Human Mating Flashcards
(104 cards)
1
Q
What are WEIRD societies
What are the issues with studying these societies in evolutionary anthropology
A
• WEIRD – Western Educated Industrialised Rich Democratic
- Only small amount of variation encompassed
- Invariably the outlier when cross-subsistence data available
- Unlikely to inform us about evolutionary origins
2
Q
What are the benefits of including small scale societies (not just WEIRD societies) in studies
A
- Universality cannot be assumed, but tested.
- Diversity better predicted by economy than geography.
- Opens up much broader range of subject areas e.g. kinship, marriage patterns etc.
- Natural fertility populations useful for testing fitness outcome
3
Q
What is Human Behavioural Ecology concerned with
A
Concerned with understanding human behavioural diversity
(within and between societies) – focus on ethnographic work.
Employs core theory from behavioural ecology; adaptationist stance.
4
Q
What is the adaptionist stance to behaviour
A
Behavioural flexibility produces adaptive responses to socioecological conditions:
- reaction norms
- phenotypic plasticity
5
Q
What is the phenotypic gambit
A
the assumption genetic architecture does not constrain which phenotypes can evolve
6
Q
What are modules in human psychology according to evolutionary psychology
A
Human psychology consists of mental modules which have been selected to deal with specific fitness related problems e.g. ‘cheater detection module’.
Modules evolved in response to pressures faced recurrently by our Pleistocene ancestors livings as HGs -in the EEA
7
Q
What is the cheater detection module
A
This module is an adaptive algorithm in the brain that once activated causes individuals to automatically look for cheaters in social exchange
such modules are operate without conscious effort and are distinct from general cognitive resources
8
Q
What do evolutionary psychologists believe about post-Neolithic psychology
A
In post-Neolithic transition populations cognition and behaviour is
maladaptive as natural selection is slow – mismatch!
• Behaviour is relatively inflexible and genetically determined.
• Human nature is universal; thus studying diversity and using
ethnographic methods is a low priority in EP; often survey based
or experimental
9
Q
How did Trivers define parental investment
A
“any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring” (Trivers 1972)
10
Q
What happens to the other sex when one sex invests considerably more in offspring
How does this relate to oogamy
A
members of the other sex will compete
for mating access to the investing sex
Female gamete requires more metabolic investment so male gametes compete with each other
11
Q
What is oogamy
A
sexual reproduction involving a small motile male gamete and a large much less motile female gamete: occurs in all higher animals and some plants.
12
Q
Other than oogamy, what increases maternal investment compared to paternal
What does this lead to
A
- internal gestation in mammals
- Breast feeding/ lactating
Females have a lower potential reproductive rate
13
Q
What is Bateman’s principle
A
in most species, variability in reproductive success (or reproductive variance) is greater in males than in females
Thus, male fitness is closely tied to mating access – quantity over quality while females must b choosier
this is a simplification and just a general trend
14
Q
Give criticisms of Bateman’s experiments
A
Birkhead argued that since Bateman’s experiments lasted only three to four days, the female fruit fly, Drosophila melanogaster, may not have needed to mate repeatedly, as it can store sperm for up to four days; if Bateman had used a species in which females had to copulate more often to fertilize their eggs, the results might have been different.
Snyder and Gowaty conducted the first in-depth analysis of the data in Bateman’s 1948 paper. They found sampling biases, mathematical errors, and selective presentation of data
15
Q
Use bird data to show females are not destined to be chaste
Do the same for primates
A
Until recently, most bird species were believed to be sexually monogamous. DNA paternity testing, however, has shown that in nearly 90% of bird species, females copulate with multiple males during each breeding season Zuleyma (2016)
In many primate species, females solicit sex from males and may mate with more than one male in quick succession. (Drea, 2005)
16
Q
Describe the results of the Clark and Hatfield (1989) experiment
A
Men are less choosy than women and more willing to engage in casual
sex…75% of men vs 0% of women agree to have sex with an attractive
stranger (Clark & Hatfield 1989).
