flies did not show a preference towards either female, while wild-type flies (i.e., flies without the mutated ''Orco'' gene) did.<ref name="olfaction Tan et al" /> The results from this experiment suggest that the ''Orco'' gene is important in discriminating between mates, and suggests an important role of olfactory cues in phenotypic familiarity.<ref name="olfaction Tan et al" />

== Sexual satiety ==
Although males typically will prefer novel mates every time the opportunity is present, there is a physical limit to the sex drive.<ref name="Tlachi-López"/> An experiment performed on rats showed that when left to reproduce to sexual satiety, the motor ejaculatory behavior, intromission, and dislodging [[Mating plug|seminal plugs]] were all possible after multiple mates, but little to no sperm would be produced during ejaculation.<ref name="Tlachi-López"/> The experiment also concluded that males that reached satiety and non-satiety males both had the similar amounts of intromissions and time spent dislodging the seminal plug.<ref name="Tlachi-López">{{Cite journal|last1=Tlachi-López|first1=José L.|last2=Eguibar|first2=Jose R.|last3=Fernández-Guasti|first3=Alonso|last4=Angélica Lucio|first4=Rosa|year=2012|title=Copulation and ejaculation in male rats under sexual satiety and the Coolidge effect|url=https://www.sciencedirect.com/science/article/abs/pii/S0031938412001692|journal=Physiology & Behavior|volume=106|issue=5|pages=626–630|doi=10.1016/j.physbeh.2012.04.020|pmid=22564534|s2cid=13589780|url-access=subscription}}</ref> Another study performed on rats showed the same results, but found data that concluded that reaching optimal chances of impregnating their mates happened after resting for 15 days.<ref name="Lucio, Rodriguez-Piedracruz">{{Cite journal|last1=Lucio|first1=Rosa Angélica|last2=Rodríguez-Piedracruz|first2=Verónica|last3=Tlachi-López|first3=José L.|last4=García-Lorenzana|first4=Mario|last5=Fernández-Guasti|first5=Alonso|date=2014-05-01|title=Copulation without seminal expulsion: the consequence of sexual satiation and the Coolidge effect|journal=Andrology|language=en|volume=2|issue=3|pages=450–457|doi=10.1111/j.2047-2927.2014.00209.x|issn=2047-2927|pmid=24677685|s2cid=21301005|doi-access=free}}</ref> These experiments would suggest that one of the major limitations on the Coolidge effect is the physical boundaries of [[gamete]] production.<ref name="Tlachi-López"/><ref name="Lucio, Rodriguez-Piedracruz" />

== Potentiality in female animals ==
While the Coolidge effect is usually demonstrated by males—that is, males displaying renewed excitement with a novel female—the body of research into the phenomenon continues to explore the potentiality of the effect in females, specifically rodents.<ref>{{Cite journal|last1=Lisk|first1=Robert D.|last2=Baron|first2=Gregory|year=1982|title=Female regulation of mating location and acceptance of new mating partners following mating to sexual satiety: The coolidge effect demonstrated in the female golden hamster|url=https://www.sciencedirect.com/science/article/abs/pii/S0163104782908226|journal=Behavioral and Neural Biology|volume=36|issue=4|pages=416–421|doi=10.1016/s0163-1047(82)90822-6|pmid=7184502|url-access=subscription}}</ref><ref name="paced and non-paced">{{Cite journal|last1=Ventura-Aquino|first1=Elisa|last2=Fernández-Guasti|first2=Alonso|year=2013|title=Reduced proceptivity and sex-motivated behaviors in the female rat after repeated copulation in paced and non-paced mating: Effect of changing the male|url=https://www.sciencedirect.com/science/article/abs/pii/S0031938413002412|journal=Physiology & Behavior|volume=120|pages=70–76|doi=10.1016/j.physbeh.2013.07.006|pmid=23916997|s2cid=24611854|url-access=subscription}}</ref><ref name="Further evidence">{{cite journal|last1=Ventura-Aquino|first1=Elisa|last2=Baños-Araujo|first2=Jorge|last3=Fernández-Guasti|first3=Alonso|last4=G. Paredes|first4=Raúl|date=February 18, 2016|title=An unknown male increases sexual incentive motivation and partner preference: Further evidence for the Coolidge effect in female rats|url=https://linkinghub.elsevier.com/retrieve/pii/S0031938416300701|journal=Physiology and Behavior|volume=158|pages=54–59|doi=10.1016/j.physbeh.2016.02.026|pmid=26902417|s2cid=7695527|url-access=subscription}}</ref> Research examining female rats has lent its support, wherein female rats showed a higher incentive motivation for unknown males over ones they had just copulated with.<ref name="Further evidence" />

In a study conducted in 2013, researchers conducted an experiment to test if the Coolidge effect could be observed in female rats.<ref name="paced and non-paced" /> In their experiment, they assigned female rats to one of two conditions: paced or non-paced. In the paced condition, females were able to control the timing of copulation, while in the non-paced condition males regulated the timing of mating.<ref name="paced and non-paced" /> Females in the paced condition were placed into an arena that was divided into two compartments which contained holes that only the female could pass through.<ref name="paced and non-paced" /> The female was placed on one side of the divided arena, and the male was placed in the opposite side; this allowed the female to enter and exit the male's side depending on the circumstances, therefore regulating the timing of copulation.<ref name="paced and non-paced" /> In the non-paced condition, both the female and male rats were placed in an undivided arena and were allowed to mate.<ref name="paced and non-paced" /> In both conditions, females were exposed to a constant, familiar male followed by a novel male.<ref name="paced and non-paced" /> Their results found that females showed a significant increase in [[Proceptive phase|proceptive]] behaviours when a novel mate was present, but only if the female could regulate mating.<ref name="paced and non-paced" /> Repeated mating with the same male also resulted in a decrease in proceptivity, which is thought to suggest sexual satiety.<ref name="paced and non-paced" /> These results suggest that the Coolidge effect may also be present in female rats.<ref name="paced and non-paced" />

Lester and Gorzalka developed a model to determine whether or not the Coolidge effect also occurs in females.<ref name="Lester" /> Their experiment, which used hamsters instead of rats, concluded that it does occur to a lesser degree in females, where the evolutionary advantage of mating with multiple partners is less straightforward.<ref name="Lester" /><ref name="Biopsych" /> It is possible that the presence of the Coolidge effect in females could serve to optimize the female's [[reproductive success]], and prevent mating with a sterile male. Mating with multiple males may reduce the probability that the female's gametes will not be successfully fertilized.<ref name="Lester" />

==See also==
*[[Adultery]]
*[[Adultery laws]]
*[[Bruce effect]]
*[[Casual sex]]
*[[Extramarital sex]]
*[[Fornication]]
*[[Hookup culture]]
*[[Premarital sex]]
*[[Promiscuity]]
*[[Swinging (sexual practice)|Swinging]]

==References==
{{reflist|30em}}

{{Calvin Coolidge|state=collapsed}}
{{Ethology}}
{{Evolutionary psychology}}

[[Category:Sexual attraction]]
[[Category:Jokes]]
[[Category:Ethology]]
[[Category:Mammalian sexuality]]
[[Category:Calvin Coolidge]]
[[Category:Evolutionary psychology]]