Evolution & Parental Investment

Recap –checking understanding Sexual Selection What is the evidence that Short term mating preferences are different for men and women?   Why would both men and women be more ‘choosy’ about long term mating choices? Can you use evidence to support? Why might women benefit from having a variety of sexual partners? Can you use evidence to support.

Additional Study on differences in inter-sexual selection – Buss and Schmitt (1993) PPts were asked how many sexual partners would you like to have in the next 2 years? Men = 8 Females = 1 PPts were then asked how many sexual partners would you like to have in a life time? Men = 18 Females = 4-5 Have can you use this evidence?

What do these quotes suggest about men? To Start… Quotes... “If you never want to see a man again, say, ‘I love you, I want to marry you. I want to have children…’ – they leave skid marks.” “A successful man is one who makes more money than his wife can spend. A successful woman is one who can find such a man.” What do these quotes suggest about men?

Lesson Objectives Thinking Ladder… To KNOW & UNDERSTAND Triver’s (1972) definition of Parental Investment. To ANALYSE the differences in maternal and paternal investment. To APPLY Parental Investment theory to understanding relationships.

Success Criteria How will I know if I am learning? By the end of the lesson… E Will be able to describe Trivers’ definition of Parental Investment. C Will be able to explain the differences in maternal and paternal investment. A Will be able explain how Parental Investment relates to relationships.

What is this man famous for? Parental Investment What is this man famous for? Infidelity, Being Unfaithful, Sexually Promiscuous

A: Explain how PI relates to relationships. Parental Investment Russell Brand brags about his sex life to the Dalai Lama. Brand told the 11,000-strong crowd: "Some of you might be surprised to see me here. I’ve gone from being Shagger of the Year three times to introducing the Dalai Lama. It has certainly been an interesting journey.” E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

A: Explain how PI relates to relationships. Parental Investment But Why? Are men unfaithful? E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

A: Explain how PI relates to relationships. Parental Investment Quality or Quantity? Trivers (1972) defined parental investment (PI) as, “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.” PI includes the provision of resources (such as food, energy and time used in obtaining food and maintaining the home and territory), time spent teaching offspring, and risks taken to protect young. Males compete for quantity of women where has women select a mate according to quality of the male and resources. This is because a women are limited in the number of offspring they have, where as men can have an unlimited number. = E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

A: Explain how PI relates to relationships. Use your text book 1 Quality or Quantity? Q: What are the differences between male and female investment in raising a family? Task: Divide a sheet of A4 paper in half and list their investments in terms of time energy, health etc. Q: Which parent invests the most? E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

Sex differences in parental investment The female egg cell is much more costly to produce than a male sperm cell. Females must nourish the offspring for 9 months, which means she can only have a limited number of offspring. It only costs a man approximately 30 minutes (possibly less!!) Breastfeeding can last for up to 4 years in some societies (Shostak, 1981). Therefore Females invest a greater amount than men. (Maternal Investment) SC = E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

Sex differences in parental investment The best way to maximise a males reproductive success is to mate with as many partners as possible Or, men need to concern themselves of the fidelity of their mates so they can be sure she’s mothering only their children Best way to maximise females reproductive success is to get the best protection/resources for her children SC = E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

Green Eyed Monster Parental Investment Buss 1992: Asked participants to imagine their partners having sex/being in love with someone else and measured stress responses. Which gender is the most jealous? Why might this be? How might it support Parental Investment theory? E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

A: Explain how PI relates to relationships. Parental Investment Sexual Jealousy Men are stressed at the idea of his partner being sexually unfaithful – because he risks investing in offspring that are not his own Women are more stressed at the idea of their partner loving someone else – and therefore the risk that resources will be diverted away from her and her family Buss 1992: Asked participants to imagine their partners having sex/being in love with someone else and measured stress responses. You can use the studies from the aggression unit  E: Define PI, C: Explain differences in maternal and paternal investment. A: Explain how PI relates to relationships.

