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Hoekom is 'n penis 'n orgaan?

Hoekom is 'n penis 'n orgaan?


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Volgens Wikipedia 'n "'n Orgaan is 'n groep weefsels met soortgelyke funksies". Ek weet niks van anatomie nie maar dit lyk nie vir my of 'n penis iewers afgebaken kan word om 'n "groep" te vorm nie. Daarom verstaan ​​ek nie hoekom 'n penis as 'n orgaan beskou word nie.

Kan jy dit vir my verduidelik?


Om eerlik te wees, dit is 'n verskriklike definisie deur Wikipedia.

Merriam-Webster definieer 'n orgaan as:

'n gedifferensieerde struktuur (soos 'n hart, nier, blaar of stam) wat uit selle en weefsel bestaan ​​en een of ander spesifieke funksie in 'n organisme verrig

of

liggaamsdele wat 'n funksie verrig of in 'n aktiwiteit saamwerk

Die belangrike kenmerk van 'n orgaan is nie die weefsels nie soortgelyke funksies het maar dat die weefsels saam 'n funksionele geheel uitmaak wat een of ander einddoel bereik.

Vir die penis bestaan ​​dit uit verskeie weefsels met verskillende funksies:

(van https://www.ncbi.nlm.nih.gov/books/NBK525966/figure/article-20668.image.f1/ - oorspronklik van Gray's Anatomy)

Die verskillende weefsels wat hier afgebeeld word: die veselagtige omhulsel, die corpora cavernosa, die septum pectiniforme, die uretra en bloedvate, die senuweeweefsel in die vel: al hierdie weefsels het verskillende individuele funksies: struktureel, erektiel, dra urine of semen, ens. .

Die sleutel wat hulle verenig in 'n orgaan is dat die funksies van die penis by die organisme vlak (hoofsaaklik seksuele funksie) word nie deur enige van hierdie weefsels alleen bedien nie, maar eerder deur hul kombinasie in 'n volledige struktuur: 'n orgaan.

Uiteindelik is orgaandefinisies ietwat op opinie gebaseer: mense is klonters en splitters, so jy kan teenstrydige definisies vind waarvoor groeperings van weefsels verskillende organe weerspieël, maar ek dink volgens die meeste standaarde sal jy vind dat die penis as 'n afsonderlike orgaan beskou word, geaffilieer met maar onderskei van die primêre geslagsorgane en geassosieerde kliere.


Anatomie van die penis, meganika van omgang

Hierdie bladsy bied inligting waarvan die meeste ouers nie bewus is wanneer hulle die besnydenisbesluit neem nie. Dokters verskaf gewoonlik nie hierdie inligting nie.

As jy jonger as 18 is, beveel ons aan dat jy hierdie inligting met jou ouers deel en bespreek.

Vir 'n verdere blik op hierdie anatomie, insluitend foto's, besoek Circumstitions (Hugh Young). Hugh se webwerf bevat ook 'n uitstekende animasie om terugtrekking te illustreer.

Dr John R. Taylor, mede-outeur van twee mediese anatomiese referate oor die voorhuid, verduidelik die jongste navorsing op die Ridged Band-webwerf.

Fig. 1. Ongeskonde volwasse penis

Hierdie illustrasie verteenwoordig 'n gemiddelde normale volwasse menslike penis. Die kop van die penis (glans) het 'n bedekking, wat die voorhuid (voorhuid) genoem word. Hierdie bedekking vou op homself in en vorm 'n dubbellaag. Die voorhuid is nie 'n 'flap' vel aan die einde van die penis, en dit is nie 'nuttelose' of 'oortollige' vel nie.

Daar is 'n mate van natuurlike variasie in die lengte van die voorhuid, wat dikwels 'n bietjie meer of minder van die glans bedek as wat geïllustreer word.

In 'n gemiddelde besnyde volwasse man, sal die area van die vel wat ontbreek as gevolg van penisverminderingschirurgie, wanneer dit regop en ontvou is, ongeveer drie by vyf duim meet, of 'n bietjie kleiner as 'n poskaart. Dit is ongeveer die helfte van die totale vel van die penis.

Strukture van die penis

  • Die buitenste voorhuidlaag is 'n voortsetting van die vel van die skag van die penis.
  • Die binneste voorhuidlaag is nie net "vel" nie, maar mukoktane weefsel van 'n unieke tipe wat nêrens anders op die liggaam voorkom nie.
  • Die geriffelde band is die raakvlak (verbinding) tussen die buitenste en binneste voorhuidlae. Wanneer die penis nie regop is nie, trek dit styf om die voorhuid se opening te vernou. Tydens oprigting vorm die geriffelde band rante wat reg rondom gaan, ongeveer halfpad af in die skag.
  • Die rooierige of perserige glans of glans penis (kop van die penis) is glad, blink, klam en uiters sensitief.
  • Die frenulum, of frenum, is 'n verbindingsmembraan aan die onderkant van die penis, soortgelyk aan dié onder die tong.

Fig. 2. Ongeskonde penis (versteekte strukture getoon).


Wat is die penis?

Die penis is die manlike geslagsorgaan en bereik sy volle grootte tydens puberteit. Benewens sy seksuele funksie, die penis dien as 'n kanaal vir urine om die liggaam te verlaat sowel as semen tydens ejakulasie. Normaalweg in 'n slap toestand, sal die penis regop word sodra dit seksueel opgewek is.

Ereksie is 'n fisiologiese verskynsel waarin die penis stewig word, vol en vergroot word, wat koïtus vergemaklik. Wanneer die penis ten spyte van seksuele stimuli nie regop word nie, kan dit 'n moontlike erektiele disfunksie beteken, wat verskeie oorsake het wat wissel van sielkundig tot fisiologies.

Uiteindelik vind ejakulasie plaas wanneer die man klimaks bereik en die semen ejakuleer. Dit kan die gevolg wees van orale seks, omgang - hetsy vaginaal of anaal of masturbasie. In die praktyk van tantriese seks, die orgasme kan vertraag word of gebeur sonder ejakulasie. Dit staan ​​ook bekend as 'n droë orgasme.

Gemiddelde penisgrootte

Die gemiddelde penisgrootte wissel regoor die wêreld tussen 12 en 16 sentimeter terwyl hy regop is.

Dit is interessant om te noem dat daar groot variasies in grootte is wanneer dit kom by die slap penis.

So, wat is die grootste penis wat ooit gemeet is? Volgens die Guinness Book of Records word daardie rekord gehou deur 'n Mexikaanse man met 'n 48 sentimeter penis, en in die tweede plek, 'n Amerikaanse akteur en skrywer met 'n 34 sentimeter penis.


Hoe menslike voortplanting werk

Van buite af het die mannetjie twee sigbare geslagsorgane, die testes (of testikels) en penis. Die testes is die primêre manlike geslagsorgane deurdat hulle sperm maak en testosteroon produseer. Die sperm is die manlike geslagsel, of gameet, en elke testikel produseer meer as 4 miljoen nuwe sperm per uur [bron: Angier]. Testosteroon is die hormoon wat manlike sekondêre geslagskenmerke soos gesig- en skaamhare, verdikte stembande en ontwikkelde spiere veroorsaak.

Die testes word buite die hoofgedeelte van die mannetjie se liggaam gehuisves, in 'n sak wat die skrotum genoem word. Hierdie ligging is belangrik, want vir die sperm om behoorlik te ontwikkel, moet hulle by 'n temperatuur ongeveer twee grade koeler as normale liggaamstemperatuur gehou word. Dit neem sperm ongeveer 4 tot 6 weke om volwasse te word, wat hulle doen terwyl hulle van elke testis na 'n opgerolde buis op die buitenste oppervlak van elke testis beweeg wat die epididimis genoem word. Sperm, wat dikwels in voorkoms met paddavissies vergelyk word, gebruik hul sterte om te reis, terwyl die kop die genetiese materiaal bevat.