17
Q
What did Bateman say about male and females
A
‘There is nearly always a combination of an undiscriminating eagerness in the males and a discriminating passivity in the females,’ wrote Bateman
Saini (2018)
18
Q
Give an example of Trivers’ work on the difference of sexual activity between sexes having an effect on popular culture
A
In August 1978, Playboy carried a story entitled
‘Do Men Need to Cheat on Their Women? A New Science Says Yes’
19
Q
According to the Bateman hypothesis what should men and women be attracted to
A
- Human offspring are highly dependent so we expect women to care about willingness and ability to invest resources, not just genes.
- Men ought to be attracted to physical signals of reproductive value (youth and health) since women’s fecundity declines with age
20
Q
What did Buss (1989) show
Give a further study that supports Buss’ conclusions
A
In a seminal EP study, Buss (1989) examined sex differences in mate choice in 37 populations.
• In all 37 populations men rated physical attractiveness as more important than women; and in 36/37 women rated financial prospects as more important than men.
• Experimental evidence for trends e.g. clothing (status cue) affects women’s preferences more
Women cared more about uniform then men (Townsend & Levy 1990b).
21
Q
What is Zahavi’s handicap principle (1975
A
: For a signal to evolve it must be costly/difficult to fake
Only those with the best genes can afford display the signal
22
Q
Give 2 examples of honest signals in humans
A
- High testosterone supresses the immune system and produces a strong jawline…only males with good genes can afford to display this signal.
- Symmetry – Ability to maintain stable development in spite of environmental pressures. Reflects genetic quality and immunocompetence
23
Q
What did Rhodes show about attractiveness
A
Averageness - Features more close to population average/less extreme deviations. Reflects heterozygosity and correlated with health (Rhodes et al 2001).
24
Q
What did Wedekind show
A
The Sweaty T-shirt Experiment
(Wedekind et al. 1995)
Women are attracted to the scent of men who have dissimilar MHC genes to
their own i.e. those with whom they will produce the healthiest offspring
Dissimilar smells also reminded them of previous sexual partners, suggesting this theory translated into real life actions – mated with individuals who are more genetically compatible with themselves
25
Why was Buss' 1989 study not representative of all humans
Cultural group explains a larger proportion of variance in mate preferences than sex!
• “The samples obtained cannot be viewed as representative of the populations in each country. In general, rural, less-educated, and lower levels of socioeconomic status are underrepresented”
Subsistence mode is meant to be a very good indicator (more so than geography: hunter gatherers in 2 different countries will be more similar to each other than to populations living in the capital cities of those countries – selective pressures) – this is not represented here
26
In what populations would we expect physical attractiveness to be particularly important
What does this indicate
If physical attractiveness is indicative of ‘good genes’ we may expect its value to be higher in populations where parasite load is a stronger pressure.
A shift in priority from resource shopping to gene shopping.
27
What did Gangestad (1993) discover about mate choice
Human data from 29 cultures indicate that people in geographical areas carrying relatively greater prevalence of pathogens value a mate’s physical attractiveness more than people in areas with relatively little pathogen incidence
28
What did Little find about mate choice
Give a hypothesis for this
Little et al. 2007 found that preference for symmetry were more strongly expressed among Hadza hunter-gatherers than European populations.
• Ache hunter-gatherers found to place more emphasis on facial averageness than participants from industrialised societies
Follows predictions: Higher pathogen stess -> more consideration given to cues of heterozygosity and immunocompetence.
29
Why is evolutionary psychology obsessed with waist-hip ratio
often cited as a principal
determinant of male mate choice.
• 0.7 is the golden ratio and a signal of optimal health and
fecundity (Wass et al. 1997).