What evidence is there for PI theory? Task 2: Using your textbook Pick out 3 pieces of evidence which you think best support Parental Investment theory. A03 Alert! Can we evaluate the evidence in terms of methods?

World records! Parental Investment The world record for the number of children is 888, fathered by Ismail the Bloodthirsty (1672-1727), an Emperor of Morocco; a Russian woman gave birth to 69 children! SC = E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

Statistical Evidence: Lone parent families Parental Investment Statistical Evidence: Lone parent families 1.9 million single parent families: 1.690 million are lone mothers 210,000 are lone fathers What does this tell us?! SC = E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

AO2/AO3: Evaluation of PI theory Parental Investment AO2/AO3: Evaluation of PI theory Inconclusive empirical support: According to Daly and Wilson (1988) children under the age of 2 are at least 60 times more likely to be killed by a step-parent – almost always a stepfather – than by a natural parent. This is exactly what evolutionary theory would predict, since step-parents and stepchildren are genetically unrelated, whereas a child inherits half its genes from each biological parent. However, most stepfathers don’t kill or abuse, and a minority of biological fathers do: these findings are difficult to square with any explanation based on shared/non-shared genes. Has societal and family structure changed significantly since Trivers published this theory in 1972? (historical validity) E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

AO2: Maternal investment There are two consequences of the high cost of maternal investment. First, infant dependency means females want male providers. Second, the expense of childrearing means that females want to ensure good quality offspring so they don’t waste their efforts. One way to achieve this is to marry a man who has good resources and is caring, but shop around for good genes through extramarital affairs with ‘studs’ – attractive men advertising good genes but no resources. Although accurate data for mistaken paternity are notoriously elusive, there is some evidence from a magazine survey of over 2700 UK women. From the results of this survey, Baker and Bellis (1990) estimated that as many as 14% of the population were products of extra-marital mating. SC = E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

AO2: Shared parental care In humans, joint parental care is desirable because of the high costs of successful reproduction. In any situation where males can increase the success of childrearing, it will pay them to do so (Dunbar, 1995). This means that in humans, males do restrict their reproductive opportunities and invest more in each individual offspring. SC = E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

Consolidation Clip Parental Investment Explain this scenario using PI Theory. Think about Mareo’s reaction. Clip E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

AO2: SEX DIFFERENCES IN PARENTAL INVESTMENT In 2008, Conservative MP Michael Gove claimed that ‘lads’ mags’ such as Zoo and Nuts reinforced a ‘shallow approach’ to women, and linked them to a rise in feckless fatherhood and family breakdown. Could this be the case, or might male attitudes to parenting actually be shaped more by biological forces (as predicted by PI theory)? Geher et al. (2007) studied 91 non-parent heterosexual undergraduates. Each completed a parental investment perception scale, which included statements such as: ‘I believe that I am very prepared to raise a child at this time in my life’. They were additionally exposed to various parenting related scenarios such as, ‘You are the parent of a three-year-old girl who has an ear infection. Your plans for the day have completely changed, as you now have to look after her’. Although there were no sex differences in self-report responses to parenting on the parental investment perception scale, there were clear differences in ANS arousal to the different parenting scenarios. Males showed significantly increased heart rate when presented with scenarios that emphasised the costs of parenting (e.g. that they would be unable to work). Researchers concluded that, consistent with predictions from PI theory, males are biologically less prepared than females to confront issues associated with parenting. E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

Learning Journal 5:00 1) Heading: Date, Unit & Topic 2) Write a summary of your learning about parental investment in less than 100 words. Can you link what have you learned to any studies from the aggression unit? 3) Check you have read your text book, and possibly one other source of information and that your notes are sufficient. E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02

Task 3 extension activity Parental Investment Task 3 extension activity Michael Gove: “lads mags encourage a shallow approach to women that causes feckless fathers and family breakdown.” Write a response to this. Use ideas from the evolutionary approach to support your argument. E: Describe PI with examples, C: Analyse evidence A: Evaluate using A02