Die penis is gemaak van sagte, sponsagtige weefsel wat kan uitsit of saamtrek. Wanneer 'n man seksueel opgewonde raak, word die penis vol bloed, wat veroorsaak dat die sponsagtige weefsels styf word en die penis regop word. Hierdie regop toestand maak dit maklik om die penis binne 'n vrou se vagina te plaas tydens seksuele omgang. Tydens seks is die manlike voortplantingstelsel steeds aan die werk, wat die sperm toerus met die hulp wat hulle nodig het om 'n eiersel te bevrug. Kom meer te wete oor hierdie proses op die volgende bladsy.


Spiere wat met die penis geassosieer word

  • 'n Enkele spier wat die wortel en ventrale oppervlak van die penis sowel as die bulboretrale kliere bedek (skakel na kliere bladsy)
  • Die funksie van hierdie spier is om die ekstrapelviese uretra van sperm leeg te maak op 'n soortgelyke manier as die urethralis spier wat die bekken uretra leegmaak.

Ischiocavernosus spiere

  • Gepaarde spiere geleë aan die wortel van die penis.
  • Verbind die penis aan die ischiale boog van die bekken.

Retractor penis Spiere

  • Gepaarde spiere wat op die kaudale werwels ontstaan ​​en op die ventrolaterale oppervlaktes van die penis invoeg.
  • Handhaaf die sigmoïede buiging van die fibroelastiese penis wanneer die spiere saamgetrek word.
  • Wanneer die spiere ontspanne is, steek die penis deur die voorhuid uit terwyl die sigmoïedbuiging ontbuig.

Hoe werk 'n penisoorplanting?

120808-O-ZZ999-003 SIHANOUKVILLE, Kambodja (8 Aug. 2012) HOPE Wêreldwye vrywilliger Dr. Cornelia Haner, links, en Kapt. William Brunner doen saam 'n operasie as 'n inligtingsuitruiling aan boord van die Military Sealift Command-hospitaalskip USNS Mercy (T) -AH 19) tydens Pacific Partnership 2012. Pacific Partnership, 'n jaarlikse US Pacific Fleet humanitêre en burgerlike bystandsending wat nou in sy sewende jaar is, bring Amerikaanse militêre personeel, gasheer- en vennootnasies, nie-regeringsorganisasies en internasionale agentskappe bymekaar om sterker verhoudings te bou en ontwikkel rampreaksievermoëns regdeur die Asië-Stille Oseaan-streek. (Foto deur Kristopher Radder/Vrygestel) KRISTOPHER RADDER

Soldate gee baie op wanneer hulle hul land’re verdedig. Vir diegene wat slagoffers word van skerpskutters en plofstof, en wat oorleef, kan dit beteken dat hulle 'n ledemaat of 'n orgaan of hul sig verloor. 'n Dikwels onuitgesproke besering is die verlies van geslagsdele. Die oorloë in Irak en Afghanistan, waar padbomme 'n konstante bedreiging is, het meer as 1 300 Amerikaanse soldate op hierdie manier vermink gelaat. Maar 'n span dokters en wetenskaplikes by Johns Hopkins Medicine is nou gereed om te help—deur die eerste penisoorplanting in die VSA uit te voer (Soortgelyke maar minder uitgebreide prosedures is in China uitgevoer op pasiënte wat dele van hul penis verloor het in ongelukke en in Suid-Afrika om gebroke besnydenis te herstel).

Daar is nie net een rede hoekom penisoorplantings so lank geneem het om in die VSA te kom nie. Deel daarvan is waarskynlik dat die oorplanting steeds eksperimenteel is–die pasiënt in China moes die prosedure omgekeer kry nadat sy liggaam die oorplanting verwerp het. Vir baie in die mediese instelling is dit 'n onnodige risiko vir pasiënte wat reeds soveel fisiese trauma ondergaan het - 'n pasiënt se lewe is nie in gevaar as hy nie 'n penis kry nie, soos hy sou wees as hy 'n nuwe lewer of 'n nier. Baie dokters dink die herstel van geslagsdele is medies (en eties) verkeerd, dat dit nie die moeite werd is om die pasiënt se immuunstelsel vir die res van sy lewe te kompromitteer nie.

Arthur Burnett, 'n uroloog en direkteur van die seksuele medisyne-genootskapprogram by Johns Hopkins Medicine wat op die chirurgiese span is, en sy kollegas, stem nie saam nie. “Ons argumenteer dat hierdie gedeeltes van mense se liggame in 'n ander lig oorweeg moet word,” sê hy. “Baie van hierdie ouens is 25 en hul geslagsdele is weg. Hulle wil net weer heel wees.”

Die Johns Hopkins-span is nou enige dag bereid om 'n skenkerpenis in te plant op 'n jong soldaat wat sy penis verloor het in 'n Afghaanse bomontploffing. Wat hulle’re wag vir is 'n skenker, of spesifiek vir die familie van 'n pas oorlede man (wat vrywillig vir orgaanskenking) om die onortodokse prosedure goed te keur. Anders as ander orgaanskenkings - wat bedoel is om lewens te red - word penisoorplantings as kosmeties beskou en dus opsioneel. Die skenker moet, benewens die gewone oorplantingsvereistes soos bypassende bloedgroep, ook dieselfde velkleur hê en binne vyf of 10 jaar oud van die ontvanger gewees het. Eers dan kan die operasie voortgaan.

Hoe sal dit werk?

Eerstens, om in aanmerking te kom vir 'n oorplanting, moet 'n gewonde soldaat ongeskonde bekkenbene hê—”Soos 'n fondament vir 'n huis,” sê Burnett. Die eerste ontvanger voldoen aan hierdie vereiste, so ook 60 ander gewonde veterane wat Johns Hopkins vir die operasie goedgekeur het. Nie een van hulle kom in aanmerking vir rekonstruktiewe chirurgie waarin die penis herbou word van weefsel wat van elders in die liggaam geneem is nie, dikwels van hul voorarms–hulle’ve verloor te veel weefsel van die penis vir dokters om dit te herbou.

Sodra 'n skenker gevind is, het dokters net 'n paar uur om die man se penis en bekkenspiere te verwyder (wat ooreenstem met die grootte van die gewonde soldaat se bekkenarea) en dit vinnig na die operasiesaal te vervoer. Burnett en 'n span van meer as 20 mediese spesialiste sal reeds die soldaat voorberei het, vel, littekens en spiere weggesny het en tientalle bloedvate, senuwees en die uretra, waardeur urine en semen vloei, blootgelê het. Soos in ander orgaanoorplantings, moet chirurge al hierdie aan die skenker se weefsel steek, maar 'n penisoorplanting is tegnies meer kompleks omdat die verbindings so baie en klein is. Die prosedure sal volgens een van die Johns Hopkins-chirurge ongeveer 12 uur duur.

Penis oorplanting

Elkeen van die 60 penisoorplantings wat die hospitaal beplan om uit te voer, sal uniek wees, afhangende van die pasiënt se besering en sy anatomie. Chirurge moet die regte hoeveelheid weefsel van die skenker se buik verwyder om in te vul wat die ontvanger ontbreek. Testikels kan nie weer geheg of vervaardig word nie. As 'n beseerde veearts testikels ontbreek, kan hy hormoonvervangingsterapie benodig om die testosteroon wat hulle gewoonlik afskei te vervang. Verder, die pasiënt’s liggaam kan die oorplanting verwerp. Om daardie risiko te verminder, sal hy 'n infusie van die skenker se beenmurg ontvang en sal immuunonderdrukkers vir die res van sy lewe neem.

