Specification: The evolutionary explanations for partner preferences, including the relationship between sexual selection and human reproductive behaviour.

Evolutionary Approach

Evolutionary approaches explain human behaviour in terms of adaptiveness and reproductive success. Such approaches argue that if a behavioural feature, for example, partner selection, has been genetically inherited by one generation from another, then it must have a specific value for the human species; it might either help humans adapt better to the environment and survive (natural selection) or might help to attract a mate and have healthy offspring (sexual selection).

Sexual Selection and Human Reproductive Behaviour

Anisogamy

Part of the sexual selection explanation of relationships includes explaining differences in partner preferences between males and females. One explanation comes from the concept of anisogamy – differences between the male and female sex cells.

Male sex cells (sperm) are produced in large quantities, replenish quickly and are created continuously from puberty to old age. Female sex cells (eggs or ova) take a lot of energy to produce, are created in limited numbers during specific time intervals, and their production only lasts for a certain number of years. These differences mean that males and females need to use different strategies to achieve reproductive success.

Before the invention of DNA testing, males could never be sure that they are the father of a particular child. As a result, a successful strategy for men would involve having sex with, and impregnating, as many women as possible in order to pass on their genes successfully. For women, however, the energetically expensive process of producing an egg, and then carrying a child in the womb for nine months, would mean that she needs a partner who will be committed to the relationship in the long run and provide resources for her and the child, ensuring the child’s survival. Therefore, females will look for a male partner who demonstrates these characteristics to enhance her, and her future offspring’s, chances of success.

These differences in mating strategies were demonstrated by Buss (1989), who surveyed over 10,000 adults in 33 countries. Buss found that females universally place more importance on resource-related characteristics in a partner, such as ambition, high intelligence and good financial prospects. Males, however, preferred younger mates and put more value on signs of a female’s ability to reproduce, such as attractiveness and modesty.

According to Buss (1995), the fact that males have much less certainty that the child they are raising is theirs can also explain the difference in jealousy experienced between males and females. Males tend to be more jealous of their partner’s sexual infidelity because this could result in a male raising someone else's child. Females, on the other hand, are more jealous of their partner’s emotional infidelity, as this may result in the withdrawal of resources from the female and the child, thereby putting the child’s survival at risk.

Inter-Sexual Selection

Anisogamy can also explain the existence of two types of sexual selection: inter-sexual selection and intrasexual selection. Inter-sexual selection is sometimes referred to as ‘female choice'. This is because it's based on the idea that females’ place a greater investment of time, energy and resources in raising a child, so they need to be more careful when choosing a partner. Females need to be sure that their partner will provide the right genetic fit, by being willing to and able to provide the necessary resources, to support them and their child. In essence, females prefer “quality over quantity” when it comes to sexual partners.

Female choosiness was illustrated in a study by Clark and Hatfield (1989). They asked male and female student volunteers to approach opposite-sex students individually on a university campus, asking them the same three questions: ‘I’ve noticed you around the campus. I find you very attractive. Will you go on a date with me/come back to my apartment/go to bed with me tonight?’. Although around 50% of both males and females agreed to go on a date, the researchers found marked gender differences in the other responses: 69% of males accepted the invitation to visit the female’s apartment compared to only 6% of women, and 75% of male students agreed to go to bed with the females; however, not a single female said ‘yes’ to the same request.

Intra-Sexual Selection

Intra-sexual selection, on the other hand, is a preferred male strategy. It refers to the evolutionary developed features that allow a male to compete with other males for a female mate. The winner of this competition reproduces and passes on the genes that contributed to his success. For example, a physically stronger and larger male will be able to fight off his competitors for access to the female, so he will produce physically stronger sons. Anisogamy suggests that “quantity over quality” is a male’s optimal mating strategy for success, meaning he will mate with as many female partners as possible.

Intra-sexual selection also can explain the differences in the body size and physical appearance between males and females which is known as physical dimorphism. As males need to compete with other males for access to a fertile female mate, sexual selection favours physically strong and aggressive males. However, females do not need to physically compete for a mate, meaning that physical strength and aggression will hold no evolutionary advantage for females and there is, therefore, no evolutionary advantage for a female to be larger or stronger in order to attract a mate.

Research Examining Sexual Selection and Human Reproductive Behaviour

The principles of sexual selection mean that males and females use different strategies to select a suitable mate. Since human females do not advertise their fertility openly, unlike some animal species (for example, redness and swelling of the genitalia of female baboons), males have evolved to pay attention to other signs in a human females’ appearance that show her ability to produce healthy offspring. Buss (1989), as mentioned earlier, has discovered that males universally put importance on attractive and healthy looks and youth, which are signs of fertility in humans.

Further evidence comes from research carried out by Singh (1993, 2002) who studied preferred waist-to-hip ratio as a sign of female fertility. Studying the measurements of the waist-to-hip ratio of the winners of the Miss America contest for a decade, she found that men generally found any waist and hip sizes attractive, as long as a ratio between them is approximately 0.7. A female having larger hips and a slim waist achieves this ratio, and men unconsciously interpret this as a sign that the woman is fertile but not currently pregnant.

Women, on the other hand, have adapted to look for the signs of male’s ability to provide resources and protect themselves and a child. For example, Waynforth and Dunbar (1995) researched ‘lonely hearts’ columns in American newspapers and discovered that women tended to describe themselves in terms of physical attractiveness and youth (‘exciting, flirty, curvy’). Men, on the other hand, advertised their resources and intelligence more than women did.

