evolutionary explanations of behavior. quiz preview 1)what researcher is famous for introducing...

Evolutionary Explanations of Behavior

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Evolutionary Explanations of Behavior

Quiz Preview

1) What researcher is famous for introducing ideas of evolutionary theory and natural selection?

2) According to evolutionary theory, traits might contribute to evolution by providing either a ___________ _____________ or a ___________ _____________.

3) What term describes the idea that heritable characteristics that provide a survival or reproductive advantage are more likely than alternative characteristics to be passed on to subsequent generations?

4) According to Buss (1990), cross-culturally, what traits do men tend to focus on in mate selection?

5) What would be an evolutionary explanation for the results of Wedekind (1995)?

6) List two major criticisms of the evolutionary perspective.

Connections to Biology

• You have probably already learned about evolution in biology. Whose ideas/ theories are evolutionary theories based upon?

• What are the basic assumptions of evolutionary theories?

• Evolutionary psychology→ theoretical perspective that examines behavioral processes in terms of their adaptive value for a species over the course of many generations

• “Survival of the fittest”– Fitness refers to the reproductive success (number of

descendants) of an individual organism relative to the average reproductive success in the population

– Variations in reproductive success are what really fuels evolutionary change.

– Must mature and thrive before reproduction

• Darwin theorized traits might contribute to evolution by providing either:– Survival advantage– Reproductive advantage

• Natural Selection→ heritable characteristics that provide a survival or reproductive advantage are more likely than alternative characteristics to be passed on to subsequent generations and thus to be “selected” over time– Identified by Charles Darwin– Works on populations rather than on individual organisms.– Tends to be extremely gradual (over thousands to millions of

generations)

• Contemporary models of evolution recognize that natural selection operates gradually on the gene pool of a population

• Adaptation→ an inherited characteristic that increased in a population (through natural selection) because it helped solve a problem of survival or reproduction during the time it emerged– Due to gradual, incremental nature of evolution,

adaptations sometimes linger in a population even though they no longer provide a survival or reproductive advantage

• What could be an evolutionary explanation for why we prefer the taste of fatty substances?

• Humans taste preference for fatty substances was adaptive in an era of hunting and gathering when dietary fat was a scarce source of important calories.

• In modern world, preference for fatty foods has become a liability for human survival

– Many aspects of human nature reflect the adaptive demands faced by our ancient ancestors rather than contemporary demands.

Evolutionary Explanations of Poll Everywhere Questions

• You are on a boat that overturns. It contains your 5-year-old and 1-year-old children (of the same sex). The boat sinks and you can only save one. Whom do you choose to save?

• That same boat contains your 40-year-old and 20-year-old children (both of the same sex). Neither can swim. As the boat sinks, whom do you choose to save?



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Evolution and Sexuality

• Which gender has the stronger sex drive? Which gender thinks more about sex, masturbates more often, initiates more sex, and makes more sacrifices to gain sex?

• Evolutionary psychologists use natural selection to explain women’s more relational and men’s more recreational approaches to sex. – While a woman incubates and nurses one infant, a male can

spread his genes through other females. • In ancestral history, women most often sent their genes

into the future by pairing wisely, men by pairing widely.

• Clark and Hartfield (1989), in 1978, sent average looking student research assistants into the Florida State University quadrangle. Spotting a person of the other sex, a researcher would approach and say, “I have been noticing you around campus and I find you to be very attractive. Would you go to bed with me tonight?” All of the women declined, some obviously irritated. But 75% of the men readily agreed, often replying with comments such as “Why do we have to wait until tonight?”

• Clark and Hatfield repeated their study in 1982 and twice more during the late 1980s AIDS era. With similar findings each time.

Evolutionary Explanations of PollEverywhere Questions

• Would you rather marry someone older or younger than yourself?

• Of the following six, which three are most important in the selection of your mate?– Good financial prospects, youth, a caring/

responsible personality, physical attractiveness, ambition and industriousness, an exciting personality



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• Factors in attraction– Some aspects of attraction cross place and time.– Men judge women as more attractive if the

women:• Women with smooth skin and a youthful face- a sign of

many child bearing years yet to come• Are physically attractive

• What would be an evolutionary explanation for why men would prefer women that are physically attractive and young?

• Research shows that cross-culturally, men prefer women with a certain waist to hip ratio. What would be an evolutionary explanation for these findings?

– Have a waist that is approximately a third narrower than their hips (a sign of future fertility)- Singh (1994) found that men tend to be interested in fat distribution as a sign of future reproductive capability rather than body mass. Across all cultures, a waist to hip ratio of around 0.7 is seen as ideal for females—regardless of whether curvier or slimmer bodies are preferred.