Selfs dan, daar’s geen waarborg dat die penis ten volle funksioneel sal wees nie, veral wanneer dit by seks kom. “Ons hoop ons kan dinge hersaamstel op 'n manier waar mans 'n ware ereksie kan kry,” sê Burnett. “Maar ons kan vind dat ons alles weer bymekaar gesit het en dat hulle dalk steeds nie kwaliteit ereksies kry nie. Dit vereis dalk hulp, soos Viagra, of sommige ouens sal dalk moet terugkom om 'n penisprostetiese te ontvang.” 'n Penisprostetiese is 'n opblaasbare sintetiese toestel wat chirurgies in die kamers van die penis ingeplant word. ’n Man met die inplanting kan vloeistof inpomp wanneer hy ook al ’n ereksie wil hê. Burnett doen elke jaar 80 van hierdie inplantings by mans wat aan erektiele disfunksie ly.

Wat van die emosionele impak?

Afgesien van die mediese uitdagings, kan die sielkundige nagevolge van 'n penisoorplanting moeilik wees. "Ons moet seker maak dat pasiënte gereed is om vorentoe te beweeg, dat hulle goed geraadpleeg word, dat die pasiënt bereid is om sy liggaam te laat rekonstrueer," sê Burnett. "Dit is 'n verandering wat soms vir 'n pasiënt of 'n gade moeilik kan wees om te aanvaar. Hulle het gemeenskap met ’n ander man se penis, as jy daaraan dink.” Om dit teë te werk, sal pasiënte sielkundige berading voor en na die operasie nodig hê en moet ondergaan word.

Terwyl die mediese instelling blykbaar huiwerig is om vir hierdie prosedures te pleit, is die publiek geneig om hierdie behoeftes te verstaan, het Burnett bevind. Hierdie mans wil vaders wees, intiem met hul beduidende ander wees. Hierdie operasie kan dit laat gebeur. As daar iets is, is hul begeerte vir die oorplanting 'n bewys van hoeveel 'n mens sal doen om weer normaal te voel.

Burnett weet nie of die skenker vir sy eerste oorplanting oor 'n paar dae of 'n paar maande sal opdaag nie. Maar sy chirurgiese span is gereed–hulle’ve uitgevoer skyn prosedures op kadawers, Burnett sê, en het gedoen droë lopies en repetisies. “Dit kan moontlik baie suksesvol wees,” sê hy. Hy hoop dat ander in sy vakgebied eendag die belangrikheid van hierdie operasie sal erken, en dat al 60 veterane wat ingeskryf het so gou moontlik hul oorplantings sal kry.

“Hopelik gaan ons vorentoe beweeg,” sê Burnett. "Ek hoop dat, met hierdie kommunikasie, selfs mediese professionele mense sal aanvaar dat dit iets is wat betekenisvol is vir pasiënte."


Relevante genitale eienskappe om te ondersoek

Genitalieë kan baie komplekse morfologieë hê, en baie van hul kenmerke kan tydens kopulasie onder seleksie wees. Sommige studies ondersoek lengte en breedte van manlike geslagsdele om hul effek op fiksheid te bepaal (hersien in Brennan en Prum 2015), maar die variasie van geslagsdele kom langs baie morfologiese asse voor wat hul komplekse vorms openbaar. Die 3-D struktuur van manlike en vroulike geslagsdele is bestudeer in waterjuffers, wat groot kompleksiteit openbaar (McPeek et al. 2009). Rowe en Arnqvist (2012) het vorm van genitale morfologie in water striders ontleed in vergelyking met nie-genitale eienskappe en tot die gevolgtrekking gekom dat die kompleksiteit van vormvariasie groter is in genitale eienskappe, en dus dat genitale studies vorm eerder as net grootte moet ondersoek.

Min studies het vormvariasie by insekte in ag geneem, wat onthul dat komplekse aspekte van vorm 'n integrale deel van fiksheid is. In Onthophagus kewers het eksperimentele evolusie onder 'n monogame versus promiskue paringsregime aan die lig gebring dat die vroulike geslagsgate waar die parameres (punt van die aegagus) anker, kleiner en moeiliker word om te bereik onder hoë seksuele seleksie, terwyl die manlike aedagus vorm verander by mannetjies Simmons et. al 2009 (Simmons en Garcia-Gonzales 2011). ’n Vergelykende studie van geslagsvorm in miskruiers het bewyse getoon vir ko-evolusie tussen die paramere vorm van mannetjies, en vroulike pygidiale flapmorfologie (Macagno et al. 2011). Ander studies het die vormvariasie by mans en wyfies beskryf met geen verdere ontleding van funksionele gevolge nie (bv. Phyllophaga hirticulata, Polihronakis 2006).

Benewens vorm, kan baie ander genitale eienskappe moontlik vroulike morfologie en geslagsfunksie beïnvloed en betrokke wees by ko-evolusionêre prosesse. Die penis in baie spesies is bedek met epiteel- en eksoskeletale uitbreidings wat stekels, rante, flappe, kelkies en vele ander kan insluit. Met die uitsondering van stekels, is die funksie van hierdie uitwerkings nie in diepte ondersoek nie. Stekels op die oppervlak van die intromitterende orgaan penetreer waarskynlik of interaksie op een of ander manier met die vroulike vaginale wand. By primate en knaagdiere lyk stekels noodsaaklik vir penis sensoriese terugvoer, en wanneer die stekels eksperimenteel verwyder word, neem mans langer om intromissie te bereik en om te ejakuleer (Dixson 1986). Dit kan wees omdat die stekels heen en weer teen die vroulike vaginale wand vryf tydens stoot, en wanneer stekels uitgeskakel word, word hierdie stimulus verminder (Dixson 1986). Die verlies van penisstekels by mense het moontlik langer kopulasieduur tot gevolg gehad (McLean et al. 2011).

Stekels kan ook mans help om 'n genitale slot te vestig en die duur van die paring te verleng as wat optimaal is vir die wyfie. Byvoorbeeld by slange kan mans met eksperimenteel verwyderde basale stekels van hul hemipene intromissie bereik, maar kopulasieduur is aansienlik korter as vir mannetjies met ongeskonde stekels (Friesen et al. 2014). Stekels kan ook funksioneer om direkte skade aan die vroulike voortplantingskanaal te veroorsaak wat 'n vertraging in herparing veroorsaak (Stockley 2002). Ander funksies kan die stimulering van ovulasie by wyfies insluit, soos in sommige soogdiere voorgestel is (Felids Zarrow en Clark 1968), of die verwydering van sperm uit vorige parings soos in Odonates (Cordero-Rivera en Córdoba-Aguilar 2010). In 'n ander artikel in hierdie uitgawe ondersoek ons ​​die rol van penisstekels in soogdiere (Orr en Brennan 2016). Ons vind bewyse dat stekels tipies teenwoordig is in spesies met groter oorblywende testesgrootte, wat daarop dui dat hierdie stekels geassosieer word met meer intense seksuele seleksie.

Wyfies het duidelik saamgegroeide reaksies op die stekels wat in manlike intromitterende organe gevind word. By saadkewers (Callosobruchus) het wyfies byvoorbeeld verdikte epiteel in hul kopulasiekanaal by spesies waar mannetjies meer stekelrige aedaguspunte het (Rönn et al. 2007), miskien om die vroulike mukosa te beskerm tydens paring. Eksperimentele evolusie het egter getoon dat onder gedwonge monogamie die manlike stekels verminder word, maar die vroulike kanaal bly dik (Cayetano et al. 2011). Hierdie oënskynlike gebrek aan 'n ko-evolusionêre reaksie kan 'n lae koste van die instandhouding van 'n verdikte oviduk op wyfies weerspieël (Cayetano et al. 2011). In hierdie stelsel is daar egter duidelike bewyse dat mans met langer stekels hoër fiksheid het (Hotzy et al. 2012).

