1.9: Homosexuality – a paradox to evolutionary biology? Flashcards
According to Kinsey, what is the frequency of human homosexuality (psychological/physiological reaction, contact until orgasm, exclusively homosexual)?
Psychological/physiological reaction: FF 28%, MM 50%
Contact until orgasm: FF 13%, MM 37%
Exclusively homosexual: FF 1-3%, MM 4%
What number of the human population is homosexual?
210 million (3% of 7 billion) Therefore homosexuality isn’t just a fluke
Why is the Kinsey Scale problematic?
The term ‘sexual orientation’, implies you can’t change
Allows rigid law to be made to discriminate against a group
Give 5 examples that don’t fit into the Kinsey’s binary scale
Zambia: to become a man as a 13 year old boy you have to perform fellitio on a man and drink the sperm – it is not a mothers milk that makes you a man, but the man’s ejaculate
Burnesha: Albanian sworn virgins
Hijra: ‘Third gender’, Indian subcontinent
Kathoey: Thailand’s ‘ladyboys’
Thomas Beatie: child-bearing trans-man, USA
Why, according to evolutionary theory, would some believe that homosexuality is maladaptive?
Evolution favours individuals with many offspring
In what way do religious communities condemn homosexuality? Give 5 examples.
As a sin against nature:
Roman-Catholic African – ‘Dogs and pigs don’t do it, why must humans?’
Christian Evangelical – ‘Even barnyard animals don’t do what homosexuals do’
Jewish – ‘Homosexuality is a sin against nature’
Muslim – ‘Even animals will not do such unnatural sex’
Hindu – ‘Homosexuality is a bizarre combination against nature’s rules’
State 7 objections to the argument that animals exhibit homosexual behaviour. Provide evidence against the objections.
Homosexuality is a pathology of captive animals BUT many wild animal species do it
Homosexuality is rare and anecdotal BUT many langur monkeys do it frequently
Homosexuality is desperation BUT only sometimes, like gorillas in all-male bands
Homosexuality is social behaviour, not sexual BUT many animals seem to reach orgasm
Animal homosexuality is bisexual, not exclusively homosexual BUT many langur monkeys, flamingos, and greylag geese never have any other sex
Homosexual behaviour isn’t the same as homosexual orientation BUT 1 in 7 male greygeese will never mate with a female and 10% of domestic sheep ram are manifestly homosexual
Human homosexuality is cultural, animals follow instincts BUT Japanese macaques differ in their sexual ‘culture’ from group to group
Is homosexuality ‘against nature’?
No
State 6 mechanisms that explain why people are homosexual
Genes: twin studies Genes: markers Hormones: intra-uterine androgen (testosterone) Hormones: birth order effect Brain structure Parenting: Freudian models
Explain how twin studies reveal that genes cause homosexuality
If homosexuality is completely hardwired by genes, then identical twins would both be homosexual → this occurs 50% of the time for monozygotic twins; 25% of the time for dizygotic twins; 12-13% of the time for siblings
So there is a genetic component, but the environmental factor of the mother’s womb also influences the sexuality of the baby
Explain how genetic markers reveal that genes cause homosexuality
Homosexual brothers are more identical at the xq28-region of the X-chromosome
X-linked genes are passed down maternally
Explain how the intra-uterine androgen (testosterone) hormone causes homosexuality
High levels of intra-uterine androgen: MM become heterosexual, FF become homosexual
Low levels of intra-uterine androgen: MM become homosexual, FF become heterosexual
Explain how the birth order effect reveals that hormones cause homosexuality
In utero, the maternal immune system responds to ‘foreign’ male histocompatibility antigens (H-Y); this influences sexual differentiation of the brain in succeeding male foetuses
The younger you are in the line of brothers, the more likely you are to be homosexual because the mother’s womb is immunised against ‘foreign’ male foetus
Explain how brain structure causes homosexuality
INAH 3 core of the hypothalamus is half the size in women and homosexual males compared to heterosexual males
Explain how the Freudian model suggests that parenting causes homosexuality
In males: mother incest taboo and father castration-anxiety causes homosexuality
In females: penis envy and fear of paternal penetration causes homosexuality
Give 6 functions of homosexuality
Population regulation Training for heterosexual sex Reciprocity Kin-selection (gay uncle hypothesis) Homosexuality is a by-product of heterozygote advantage Parasitic memes
Explain how homosexuality regulates populations
In times of resource scarcity, homosexuality reduces pressure on reproductive individuals (This is an example of group selection fallacy)
Explain how homosexuality trains individuals for heterosexual sex
Individuals practice courtship, how to control physiological reactions, how to position the body, genital action, and orgasms (e.g. dolphins)
Explain how homosexuality is a form of social reciprocity
Sex is a social tool through which individuals reward each other with pleasure, which enables trust and alliances to form (e.g. famous gay/bisexual warriors Gilgamesh and Enkidu)
Explain how homosexuality produces stronger kin offspring. Give 4 examples.
Non-breeding individuals can increase their own fitness by foregoing their own direct reproduction (they have few offspring and reduced competitiveness) and instead help kin to have more surviving offspring (cooperative breeding)
Parental manipulation also reinforces homosexual behaviour in offspring: younger males in a family are more likely to be homosexual and more likely to be helpers in the family
For example:
- Homosexual male groups went out hunting in early hunter-gatherer groups
- Catholic priest, ballet-dancer, and fashion-designer shamanism: they are potent in transporting us into a different sentient space, they are social agents who bind a group together
- Homosexual men have higher IQ than heterosexual men on average, they earn more money, they have special talents, they are overachievers, they can wield more influence
- The Fa’afine in Samoa are effeminate males who have sex with heterosexual men, they describe the purpose of their life is to be helpers, they take care of their nephews and nieces very well
Explain how homosexuality is a by-product of heterozygote advantage
Homosexuality is recessive homozygous
The recessive homosexual allele is beneficial to heterozygotes who have it but detrimental for recessive homozygotes
Females who carry the male homosexual recessive allele have increased reproduction, but males who are homozygous for the recessive allele have reduced reproduction
Therefore homosexuals potentially exist to carry the allele that is beneficial for female reproduction
Explain how parasitic memes reveal that homosexuality has a social function (Dawkins). Give 2 examples.
Memes are units of information stored in you brain
They are parasitic because they take away they energy you would otherwise put into evolutionary mechanism
Homosexuals can therefore put more energy into memes, because they do not put energy into reproduction
A lot of homosexuals are famous for their cultural contributions; reproduction through brains/creativity rather than physically
(E.g. Oscar Wilde, Leonardo da Vinci)
