7. Same Sex Aggression- Challenge hypothesis

Question 1

What are the costs of Testosterone?

Answer 1

Wingfield et al. 2001

• Interference with paternal care
• Exposure to predators
• Increase risk of injury
• Loss of fat stores
• And possibly immune system function and oncogenic (tumour casing) effects.

Question 2

Why would we expect to find T in human aggression?

Answer 2

• the clear association between age and physical aggression  young adult males show higher levels of physical aggression, violence and homicides to members of the same sex (Archer, 2004) than do other age and sex categories.  fit the view that human male aggression is, like that of many other mammals heightened when reproductive competition is most intense
• Among birds and mammals, one widespread mechanism that increases the readiness of males to fight during phases of the life-history when reproductive opportunities are greatest is the action of testosterone on areas of the brain controlling aggressive behavior (Archer, 1988). T is enhanced at times in life when males need to compete for receptive females or the resources necessary to attract such females, i.e. in the breeding season or after sexual maturity.

Question 3

How true is it that T controls violence in males in a linear fashion?

Answer 3

The view that testosterone secreted by males at puberty and throughout adult life facilitates human male aggression, despite its superficial appeal and its incorporation into media accounts of young men’s behavior, is at best an oversimplification.

The consensus is that there is a weak and inconsistent association between testosterone levels and aggression in adults (Archer 2006), and that the administration of testosterone to volunteers typically does not increase their aggression (O’Connor et al., 2004).

Question 4

Who made the Challenge Hypothesis?

Answer 4

Wingfield et al, 1990

Question 5

who made the argument that the challenger hypothesis could also be applied to humans?

Answer 5

Archer (2006) makes the argument that this can be applied to humans also.

Question 6

what does the challenge hypothesis stipulate?

Answer 6

• there are specific context-dependent increases in testosterone levels that are associated with aggression
• T levels rise to moderate levels at the start of the breeding season and these levels support reproductive physiology and behaviour.
• During challenges to males in contexts that are relevant to reproduction, T levels rise further
• This in turn facilitates aggression in the context of territory formation, dominance disputes and mate guarding (Wingfield et al. 2000).
• Then.. when males are required to care for offspring, their T levels decrease.

Question 7

Support for challenger hypothesis in Animals

Answer 7

Administering high levels of exogenous testosterone to several species of birds increased their mating and aggressive behaviour and supressed their paternal behaviour –Wingfield, 1984.

Question 8

support for Challenger hypothesis adaptation in chimps. Background to study

Answer 8

Muller and Wrangham 2004

o unlike the bird species on which the hypothesis was based, chimpanzees are neither seasonal breeders nor monogamous.
o Reasoning that the hypothesis may apply in different ways to mammals, the researchers predicted that since access to receptive and fertile females was relatively uncommon for male chimpanzees, there should be maximal aggression at such times. Indeed, it is known that males are more aggressive in the presence of parous estrous females.
o Muller and Wrangham also predicted that testosterone levels would be greater for dominant than for low-status males, since dominant males were more aggressive at all times.

Question 9

support for Challenger hypothesis adaptation in chimps. Predictions

Answer 9

Muller and Wrangham also predicted that testosterone levels would be greater for dominant than for low-status males, since dominant males were more aggressive at all times.

Question 10

support for Challenger hypothesis adaptation in chimps. Findings

Answer 10

o Got urine samples from chimps and found support for their modified version of challenger hypothesis in a number of ways:
o 1) When parous (offspring bearing) females were in estrus, there was a significant increase in testosterone and also an increase in aggressive competition. This did not occur in the presence of nulliparous females, whom males generally find less attractive but with whom they still copulate
o 2) Also consistent with predictions, dominant males were more aggressive than low-ranking ones, and produced higher levels of testosterone

Question 11

why would we expect to see the challenge hypothesis in humans males?

Answer 11

The range of possible mating systems, which can be linked to ecological conditions prompts the suggestion that there could be a role of testosterone in these alternative mating systems in humans.

Question 12

how do humans vary from chimps and how do human males vary to each other?

Answer 12

Humans show neither breeding seasons nor oestrus.

They show paternal care, but the extent to which individual males are committed to paternal care is variable both according to ecological conditions and according to individual variation. There may be considerable variation between men in this and other attributes resulting from sexual selection, for example in mate choice preferences and physical aggression.

Question 13

who extended the challenge hypothesis to incorporate individual differences?

Answer 13

Archer 2006

Question 14

what 6 predictions did Archer make about the challenge hypothesis in males?

Answer 14

1) there is no increase in aggression at puberty
2) Men respond to sexual arousal/ threat with increased T
3) The T response to challenge increases aggression
4) T levels lower in paternal men
5) Aggressive dominance is correlated with T
6) T is associated with alternative life history strategies

Question 15

how can Archer’s 4 and 5th hypothesis be extended into the 6th?