Die morfologie van die glanspenis by sommige gewerwelde diere is waarskynlik ook 'n relevante kenmerk wat selde ondersoek is. Die glans of penispunt kan uitgebrei en veranderlik oor groepe heen wees (Eberhard 1985). Die glans kan 'n verskeidenheid funksies dien, van die vestiging van 'n geslagslot (bv. by skilpaaie waar mannetjies nie maklik aan wyfies kan vashou tydens paring nie), tot die suksesvolle oordrag van die ejakulasie na die wyfie te verseker deur 'n seël met haar kloakkamer te vorm ( bv. in krokodille, Johnston et al. 2013 Moore et al. 2016). In spesies waar 'n genitale slot glansmorfologie kan aandryf, kan die glans breër as die skag wees, en veral uitgebreide koppieagtige vorms ontwikkel (skilpaaie en krokodille), terwyl in spesies waar die penispunt spermoordrag nader aan die baarmoeder vergemaklik, penispunt kan 'n meer filiforme vorm hê soos by baie hoefdiere en sommige seesoogdiere. Hierdie punt kan soms spiraalvormig wees of ten minste 'n bietjie krul hê, soos byvoorbeeld gesien in die vark (Sus domesticus). Hierdie vorm kan die wyfie stimuleer deur teen haar servikale rante te vryf, en die afwesigheid van hierdie stimulasie lei tot dramaties laer dragtigheidsyfers (Bonet et al. 2013).

Ten slotte is 'n penisbeen of baculum teenwoordig in baie soogdiere, maar afwesig in ander, wat bewyse toon van 'n dinamiese evolusionêre geskiedenis (Schultz et al. 2016). Die baculum is veronderstel om baie funksies te dien wat meganiese ondersteuning tydens kopulasie insluit, die fasilitering van intromissie, stimulering van die vrou, ens. (Paterson en Thaeler 1982 Larivière en Fergusson 2002 hersien in Schultz et al. 2016). Die meeste van hierdie hipoteses is nog nie formeel getoets nie, en verdere kennis oor kopulerende meganika is nodig om dit te doen.

Ko-evolusie tussen vorm en funksie

Manlike morfologiese genitale kenmerke kan 'n vroulike reaksie ontlok wat veranderinge in haar kopulatoriese fisiologie en gedrag insluit, sowel as ander morfologiese kenmerke as vorm. Hierdie gevarieerde vroulike reaksies kan op hul beurt bepaalde genitale kenmerke van mans selekteer, wat tot ko-evolusionêre siklusse lei. Vroue kan byvoorbeeld sensoriese strukture ontwikkel om genitale kenmerke van maats te onderskei (soos bepleit deur Eberhard 1985, 1996). Die vermoë van wyfies om stimuli van die mannetjies aan te voel is waarskynlik deurslaggewend in die vorming van manlike morfologie en omgekeerd. Vaginale innervasie is welbekend en bestudeer in mense (bv. Song et al. 2009), rotte (bv. Peters et al. 1987), en hoender en ander (bv. Gilbert en Lake 1963 Giraldi et al. 2004). Die bevordering van ons begrip van of en hoe vroue verskille tussen kenmerke van manlike geslagsdele kan aanvoel, sal ondersteunende bewyse bied vir 'n meganisme van kriptiese vroulike keuse wat tydens kopulasie kan funksioneer soos voorgestel deur Eberhard (1985 1996).

Wyfies kan ook morfologiese kenmerke ontwikkel om hulself te weerstaan ​​of te beskerm teen potensiële skade aan hul eierleier (bv. verdikte epiteel, anti-gryp toestelle, ens.). Die afwesigheid van sulke openlike beskermende morfologiese kenmerke dui egter nie daarop dat teenmaatreëls vir manlike manipulasie of skade by vroue afwesig is nie (teenoor Eberhard 2004a, b 2006). Wyfies kan meer subtiele maniere gebruik om beheer oor paring te herwin, insluitend gedrags- en fisiologiese veranderinge tydens paring. Vroue kan byvoorbeeld op gedrag of fisiologie staatmaak om te verhoed dat mans 'n voordeel kry tydens kopulasie (bv. Arnqvist en Rowe 2005). Rooikantige kousbandslang (Thamnophs sirtalis) mannetjies het 'n basale ruggraat in hul hemipene wat kopulasieduur verleng wat groter kopulatoriese proppe produseer, soos gedemonstreer deur ruggraatablasie-eksperimente (Friesen et al. 2014). Wyfies gebruik gedrag (liggaamsrolle) en fisiologie (druk hul vaginale sakspiere) om die duur van kopulasie en dus die grootte van die kopulasieprop te beperk, soos gedemonstreer deur eksperimente wat die vroulike vagina verdoof (Friesen et al. 2014 in pers). Na narkose het wyfies langer kopuleer en meer sperm in hul ovidukte gehad ná paring (Friesen et al. in druk). Kopulasieduur word ook verleng wanneer die vagina van vroulike marmosette verdoof word met plaaslike verdowing (Dixson 1986).

Die funksie van manlike genitale morfologie kan ook beïnvloed word deur vroulike gedrag by guppies, waar die kloue aan die einde van die manlike gonopodium funksioneer om tot drie keer meer sperm oor te dra wanneer met onontvanklike maar nie ontvanklike wyfies gepaar word (Kwan et al. 2013) ). Ko-evolusie vind dus nie altyd tussen morfologiese strukture plaas nie, maar kan tussen morfologiese strukture en kopulasie, gedrag en fisiologie plaasvind.


Die angswekkende geslagsorgane van manlike skilpaaie

Van die baie onaangename en onakkurate stereotipes wat oor diere in die populêre bewussyn gehandhaaf word, is een van die mees frustrerende wat ek noem "old man turtle". Dit is die idee dat skilpaaie (waarmee ek bedoel, alle lede van Testudines) soos afgeleefde, swak, benerige ou mannetjies is wat in 'n boks gehuisves word. Dit is nie regverdig nie, en dit is glad nie akkuraat nie.

Hier kyk ons ​​na net een aspek van skilpadanatomie. In ooreenstemming met die dom "old man turtle" idee, sou populêre kultuur dit hê dat skilpaaie swak, slap, mal organismes is met dowwe sosiale lewens, belemmerde en skaars funksionele interne organe en ondermaatse geslagsorgane. Wel, wag 'n verdomde minuut ...

Waarskuwing: die volgende artikel kan as ongeskik beskou word om deur minderjariges, of enigiemand wat deur die uitheemse penivaginale kobra in Prometheus. want daardie ding is mak in vergelyking met die penis van 'n skilpad.

Glo dit of moenie, skilpaaie is gruwelik goed toegerus, en as die gedagte om meer oor die geslagsdele van hierdie o-so-verrassende reptiele te leer, jou nie aanspreek nie, kyk nou weg. Laaste waarskuwing. Ok, hier gaan ons.

Hidrouliese intromitterende manlike geslagsorgane - 'n verskeidenheid gewilde, alternatiewe name is beskikbaar - is nie uniek aan soogdiere onder vierpotiges nie. Hulle is ook teenwoordig in plaveisel, archosaurs en skilpaaie. Hierdie filogenetiese verspreiding het daartoe gelei dat sommige skrywers tot die gevolgtrekking gekom het dat hierdie organe teenwoordig was in amniote gemeenskaplike voorouers. In hul besonderhede is die organe van hierdie groepe egter almal heeltemal anders en eintlik gevorm uit nie-homologe weefsels. Soos aangetoon deur Kelly (2002), het manlike intromitterende organe dus by meer as een geleentheid onafhanklik onder viervoetpote ontstaan. Die skilpadpenis, byvoorbeeld, bevat slegs een vaskulêre erektiele liggaam en ontwikkel op die ventrale oppervlak van die cloaca, terwyl die soogdierpenis twee erektiele liggame bevat en afkomstig is van nie-kloakale weefsel. In die diagram hierbo – van Kelly (2002) – word die penisse van skilpaaie, voëls, soogdiere en slange in dwarssnit vergelyk. Let op hoe verskillend die organe is in hul deursneestruktuur.

Penis of fallus? Ahh, keuse.

