Evolutionary Psychology Test 2

Parental Investment Theory

men evolved a greater desire for casual sex.

reproductive advantage is increased offspring production.

Potential Costs of Short Term Mating For Bed

STD’s, Social Reputation, Child Survival, Violence From Mates Partners.

Adaptive Problems Men Must Solve

• Partner number or variety – Desire for multiple mates.

• Sexual accessibility – Preference for sexually available women.

• Identifying fertility – Preference for cues of fertility.

• Avoiding commitment – Preference for low-investment partners.

Sperm Competition Theory

the evolutionary hypothesis that when females mate with multiple males within a short timeframe, the sperm of different males compete to fertilize her egg.

Evidence Supporting Sperm Competition Theory

Physiological Evidence

• Testicle size – Indicating sperm competition.

• Variations in sperm insemination – Increased sperm count after separation from a mate.

Psychological Evidence

• Desire for a variety of sex partners – Men desire more partners than women.

• Time elapsed before seeking intercourse – Men seek sex sooner.

• Lowering of standards – Men lower standards for short-term mates.

• Sexual fantasies and sex drive – More frequent and variety-seeking fantasies in men.

Behavioral Evidence

• Extramarital affairs – More frequent in men.

• Prostitution and OnlyFans – Men are primary consumers.

• Hookup culture, FWB relationships, and social media (e.g., Snapchat, Tinder) – Men more likely to pursue short-term sex.

Evidence for Women’s Short-Term Mating

• Women engage in casual sex across cultures.

• Orgasm function – Potential role in sperm selection.

• Timing of affairs – Occur during peak fertility.

Hypotheses About Adaptive Benefits for Women

• Resource Hypotheses – An individual may engage in mating behavior (including infidelity or manipulation) to obtain material benefits, protection, or higher social standing.

• Genetic Benefit Hypotheses –Sometimes, the social mate provides resources but may not be the "best" genetically. The individual might seek genetic benefits elsewhere (via affairs, for example) to enhance offspring quality.

• Mate-Switching Hypotheses –If a current mate is low quality, abusive, or offers fewer resources, an individual might engage in mating behaviors (flirting, infidelity) to "trade up" to a better partner.

• Short-Term for Long-Term Goals Hypothesis –Short-term mating or flirting may be used as a strategy to assess potential long-term partners. Engaging in short-term relationships provides information about mate quality, investment potential, or compatibility.

• Mate Manipulation Hypothesis – he Mate Manipulation Hypothesis is a theory from evolutionary psychology that suggests individuals use certain behaviors or tactics to manipulate their romantic or sexual partners (or potential partners) to maximize their own reproductive success

Costs of Short-Term Mating for Women

• Reputational damage

• Risk of physical abuse

• Pregnancy without male investment

• STDs and competition among offspring

Psychological and Physiological Adaptations

• Sexual jealousy – Emotional response to infidelity, motivating mate guarding.

• Attraction-reduction effect – Decline in attraction after sex, possibly reducing commitment.

Physiological adaptations are biological traits that have evolved to improve reproductive success and survival. In mating, these include:

• Testicle size – Larger testes indicate sperm competition in species with multiple mating partners.

• Sperm competition mechanisms – Increased sperm production after time apart from a mate.

• Time to copulation differences – Men are more likely to seek sex quickly compared to women.

• Mate guarding behaviors – Physical and hormonal responses to reduce partner infidelity risks.

Why Men Benefit from Marriage and Commitment

• Attracting mates – Women often required reliable signs of male commitment before consenting to sex.

• Higher-quality mates – Men willing to commit could attract more desirable women.

• Increased paternity certainty – Marriage provided repeated sexual access, reducing the risk of cuckoldry.

• Increased child survival – Children with an investing father had a higher survival rate.

• Reproductive success – Paternal investment helped children succeed in survival and mating.

• Higher social status – Marriage increased a man’s status, bringing additional benefits.

• Coalitional allies – Marriage provided allies through a wife’s family.

• Access to partner’s resources – In modern settings, marriage can grant access to a wife’s wealth.

• Increased lifespan – Married men tend to live longer, especially those married to younger women.