• WHR has stayed constant in over 40 years of playboy
centrefolds and Miss USA models (Singh 1993)
'More feminine' waist-hip ratio associated with greater extra-pair sex (Hughes, 2004)
30
Describe how attractiveness changes with BMI
body-mass index has an inverted-U relationship with
fecundity + in resource deprived areas, body mass is positively associated with health
Tovee et al. 2006 Contrasted British men, Zulu men living in S.Af, Zulu men who migrated to UK and Zulu men born in UK.
• Different cultural ideals of attractiveness based on local conditions rather than universal preferences.
• Intra-individual flexibility in preferences rather than genetic determinism.
31
Describe the findings of Tovee (2006)
In WEIRD societies where obesity is more of an issue lower ratio is preferred – opposite in non-WEIRD societies Tovee 2006 – British vs Zulu men
Native Zulu men living in SA had inverse opinions of British men
Native Zulu men who had migrated to UK had intermediate opinions when compared to native Zulu living in SA (not quite as negative correlation)
Zulu men born in UK virtually identical to opinions of British men
Preferences are updated with local conditions and not purely genetically determined – even if genetic heritage was very different conditions
32
What is the issue with EP explaining mate preference having evolved in the EEA
EP emphasises that mate preferences evolved based on the EEA yet ignores lack of storage and material wealth accumulation.
EPs suggest that women are attracted to rich men to provide BUT hunter gatherers don’t accumulate wealth
33
EP predictions of attractiveness do not hold up in Marlowe’s 2005 study . Explain
• Hunter-gatherer men place far more emphasis on women being hard-working than in US college
samples; and do not value good looks significantly more than women (Marlowe 2005).
• In industrialised societies financially independence predicts likelihood of women prioritising attractiveness over financial prospects.
34
How does the person choosing the mate differ between populations
In a vast number of cultures parents exercise
control over their children’s marital decision.
• Extensive education postpones marriage in
industrialised societies until an age of
independence.
35
What did Apostolou 2010 find about mate choice in agro-pastoralist societies
- skills required for subsistence are achieved at
an earlier age, thus marriage doesn’t need to be postponed.
- production in based on private ownership and
thus dependence on parents is extremely high as is parental interest in partner choice (more
to lose)
36
Summarise the mate choice lecture (5)
* Females usually invest more in offspring + fitness not a function of number of mates unlike males -> females choosier.
* Female mate choice consider genetic and resource contribution of males. Given high PI required by human offspring, women concerned with resource access of males.
* Men place more emphasis on physical attractiveness which (honestly) signals reproductive value.
* Ecological conditions can vary the relative importance of characteristics (e.g. pathogen load and attractiveness); as well as actual preferences (e.g. resource abundance and body type). Preferences appear to be flexible.
* Labour and parenting roles vary within and between subsistence modes, which has knock on effects for partner choice.
37
What did Low claim was so interesting about human mating systems
“Human mating systems are particularly interesting. The extent of within-species variation is extraordinary. Most of the mating systems known in other species occur within the single species Homo sapiens.” (Low 2003)
38
Define the following
Polygyny
Polyandry
Polygynandry
Polygyny =
One man with many women
Polyandry =
One woman, many men
Polygynandry=
Many men, many women
39
Give an example of how social monogamy doesn't necessarily match with social monogamy
90% of birds form monogamous unions but this doesn’t match with genetics – socially monogamous but not genetically monogamous – in some groups more than 50% of offspring can have a different genetic father to their social father
Often not got official definitions for 2 people as a mating pair
40
Which mating system is most common in humans
Polygyny is most common - >80% of all societies (some and general polygyny) – ‘some’ is tricky bc defined as 20% or fewer of men are polygynous – what if there was a society of 100 men and 100 women but 1 man married 100 women – this would be ‘some’ polygyny
41
What might be a better way to class proportion of people who are polygynous
Better to class polygyny as proportion of women who are polygynous
42
Describe the reproductive trade-offs for males
* Minimal physiological constraints on male reproductive output…many potential reproductive strategies.
* Fundamental trade-off is between mating effort and parenting effort.
