1. Evolution and human aggression

2. Evolutionary explanations of human aggression
Aggression is adaptive
Discuss reasons for this statement
Survival
Increase chances of procreation

3. The evolutionary approach to explaining aggression sees aggression in terms of its ability to increase survival chances therefore to enhance reproductive success.
How can aggression improve survival chances?

4. Aggressive behaviour has evolved to serve adaptive problems of social living
Gain territory and resources i.e. children bullying others for money or toys, adults mugging and warfare.
Defending against attacks: aggression to prevent loss of resources and status necessary for reproductive fitness i.e. “stick up for yourself.

5. Inflicting cost on same sex-rivals: aggression between same sex members to aid in the competition for resources and mates i.e. men fighting over women.
Negotiating status and power hierarchies: aggression to gain prestige and dominance among same-sex members i.e. gang violence to “prove oneself” to aid sexual selection by opposite sex members i.e. women attracted to dominant and powerful men.

6. Deterring rivals from future aggression: aggression to maintain dominance and fear in others i.e. making threatening gestures, reinforcing aggressive reputation, maintaining an aggressive appearance
Deterring mates from infidelity: aggression against opposite-sex members to maintain fidelity of desired long-term mates and ensuring paternity i.e. wife-battering

7. Evolutionary explanations of human aggression
Jealousy is an adaptive response
Why?
To deal with the threat of paternal uncertainty from acts of infidelity

8. Jealousy and aggression
Emotional response to anticipated loss of affection and/or status
99% of married people expect spouses to be faithful however 11% of women and 21% of men admit to extramarital sex.
Infidelity:
Unfaithfulness of sexual partners.
Sexual infidelity:
Any behaviour involving sexual contact i.e. kissing, touching, sexual intercourse
Emotional infidelity:
Formation of affectional attachment to another person, can involve flirting, intimate conversations

9. Why do men and women express jealousy differently?
Need to compete with other males for access to choosy females
Lower status men are willing to take greater risks by using aggression or face genetic extinction.
What about reconstituted families, adoption and fostering?
If the female is unfaithful the man faces paternity uncertainly
Human males cannot risk wasting investment on offspring who are not their own so they should show more jealous violent aggression relating to female fidelity- both towards the male competitors and their long-term female mates if infidelity is suspected especially if the female is young and reproductively valuable

10. Infidelity and jealousy
Cuckoldry and sexual jealousy:
As fertilisation is hidden from men as it happens inside the woman, men are always at risk of cuckoldry.
The consequence of cuckoldry is that the man might unwittingly invest his resource in offspring that are not his own.
Jealousy, therefore deters the female partner from sexual infidelity.

11. Mate retention and violence
Buss (1988) suggests that men have evolved a number of strategies to keep their partners.
‘direct guarding’ (vigilance) of the female which restricts access to other males to their partners. E.g. unexpectedly arriving home to see what she is up to.
‘negative inducements’ (violence) which act as deterrent of sexual infidelity. Dobash and Dobash (1984) Battered women cite jealously as key cause.

12. If a male is unfaithful the female partner risks losing his time, resources, energy, protection and commitment to her children.
Human females can always guarantee that their offspring are their own and compete with other females for the quality of men rather than for the availability.
40% of domestic violence victims are men in 2009 according to the British Crime Survey .
Women take fewer risk with violence and use more indirect form of aggression.

13. Research evidence Male-male aggression
Cross-culturally, human violent aggression and homicide is far more common in males, against other males (Daly and Wilson, 1988).
Homicide is more common in poor and unmarried men than richer, married ones (Wilson and Daly, 1985).
Sexual jealousy produces more male-male homicides than female-female.
Female-female aggression
Female aggression is more verbal against other women to maintain status and reduce the attractiveness of competitors, especially by using verbal criticism of the physical unattractiveness of other females and their promiscuity (for men looking for long-term mates with sexual fidelity) to lower their appeal in the eyes of men
(Buss and Dedden, 1990).

