Glenn Wilson PhD, Gresham College, London

1. FOR BETTER OR WORSE? HOW WE PICK OUR PARTNERS Glenn Wilson PhD, Gresham College, London

2. PARTNER PRIORITIES Physical attractiveness is valued by both men and women but women place more importance on traits relevant to resource provision (wealth, status, dominance, creativity, generosity). For men, the priority is fertility (youth and beauty). Hence trade-offs are not uncommon. Mrs Merton: “Debbie, what was it that first attracted you to millionaire Paul Daniels?”

3. PARENTAL INVESTMENT Females are more picky about partners because they invest more in parenthood. Eggs are scarcer than sperm and the costs of squandering them high (Trivers, 1972). Hence men favour short-term strategies while women look for commitment. Men are also more inclined to be visually aroused and promiscuous. Males compete with each other for access to fertile females and enterprising courtship is usually required.

4. Data from Symons & Ellis, 1989.

5. A SCIENCE OF PARTNER MATCHING? Many superstitious and bogus theories: • Astrology • Palm-reading • Biorhythms • Numerology Opposites attract is a popular lay theory but has little supporting evidence. Similarity (“birds of a feather”) is best supported. People gravitate towards, and are happier with, those who are like themselves.

6. A COMPATIBLE PAIR: SHARED TASTES

8. MATCHED COUPLES DO BETTER Couples who are similar in body build and whose physical attractiveness is roughly equivalent are more likely to get together and to stay together. Couples matched on certain personality traits like agreeableness, conscientiousness and openness are also more likely to stay together (Rammstedt & Schupp, 2008), though other traits (extraversion & emotional instability) do not show assortative mating. Prospects bleak?

9. ESTABLISHED AREAS OF HOMOGAMY • Age (albeit males slightly older) • Race and religion • Socioeconomic status/IQ/education • Anthropometrics (e.g., height, weight) • Physical attractiveness • Personality (but only certain traits) • Attitudes/leisure interests/habits • Sex drive & permissiveness

10. TYPICAL GENDER DIFFERENCES Where men and women differ significantly on a trait, relationships work best if a couple replicates that difference. Tall men marry tall women but not as tall as themselves; short men marry women even shorter. Reversals of this tend to be unstable. With personality, couples are happier when traditional differences are present (he tougher, she more sensitive). Both partners are happier if the male is slightly older (3-5 yrs).

11. AGE RANGES OF PREFERRED PARTNERS Men generally prefer younger women; women prefer older men (Data from Kenrick & Keefe,1992).

12. COUPLES WHERE MAN IS OLDER ARE MORE FERTILE From Fieder & Huber (2007)

13. THE COMPATIBILITY QUOTIENT (CQ) Comprises 25 items covering areas known through research to be important for relationship success. Answered independently by two individuals. Each item offers 5 response categories arranged on scale such that those further removed are less compatible. A total discrepancy score is calculated between the responses of the two people. This “raw score” is converted to a CQ based on a normal curve of M = 100, SD = 15 (c.f. IQ)

14. TYPICAL ITEM What is your view of pornography? 1. Disgusting 2. Prefer to avoid 3. OK sometimes 4. Harmless fun 5. A great turn-on (Answers 1 and 5 are most incompatible; those adjacent much less so. CQ scores are derived from total discrepancy summed across all items and applied to the normal curve).

15. MEANING OF CQ SCORES 145+ Freak identity: Typical of test-retest reliability (same person doing the test twice) or identical twins. 130-144 Extremely compatible: Exceptionally high degree of similarity. <2% of couples. 115-129 Very compatible: <20% of couples. 100-114 Above average: Might work but issues to be dealt with. 85-99 Below average: Warning bells sounding. 70-84 Rather incompatible: Loud warning bells. <70 Incompatible: Don’t even think about it! Validity of the CQ was established by showing that couples have higher CQs than randomly paired individuals and that happily married couples have higher CQs than those less contented.

16. POSSIBLE APPLICATIONS OF CQ Locating someone compatible that you have not yet met e.g., through dating websites. Assessing prospects for long-term happiness with a new partner in early stages of courtship. Diagnosing problematic areas in prenuptial or marriage guidance counselling. Assigning airline seating, holiday or dormitory-type accommodation.

17. SPEED-DATE CHOICES CQ scores predict desire to pursue a relationship after a brief (3-min) speed-date encounter and even immediate (first 30 sec.) attraction. Mean CQs: Mutually attracted couples: 108.0 Couples wanting to meet again: 107.7 Not attracted: 101.2 Couples not wanting to meet again: 102.7 Effects driven mainly by female preferences. Women seem to be better at detecting compatible long-term partners, or is it that men are just thinking short-term? (Wilson, Cousins & Fink, 2006).

18. EXPLANATIONS FOR THE SIMILARITY EFFECT • Propinquity– we meet & marry people who are similar because they work/live nearby. • Sharing activities – “those who play together stay together”. • Egotism – preferring people who agree with us on controversial issues and who remind us of ourselves. • Genetic similarity – attraction to those who share our own genes. • Imprinting – modelling partner on opposite-sex parent.

19. I LIKE YOU – YOU’RE LIKE ME People with alliterative first names (e.g. Barry & Barbara) pair off more than chance. Same surname marriages also exceed chance: (e.g., Smith/Smith 198, Jones/Jones 125, Smith/Jones 62). People given arbitrary codes similar to our own birth-date are judged more likeable. (Jones et al, 2004)

20. GENETICS OF PARTNER CHOICE Rushton & Bons (2005) studied 174 MZ and 148 DZ twin pairs as well as their best friends and spouses. MZ twins chose partners (& friends) more similar to those of their co-twins than did DZ twins (esp. with respect to heritable traits). Variation in partner choice estimated as 34% genetic, 12% sharedenvironment(e.g., family values) 54% unique environment (e.g., being at the right place/right time). Argued that choosing genetically similar partners helps perpetuate one’s own genes.