* Strategies not dichotomous/ mutually exclusive; optimisation when marginal benefit of one activity equal to marginal opportunity cost.
* Determined by e.g. operational sex ratio, dependency of offspring, individual mate value, availability of alloparents etc.
43
Why do humans have extended growth after birth
Children must be born early bc birth canal so narrow – growth must happen after birth
OR
limits to maternal metabolism are the primary constraints on human gestation length and fetal growth. Although pelvic remodeling and encephalization during hominin evolution contributed to the present parturitional difficulty, there is little evidence that pelvic constraints have altered the timing of birth (Dunsworth 2012)
44
When may paternal effort be ecologically enforced
In certain ecologies the dependence on paternal investment is so high that a parenting heavy strategy is only viable one
Inuit societies -polygamy almost non-existent
45
In which societies is monogamy more likely to emerge in
More likely if male care is not substitutable with maternal
effort…no man can afford offspring from multiple wives.
• Ecological factors associated with monogamy include
environment harshness/ low productivity/ low
temperatures(Low 2003)
If men are providing majority of calories etc they cannot afford to support multiple families
No good conceiving multiple children if they all die lol
Survival and reproduction are just as important as fertility
46
How does likelihood of monogamy change with gender roles
As women’s contribution to supplies increases, likelihood of monogamy decreases
47
Give an example of the variation between societies found by Blurton Jones about the effect of father presence on children
How does this affect divorce rate
Relative increase in mortality if father is absent (Hadza=1 which means no difference vs Ache where children without a father are considered burdens so are killed (1.62))
Blurton Jones et al. 2000
Where men are less important divorce rate is higher – parenting vs mating
48
What is the Fertility units per male
Created by combining operational sex ratio with total fertility rate (how many conceptions per man)
very high for Ache - more than double that of the !Kung
49
Describe lekking
What species does this exist in
* Males aggregate at a lekking ‘arena’ and perform display.
* Females arrive in search of no resource other than male genes.
* Extreme reproductive skew. - All females choose males of the best genes – only gene shopping (Many females want few best males)
* No male parental investment.
Sage Grouse
Males puff out air sacs on chest – display size and health – signals of heritable fitness
50
Does lekking happen in humans
Doesn’t have much in humans but see Gerewol festival of the Woddabe
Physical stamina required
Good teeth – oral health indicator of general health
Gerewol only happens during times of abundance
When women can focus less on provisioning and more on gene shopping
51
What did Low find about when pathogen stress is high
• When pathogen stress is high female choice determined more by gene shopping…those men with
the best genes have multiple wives.
• Low found that pathogen stress explains 30% variation in polygyny rates in the SCCS.
Low 1990
52
Describe the polygyny threshold
Orians 1969
Used to explain polygyny in birds in terms of territory
Female fitness as a function of male resources
Female always fitter in monogamy than polygamy (for any given level of male resource, female is fitter if she is the only wife cf. the second wife)#
But there are corresponding levels of fitness where she would be as fit as the second wife of a richer male than the only wife of a poorer man (R2 vs R1 – polygyny threshold)
Polygyny may be worthwhile when the richest partnered male is so much richer than the richest single man – higher fitness with richer partnered male
ADAPTIVE DECISION
53
What are 3 predictions fromthe Polygyny Threshold
1a. Polygyny rates across societies should be associated with the level of male wealth stratification.
1b. Resource rich males should achieve polygyny.
2. Polygynously paired women should achieve the same fitness as monogamous counterparts
54
Who are the Kipsigis
agro-pastoralists in SW Kenya
first population of humans where Orians' polygyny threshold was applied
Natural fertility population with high TFR.
Plot size strong predictor of food availability and purchasing power; Size of man’s farming plot very closely related to ability to provide for his family
55
Describe the marriage system of the Kipsigis
High marital stability. Men recorded as having up to 12 wives.
56
How do PTH predictions fit with polygyny in the Kipsigis
• Male RS is a function of land ownership; relationship largely mediated via polygyny (Borgerhoff Mulder 1987)
Polygynously paired women do not suffer lower fertility or offspring survival (BM’88; 89).