'n Intromitterende orgaan van hierdie soort word tipies 'n 'penis' genoem. Sommige navorsers stel voor dat hierdie term tot soogdiere beperk moet word en dat die organe van skilpaaie en archosaurs wat ooreenstem met mekaar, eerder fallusse genoem moet word (Isles 2009). Ander argumenteer egter dat daar niks omtrent die term 'penis' is wat beteken dat dit op hierdie manier beperk moet word nie, en daar is inderdaad niks besonders aan die soogdierpenis as ons dit vergelyk met die intromitterende organe van ander viervoetiges nie. . Gevolglik noem sommige bioloë wat oor intromitterende organe publiseer konsekwent al hierdie organe penisse (bv. Kelly 2002, 2004, McCracken 2000). Bioloë het beslis nie in die verlede 'n probleem gehad om die term 'penis' vir die skilpadorgaan te gebruik nie (bv. Zug 1966).

Hoe om 'n skilpadpenis te bou

Die skilpadpenis is, soos dié van 'n soogdier, 'n hidrouliese silinder wat deur vloeistof verswelg word en relatief bestand is teen buiging wanneer dit regop is. Sy enkele erektiele liggaam is verdeel in 'n kollageenagtige corpus fibrosum en 'n hoogs gevaskulariseerde, uitbreibare corpus spongiosum. Soos 'n skilpad se penis opblaas, kan sy lengte met byna 50% toeneem, sy breedte met 75% en sy diepte met 10%. Selfs 'n onopgeblaasde penis - weggesteek in die cloaca - is groot. Meer oor die kwessie van grootte later.

'n Paar lang retractorspiere strek oor die grootste deel van die lengte van die orgaan se dorsale oppervlak, en heg binne die liggaamsholte aan die lumbale werwels. Wanneer dit in rus is, word die penis verdubbel op homself binne die cloaca, en dit is die sametrekking van die terugtrekspiere wat veroorsaak dat dit ontdubbel en uitsteek (Gadow 1887). Tydens ereksie kom die penis eers na vore en wys agtertoe "as die grootte en spanning verhoog die penis buig ventraal en dan effens anterior" (Zug 1966, p. 4). Bishop & Kendall (1929) het bevind dat skilpadpenis-retractorspiere "fisiologies robuust" en van "tekstreme uithouvermoë" was.

Kollageenvesels versterk die peniswand en is óf langs, óf loodreg op, die orgaan se lang-as gerangskik, en in hierdie opsig is die skilpadpenis oppervlakkig soortgelyk aan 'n soogdier. Terwyl die soogdierpenis egter net een laag langasvesels en een laag loodregte vesels het, het die wande van die skilpadpenis veelvuldige lae van hierdie vesels. Hierdie reeks verstywende kollageenvesels stem egter steeds baie ooreen in skilpaaie en soogdiere: soos opgemerk deur Diane Kelly in die titel van haar 2004 referaat " Skilpad- en soogdierpenisontwerpe is anatomies konvergent" (Kelly 2004). Die sterk ooreenkoms wat in die erektiele organe van hierdie filogeneties uiteenlopende groepe waargeneem word, dui daarop dat daar min funksionele oplossings is wat die evolusie van silindriese, opblaasbare intromitterende organe toelaat (Kelly 2002, 2004). Kelly is bekend vir haar vorige werk, wat wyd in die media gerapporteer is, oor penis-anatomie in gordeldiere (Kelly 1997) wat as paddoders naby Tallahassee, Florida, versamel is. Haar publikasies kan gratis van haar tuisblad hier verkry word.

Wat die algehele makrostruktuur betref, bestaan ​​die skilpadpenis uit 'n skag en 'n duidelike kop, of glans, wat tipies donkergrys, pers of swarterig is.

'n Lang seminale groef, aan beide kante omring deur verhewe rante (genoem seminale rante), strek vanaf die uretrale opening af by die basis van die penis tot by die glans. Dit is duidelik dat ons hier praat van 'n blootgestelde groef, nie 'n ingeslote binnebuis soos dié wat by soogdiere voorkom nie. Soogdiere is eintlik ongewoon in die besit van 'n ingeslote buis in die penis: seminale groewe is die norm wanneer ons na die organe van akkedisse en slange, krokodille en voëls kyk.

Die seminale rante in 'n skilpad is die grootste reg langs die glans naby die glans, hulle is aan beide kante omring deur splete, of sinusse. Anterior en posterior pare sinusse is ook teenwoordig op die boonste oppervlak van die glans. Hierdie strukture, wat met mobiele velvoue geassosieer word, gee die glans 'n besliste vreemdelingagtige, onbekende voorkoms vir ons primate. Dit lyk asof skilpaaie in staat is om die bewegings van die rante rondom die seminale groef sowel as die openinge en voue op die kop van die glans te beheer. Die strukture op die boonste oppervlak van die glans kan in werklikheid oop en toe, op 'blomagtige' manier, in 'n soort polsende of kloppende beweging. Daar is 'n paar besonder innemende video's wat dit op YouTube wys (een, wat hier verskyn, wys 'n Rooipootskilpad Chelonoidis carbonaria forming a strong relationship with a rubber ball). However you respond to these images, don't feel ashamed.

The precise configuration of sinuses and associated folds, and thus the overall form of the glans, varies from group to group (Zug 1966). Some of the configurations involved look terrifying others look really terrifying. The penis as a whole is seemingly simplest in sea turtles*. Here, the glans is pointed, with the seminal groove terminating in a single, deep fold. In mud turtles (Kinosternidae), big-headed turtles (Platysternon), land tortoises (Testudinidae), and batagurid and emydid river turtles, the glans is broad and fat. In many species, there's a pointed medial process at the tip of the glans. In land tortoises and the New Guinea pig-nosed turtle (Carettochelys insculpta), the seminal groove is bifurcated at its distal end in Carettochelys, the tip of the glans has a tri-lobed appearance where each branch of the seminal groove extends distolaterally into its own lateral lobe, separated on the midline by a distomedial lobe (Zug 1966). Carettochelys is odd in lacking sinuses on its penis.

* Some experts prefer to write the name ‘seaturtle'. I don't think that this suggestion has caught on yet, so will stick with ‘sea turtle' here (and equivalent terms for other turtle groups).

Softshell turtles (Trionychidae) go one (or two) better, since their glans is five-lobed. Again, the seminal groove is bifurcated, with each branch leading distolaterally to the tip of a pointed proximolateral structure. But, before reaching the tip of that proximolateral structure, the groove branches again, with this more distal branch of the groove extending to the tip of a pointed distolateral structure (Zug 1966). Softshell turtles thus discharge semen from four distinct branches of the seminal groove. This might leave you wondering what the insides of a female softshell's cloaca are like. That's an issue I should discuss some other time.

Why do we need phylogenies? Hoekom? To give us an evolutionary backbone to hang our hypotheses on, stupid.

Incidentally, the anatomically ‘simple' penis present in sea turtles has sometimes been regarded as peculiar given that phylogenies typically find this group to be nested fairly deep within Cryptodira (the so-called ‘hidden-necked turtle' clade). This topology means that sea turtles are surrounded in the phylogeny by softshells, snapping turtles, mud turtles and tortoises and river turtles (e.g., Gaffney & Melyan 1988, Shaffer et al. 1997, Hirayama et al. 2000), all of which have complex penises.

So, is it that the sea turtle penis has become secondarily ‘simplified' – presumably as a consequence of adaptation to pelagic life – or is it that the different, complex penises present in the other lineages evolved their complexity independently? To be honest, this issue hasn't been examined in detail in any phylogenetic analysis (to my knowledge). However, Joyce (2007) has more recently found sea turtles to be the sister-group to all remaining cryptodires. If this is correct, it might mean that the simplicity of the sea turtle penis is a primitive feature… but what about pleurodires (the so-called ‘side-necked turtles')?

