Evolutionary psychological science is a comparatively “ new field that utilizes the rules of Darwinian natural choice in the survey of the human head ” ( Workman & A ; Reader, 2008 ) . Development is said to happen when natural choice, “ the differential generative success of different phenotypes ensuing from the interaction of beings with their environment ” ( Campbell & A ; Reece, 2002 ) , causes alterations in the comparative frequences of allelomorphs in the cistron pool. In general, the evolutionary attack to human behavior focal points on why a behavior exists.
Homosexuality- The Darwinian Paradox
Worlds are sexually generative species, with offspring produced merely via copulating with persons of the opposite sex. Harmonizing to the Darwinian position of natural choice, persons should seek to maximise generative success, as any mechanism that lowers the likeliness of successful reproduction will be unfeelingly selected against. However, research worldwide has invariably revealed the omnipresent presence of a little but relentless population of homophiles, or “ people who have sex merely with others of the same biological sex ” ( Kirkpatrick, 2000 ) . Surveies have found that about 5-7 % of work forces and 2.5-3.6 % of adult females are homophiles ( Binson, Michaels, Stall, Coates, & A ; Gagnon, 1995 ) ( Diamond, 1993 ) ( Rogers & A ; Turner, 1991 ) ( Sell, Wells, & A ; Wypij, 1995 ) . This is despite research disclosure that both homosexual males and females have far fewer offspring than their heterosexual opposite numbers ( LeVay, 1996 ) , and that merely a little to moderate proportion of the discrepancy in sexual orientation can be accounted for by heritability ( Bailey, Dunne, & A ; Martin, 2000 ) ( Bailey & A ; Pillard, 1991 ) ( Kendler, Thornton, Gilman, & A ; Kessler, 2000 ) . Such information presents a echt evolutionary mystifier for psychologists.
Definitions and Footings
For the intent of this paper, I have adopted Kirkpatrick ‘s ( 2000 ) definitions of the undermentioned footings. The term homosexual behaviour refers to “ the single Acts of the Apostless of homophiles ” . Homosexual orientation is “ the form of emotional, romantic or sexual attractive force to another individual of the same sex ” . It is different from homosexual behavior, because non all persons will show their sexual orientation in their actions.
Purpose and Aims
In this reappraisal, I will critically analyze four of the most pertinent evolutionary accounts of homosexual orientation, and behavior, in worlds. A drumhead for each theory will be given, followed by its back uping grounds and restrictions. Future waies for this country of research will be proposed.
Evolutionary Theories of Homosexual Orientation in Humans
Parental Manipulation Theory
The Parental Manipulation Theory is based on the construct of parental investing, whereby “ any investing by the parent in an single progeny will diminish the parent ‘s ability to put in other offspring ” ( Campbell & A ; Reece, 2002 ) . In the Parental Manipulation Theory ( Trivers, 1974 ) as cited in ( Kirkpatrick, 2000 ) ( Rahman & A ; Wilson, 2003 ) , parents induce homosexualism through the ordinance of resources or the socialisation of the offspring to do them less competitory in generative functions, so that they will help in raising siblings or the progeny of siblings. In other words, homosexual offspring benefits parental reproduction.
Supporting grounds. There is merely anecdotal support for the Parent Manipulation Theory. Kirkpatrick ( 2000 ) lists some anthropological grounds that parents encourage homosexual dealingss between boies and other influential and powerful males.
Criticisms and restrictions. This theory is counter-intuitively at odds with the larger Darwinian impression of parental inclusive fittingness, which will be elaborated below.
Kin Selection Theory
The Kin Selection Theory is based on the impression of inclusive fittingness, which is “ an person ‘s entire generative fittingness ” . This is made up of “ the amount of his or her direct fittingness -due to the person ‘s ain reproduction, and indirect fitness- due to reproduction by relations as a effect of the person ‘s actions ” ( Campbell & A ; Reece, 2002 ) . Harmonizing to Wilson ( 1975 ) , homosexual persons might hold helped household members through resource proviso or child care in the hereditary environment. This would hold helped their household members to reproduce more successfully that they would hold otherwise, increasing the generative fittingness of the household and hence, the person ‘s ain inclusive fittingness. Therefore, even though homophiles do non hold their ain kids, the cistrons for homosexual behavior would hold been propagated indirectly through relations. This theory besides implies that persons become homosexual at their ain agreement.