Answer 15

They highlight that there are adaptive costs, as well as benefits of high T levels. Thus there is a trade-off between mating effort (supported by high T levels) which involves the cost of high T levels but may lead to enhanced fitness benefits and parental effort (supported by lower T levels), which involves a lower cost and lower fitness benefit).

Testosterone levels vary among human males, and this variation may reflect a relatively enduring preference for one of two life-history strategies

Question 16

what would be the two life-history strategies in males.

Answer 16

The first (high parental investment) involves an emphasis on long-term commitment to one mate and paternal care, accompanied by low mating effort, whereas the second (low parental investment) involves low commitment to one mate and no paternal care, accompanied by high mating effort.

Question 17

what are we unlikely to see in life-history strategies in human males?

Answer 17

. It is unlikely that these will be absolute differences in humans, as they are in the males of some other species. Rather there will be relative differences in the degree to which males devote time and energy to mating and parental effort. These individual differences will be associated with differences in testosterone levels, and they represent long-term differences in life history strategies.

Question 18

evidence for hypothesis 1) No increase in aggression at puberty

Answer 18

• Halpern et al 1994- reported 3 year longitudinal study of 100 adolescent boys, whose initial mean age was 13.3 years. Measures included plasma hormone levels and a self-report rating of physical and verbal aggression, the OMAI, which showed high correlations with testosterone among 15–17 year old boys. Although, as expected, testosterone levels greatly increased when the boys went through puberty, no change in direct aggression was found, and there was no correlation between testosterone and aggression. In the same sample, there was a clear increase in sexual activity as the boys went through puberty.
• Results supported by many other studies, as a meta-analysis by Archer, 2004 showed that sex differences in direct aggression did not show a pronounced increase at puberty (self reports, peer reports)

Question 19

why was hypothesis 1 that aggression would not increase at puberty made?

Answer 19

challenger hypothesis makes clear that there are two types of testosterone-behavior relationships, the first is to support courtship and mating, and the second is to facilitate competitive behavior in relevant circumstances. The first occurs in birds throughout the breeding season in seasonal breeders, and from sexual maturation onwards in non-seasonal breeders. The second involves increases in testosterone that are facilitated by reproductive competition. We would therefore expect no testosterone-induced increase in aggression at puberty in human males, in contrast to the facilitation of sexual interest by testosterone at this time.

Question 20

evidence for 2.1 men respond to sexual arousal with incresed T

Answer 20

• Roney et al. 2003- measuring men’s testosterone levels as a consequence of brief interactions with a potential mate- exposed young men to a brief friendly conversation with young women or (as a control) young men. Although they found a significant increase in testosterone levels after interacting with the woman there was also a non-significant increase among the participants who interacted with the young man rendering the difference between the two conditions non-significant for this small sample However, from the challenge hypothesis we might predict an increase in testosterone levels when meeting a young man for the first time, as he might represent a competitor. The study did therefore provide clear evidence that interacting with a potential mate raised young men’s testosterone levels. Further, it was found that this increase was largely restricted to those men who said that they had had a recent sexual experience. There was also a strong correlation between testosterone levels and the woman confederate’s ratings of the male participant’s display behaviour towards her.

Hellhammer et al. (1985) examined salivary testosterone levels among 20 young men before, during, and after exposure to erotic, sexual, aggressive, stressful, and neutral films. Testosterone levels showed an increase 15 min after the beginning of the erotic and sexual films. No sig increases for other types of film.

Question 21

evidence for 2.2 men respond to threat with increased T

Answer 21

Archer 2006- conducted a meta-analysis on situations where men were in competition either lab studies or in real life sports. 23 samples found that there was an increase in T during the competition irrespective of whether it involved a contrived laboratory task or a sport competition. We can therefore conclude from the evidence on competitions that there is a small anticipatory rise in testosterone before sport competitions and that overall there is evidence of a small increase from before to after a competitive situation.

Cohen et al. (1996) reported an experimental study of students from the North and the South of the United States, in which they were insulted or not insulted, and their subsequent behaviour and physiology studied. There were greater increases in testosterone from before to after the insult among insulted southerners than in the other three conditions (insulted northerners and both non-insulted conditions), and also much higher cortisol levels. These physiological changes paralleled several psychological changes. These included greater immediate expression of anger, being more likely to complete a questionnaire involving sexual jealousy with violence, greater willingness to challenge a larger individual, and being more domineering to a smaller person. This study indicates that young men who are from a culture where honour is important do respond to an insult- a challenge to honour- with an increase in T and with more aggressive, domineering, behaviour. Whether the testosterone surge plays any causal role cannot be inferred from the study

Question 22

evidence for 3. T response to challenge increases agression

Answer 22

• Berman et al. 1993- lab study using competitive situation designed to assess aggression found that higher plasma T levels predicted higher aggression levels- used a a competitive reaction time task in which participants administered shocks to a supposed confederate. Positive correlation between initial T levels and subsequent aggression but also evidence that high T participants were more motivated in the task than were low T participants implicating individual difference.