Pleurodires – the closest living relatives of cryptodires – aren't as well studied as cryptodires, and less information is available on their genitalia. What little data I've seen (e.g., Cabral et al. 2011) suggests that the penises of some taxa at least are simple (that is, with a slender, pointed glans and little in the way of crazy folds and lobes) and superficially similar to those of sea turtles. My impression at the moment is that pleurodires and sea turtles share a ‘simple' penis as a symplesiomorphy (= shared primitive character), but this could be very wrong since I've seen little information on the pleurodire penis.

How big? BIG.

As interesting as it is from the point of view of embryology, phylogeny, microanatomy and detailed anatomy, one thing particularly eye-opening (no pun intended) about the turtle penis is its SIZE. It really is large and formidable in some species. It's perfectly normal for some tortoise species to have a penis that is half the length, or more, of the plastron. I would guess that in a tortoise with a total length of 20 cm, the penis might be 8 cm long. (Featured here are giant tortoises mating. These animals are identified on wikipedia as Galapagos tortoises, but - following help from Jeannot Tihoti Mahaɺ - I think they're Aldabran giants. Look carefully! Photo by Minglex, licensed under Creative Commons Attribution 3.0 Unported license.)

So, small turtles can have proportionally huge organs. What about big turtles? Unfortunately, little data is available. A few days ago, Roger Close asked me on facebook if we know anything about the size of the male organ in Galápagos giant tortoises (Chelonoidis nigra and kin). While mating behaviour in Galápagos tortoises has been filmed many times, I have yet to see any good images of genital anatomy in these animals. Petterer & Neuville (1914) described penis morphology in Aldabran giant tortoises Aldabrachelys gigantea*, but didn't provide much information. If you have useful data, please say so!

*If you follow these things, I would say that this name has rightfully won out over Dipsochelys dussumieri. Does anyone know if the ICZN has published a ruling yet?

Sea turtles are another group of turtles famous for reaching large size. Surely they have large penises. Ja. In a Green turtle Chelonia mydas (maximum length c. 1.5 m, carapace length c. 80-110 cm), the penis is typically more than 30 cm long (Hamann et al. 2003). Hold your hands 30 cm apart and think about that enormous penis for just a moment.

What about the Leathery turtle Dermochelys coriacea? This amazing giant can exceed 2.2 m in total length and have a carapace length of 1.7 m. The original version of the article you're reading now was published back in 2007, and since then a Leathery turtle Dermochelys coriacea dissection has been featured on TV as part of the fantastic series Inside Nature's Giants. Unfortunately, I missed it when it was on and haven't been able to see it yet. Joy Reidenberg told me at the time that the male individual they examined was, indeed, well endowed. As you can see from the two screen-shots shown here, she wasn't kidding. [Thanks loads to Markus Bühler and Emilio Río Rodríguez for help in getting the images at short notice.]

You have an enormous penis — so, what do you do with it?

While it might seem like a bloody stupid question, you have to wonder exactly what it is that turtles do with these sometimes enormous organs. The evolution of the shell probably means that male turtles were forced to evolve innovative penises in order to make genital contact with their partners. In sea turtles, males have proportionally enlarged, prehensile tails, and the tails of other kinds of turtle are also usually longer and bulkier in males than they are in females. The cloaca isn't situated at the base of the tail, but some distance along its length, so it seems that part of the distance that the penis needs to reach in order to inseminate the female is covered by tail-reach, not by penis-reach alone. Incidentally, some fossil Cretaceous sea turtles have regtig long tails – way longer than those of any modern sea turtles. This may or may not mean something for penis anatomy, but I don't think we'll ever know.

As is the case in other tetrapods that possess proportionally large sexual organs (including certain ducks, cetaceans and, yes, some primates), observational data suggests that male turtles mag employ their organs in display or aggression. Honda (2001) had this to say about captive specimens of the Common box turtle Terrapene carolina:

Sometimes males will distend their organ neither while mating, nor while in the presence of females. Usually while bathing or drinking, the turtle will submerge the front half of his body, rise up on his back legs, and drop his organ through the cloaca. It is a sight to behold, and one that can startle both novice and experienced herpetoculturalists alike. The organ itself is large in proportion to the turtle, and dark purple in color. After several seconds, the turtle will retract the organ back through the cloaca. It may repeat this process once or twice.


Does a Millipede Have a Penis? Wel. Define 'Penis'

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For humans and other vertebrates, the literal response to the question of what makes a penis is that it consists, to varying degrees, of connective tissue, spongy swellable tissue, muscles, and a blood supply. And it’s pretty straightforward to see many vertebrate organs that look like penises, call them that (“and that’s a penis, and that’s a penis!”), and be right. Maar nie altyd nie.

If you were on Mars and found an animal with something you suspected was a penis, what features would you use to rule your hypothesis in—or out? How about “something that inserts into a partner’s genitalia during copulation and transmits gametes”? Seems reasonable, although it’s even possible to argue about what copulation is. Some other time. Let’s look at some of the things that animals insert into their partner’s genitalia during copulation and see if they fit this vision of a “penis.”

Millipedes are probably best known for all those legs, although it’s not the thousand that the name implies. The millipede record holder for most legs has only 750, and most have far fewer. You can distinguish a member of the eighty thousand or so species of millipedes from its less speciose centipede doppelgängers by how many legs they have per segment, if you want to get that close. Millipedes have two pairs of legs per segment, while centipedes have one.

The millipede leg pairs of interest for our purposes are the eighth ones, which these animals use as intromitta, or gonopods (which basically means “feet that copulate”). These arthropods are not alone among their arthropodish kind in coopting an appendage this way. The genetics of limb building also might contribute to phallus formation in vertebrates. These realities give fresh relevance to tired, aspirational penis-related jokes about “third legs,” although as noted, it’s the eighth pair of legs in millipedes.

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The eighth pair of legs isn’t the entire copulatory story for these multipoded animals, at least for the well-studied members of the genus Parafontaria. These species also pull in the services of the second pair of legs, which is where their genital openings are. Rather than getting involved in intromission, though, as you might think genitalia would, this pair of legs near the genitalia simply source sperm for the eighth pair.

An amorous millipede begins courting by first trying to insert his uncharged eighth-leg-pair intromitta into his partner of choice. If she does not reject this trial poke and he’s successful, his second pair of legs will charge up the old eighth pair with sperm. Now fully loaded, he’ll intromit again, this time with the goods. The pair will become immobile and stay coupled for 29 to 215 minutes.

Why would a millipede have any need to do a dry run with its legs-slash-intromitta when life is short, especially for millipedes, and dangers probably lurk all around while he stalls with a test poke? If you’ll recall, millipede species are copious in number. Millipedes are only millipedes, and they can make mistakes about which species is which. In this genus, at least, the test thrust is one way for the suitor to confirm that his target partner is, in fact, the right fit for his intromittent legs. This quick test saves him from wasting a bolus of precious (seriously) sperm on a millipede inamorata from the wrong species. Given how long that second bout can last, it’s probably also a way to make sure the male is investing all of that precious time on the right mating partner.

You probably never pictured yourself viewing millipedes as a pattern of normal sex behavior, but now’s the time. Although employing four pairs of legs to inseminate a female seems outside the bounds of human experience (and it is), the millipede at least inserts the intromittum into the partner’s genitalia. The first time, there is no sperm, but the second time, if there is a second time, the sperm cometh. For millipedes, we’ll have to split the difference on whether they meet our test of “something that inserts into a partner’s genitalia during copulation and transmits gametes.”

We can’t say that much for the many species of insect that skip that bit completely and just inject sperm any old place on a mate’s body. Some flatworms also have no choice but to do this because of a lack of a “receptive female aperture,” as one embryologist put it. There are no genitalia to serve as the insertee, so the animal is forced to use a “stylet” at the tip of its “protrusible sperm duct” to pierce the partner’s body just about anywhere. Following the piercing, the injected sperm undergo a great migration through the partner to the eggs.