Supporting grounds. Associated with the Kin Selection Theory are the subordinate hypotheses that male homosexualism is associated with birth order and empathy. Research has shown that male homophiles tend to be subsequently in the birth order, and have a larger figure of older brothers than straight persons ( Blanchard R. , 2001 ) ( Blanchard, Zucker, Siegelman, Dickey, & A ; Klassen, 1998 ) ( Bogaert, 2006 ) . Such consequences are said to take down non-reproduction costs for homophiles, as the household ‘s resources would hold already been invested in the older brothers.
Research by ( Salais & A ; Fischer, 1995 ) have besides shown that homosexual work forces more empathetic than heterosexual work forces. This consequence is said to back up the selfless constituents of the Kin Selection Theory. This survey, nevertheless, has been criticised for being ill designed. Bobrow and Bailey ( 2001 ) argued that the homosexual sample in the survey was mostly obtained from a spiritual group, which may account for the increased selflessness, and that exposing general selflessness might non intend that one will demo selflessness towards his family.
Criticisms and restrictions. There are several lines of grounds that do non back up the Kin Selection Theory. First, Bobrow & A ; Bailey ( 2001 ) found that homosexual work forces were no more likely than heterosexual work forces to impart resources toward household members. In fact, they were found to be more alienated from household members, particularly from their male parents and oldest siblings. Furthermore, in a survey by Rahman and Hull ( 2005 ) , it was besides found that there were no important differences between heterosexual and homosexual work forces in general familial affinity, willingness to supply fiscal and emotional resources, and benevolent inclinations.
The Kin Selection Theory has besides been criticized on several evidences. First, the grade of selflessness toward kin would hold to be highly big to countervail the loss of direct reproduction ( McKnight ( 1997 ) as cited in ( Bobrow & A ; Bailey, 2001 ) . Homosexuality besides seems ”poorly designed ” for its alleged map ( Bobrow & A ; Bailey, 2001 ) , as it would do more sense for homophiles to be an nonsexual species if they were to give clip and attempt in assisting out their siblings.
Balanced Polymorphism- Female Choice
Balanced polymorphism is “ the ability of natural choice to keep diverseness in a population ” ( Campbell & A ; Reece, 2002 ) , while the construct of female pick suggests that “ females should be more selective than males when it comes to taking a sexual spouse because they invest more to a great extent in offspring ” ( Workman & A ; Reader, 2008 ) . Harmonizing to Miller ‘s ( 2000 ) Balanced Polymorphism Theory of human homosexual orientation, female choice of fostering qualities in males additions feminising allelomorphs in the cistron pool, with the attendant cost of homosexualism in some work forces.
Harmonizing to this theory ( Miller, 2000 ) , sexual orientation is a polygenic trait that exists on a dimension of masculinity-femininity. A typical male would show more empathy, tenderness and kindness as he would hold inherited merely a few of the allelomorphs that partly prevented androgenisation of the encephalon. In the hereditary environment, such qualities would hold made them to be better male parents and more attractive couples, taking to greater generative success, and therefore guaranting the endurance of the allelomorphs in the cistron pool. A heterosexual adult male who does non hold any of these allelomorphs would expose more aggressive and psychopathologic features, doing him unattractive to adult females. Miller speculated that a little figure of work forces could hold inherited a high figure of these cistrons that so cause the encephalon organisation to develop in an highly feminine way, giving rise to a homosexual orientation. Miller farther suggested the presence of a similar masculinizing mechanism in tribades.
Supporting grounds. Research has revealed that adult females do so prefer work forces with more feminized facial characteristics ( Rhodes, Hickford, & A ; Jeffery, 2000 ) , particularly if they are traveling to be long-run couples ( Penton-Voak, et al. , 1999 ) . Women besides prefer work forces who are sort and empathetic as couples ( Geary, Vigil, & A ; Byrd-Craven, 2004 ) . Research has besides found that straight persons with a homosexual twin tend to hold more opposite-sex spouses than do heterosexual twin braces, proposing that cistrons predisposing to homosexualism may confabulate a coupling advantage in straight persons, explicating the continuity of homosexualism in the population ( Zietsch, et al. , 2008 ) .