Question 23

evidence against 3. The T response to challenge increases aggression but issue with this also

Answer 23

Archer 2006- meta analysis on humans injected with T and effects and concluded that there is no consistent evidence for increases in measures associated with aggression following the artificial raises of testosterone levels, yet argues that this may be because many of these studies are not designed to specifically test predictions from the challenge hypothesis, for example that testosterone may increase competitiveeness between males, especially where some status-related outcome is at stake. Suggest that Men whose disposition makes them prone to be directly competitive with other men may react more strongly when their testosterone levels are artificially raised.

Question 24

Why was it predicted that 4. T levels are lower among paternal men in animals

Answer 24

• There is evidence for a consistent pattern of hormonal changes in paternal birds and mammals (at around the time of birth, which does not occur in males of non-paternal species (Wingfield et al., 1990, 2000)

Question 25

evidence for 4. T levels are lower among paternal men

Answer 25

* Does this exist in humans- Storey et al (2000) measured salivary T levels from 24 couples at one of 4 times before and birth- T levels were 33% lower in samples taken in the early postnatal than in the late prenatal phase in men. Additionally, men who were more responsive to auditory, visual and olfactory cues from newborn infants had lower testosterone levels, or larger decreases from before. * Berg and Wynne-Edwards (2001) also found that testosterone levels were lower in the fathers than in 14 age-matched controls.

Question 26

what can we say overall about T levels in paternal men?

Answer 26

• Although the evidence is based on few studies involving small samples, it seems clear that fatherhood is associated with lowered testosterone levels. There is also evidence of lowered testosterone levels, and other hormonal changes, similar to those found in other paternal species, at the time of birth and infant care. This is also the pattern predicted from the challenge hypothesis.

Question 27

who argued similarities in hormonal changes in maternity and paternity

Answer 27

• Wynne Edwards (2001) has argued that the hormonal changes associated with paternity involve homologous neuroendocrine circuits to those involved in changes associated with maternity.

Question 28

why would we expect hypothesis 5. Aggressive dominance is correlated with T levels to be true in humans

Answer 28

• In non-humans dominance based least initially on physically-based contests- probably also the case in most pre-state human societies and in modern world societies where there is no effective rule of law- thus predict that aggression based dominance will be associated with higher T levels- but other forms of dominance, such as those achieved through social networks or occupational skills, will not necessarily relate to testosterone levels in this way

Question 29

evidence for Aggressive dominance being related to T

Answer 29

* Studies involving prisoners generally reported higher testosterone levels among those classed as aggressive or violent than in non-violent prisoners * Archer, 2006- for the majority of studies there is a consistent association between testosterone levels and various measures of dominance. * Schaal et al. (1996) distinguished between having a history of fights, toughness, and leadership (assessed by others) in a longitudinal sample of boys aged 6–12. Those with a history of many fights had lower testosterone levels than those with fewer fights. At age 13, it was the boys who were rated as tough by unfamiliar peers who had high testosterone levels. A combination of high ratings on toughness and on leadership predicted the highest levels of testosterone in this sample. * van Honk et al. (1999) found that testosterone levels measured 6 h previously were more closely associated with attending to angry faces on a Stroop task than were levels taken 4 h before or concurrently. They suggested that this is another manifestation of the association between physically-based dominance and testosterone levels, since aggressively dominant people are likely to perceive an angry face as a challenge and stare at it rather than looking away. These associations were found in both sexes and were stronger for women than for men.

Question 30

6) testosterone is associated with alternative life history strategies - this in itself leads to 4 further predictions what are these?

Answer 30

1) testosterone and the allocation of mating versus parental effort (pursuit of extra-pair/ short term relationships as opposed to stability of one relationship and parental effort. 2) T levels and personality characteristics that may predispose individuals to enter such different life courses 3) associations between T and antisocial activities that would tend to be associated with a shorter-term, higher-risk, reproductive strategy. 4) there are studies relevant to the issue of whether the associations found in adulthood are likely to be in place early in life, and hence represent enduring specialized life history strategies

Question 31

evidence for 6.1 testosterone mating versus paternal effort

Answer 31

* Burnham et al., 2003 reported than young unpaired men had higher T levels than unmarried men in committed romantic relationships, who had similar levels to those of unmarried men without children. * In a sample of over 4462 military veterans, testosterone levels were positively associated with not marrying and with marital instability, and negatively with measures of marital quality, such as spending less time with their wives, and more extra-marital sex (Dabbs and Morris, 1990)

