U3-A

Parenting: Maternal and Paternal Involvement & Parent-

Offspring Conflict
Introduction:
From an evolutionary perspective, parenting refers to the behaviors aimed at ensuring the survival
and reproductive success of offspring, who carry an individual’s genetic material. However, maternal
and paternal investment in parenting differ due to evolutionary pressures, and these differences can
lead to conflict between parents and offspring.

Maternal Involvement:

Mothers generally show greater parenting investment due to biological and evolutionary reasons:

 Certainty of maternity makes mothers always 100% sure that the child carries their genes.

 High biological costs like pregnancy, childbirth, and breastfeeding naturally lead to high
parental investment.

 Human infants are born helpless and require prolonged care, which mothers are
evolutionarily adapted to provide.

 Studies (e.g., Anderson & Rutherford, 2013) show maternal nesting behaviors during
pregnancy, reinforcing this natural inclination.

Paternal Involvement:

Fathers' investment is generally lower and more variable. Two evolutionary hypotheses explain this:

1. Paternity Uncertainty Hypothesis:

Males are never fully sure the child is biologically theirs, which discourages heavy
investment.

2. Mating Opportunity Cost Hypothesis:

Since men can theoretically father many children in a short time, investing too much in one
child may reduce other reproductive opportunities. Hence, the cost of parenting is higher for
men in evolutionary terms.

However, male investment increases under certain conditions (e.g., low mating opportunities or high
paternal certainty).

Parent-Offspring Conflict:

According to Trivers’ theory (1974), conflicts between parents and children are natural and stem
from differing genetic interests:
  A child shares 50% of genes with each parent, but values its own survival more than that of
siblings or parents.

 Resource allocation is a common area of conflict—children demand more resources than

parents prefer to give.

 These conflicts arise in everyday decisions like weaning, sibling rivalry, and even in utero,
where fetuses may extract more resources from the mother’s body than is optimal for her
health (Haig, 1993).

Conclusion:
In sum, evolutionary psychology explains maternal and paternal involvement through biological
certainty and reproductive costs. While mothers invest heavily due to gestation and caregiving roles,
fathers are more strategic in their involvement. Parent-offspring conflict arises due to unequal
genetic interests and competition for resources, and it is considered an adaptive part of human
evolution.

U3-B
Kinship: Theory of Implicit and Inclusive Fitness and Its
Empirical Support
Introduction:
Kinship plays a crucial role in evolutionary psychology as it directly influences survival and
reproductive success. While direct reproduction ensures the passing of one's genes, aiding
genetically related individuals also increases the likelihood of shared genes being transmitted to
future generations. This is the foundation of inclusive fitness theory, which explains why humans
exhibit altruistic behaviors toward kin and prioritize close relatives over distant ones or strangers.

Theory of Implicit and Inclusive Fitness:

1. Inclusive Fitness Concept (Hamilton, 1964):

Inclusive fitness is defined as an individual’s own reproductive success plus the impact the individual
has on the reproductive success of genetically related others. This theory expanded Darwin’s notion
of "survival of the fittest" to include "survival of the genes," even if passed on by kin.

2. Hamilton’s Rule (c < rb):

Hamilton formalized the conditions under which altruism could evolve.

 c = cost to the altruist (in terms of reduced reproductive success)

 r = coefficient of genetic relatedness between helper and recipient

 b = benefit to the recipient (in terms of reproductive success)

Altruistic behavior will evolve when the cost to the helper is less than the benefit to the
recipient, weighted by their genetic relatedness.

3. Implications of the Rule:

  Closer relatives (e.g., siblings, parents, children—r = 0.5) receive more help than distant ones
(e.g., cousins—r = 0.125).

 Altruistic traits that follow this principle are evolutionarily favored, while traits violating it are
naturally deselected. This is called evolvability constraint.

Theoretical Applications of Inclusive Fitness in Kinship:

A. Sibling Relationships:
Siblings share 50% of their genes. Though they compete for parental resources, they also cooperate
in times of need. According to Sulloway (1996), birth order affects sibling behavior:

 First-borns are more conforming to parental expectations.

 Later-borns adopt rebellious roles for differentiation.

 Youngest often receive the most indulgent care.

B. Half-Siblings:
With only 25% genetic relatedness, altruism toward half-siblings is lower. Children from different
fathers/mothers may compete intensely for maternal care.