Criticisms and restrictions. In a survey conducted by ( Santtila, et al. , 2009 ) , the research workers did non happen that heterosexual work forces with a homosexual brother have an advantage in several fitness-linked variables as compared to heterosexual work forces with heterosexual brothers.
The Balanced Polymorphism- Female Choice theory has besides been criticized because it assumes that attractive force to other males is a feminine, and non masculine, characteristic ( Muscarella F. , 2006 ) . This theory can potentially fall in if grounds turn outing otherwise is found. Muscarella ( 2006 ) besides argued that the theory is non a penurious account of the development for loving, sensitive, and begeting behaviour in human males.
Evolutionary Theories of Homosexual Behaviour in Humans
Alliance Formation Theory
Recently, several research workers have argued that it is deficient for the survey of homosexualism to be restricted to that of homosexual orientation, as sexual orientation may non interpret into sexual Acts of the Apostless. They proposed an Alliance Formation Theory to explicate the presence of homosexual behavior in the human population.
Ross and Wells ( 2000 ) argued that homosexual behaviour is an exaptation of homosocial behaviour. An exaptation “ is a construction that evolves and maps in one environmental context, but that can execute extra maps when placed in some new environment ” ( Campbell & A ; Reece, 2002 ) . Therefore, natural choice acts upon it. Harmonizing to Ross and Wells ( 2000 ) , male homosocial behaviour could hold contributed to male endurance through the formation of societal support and increasing entree to resources. Homosexual behaviour would hold strengthened homosocial bonds and as a effect be acted upon by natural choice.
Kirkpatrick ( 2000 ) argued that homosexualism serves non-reproductive maps, such as the creative activity and care of long-run supportive same-sex confederations. Such survival scheme AIDSs in resource competition or co-operative defence in the hereditary environment, leting homosexualism to be under positive choice.
Muscarella ( 1999 ) ( 2000 ) ( 2006 ) further postulated that such male-male confederations allowed low-status males to hike themselves up the group hierarchy, and thereby increasing their generative success. Such behaviour was said to be adaptative in the hereditary environment, where there was an absence of females and the presence of stiffly hierarchal male groups, with immature grownups likely “ sexually segregated and socially peripheralized ” . He elaborated that this theory parsimoniously explains why the most male-male sexual behaviour is of the cross-generational, dominance-submission type.
Supporting grounds. In an empirical survey conducted by ( Muscarella, Cevallos, Siler-Knogl, & A ; Peterson, 2005 ) , marks who engaged in homosexual behaviour were perceived by both male and female perceivers as likely to hold greater societal position and generative chances when the behaviour was said to reenforce an confederation that will take to increased societal chances. Other support for the Alliance Formation Theory, nevertheless, is chiefly anecdotal and anthropological in nature ( see ( Kirkpatrick, 2000 ) .
Criticisms and restrictions. The Alliance Formation Theory has been criticized on several evidences. Buss ( 2008 ) argued that there is no grounds that the bulk of work forces in most civilizations use homosexual behavior as an confederation formation scheme. There is besides no grounds that work forces who engage in homosexual behavior are more successful, or mount up the position ladder at a faster rate, than those who do non organize such confederations ( Buss D. M. , 2008 ) .
Homosexuality is a multi-faceted phenomenon with a big grade of single differences ( Bailey, Kim, Hills, & A ; Linsenmeier, 1997 ) . A good theory of homosexual orientation does non merely hold to be precise and internally consistent, it must besides account for known empirical findings more parsimoniously, and be evidentially more persuasive than any other viing theories ( Buss, Haselton, Shackelford, Bleske, & A ; Wakefield, 1998 ) as cited in ( Muscarella F. , 2006 ) . Therefore, it seems extremely improbable that a good evolutionary theory of homosexual orientation is available, at least for the present minute.
It is instead disappointing that most of the evolutionary accounts of homosexual orientation are by and large soundless on the issues of sapphism, or female-female sexual orientation. More research needs to be conducted in this country so that a comprehensive evolutionary theory of homosexual orientation can be developed.