14. INTER-SEXUAL JEALOUSY AGGRESSION
Most male non-sexual aggression against women involves girlfriends and spouses due to sexual jealousy.
In a study of 36 Baltimore spousal homicides, 25 were attributed to jealousy, and the wives were the victims in 24 of these cases (Guttmacher, 1955).
Verbal aggression and non-lethal physical violence against mates is often similar in men and women, but spousal homicide by women is less frequent and often due to defense against a jealous abusive husband (Daly and Wilson, 1988).
Young wives/girlfriends are more likely to be killed than older ones (Daly and Wilson, 1988).
In 100 cases of spousal violence, the husbands' frustration over their inability to control their wives and accusations of infidelity were the most reported causal factors (Whitehurst, 1971).
In a study of battered women, 57 out of 60 attributed the violence to their husband's extreme jealousy and possessiveness (Hilberman and Munson, 1978).

15. Task
Pick two pieces of evidence and explain HOW they support the role of evolution and natural selection to explain aggression

16. Evaluation
Harris (2003) found the results from forced-choice studies about males being more stressed by sexual infidelity and females by emotional infidelity to be true of imagined scenarios, but in real instances both males and females felt threatened by emotional fidelity. The results from the imagined scenarios might be explained as males being aroused by images of sexual infidelity rather than feeling threatened.

17. Cultural differences (Brase study p.18 booklet)
Cultural differences in murder rates of wives by husbands and in the degree of anxiety felt in response to sexual infidelity by males suggest that factors other than those determined by evolution play a part.
Cultural differences (Brase study p.18 booklet)
Most relationships where a partner is or has been unfaithful continue or end without physical violence.

18. Dreznick (2004) suggested that there may be an alternative explanation to evolutionary theory such as a difference in beliefs of what constitutes infidelity. If men do not perceive emotional infidelity as infidelity, then they would not be particularly jealous in response to a partner’s emotional infidelity. .

19. Forced-choice methodology does not allow participants to specify the level or quantity of their agreement. In Buss et al.'s (1992) original study, although more men were distressed than women by sexual infidelity (49 per cent compared to 19 per cent), 51 per cent of men were distressed by emotional infidelity, compared to women's 81 per cent - that is, more men were distressed by emotional than sexual jealousy, which goes against evolutionary theory

20. Some critics feel that evolutionary explanations justify violence by men against women as natural and inevitable.
on average, two women a week in England and Wales are killed by a violent partner or ex-partner. Killing a partner because of infidelity “crime passionel” is no longer accepted as a defense in court (since 2008)

21. The evolutionary perspective offers an explanation of how aggressive behaviour due to suspicions of infidelity may arise as a result of natural selection.
Evolutionary explanations account for male and female differences in their experiences of infidelity and jealousy as due to different selective pressures, and therefore are not gender biased.
Evolutionary theory brings explanations of infidelity and jealousy down to the level of genes and therefore can be perceived as being reductionist. It is also determinist, as it disregards any role for free will in behaviour relating to infidelity and jealousy.
Cultural differences

22. What does this tell us?
Compare the biological, psychodynamic and evolutionary causes of aggression.
Which do you think explains aggression best? Explain your reasoning.

23. Links to issues and Debates
Ethics – e.g. studying aggression and how findings are used; in the research itself such as issues of confidentiality and informed consent.
Reductionism – e.g. focusing specifically on aggression when studying the brain.
Nature-nurture – e.g. brain localisation in aggression and environmental influences on aggression.
The use of psychological knowledge within society – e.g. understanding causes of aggression, in order to perhaps deal with them.
Can you spot the links to Issues and Debates in today’s lesson????

24. Homework
Read sheet ‘Evolutionary explanations for Human Aggression’ and make notes about the role of evolution and natural selection as explanations of aggression.
Be prepared to discuss this in class next lesson.