Although the lack of an obvious opening for sperm deposition explains this sloppy target practice on the part of flatworms, it doesn’t explain all cases of hypodermic sperm delivery. Some species of spiders and insects, which are not especially closely related groups, have evolved this adaptation and use quite similar forms to achieve it. Whatever the pressures are that shape the hypodermic intromitta, they seem to converge again and again on the same structure: something stabby but with a hollow tube to deliver sperm. But it doesn’t deliver the sperm into the genitalia, definitely not meeting the criterion of “something that inserts into a partner’s genitalia during copulation and transmits gametes.” For now, let’s just call these “intromitta” and not get any more specific.

How about this adaptation in many insects: the aedeagus?

This structure is penislike and comes in all kinds of shapes and sizes. It’s an outward extension of rigid plates covering the insect abdomen, connected by ducts to the testes so that sperm can be delivered on demand. It’s essentially well-armored abdominal intromitta.

And well armatured, too. These intromitta can be long and spiraling and have hooks and flaps and valves or claspers for grabbing the female. They can look quite alarming from a human perspective, or “gaze,” as the sociologists call it. Humans have spent a lot of time gazing at these structures, in fact, because it’s one of the primary ways they sort out species from each other. We even make videos of them in the act. The genre of “arthropod (and invertebrate) sex films” is small but mighty.

About 99 million years ago, a spider-ish animal—a member of a group of arachnids called the harvestmen and more familiarly known to some as “daddy longlegs”—was skittering around in a tropical forest when it suddenly met its end inside a dollop of sap. Unluckily for it, but better for us, the sap preserved what is currently the world’s oldest fossilized erection. The harvestman not-spider clearly had a penis—erect, tubelike genitalia, probably inserted into a female (or would have been had it not been for that damned sap), ready to deposit sperm. So sure, you think, harvestmen are a safe bet for “yes, that is absolutely, unequivocally a penis.”

You probably saw this coming: not all harvestmen meet these criteria. One group of these animals, a suborder called Cyphophthalmi but more commonly known as mite harvestmen, falls a little short. This ticklike group of not-exactly spiders are tiny, moss-dwelling little jewels that are only a few millimeters long. They don’t seem to share the obvious penis of their harvestbrethren and have genitalia that don’t intromit—instead, they evert, or flip it out.

These tiny animals use this eversible structure to poke their spermatophores—packets of sperm on a stick—into their partner’s genitalia without inserting the structure itself. When an animal uses this kind of tube to deposit eggs, the tube is called an “ovipositor.” So I guess that means the genitalia on these spiders are not so much an intromittum as they are a “spermopositor.”

Harvestmen (besides these mite harvestmen) stand out with their true penises because most arachnids don’t have a special structure devoted solely to intromission. If a spermatophore is a sperm packet on a stick, then the structures spiders favor is like a pair of elaborately wrapped sperm packets on a pair of sticks (actually leglike appendages known as pedipalps.) Spider intromitta are called palpal organs, and each is tipped with a hard structure called an embolus. This structure releases the sperm bolus into the female 1 once the spider’s “arm,” or pedipalp, thrusts it into her. The average palpal organ looks very much like a mitten at the tip of the spider’s arm, but the embellishments of the mitten (intromitten?) vary from species to species. Some are quite hairy and large, with folds, extensions, and pointy bits, while others are simpler and less daunting. 2

1 In some cases, the encapsulated sperm can stay alive for a year or more inside the female’s reproductive tract, until she is ready to use it.

2 I looked at the pedipalps of hundreds of species of spiders while writing this book and became so fascinated by them that I can barely keep myself from picking up every spider I see to check out their little intromittens.

The way spiders use their pedipalps can illuminate the question of “what makes a penis.” The male has a pore where sperm emerges. He captures the sperm on silk he’s prepared for the purpose and draws it up like fluid into a turkey baster, pulling it into his palpal bulb at the end of his pedipalp and stuffs the bulb into the female, releasing the sperm. The two steps of insertion and ejaculation can take no more than a five-count in some species.

Is the pedipalp–palpal bulb combination a penis? It involves a tube, intromission, and ejaculation. It seems to fulfill all of the elements of “something that inserts into a partner’s genitalia during copulation and transmits gametes” and then some.

But the spider also uses its pedipalps to taste and smell, definitely not familiar uses of a penis to us. Some spiders even use part of the pedipalp, a bit just under the palpal bulb at the tip, to make music (stridulate) as part of a courtship ritual. That’s not very penislike from our perspective (I’ve yet to hear of a human penis making music), either, but perhaps we should start viewing these organs as what they are: penis capable, sure, but also able to do so much more in the world of sensory communication and courtship.

Barnacles have long attracted the attention of naturalists, while also leaving some of them deeply confused. Carl Linnaeus, the Swedish botanist, is best known for his publication Systema Naturae, in which he laid out the hierarchy for classifying organisms. Barnacles seem to have mystified him, and he consigned them to the “Animalia Paradoxa” (paradoxical animals) section of his first iteration of Systema Naturae, sandwiched in between Draco (dragons) and the Phoenix (the Phoenix). He also seems to have thought, along with others before him, that barnacles originated from rotting plant life on beaches.

His misapprehension in that regard had deep roots. For centuries in Europe, at least, the origin of barnacles had left many a protoscientist baffled. As late as 1661, the first president of the newly founded, highly respected scientific body the Royal Society posited the most preposterous of the barnacle origin stories. Sir Robert Moray, who is not responsible for the name of the eel, 3 stood before the august body and read, with a sober face, a paper of his own describing a “bird-like creature” within the shell of a barnacle on a ship and making the argument that the barnacle goose, a resident of the British Isles, had developed by metamorphosis from this odd-looking, ship-adherent creature. Yes, he proposed that a bird had started life as a barnacle. Science is at its heart the process of changing conclusions with new information. After sufficient investigation, we can say with 100 percent certainty that barnacles do not morph into birds. 4

3 The Moray eel’s designation comes to us etymologically by way of Greek through Latin to Portuguese.

4 In his defense, this association of barnacles and baby birds existed far beyond the shores of a tiny European island. It possibly stems from the sight of the feathery cirri (the barnacle’s eight legs), which may have left an impression of a downy bird, although the role in this scenario of the often lengthy penis emerging from within this pile of apparent fluff is unclear.

Perhaps you have heard of Charles Darwin (1809–1882) and could even name what one group of researchers has described as his “monumental work.” If you’re thinking of Oor die oorsprong van spesies 4 as the tome that high praise references, you’re wrong. The phrase describes Darwin’s runaway best seller 5 on barnacle taxonomy, or classification, which he wrote following more than seven years of study. Darwin, secure of his audience, one presumes, published his work in a series of four monographs, no doubt leaving readers panting for more after completing each installment. All of which is to say, naturalists are bonkers for barnacles. 6

4 In which case, to be accurate, you should be thinking, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, because those Victorians were wordy.

6 And in fairness, the public was bonkers for naturalists. Darwin’s partner in proposing natural selection as a mechanism for evolution was Alfred Russel Wallace, but Wallace himself was best known in the 19th century for his (truly) bestselling book, The Malay Archipelago, the story of his adventures and explorations in the area around Malaysia, which was published in 1869 and hasn’t been out of print since. Wallace is widely regarded as having defined the field of biogeography, and he found beetles far more fascinating than barnacles.

Apart from wild speculation about barnacles and birds, the other attraction of these odd crustaceans is their genitalia. The general barnacle intromittum is a long cylinder of stacked, folded rings, like a sperm-delivering Slinky with a membrane around it. These organs have bristly extensions called setae, which the barnacles can fan out to sense chemicals in their environment that signal the presence of a potential mate.