57
How is inequality assessed cross-culturally
the Gini co-efficient
deepness of Lorenz curve shows level of inequality
deeper= more inequal
A/total area
look at image
58
How was the Gini coefficient used to examine polygyny cross-culturally
In an analysis of 29 societies Ross et al. 2018 found some anomalies where polygyny rates where lower than expected based on the Gini.
• Ross et al. argue the agriculturalists societies follow a wealth distribution driven by a few elites, who do not have wives proportional to their wealth because of the diminishing marginal fitness returns on number of wives.
59
What is an issue with the Gini coefficient
Gini co-efficient misses does not give full picture of inequality – same total level of inequality can be structured in different ways e.g. a few extremely rich vs a few extremely poor.
60
What is the The Polygyny-Fertility Hypothesis
Is there any evidence to back this up
What may be a problem with this hypothesis
The claim: Polygynously paired women achieve lower fertility than monogamously paired women (Bean & Mineau 1986).
• A meta-analysis found evidence for the P-F hypothesis in 64 of the 86 studies
(Josephson 2000).
How can it be reconciled with the polygyny threshold model
61
Describe the Mormon population (4)
• Practiced polygyny publicly for second half of 19th century.
• Appear to have been a natural fertility population.
• Claims about female biased sex ratio not corroborated by census (May 1992).
Up to 16 wives and fertility was still high
62
In what types of unequal societies would polygyny not match Gini
If the Lorenz curve is very deep (nearly right angle) very few men are really really rich
Their wealth doesn’t directly translate to nuumebr of wives – diminishing returns
Unlikely to have 50 wives to 1 man
Doesn’t pay off to have an extra wife
Eg limits of paternal investment (cannot provide for 50 families); conflict between wives; risk of STIs etc
Higher polygyny rates in societies with moderate to high inequality cf extremely high inequality
63
Give one reason why Josephson's analysis might have wrongly evidenced polygyny fertility hypothesis
Self selection?
Women who end up in polygynous marriages are already less likely to be fertile (eg a sterile man may take another wife if first wasn’t getting pregnant, same if the first wife is sterile; women unmarried at older ages are more likely to become second wives)
Not a result of polygyny?
64
What did Josephson find in 2002 regarding fertility
What was also found
Age specific fertility curves – a monogamous women at any given age is more likely to have higher fertility than a polygynous wife
This effect has disappeared by grandchildren (Josephson 1993)
65
Why may polygynous women having lower fertility still be adaptive
Sexy sons
Males who achieve multiple mates are more likely to have sons who achieve multiple mates
Polygynous women had fewer kids but sons had more wives due to some trait the original husband had - higher reproductive success
(Josephson 2002, 1993)
66
Summarise the first lecture on marriage systems (4)
• Environmental harshness may result in ‘ecologically imposed’ monogamy, where men cannot ‘afford’ multiple families.
• Male contribution is rarely limited to genetic material in human populations and thus
pure lek mating is rare/absent…but polygyny rates are associated with pathogen stress.
• The PTM offers predictive power re. the cross-cultural prevalence of polygyny, particularly if you account for
specific distribution of wealth.
• Some polygyny appears to be maladaptive for women owing to the polygyny-fertility trend; but could be artefacts of study design/short term proxies of fitness.
67
Give an overview of Dogon society
The Dogon from Mali rely on millet, cereals and onions as a cash crop.
• ~50% of men are polygynous.
Extremely high offspring mortality:
- 20% under 12mo
- 46% under 5yrs
- polygyny large risk factor (Lowered child survival due to diluted male investment – see Strassman 1997/2000 )
68
Why does Dogon polygyny not fit with female choice models
Why may polygyny may persist
Polygynously married men achieve higher fitness but their wives experience
lower fitness than their monogamous counterparts.