Evaluation of Evolutionary Explanations of Relationships

Evolutionary explanations ignore the significant social and cultural changes that Western societies have experienced in the past 100 years, in terms of gender equality and women’s independence. Kasser and Sharma (1999) found, in their analysis of 37 cultures, that females mostly valued a mate with resources in societies where women’s access to education and the workplace was severely limited. However, women in modern Western societies may no longer be looking for a man to provide them with resources and thus other qualities in a mate become more important such as being thoughtful or having a good sense of humour. This means that evolutionary explanations are limited, since they only explain human mate choice in terms of evolutionary adaptiveness, ignoring other important factors, such as culture and social norms.

There are many methodological weaknesses in the research which evolutionary psychologists’ use to support their claims that women prefer high-status and well-resourced men. Most of the studies into females’ choice of mates were carried out on undergraduate students. As these women were expected to achieve a high education status leading to a secure income, their preference for high-status men may stem from similar interests and prospects, rather than an innate mechanism. Furthermore, research into evolutionary explanations may also lack validity since studies only measure expressed partner preferences rather than real-life ones. Since research often takes a retrospective approach, largely based on speculations about what may or may not have been evolutionary adaptive for our ancestors, it means that there is no reliable way to check whether these suggestions are valid.

 Mate choice may be more complicated than suggested by evolutionary explanations. For example, research by Penton-Voak et al. (1999) suggests that females’ mate preferences change across the menstrual cycle. They found that females preferred a partner with strongly expressed masculine features during their fertile period but showed a higher preference for a partner with slightly feminised features as a long-term mate. This may be because masculine appearance suggests a healthier immune system - which would be advantageous to pass to offspring - while slightly feminine features suggest kindness and parental cooperation which are very desirable traits in a long-term partner.  Thus, arriving at a clear-cut conclusion for mate selection using evolutionary principles may not be as simple as initially thought.

Extension Evaluation: Issues & Debates

Evolutionary explanations of relationships suffer from evolutionary reductionism, as they argue that strategies for choosing a mate are the result of genetic inheritance and a striving for reproductive success. However, this is not always straightforward in real life, where individual differences in partner’s choice play a huge part. For example, evolutionary explanations fail to account for homosexual relationships where the choice of partner does not result in reproductive success and so doesn't have an evolutionary advantage. Likewise, evolutionary explanations of relationships also suffer from determinism, as they seem to claim that choice strategies are determined by a person’s gender and that humans are attracted to people who will have, provide and/or care for offspring.

Furthermore, evolutionary explanations of mate preference also emphasise the differences in what males and females look for in a potential partner. This exaggeration of the differences between the genders is known as an alpha bias, where the differences between males and females may be overstated. It is plausible to argue that males and females look for similar characteristics, such as loyalty and kindness, and such characteristics are not reported in the research, which tends to look for marked differences.

Possible exam questions

Possible Exam Questions

1. Define the term sexual selection. (2 marks)

2. Identify which two responses from A, B, C, D and E below are important features in evolutionary explanations for partner preferences. (2 marks)

Anisogamy

Inter-sexual selection

Self-disclosure

Contraception

Complementarity

3. A researcher from a red-brick university in the UK is completing the references section of her scientific report on human relationships. She needs help to modify the information below into the correct format for submission to her academic tutor. She has the following information:

Charles Darwin wrote a book in 1859 entitled ‘On the origin of species’. It was published in London by John Murray.

Write the full reference for this publication so that it is appropriate to appear in the reference section of the scientific report. (2 marks)

4. Explain what is meant by inter-sexual selection. (3 marks)

5. Briefly outline an evolutionary explanation for partner preferences. (3 marks)

6. Explain one limitation of the evolutionary explanation for partner preferences. (3 marks)

7. Describe one evolutionary explanation for partner preferences. (6 marks)

8. A psychologist wanted to carry out a study into the changes in partner preferences in the UK between three generations, using interview technique. He carried out face-to-face interviews with three groups of participants with 30 people in each and an equal male/female split: 20-25 years old; 40-45 years old and 60-70 years old. Participants were asked a variety of questions about their choice of partner and marital satisfaction. The psychologist found that 12 females in the 60-70 years age group valued high status men when just five in the 20-25 years age group did.

a) Suggest one question that could be asked in this interview. (2 marks)

b) Explain two reasons why an interview may be a more suitable technique for this research than a questionnaire. (4 marks)

c) Explain two differences between structured and semi-structured interviews. (4 marks)

d) Calculate the percentage of females in the 60-70 years and the 20-25 years age groups showing a preference for high-status men. Show your working. (4 marks)

9. Explain one limitation of the sexual selection explanation of partner preferences. (3 marks)

10. Simon has recently split up with his girlfriend of 6 years and decided to place an advert on a dating website. He describes himself as an intelligent 36-year-old with a stable job who is looking for a 25-30 years old woman with a sexy figure and a bubbly personality.

Using your knowledge of sexual selection theory, explain Simon’s advert. (4 marks)

11. Briefly outline the findings of one study into evolutionary explanations for partner preferences. (4 marks)

12. Monica is a beautiful 21-year-old teaching assistant who has just married her husband Chandler, a 48- year old Executive Head Teacher responsible for overseeing six secondary schools. The couple do not have any children together, but Monica hopes to become pregnant imminently.

With reference to the case of Monica and Chandler, explain the relationship between sexual selection and human reproductive behaviour. (5 marks)

13. Briefly outline and evaluate evolutionary explanations of partner preferences. (8 marks)

14. Discuss what research has shown about partner preferences in males and females. (8 marks)

15. Describe and evaluate the relationship between sexual selection and human reproductive behaviour. (16 marks)

16. Discuss evolutionary explanations of partner preferences. (16 marks)