– Women are especially attracted to men who seem:• Mature, dominant, bold and affluent- attributes that connote

a capacity to support and protect

– In looking for a mate, women prefer men with • Potential for long-term mating and investment in their

offspring – Offspring of men who stayed around probably had greater survival

prospects– Long-term mates contribute protection and support– For men there are trade-offs between seeking to distribute one’s

genes widely and being willing to co-parent

• Financial potential (ability to invest material resources in children)


– Each sex tends to advertise the qualities that maximize its odds of attracting desirable partners

• Women spend time and money on appearance• Men try to establish their status and dominance• In singles ads, women tend to offer looks and seek

status; men tend to do the opposite• Women report that they are most upset when men

exaggerate their social status, their financial resources or depth of their romantic commitment to the woman, whereas men are most upset when women conceal a history of promiscuity.

Jigsaw Essay Instructions

• With your group, read your assigned study and consider the following two questions:– What would be an evolutionary explanation for the results

of the study?– What are some limitations of the study you are assigned

that might limit the conclusions you are making? What are some strengths?

• Within your group assign one of the following roles to each person- claim writer, commentary writer, evaluator.– On p. 67 In your notebook, complete your assigned role.


• Claim Criteria– Does it directly tie back to the objective?– Does it give an overview of what you will be arguing in the

paragraph?• Commentary Criteria

– Does it tie specific evidence from the study back to the objective?

• Evaluation Criteria– Does the evaluation address some limitations of the study that

might limit the conclusions you are making?– Does the evaluation address some strengths of the study that

might strengthen the conclusions you are making?


• Come together with your group and critique one another’s responses. Make suggestions for what can be done to make each response better according to the criteria we established as a class. Make corrections to each the claim, commentary and evaluation constructed by your group members, and use the handout you were given to construct one paragraph using your study to answer the objective. You will present this paragraph to the class.

– Buss et al. (1990) conducted a study as part of the International Mate Selection Project to identify the characteristics that individuals valued in potential mates worldwide.

• Participant were 9, 474 individuals from 37 cross-cultural samples (33 countries and five islands on six continents; mean age 23.15). The data was collected through two questionnaires and translated.

– One questionnaire asked subjects to rate each of 18 characteristics on how important or desirable it would be in choosing a mate on a four-point scale ranging from 0 (irrelevant or unimportant) to 3 (indispensable)

– The second questionnaire asked subjects to rank each characteristic on its desirability in someone they might marry. They were instructed to give a ‘1’ to the most desirable characteristic, ‘2’ to the send most desirable, etc.

• “Good financial prospects”, “good earning capacity”, ambition and social status were consistently valued more in a partner by women than men cross-culturally. This was hypothesized to signify male capacity for providing resources for offspring.

• “Youth” is valued more by men than by women cross culturally. Men prefer wives that are younger but how much younger depends on the culture.

• “Physical attractiveness” in a partner is valued more by men than women. Cross-cultural norms of physical attractiveness are, for example, clear and supple skin, full lips and regular features.

• In line with evolutionary theories, youth and physical attractiveness were hypothesized to signify female reproductive value.

– Evaluation• Cultural limitations since the questionnaires originated in

the United States. Future research could start within each culture to identify preferred mate characteristics that may have been missed.

• The study suffered from problems of translation. Back translation in the questionnaires, which could decrease the validity of the results.

• Samples from each country were not representative so generalizability is limited. Rural, less educated and lower levels of socioeconomic status are underrepresented.

Evolutionary Explanation for Partner Selection Based on Genes

• According to evolutionary theories, natural selection would favor couples that have genes which mutually enhance their offspring’s chances of survival.

• Wedekind (1995) Sweaty t-shirt experiment to investigate mate preferences based on genetic makeup in relation to immune system functioning.– The experiment studied whether females would be able to

identify males who had a genetic make-up which, in combination with her own, would boost the immune system of potential children. The study focused on a particular complex of genes (MHC genes) in the immune system known for the ability to protect against pathogens.

• Major histocompatibility complex (MHC) genes are co-dominant, which means that both sets of inherited genes have an effect on the child’s immune system; so, the more diverse the MHC genes of the parents, the stronger the immune system of the offspring. It would be obviously beneficial, therefore, to have evolved systems of recognizing individuals with different MHC genes and preferentially selecting them to breed with.