21. GENETIC SEXUAL ATTRACTION When close family members are reunited after being raised separately they often experience immediate and powerful sexual attraction. These siblings, Patrick & Susan Stubing live together in Germany and have two children despite having been jailed for incest. They did not meet until their 20s, hence no Westermarck Effect.

22. COUSIN MARRIAGE Cousin marriage is forbidden in many places although the genetic overlap (25%) is less problematic than with siblings (50%). Darwin married his cousin Emma shortly after returning from his Beagle voyage.

23. CHILDHOOD IMPRINTING OF SEX TARGETS Cross-fostering studies (Kendrick et al, 1998) reveal importance of mother-image. Lambs raised by a goat mother (left) and kids raised by a sheep mother (right) fancy the “wrong” species when grown up (esp. true for males, who depend more on visual “targets”.)

24. THE OEDIPUS EFFECT Hawaiians of mixed race tend to marry into ethnic group of opposite-sex parent (Jedlicka 1980). Daughters of older men choose older partners (Zei et al, 1981). Women fall in love with men of eye colour more similar to their father than their mother (Wilson & Barrett 1987). Both men and women choose partners more similar to their opposite-sex parent in both eye and haircolour (Little et al, 2003). Photos of wives are correctly matched by external judges to mothers-in-law beyond chance (Bereczkei et al 2004).

25. MATCHING PARTNER WITH PARENT Partner preferences are affected by the quality of parent-child relationships. Daughters with good relationships with their father prefer men with similar facial structure - those with bad relationships do not. (Wiszewska et al, 2007).

26. ONE’S SPITTING IMAGE? Resemblance between men’s wives and their mothers is greater when the relationship with the mother was good (Bereczkei et al, 2004)

27. FAMILIAL SMELLS The major histocompatibility complex (MHC) governs our immune system and can be detected by smell. Animals prefer to mate with individuals of dissimilar MHC, which would serve to broaden the immune system of their offspring. There is some evidence that this applies to humans but women vary according to their breeding mode. They prefer dissimilar mates when fertile and similar mates when needing family support (e.g., when already pregnant). Women are more affected by smell than men, which might be why they are so fond of kissing – chance to sample the chemicals. (Havlicek & Roberts, 2009)

28. INSTINCTS THAT DESTABILISE MARRIAGE

29. A SEVEN YEAR ITCH? There may be some truth to the idea of a “seven year itch”. According to a UK MORI poll, one in five wives wish they were not married and one in seven husbands. Peak discontent occurs in years 6-9 of marriage, when a third of people wish they were not married. Cross-culturally, the peak for actual divorce occurs earlier (around 4 years into marriage, which might connect with the period of time needed to raise an infant.

30. DIVORCE DECLINING Divorce rates depend on the strength of social pressures against. They increased steeply in the Western world following the liberalisation of divorce laws but are now declining because people are marrying later or not at all. Divorce rates: England & Wales

32. Data from Buckle et al, 1996.

33. LOVE-RAT GENES Sexual novelty-seeking is more striking in males than females because of prenatal effects of testosterone on the brain. The evolutionary basis of the sex difference is parental investment. Specific genes that relate to vasopressin levels are associated with bonding deficits and marital problems in men. (Walum et al, 2000 .

34. FEMALE INFIDELITY Women also have motives for “extra-pair copulation”. e.g., fertility insurance (2-3% of children apparently not sired by official father) and mate retention (keeping partner on his toes). Twin studies (Cherkas et al, 2004) show that variation in female infidelity is 41% genetic. (22% of sample reported infidelity to a long-term partner).

35. SPERM COMPETITION A clue that human females have a natural capacity for infidelity comes from comparisons among the apes. Gorillas defend harems by strength, hence their sperm does not need to compete with rivals and their testicles are small. Humans are nearer to the chimpanzee pattern, where female promiscuity promotes selection of larger testicles. In monogamous species (e.g., gibbons) males and females are the same size.

36. MATE POACHING AND RETENTION Mate poaching tactics: Flaunting physical charms (esp. women), advertising wealth, e.g., by expensive gifts, getting the partner drunk (esp. men), sense of humour, flattery, befriending the couple and awaiting an opportunity (both men and women). Mate retention tactics: Enhancing looks, flirtation, signals of possession (esp. women), vigilance, threatening rivals, concealing the mate (esp. men) monopolising time, punishing infidelity, being derogatory about competitors (both).

37. JEALOUSY: HIS AND HERS Jealousy has a different focus for men and women. For men it is the act of penetration, hence the risk that they will put resources into offspring not carrying their genes. For women the main concern is that her partner will form an alternative emotional attachment and thus transfer resources.

38. THE EVOLUTIONARY ARMS RACE Both men and women have evolved cryptic tactics for selecting, attracting, poaching, retaining and disposing of mates. These are overlapping, complex and equally devious. Flirtation, for example, may be used either for mate-poaching (stealing someone else’s partner) or mate retention (keeping one’s own partner vigilant). Strategies differ according the phase of a woman’s cycle and whether a short encounter or long-term mate is sought. All are geared to maximising the chances that the individual’s genes will be passed to the next generation.