Importance of Fertility and Reproductive Value

• Reproductive value refers to the number of children a person of a given age and sex is likely to have in the future. Younger women have a higher reproductive value because they have more potential future reproductive years.

• Fertility is defined as actual reproductive performance, measured by the number of viable offspring produced. Women in their mid-20s tend to be the most fertile.

• Since men cannot directly observe a woman’s reproductive value, selection shaped male preferences for observable traits correlated with reproductive potential, such as youth and health.

Role of Paternity Certainty and Male Commitment

• Human males face a unique adaptive challenge: paternity uncertainty, since fertilization occurs internally within females.

• Marriage and long-term commitment increase a man's certainty of paternity by ensuring repeated sexual access to a single partner.

• Commitment also provides social and evolutionary benefits:

  1. Higher-quality mates – Women prefer men who show signs of long-term investment.

  2. Increased survival of offspring – Children with paternal investment have better chances of survival.

  3. Higher social status – In many cultures, being married elevates a man's social standing, increasing access to resources and allies.

  4. Longer lifespan – Married men tend to live longer, particularly if married to younger women.

Cues to Female Fertility & Reproductive Value- Physical Attractiveness

• Facial Symmetry – A cue to developmental stability, indicating resistance to environmental stressors and good genes.

• Clear Skin – Signals health and the absence of disease. Smooth, unblemished skin is universally attractive.

• Waist-to-Hip Ratio (WHR) –

  • A low WHR (≈0.70) is universally preferred because it correlates with higher fertility and better reproductive health.

  • Women with lower WHRs have higher estradiol levels, a hormone associated with reproductive success.

Cues to Female Fertility & Reproductive Value- Behavioral Cues

• Youthfulness – Since fertility declines with age, men evolved a preference for youthful features (e.g., bright eyes, full lips, and smooth skin).

• Energy Levels & Gait – A lively, youthful gait and high energy levels are indicators of good health and reproductive potential.

• Vocal Pitch – Higher-pitched female voices are perceived as more feminine and attractive, and they correlate with youth and estrogen levels.

Why Men Commit to Long-Term Mates-Paternal Investment Benefits

• Human infants require prolonged care, unlike other primates. A father’s investment increases child survival rates.

• Among the Ache Indians of Paraguay, children without an investing father have a 10% higher death rate.

• Fathers provide teaching, protection, and resources, improving their offspring’s chances of future reproductive success.

Why Men Commit to Long-Term Mates- Cooperative Benefits → Raising Offspring Successfully

Marriage and long-term commitment increase cooperation between parents, leading to:

• Better survival rates for children.

• Stronger kin networks for protection and resource sharing.

• Social alliances that benefit both the man and his offspring.

Parental Investment & Sexual Selection

• Parental investment is defined 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” (Trivers, 1972).

• The sex that invests more in offspring (typically females) is more selective about mating, while the sex that invests less (typically males) competes for access to mates.

Differences in Male vs. Female Investment:

• Females: Produce larger gametes (eggs), experience internal fertilization, gestation, and lactation. This leads to high parental investment.

• Males: Produce smaller gametes (sperm), do not experience gestation or lactation, and have the potential for higher reproductive rates with less obligatory investment.

Preferences for Resource Acquisition, Commitment, and Protection:

• Women evolved to prefer mates with access to resources, commitment, and protective abilities.

• This ensures that their offspring survive and thrive in competitive environments.

Cues Like Generosity, Stability, Ambition, and Emotional Stability:

• Generosity signals a willingness to share resources.

• Stability and emotional stability indicate reliability in providing resources and protection over time.

• Ambition and industriousness are predictors of a man’s ability to acquire resources.

Age-Related Patterns in Research:

• Across cultures, women prefer men who are about 3.5 years older on average.

• Older men tend to have greater resources, higher social status, and more life experience, making them more attractive long-term partners.

Empirical Evidence for Women’s Mate Preferences- Financial Resources, Social Status, and Financial Prospects:

• Women consistently rate financial resources as an important factor in mate selection.

• Cross-cultural studies confirm that women value financial prospects roughly twice as much as men do.