– A group of 94 students (half male and half female) participated in the experiment. Each man was given a clean t-shirt (to be kept in a plastic bag) and asked him to wear it for two nights. To ensure a strong body odor, he gave the men supplies of odor free soap and aftershave and asked them to remain as “odor neutral” as possible.

– After two days the women were asked to rate how agreeable they found the smell of the t-shirts. The women had to smell seven different t-shirts. One was a control. Three of them contained t-shirts from men with an immune system similar to their own. Three contained t-shirts from men with an immune system that was dissimilar to the women’s own—this should be the best match in terms of genes.

– Results showed that women preferred the odors of men with an immune system dissimilar to their own. This lends support to the evolutionary explanations of mate selection in humans.

• However, preference was reversed it the women were on birth control.

– Odors of MHC-dissimilar men reminded the female test persons of their own mates or ex-mates twice as often as those of MHC-similar male odors, indicating that MHC-dependent body odor preferences play a central role in actual mate choice.

• What would be the evolutionary explanation of these results?

• The experiment demonstrated that attraction was influenced by biological factors. The women preferred men with a genetic make-up that could increase the health of potential babies.

Critiquing the Evolutionary Approach

• Starts with and effect (such as the gender sexuality difference) and works backwards to propose and explanation– May involve hindsight bias

• Difficult to test empirically and may be susceptible to confirmation bias

• Evolutionary theory is reductionistic and overly deterministic. Other levels of explanation are necessary.


• Underestimates or ignores the learning capabilities which influence behavior and that may even over-ride the influence of genetic evolution on behavior.

• Underestimates influence of culture in determining behavior– For example, Buss (1990) also found several cross-cultural

variations in preferences for mate selection that could not be accounted for by the evolutionary perspective. For example, the desire for chastity, or virginity, proved to vary the most cross-culturally. Chastity was valued in China, India, Taiwan, Palestinian Israel, and Iran. Respondents in the Netherlands and the Scandinavian countries did not care about chastity.

Final Quiz

1) What researcher is famous for introducing ideas of evolutionary theory and natural selection?

2) According to evolutionary theory, traits might contribute to evolution by providing either a ___________ _____________ or a ___________ _____________.

3) What term describes the idea that heritable characteristics that provide a survival or reproductive advantage are more likely than alternative characteristics to be passed on to subsequent generations?

4) According to Buss (1990), cross-culturally, what traits do men tend to focus on in mate selection?

5) What would be an evolutionary explanation for the results of Wedekind (1995)?

6) List two major criticisms of the evolutionary perspective?

Evolution and Emotion

• Rate each of the following pictures based on how much they disgust you.

• Scale of 1-5– 1 means it does not disgust you at all– 5 means extremely disgusting

• Text all answers to 37607

5- Text 794704- Text 794733- Text 794922- Text 795121- Text 79513

5- Text 80178 4- Text 801793- Text 801802- Text 801811- Text 80329

Evolution and Emotion• Some evolutionary psychologists argue that the emotion of

disgust allowed our ancestors to survive long enough to produce offspring, who in turn passed on the same sensitivities to us.

• Fessler (2006) investigated the nausea experienced by women in their first trimester of pregnancy.– Hypothesized that the nausea response helps compensate for

suppressed immune system.– Gathered 496 healthy pregnant women and after asking them a

series of questions to determine if they were experiencing morning sickness, he asked them to consider 32 potential stomach turning scenarios

• Women were asked to rank how disgusting they found each scenario

Evolution and Emotion

– Women in their first trimester (when immune system is lowered) scored much higher across the board in disgust sensitivity than their counterparts in the second and third trimesters

– When Fessler controlled for morning sickness, the response only held for disgusting scenarios involving food, such as maggots on a piece of meat

– Fessler argues that since many of the most dangerous diseases are food-born natural selection may have helped compensate for increased susceptibility for disease during this risky period of pregnancy be increasing the urge to be picky about food.

Evolution and Emotion• Curtis et al. (2004) carried out research on the

Internet to test whether there were patterns in people’s disgust responses– Participants (77,000 from 165 countries) were shown 20

images and asked to rank their level of disgust.• Among images were seven pairs in which one was infectious or

potentially harmful to the immune system, and the other was visually similar but non-infectious

• Disgust reaction was most strongly elicited for those images which threaten one’s immune system

• Disgust reaction decreased with age• Women had higher disgust reactions than men (supports idea of

disgust as key to reproduction)

Poll: On a scale of 1-5, how much does picture...


• Starts with an effect (such as the gender sexuality difference) and works backwards to propose an explanation– May involve hindsight bias

• Difficult to test empirically and may be susceptible to confirmation bias

• Underestimates influence of culture in determining behavior

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