Polygyny may persist due to biased sex ratio:
- higher male mortality
- male emigration to cities
69
Why is there a biased sex ratio in the Dogon
At marital age fewer men cf women due to increased mortality and male emigration to cities (increased infrastructure and economic opportunities)
-higher male mortality
70
What helps maintain the patriarchy in Dogon society (6)
Patrilocal + related women cannot marry into same patriclan (therefore men have a huge local network while women are isolated – less control to prevent husband taking another wife)
Hwomen work harder and restricted to low quality foods.
Patrilineal units of related men exert control over women’s behaviour
practice FGM
There are male only spaces women aren’t allowed to enter
Religion
71
How do Dogon men use religion for mate guarding
Women in the traditional religion are exiled for five nights to menstrual huts; during the day work
in the fields.
religion uses the ideology of menstrual pollution as the supernatural enforcement mechanism to coerce women to disclose their menses by going to the menstrual hut.
Hormonal data showed that fear of breaking these religious taboos enforced honest signaling to the men of the husband’s family, who situate the menstrual huts in close proximity to the toguna, which is a shade shelter specific to the males of a given patrilineage
Use of menstrual huts allow husbands (+relatives) to track their wives’ reproductive status and guard them during fecund period - husband can adapt behvaiour to monitor her behaviour and sex her more often
Strassan 2012
72
What is the Dogon shade shelter specific to the males of a given patrilineage called
toguna
73
What did Strassman find about nonpaternity in Dogon societies
Strassman interviewed women to see if there is a relation between use of menstrual huts and cases of non-paternity where social father is not biological – found that women who were NOT following hut regime were more likely to have child from illegitimate affair – extra pair copulations
5x lower cases of non paternity in Dogon indigenous religion cf Xianity, less of a difference in Islam bc women have to tell men when they are menstruating bc it alters when they can pray
Strassman 2012
74
What kind of polygyny is polygyny threshold model
what is the other kind of polygyny
In BE literature PTM is territory/resource defense polygyny
female defense polygyny when females are spatially clumped e.g. for suitable parturition site.
75
In what type of polygyny is intra-sexual dimorphism greater
female defense
Intra-sexual competition drives mating access > high sexual-dimorphism as males compete to monopolise harem
Often maladaptive for women
76
Which type of polygyny is more common in human history
Female defence is more common in humans than resource defence
Eg harems of Ottoman sultans – 400 rooms for women which are guarded by 1000 castrated guards – not sex dimorphism but similar situation
77
What did Zerjal et al find regarding human female defense polygyny
identified a Y-chromosomal lineage with several unusual features.
found in 16 populations throughout a large region of Asia and was present at high frequency: ∼8% of the men in this region carry it, and it thus makes up ∼0.5% of the world total. The pattern of variation within the lineage suggested that it originated in Mongolia ∼1,000 years ago
The lineage is carried by likely male-line descendants of Genghis Khan, and we therefore propose that it has spread by a novel form of social selection resulting from their behavior
Zerjal et al. 2013
78
How common is socially imposed monogamy
In ~17% of societies in SCCS polygamy is forbidden
79
Describe the group competition hypothesis (6)
• In small-scale foraging societies polygyny is not ‘destructive’:
-ecological constraints keep level low 0-15%
-male mortality is high -> few reproductive losers
• In stratified complex societies polygyny leads to:
-high intra-sexual competition
-risk taking psychology
Population level of unmarried men associated with rate of rape, murder and theft.
* Inter-group competition between complex societies is based on economic output, armies, innovation, offspring quality etc…
* Group competitiveness reduced by within-group intra-sexual competition.
* Leaders had incentive to enforce monogamy on general population.
* Groups with norms and institutions enforcing monogamy (and punishing violation) were successful and expanded.
(Henrich et al. 2012)
80
What did Murdock claim about polyandry
“Polyandry is so infrequent…there is no justification for assigning to it an important place in the evolution of social organisation.”