Question 32

evidence for 6.2 testosterone and antisocial activities

Answer 32

* Using data from the large sample of military veterans, Dabbs et al. (1990) did find an association between testosterone levels and an antisocial personality, alcoholism and drug use (DSM-III criteria), although the magnitude was small. In an analysis of the same sample, Dabbs and Morris (1990) found that those with the top 10% testosterone levels were higher on antisocial activities including assaults than the remaining sample. * Stanford et al., 2003- One characteristic that is often associated with heightened aggression is impulsivity. * In review Archer (2006) says that from a number of studies looked at- It is likely that testosterone is associated with uninhibited, risk-taking, behavior that fits men poorly for achievement in higher-status occupations in organizations

Question 33

evidence for 6.3 personality and behavioral characteristics

Answer 33

* Underlying the associations between testosterone and characteristics associated with preferences for shorter-term mating strategies and more uninhibited behavior there should be a comparable link between testosterone and personality profiles, and also with behavior associated with personality characteristics. * Daitzman and Zuckerman (1980) found higher testosterone levels among 20 young men with high disinhibition scores than those with low disinhibition scores.

Question 34

evidence for 6.4 are these factors associated with life history strategies

Answer 34

* If the associations between testosterone and the characteristics reviewed in Sections 9 and 10 are associated with alternative life history strategies, it is likely that they will be present early in life, before puberty. * Archer (2006) meta-analysis association between T and aggression occurs in males but not in females in childhood. * These findings suggest that high and low testosterone males may tend to set out on different life courses equivalent to alternative life history strategies, and that these differences are apparent from relatively early ages, at least well before puberty. How these individuals progress will of course depend on how their social circumstances interact with their dispositions. Evidence from the large-scale study of US military veterans indicates that associations between testosterone and overt antisocial activity, and with occupational status, are accentuated by living in a low social class environment, and attenuated by living in a higher social class environment. Overall the evidence indicates an association of these life history strategies with testosterone levels and that the association is found before puberty for boys.

Question 35

what in conclusion can be said about the challenge hypothesis?

Answer 35

• Challenge hypothesis has a sounder basis in ET than the ‘mouse model’ which supposes a straightforward influence of testosterone on aggression in males from puberty onwards

Question 36

what is adaptive about the challenge hypothesis?

Answer 36

As a result, of the costs of high levels of testosterone, it would be adaptive to avoid maintaining consistently high levels throughout adulthood. Thus, if testosterone can be kept relatively low, and yet still support reproductive physiology and behavior, this will be more adaptive than maintaining consistently high levels. Further, if levels can be raised under conditions of reproductively-related competition, when behavior associated with a rise in testosterone is required, this again would be more adaptive than maintaining consistently high levels. Thus, the challenge hypothesis essentially involves an adaptive mechanism that avoids the high costs of testosterone (Wingfield et al., 2001).

Question 37

what improvements could be made with research into T

Answer 37

A further point that could be important in future studies concerns individual differences in the sensitivity of receptors to the action of testosterone (Manning et al., 2003). Taking into account receptor sensitivity may yield higher associations between testosterone and behavioral variables than is apparent in existing studies.

Question 38

what did wingfield note about female T

Answer 38

• Although the challenge hypothesis is concerned with males, Wingfield et al. (2000) did note that there was considerable variation in testosterone levels between females of different bird species.

Question 39

what can be said overall about the challenge hypothesis and females?

Answer 39

Some similarities with T to males but seem this may be more to do with protection of children as opposed to fighting for mate choice as much

Question 40

when are T levels more pronounced in females of a species?

Answer 40

• When sexual dimorphism was less pronounced, as in monogamous species, testosterone levels of females relative to those of males are higher, and it is possible that testosterone may be involved in female competition.

Question 41

what studies indicate that T may play a role in aggression for females?

Answer 41

o Amongst others o The association between testosterone and aggression was found to be higher for female than male samples (Archer et al., 2005). o Van Honk et al., 2001- when T administered to young women there were heightened reflexes to angry faces, which was attributed to the hormone facilitating dominance behaviour. o A further study showed that women with higher androgen levels had higher occupational status, possibly as a result of their being more assertive (Baucom et al., 1985)

Question 42

what do findings of female T levels suggest/ support?

Answer 42

* All these studies indicate that women may respond with increased testosterone to challenging situations, and that they show similar correlations between testosterone and personality characteristics such as aggressiveness and dominance. * This finding fits the suggestion (Wingfield et al., 2000) that in species where sexual dimorphism is less pronounced, and there is more paternal care, testosterone plays an important part in female competition for resources, and for males and their parental investment