• Higher social status is associated with greater access to resources and social connections, making it a desirable trait in mates.

Physical Protection → Height, Strength, Athleticism:

• Women prefer taller men, as height is linked to dominance, protection, and social status.

• Athletic ability signals physical prowess, which can deter threats and provide better hunting and resource acquisition.

• Men with broad shoulders, muscular builds, and strength are viewed as more desirable for long-term mating.

Emotional Stability and Kindness as Indicators of Commitment:

• Emotional stability predicts a low likelihood of unpredictable behavior and consistent investment in offspring.

• Kindness and altruism are universal traits preferred by women, as they indicate a man’s willingness to provide and nurture.

Commitment Cues → Acts of Love, Exclusivity, Willingness to Invest:

• Men demonstrate commitment through acts of love, such as gift-giving, expressing emotions, and investing time and resources into a relationship.

• Exclusivity and fidelity signal a man’s dedication to one partner, increasing paternal certainty and investment.

• Men who engage in positive interactions with children are viewed as more attractive for long-term relationships.

The Role of Love in Signaling Long-Term Mate Value:

• Love is a universal phenomenon across cultures, with studies showing that it enhances relationship satisfaction and ensures long-term investment.

• Research indicates that acts of love, such as talking about marriage and future planning, are reliable signals of commitment.

• fMRI studies suggest that love activates brain regions linked to reward and attachment, reinforcing long-term bonding and investment in a mate.

Differences in Maternal vs. Paternal Investment:

• Maternal investment is typically higher due to gestation, lactation, and direct child care, which are obligatory in most mammalian species.

• Paternal investment varies and is influenced by paternity certainty and mating opportunity costs.

  • Paternity Uncertainty Hypothesis: Since men cannot be 100% sure of genetic relatedness, they invest less in offspring than mothers.

  • Mating Opportunity Cost Hypothesis: Investing time in children limits a male’s ability to pursue additional mates, making paternal care a trade-off.

Factors Influencing Which Children Receive More Investment

• Genetic Relatedness: Parents invest more in children they believe are biologically theirs.

• Health & Viability: Healthier children are prioritized because they have a higher chance of survival and reproduction.

• Birth Order: Firstborns often receive more investment as they represent a parent’s initial reproductive success.

• Parental Resources: When resources are scarce, parents may selectively invest in children who show greater survival potential.

Evolutionary Explanations for Differences in Step-Parent Investment

• Step-parents invest less in stepchildren because they do not share genetic relatedness.

• Studies show stepchildren are at higher risk of abuse or neglect compared to biological children (referred to as the Cinderella Effect).

• Infanticide risk is higher in stepfamilies because new mates may not want to invest in unrelated offspring and may prioritize future reproduction with their own genes.

Mother-Offspring Conflict

• Weaning Conflict:

  • Offspring want to continue receiving maternal resources (breastfeeding), while mothers want to wean children to conserve resources for future offspring.

  • This leads to a period of resistance and struggle between mother and child.

• In Utero Resource Allocation:

  • Fetal competition for nutrients can lead to conflict between mother and fetus.

  • Example: The fetus releases human chorionic gonadotropin (hCG) to keep the pregnancy viable, while the mother’s body regulates nutrient flow to maintain her own health.

Kin Networks & Alloparenting

• Grandmother Hypothesis:

  • Suggests that post-reproductive women (grandmothers) enhance offspring survival by helping raise grandchildren.

  • This provides an evolutionary advantage by increasing indirect fitness (ensuring genes survive through younger generations).

• Cooperative Breeding Benefits:

  • Human children require extended care, making cooperative child-rearing (alloparenting) beneficial.

  • Siblings, aunts, and unrelated group members may help raise children, improving survival rates.

Altricial

Altricial: Offspring are born helpless and underdeveloped, requiring long-term care (e.g., human infants).

Precocial

Precocial: Offspring are born more mature and independent, requiring less parental care (e.g., horses, deer).

Cuckoldry Threat:

• Refers to the risk of investing in offspring that are not biologically one's own.

• This explains male jealousy and mate-guarding behaviors, as men seek to ensure paternal certainty.