(Murdock 1949
81
How common is polyandry
• Traditional estimates of polyandry very low:
- 4/565 (World Ethnographic Sample)
- 7/1167 (Ethnographic Atlas)
82
What is the The Polyandry Paradox
- Female fertility not a function of number of mates…incentive?
- Low paternity certainty carries risk of withdrawal of paternal investment…why would males be complicit?
83
Describe the steps leading to most nation states having socially imposed monogamy
```
SIM
->
Decreased intrasexual selection and decreased payoffs for mating effort
->
increased parental investment and cooperation with a decrease in crime
->
increased offspring quality and output
->
increased innovation and economic growth
```
84
What are the classic cases of polyandry
eg?
Polyandry is virtually always agricultural societies of Himalayan regions of India, Nepal & Tibet (classical/formal polyandry).
eg
• Limi – Indigenous Tibetan culture in NW Nepal
– Fraternal polyandry (range 0-5; mean 2.4)
– Brothers should be treated equally by wife
– No attempt at identifying biological father
– Relatively high marital instability
85
Is there any evidence for polyandry arising from biased sex ratio
Lack of support for sex ratio arguments (Beall et al. 1981):
- in 15-44 age-group SR is actually female-biased.
- 31% of reproductively aged women unmarried.
- 30% of junior brothers become celibate monks
86
What is the most likely explanation for classical polyandry
• An issue of land scarcity in harsh environments:
-Majority of families have less than 1 acre of arable land
(Goldstein 1976)
- Partition amongst multiple sons would result in plots below minimum viable size.
- Parents force eldest heir to allow younger brothers to join the family – best of a bad situation from their perspective allows family estate to remain in tact with concentrated labour - usually fraternal polyandry - kin selection
lots of marital instability and more than 2 husbands is rare
87
Describe informal polyandry
Informal cases:
- rates lower than in the classical cases
- cohabitation and marriage with one male
- other mates still socially recognised and have parenting responsibilities toward woman’s offspring.
88
What did Walker find regarding informal polyandry
• In lowland South-America partible paternity beliefs are more common than biologically accurate beliefs (Walker et al. 2010).
• Numerous adaptive hypotheses set out by Walker…much more testing
required.
89
What did Starkweather find regarding informal polyandry
Starkweather et al. 2012 identify 53 non-classical/informal cases.
Found associations with male production (multiple investors hypothesis), male mortality (insurance hypothesis) and sex ratio
90
Give an example of a population which practices informal polyandry
What do they live off
Why may this marriage system have arisen
the Bari
subsist on low quality horticulture (manioc) supplemented by male fishing and hunting.
High mortality risk – territoriality + outside violence from oil companies and other stakeholders.
Secondary fathers required to provide fish and game, usually good hunters with more influence.
23% of pregnancies involved a second fathers; Survival (to age 15) odds ratio 2.28 (Beckermann et al. 1998).
Secondary fathers act as insurance - When woman gives birth she will give a list of all the men she has had sex with and indigenous midwife will go and tell each man he has a child so have obligations to provide fish and game
91
Give examples of homosexual sex in insects
Indirect insemination in flour beetles
Courtship/mating practice in fruit - Males who have gay sex before sexual maturity are more successful in gaining mates
92
Give examples of homosexuality in bonobos
GG rubbing?
Females rub genitals on each other
Also ‘penis fencing’, testicle massage
Function to form bonds between participants
GG rubbing occurs when an immigrant enters the group and wants to integrate so does it with a high status female
Sex is important for reconciliation
93
Give examples of gay sex being used for alliance formation
Idu period – samurais would have gay sex with younger male apprentices – shudo
Native American societies – gay sex formed alliances in war etc and they could now eat each others food and lodge in their cabins etc
Means of cooperative defense, increases resources etc
Otoro, Melanesian culture
After a heterosexual marriage, wife’s brother will have sex with new husband/ now brother in law to cement good relations
Explains bisexual behaviour
94
What has been found in twin studies regarding sexual orientation
Some genetic determinants it appears – 35% of homosexuality in male twins was accounted for by genetics (20% for females)
(e.g. Langstrom et al. 2010).