None of this can start, though, until a hermaphroditic barnacle’s “female function” is in place. This function involves sending out “female” chemical signals to neighbors, activating their “male functions,” and leading them to unroll their long penises from among their cirri to feel around for that chemically alluring “female.” If the barnacle locates a welcoming mantle cavity with its penis, it pokes its intromittum into it, ejects some semen, and then, if events warrant, does it a few times more.


Why Is The Penis Shaped Like That? (EXCERPT)

Excerpted from "WHY IS THE PENIS SHAPED LIKE THAT? …And Other Reflections on Being Human" by Jesse Bering. Published July 7th by Scientific American/Farrar, Straus and Giroux, LLC. Copyright © 2012 by Jesse Bering. Alle regte voorbehou.

If you’ve ever had a good long look at the human phallus, whether yours or someone else’s, you’ve probably scratched your head over its peculiar shape.

Let’s face it: it’s not the most intuitively configured appendage in all of evolution. But according to the evolutionary psychologist Gordon Gallup, the human penis is actually an impressive “tool” in the truest sense of the word, one manufactured by nature over hundreds of thousands of years of human evolution.

You may be surprised to discover just how highly specialized a tool it is. Furthermore, you’d be amazed at what its appearance can tell us about the nature of our sexuality. If you think there’s only one way to use your penis, that it’s merely an instrument of internal fertilization that doesn’t require further thought, or that size doesn’t matter, well, that just goes to show how much you can learn from Gallup’s research findings.

Gallup’s approach to studying the design of the human penis is a perfect example of reverse engineering as the term is used in the field of evolutionary psychology. That is to say, if you start with what you see today—in this case, the oddly shaped penis, with its bulbous glans (the “head,” in common parlance), its long, rigid shaft, and the coronal ridge that forms a sort of umbrella-lip between these two parts—and work your way backward regarding how it came to look like that, the reverse engineer is able to posit a set of function based hypotheses derived from evolutionary theory.

For the evolutionary psychologist, the pressing questions are, essentially, Why is it like that? and What is that for? The answer isn’t always that it’s a biological adaptation—that it solved some evolutionary problem and therefore gave our ancestors a competitive edge in terms of their reproductive success. Sometimes a trait is just a “by- product” of other adaptations.

Blood isn’t red, for example, because red worked better than green or yellow or blue, but only because it contains the red hemoglobin protein, which happens to be an excellent transporter of oxygen and carbon dioxide. But in the case of the human penis, all signs point to a genuine adaptive reason that it has come to look the way it does.

If you were to examine the penis objectively—please don’t do this in a public place or without the other person’s permission—and compare the shape of this organ with the design of the same organ in other species, you’d notice the following uniquely human characteristics. First, despite variation in size between individuals, the human penis is especially large compared with that of other primates. When erect, it measures on average between five and six inches in length and about five inches in circumference.

Even the most well-endowed chimpanzee, the species that is our closest living relative, doesn’t come anywhere near this. Rather, even after correcting for overall mass and body size, chimp penises are about half the size of human penises in both length and circumference.

In addition, only the human species has such a distinctive mushroom-capped glans, which is connected to the shaft by a thin tissue of frenulum (the delicate tab of skin just beneath the urethra). Chimpanzees, gorillas, and orangutans have a much less extravagant phallic design—more or less all shaft. It turns out that one of the most significant features of the human penis isn’t so much the glans per se as the coronal ridge it forms underneath.

Magnetic imaging studies of heterosexual couples having sex reveal that during coitus, the typical penis completely expands and occupies the vaginal tract and with full penetration can even reach the woman’s cervix and lift her uterus. This, combined with the fact that human ejaculate is expelled with great force and over considerable distance (up to two feet if not contained), suggests that men are designed to release sperm into the uppermost portion of the vagina possible.

In an article published in the journal Evolutionary Psychology, Gallup and Rebecca Burch argue that “a longer penis would not only have been an advantage for leaving semen in a less accessible part of the vagina, but by filling and expanding the vagina it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity.”

This “semen displacement theory” is the most intriguing part of Gallup’s story. Since sperm cells can survive in a woman’s cervical mucus for up to several days, if she has more than one male sexual partner over this period of time, say within forty-eight hours, then the sperm of these two men are competing for reproductive access to her ovum.

So how did nature equip men to solve the adaptive problem of other men impregnating their sexual partners? The answer, according to Gallup, is that their penises were sculpted in such a way that the organ would effectively displace the semen of competitors from their partner’s vagina, a well-synchronized effect facilitated by the “upsuck” of thrusting during intercourse.

Specifically, the coronal ridge offers a special removal service by expunging foreign sperm. According to this analysis, the effect of thrusting would be to draw other men’s sperm away from the cervix and back around the glans, thus scooping out the semen deposited by a sexual rival.

You might think this is all fine and dandy, but one can’t possibly prove such a thing. You’d be underestimating Gallup. In a series of studies published in Evolution and Human Behavior, Gallup and a team of his students put the semen displacement hypothesis to the test using artificial human genitalia of different shapes and sizes. Findings from the study may not have “proved” the semen displacement hypothesis, but they certainly confirmed its principal points.

The researchers selected several sets of prosthetic genitals from erotic novelty stores, including a realistic latex vagina, sold as a masturbation pal for lonely straight men, and three artificial phalluses. Whereas the first two phalluses closely resembled an actual human penis, varying only in the coronal ridge properties, the third (the control phallus) was the bland and headless horseman of the bunch.

Next, the researchers borrowed a recipe for simulated semen. The recipe “consisted of 0.08 cups of sifted, white, unbleached flour mixed with 1.06 cups of water. This mixture was brought to a boil, simmered for 15 minutes while being stirred, and allowed to cool.”

In a controlled series of “displacement trials,” the vagina was loaded with this fake semen, and the phalluses were inserted at varying depths (to simulate thrusting) and removed, whereupon the latex orifice was examined to determine how much semen had been displaced from it. As predicted, the two phalluses with the coronal ridges displaced significantly more semen from the vagina (each removed 91 percent) than the “headless” control (35.3 percent).

For the second part of the study, Gallup administered a series of survey questions to college-age students about their sexual history. Drawing from previous studies that showed how sexual jealousy inspires predictable (and biologically adaptive) “mateguarding” responses in human males, these questions were meant to determine whether certain “penile behavior” (my term, not theirs) could be expected based on the men’s suspicion of infidelity in their partners.

In the first of these anonymous questionnaires, heterosexual men and women reported that in the wake of allegations of female cheating, men thrust deeper and faster. Results from a second questionnaire revealed that upon first being sexually reunited after time apart, couples engaged in more vigorous sex— amely, compared with baseline sexual activity where couples see each other more regularly, vaginal intercourse following periods of separation involved deeper and quicker thrusting.

Hopefully, you’re thinking as an evolutionary psychologist at this point and can infer what these survey data mean: by using their penises proficiently as a semen displacement device, men are subconsciously (in some cases consciously) combating the possibility that their partners have had sex with another man in their absence.

Once ejaculation has occurred, men typically become flaccid fairly quickly, and further stimulation of the penis is even uncomfortable. This is important because continued thrusting would be self-defeating: the man would essentially be removing his own sperm at that point.

Doubtful about this interpretation? The really beautiful thing about evolutionary psychology—or the most frustrating, if you’re one of its many critics—is that you don’t have to believe it’s true for it to work precisely this way. Natural selection doesn’t much mind if you favor an alternative explanation for why you get so randy upon being reunited with your partner. Your penis will go about its business of displacing sperm regardless.

It’s perhaps useful to reflect in closing on cat penises. Like human males, male cats possess remarkably specialized penises. They come equipped with a band of about 150 sharp, backward-pointing spines that, literally, rake the internal walls of the female cat’s vagina (hence the deafening yowl that often accompanies feline sex). This both triggers ovulation and displaces the sperm of prior males that may have recently mounted her.

We should give thanks—and I say this as a gay man, and one not without some stakes in this whole painful affair—that evolution took a somewhat gentler course in our species.