Human Reproductive Behaviour and Sexual Selection (Relationships) Flashcards
Natural Selection
the gradual process by which nature selects the forms most fit to survive and reproduce in a given environment.
• the individuals with characteristics that are most suited to the environment are more likely to survive and reproduce
• the genes that allowed the individuals to be successful are passed onto the offspring in the next generation
• we have evolved adaptive behaviours that ensure our survival
Sexual Selection
• it seems that some individuals possess characteristics which do not immediately appear to be beneficial to their survival
• sexual selection argue that if a characteristic increases the chances of reproduction then the characteristic will be adaptive because the animal will have more offspring
• sexual selection is the selection of characteristics that increase mating success
Anisogamy
• humans are anisogamous- they produce gametes (reproductive cells) of different sizes
• male gametes are sperm: contain genetic material, stream line, lots of mitochondria, many of them, enzymes
• female gametes are eggs: contain genetic material, only one released, larger
Inter and Intra sexual selectin
In anisogamous species, the female invests more energy in reproduction than the male, so it leads to two different types of sexual
selection…
-inter-sexual selection: (preferred choice of females) is where one sex chooses traits they desire in the other sex (like the birds of paradise)- this selection is between the sexes- quality strategy (selective)
• preferred because females make a greater investment of time, commitment and resources before, during and after birth (Trivers 1972)
• females choose to mate with males who are strong and can provide resources, males choose females who look youthful as a sign of fertility
-intra-sexual selection: (usually males) competition between members of same sex- this selection is within each sex- quantity strategy (indiscriminate)
Sexual Strategies Theory
• sexual strategies theory (SST) is an evolutionary theory of mating strategies that both males and females adopt under different circumstances. Buss and Schmitt (1993) depending on culture, social context, parental influence, and personal mate value (desirability in the ‘mating market’)
• female strategies of careful mate selection, monogamy and high parental investment maximise chances of successful reproduction. Females seek males displaying genetic fitness, such as strength, status and resources
(Female Intersexual strategies) Fisher (1930)
sexy sons hypothesis
• a woman chooses a man because he has a characteristic she wants (e.g. tall male)
• any male children she has will inherit this characteristic and will be more desirable to women
• over generations the characteristic becomes more pronounced- this is known as the runaway process
• this only stops when the trait becomes too costly or female preference changes
(Female Intersexual strategies) Zahazi (1975)
handicap hypothesis
• a woman chooses a man with handicaps because it advertises his ability to thrive despite handicaps, demonstrating genetic superiority
• e.g. females finding males attractive who drink or take drugs in large amounts- demonstrated an ability to handle toxins, a sign of genetic fitness
(Male Intrasexual strategies) Quantity over quality
• this refers to the competition between members of the same sex for access to members of the opposite sex
• in most cases this means males fighting with each other for access to females
(Male Intrasexual strategies) Sexual dimorphism
is a result of mate competition
• the winners get to mate and pass on their genes. Whatever traits lead to success in these same-sex contests will be passed on to the next generation
sexual dimorphism concerns the different characteristics that males and females possess • males on average 12-15% larger than females • also includes secondary sexual characteristics • males: deeper voice, facial hair • females: breasts, hips, smoother skin
These features increase the chances of survival into adulthood and sexual maturity, where genes are passed to the next generation
(Male Intrasexual strategies) Sneak Copulation
• males mate with females other than their partners if given the opportunity as it increases their chances of reproductive success
• women gain from this by having a wider genetic diversity to their children, increasing survival chances
• women can also gain by being in a relationship with a resource-rich male, while copulating with a genetically fit stud
(Male Intrasexual strategies) Sperm Competition
• physically size matters for men
• behaviourally- aggression could work
• compete by producing larger testicles bigger ejaculations and faster-swimming sperm
Cartwright 2000
both men and women prefer symmetrical faces
• symmetry equates with reproductive fitness
• Cartwright also found that women with symmetrical breasts are more fertile
• AND women with symmetrical male partners have the most orgasms
• supports the concept that physical attractiveness is driven by increased ability to reproduce
Buss 1989
‘What do Women want?’
• conducted large cross-cultural study into human mating preferences
• >10,000 people, 37 cultures across 33 countries
• found consistent sex differences
Women wanted: good financial providers, ambition and industriousness, tall and strong, older than them, symmetrical face and body
Men wanted: younger, chaste, healthy and physically symmetrical good waist to hip ratio
• supports the predictions about sex differences in partner preference are biological in nature
(Evaluation of evolutionary explanation) oversimplification
• the evolutionary explanation presumes heterosexuality and that all relationships are sexual
• it cannot explain couples choosing not to have children as it assumes all relationships are motivated by a desire to reproduce
Clark and Hatfield 1989
• attractive male and female psychology students (confederates) approached opposite sex strangers on a university campus and asked one of three questions:
• would you go out with me tonight?
• would you come over to my apartment tonight?
• would you go to bed with me tonight?
Question: Female positive response / Male positive response
1: 50% / 50%
2: 6% / 69%
3: 0% / 75%