95
What is the sexual antagonism hypothesis
- genes resulting in fitness reduction in one sex are maintained by selection due to fitness enhancing effects in the other sex.
- evidence for higher fertility among female relatives of homosexual men in numerous populations (Camperio-Ciani et al 2004).
96
How can kin selection hypothesis be applied to homosexuality
homosexual individuals may achieve same inclusive fitness indirectly, by
helping rearing offspring of close relatives.
97
Give an example of a society where gender is not a binary
• Samoan fa’afafine:
- translates as: in the manner of a woman
- assigned on basis of ‘non-male’ childhood behaviour
- recognised third gender + no stigma
- sexually attracted heterosexual men.
98
How do the • Samoan fa’afafine help explain the maintenance of homosexuality in humanity
• Some support for sexually antagonistic and kin selection:
-mothers and grandmothers of fa’afafine have higher
reproductive output (VanderLaan et al. 2012)
-fa’afafine score higher on avuncular tendencies scale
(Vasey & VanderLaan 2010)
The fa’afafine invest much more than other genders?
99
Give a summary of the less well explored cases of human marriage systems
• Some occurrence of human polygyny is better explained by male coercion/female-defense polygyny than female choice – no singular explanation.
• Socially imposed monogamy may be an example of cultural group selection,
where punishment prevents cheating and enhances group competitiveness by reducing intra-sexual competition.
• Formal polyandry is extremely rare and limited to harsh environments where productive land is too scarce to be partitioned among brothers. Informal cases may represent female strategies to gain extra paternal investment for offspring/an insurance against high male mortality.
• Bisexual behaviour is common in the animal kingdom - plays an important role in alliance formation. Principal evo hypotheses for strict homosexuality include:
sexual antagonistic selection, kin selection.
100
What did Fleischman find regarding homosexuality
Why is this important
in women (n=92), homoerotic motivation was positively associated with progesterone, a hormone that has been shown to promote affiliative bonding
men in an affiliative priming condition were more likely to endorse engaging in homoerotic behavior compared to those primed with neutral or sexual concepts, and this effect was more pronounced in men with high progesterone.
first experimental evidence for the hypothesis that human homoerotic behavior serves the ultimate function of enhancing affiliation as well as alliance formation and maintenance
Fleischman 2015
101
What did Reed argue about homosexuality
What were the predictions of his hypothesis
proposed sexuality exists on a spectrum from anisogamy preferences (preferring gametes of different sizes) to isogamy preferences (preferring similarly sized gametes)
1) between species, the presence of same-sex sexual behaviors will be more likely to occur as sperm to egg ratios approach 1:1.
2) within species, those individuals with greater sperm lengths will be more likely to exhibit same-sex sexual behaviors than those with lesser sperm lengths
102
Give an example of an honest signal in human males
Voice pitch -> higher testosterone increases vocal fold width making pitch lower
Men with deeper voices are associated with a
greater number of reported sexual partners (Puts, 2006), and greater reproductive success (Marlowe, 2007) than are higher-pitched men's voices.
Men with deeper voices also have more extra-pair sex (Hughes, 2004)
Females are more likely to think a deeper voiced man will cheat (Feinberg, 2011)
103
Give an example of how Trivers was sexist
told a reporter Hrdy should focus on being a mother rather than a biologist
104
Give 2 studies to counter Hatfield and Clarke's (1989) experiment
Conley (2011) showed:
1) the large gender differences from the original Clark and Hatfield study could be eliminated by asking participants to imagine proposals from (attractive and unattractive) famous individuals, friends, and same-gender individuals.
2) The extent to which women and men believed that the proposer would be sexually skilled predicted how likely they would be to engage in casual sex with this individual
Fisher (2005) highlights Hatfield and Clarke's findings have never been replicated and that context makes a big difference
(eg age difference, setting etc)