C. Grandparents:
Grandparents share 25% genetic relatedness with grandchildren. The “grandmother hypothesis”
suggests that post-menopausal women (especially maternal grandmothers) invest heavily in
grandchildren, enhancing their genetic legacy. Maternal grandmothers are biologically the most
certain of genetic ties.

D. Kinship Terminology and Universals:

Daly, Salmon & Wilson (1997) predicted universal patterns in kin cognition and behavior:

 Ego-centered terminology (e.g., my aunt).

 Differentiation by sex, generation, and genetic closeness.

 Emotional closeness and cooperation mirror genetic relatedness.

 Kin terms are used to invoke familiarity and solicit help even from strangers (e.g., "brother,
help me").

Empirical Support for Inclusive Fitness Theory:

1. Helping Behavior (Burnstein, Crandall & Kitayama, 1994):

Participants were more likely to help genetically closer relatives than distant ones or strangers,
especially in life-or-death situations.

 Younger kin were prioritized over older ones due to higher reproductive potential.

 Altruistic acts like rescuing from a fire followed Hamilton’s rule.

2. Siblings vs Friends (Stewart-Williams, 2008):

While participants felt emotionally closer to friends/mates, they were more likely to help siblings
when the cost of helping was high—indicating inclusive fitness taking precedence over emotional
bonds.

3. Kin Recognition Mechanisms:

 Smell: Infants can recognize their mother’s scent (Cernoch & Porter, 1985).

 Linguistic Labels: Languages differentiate kin based on lineage and relatedness (e.g., Marathi
distinguishes mama and kaka).

 Facial Resemblance: Kin recognition is enhanced by physical similarity, supporting selective

helping.

4. Stress and Kin Presence (Flinn et al., 2005):

Children in single-parent homes with no kin support showed higher cortisol levels, a marker of stress.
Presence of kin, especially maternal, helped reduce stress and enhanced well-being.

5. Grandparent Investment (DeKay, 1995):

Among four grandparents, maternal grandmothers were reported to invest most—supporting
predictions of certainty in maternal lineage influencing altruistic behavior.

6. Vigilance Over Kin Mating (Faulkner & Schaller, 2007):

People are more protective of their sisters’ mates than brothers’, aligning with the higher
reproductive risk and investment for women.

7. Emotional Closeness (Korchmaros & Kenny, 2001):

Emotional closeness was found to be positively correlated with genetic closeness. Emotional bonds
can act as proximate mechanisms guiding inclusive fitness-based behaviors.

Conclusion:

The theory of inclusive fitness provides a powerful framework to understand why humans prioritize
close kin in their altruistic behaviors. Hamilton’s rule gives a mathematical model predicting when
such behavior is likely to occur. Empirical findings from multiple cultures support the notion that
both genetic relatedness and reproductive value shape helping behavior, kin investment, and
emotional closeness. This demonstrates that kinship is not just social, but deeply rooted in
evolutionary psychology.

U3-C
Evolution of Cooperation and Reciprocal Altruism
Introduction:
Cooperation, defined as working together for mutual benefit, is a key adaptive behavior seen across
species and human cultures. It enables individuals to achieve common goals, such as hunting, child-
rearing, or defending territory. However, cooperation poses an evolutionary puzzle: why would an
individual help another at a cost to themselves, especially if the other is not a genetic relative?

Reciprocal Altruism Theory (Trivers, 1971):

Reciprocal altruism refers to the exchange of helpful acts between non-kin with the expectation that
the favor will be returned in the future. It transforms altruism into an adaptive behavior by ensuring
mutual benefit over time. For instance, a hunter who shares his game today may receive help when
unsuccessful in the future.

Humans who practiced this kind of cooperation were more likely to survive and reproduce, making
reciprocal altruism an evolved social strategy.

Conditions for Reciprocal Altruism to Evolve:

1. Frequent interactions among individuals.

2. Memory of past interactions.

3. Ability to detect and punish cheaters.

4. Benefit to recipient > cost to donor over time.

Prisoner’s Dilemma and Tit-for-Tat Strategy:

The Prisoner’s Dilemma illustrates the conflict between individual and collective gain.

 If both cooperate: moderate reward (R).

 If one defects while the other cooperates: defector gains (T), cooperator suffers (Sucker’s
payoff).

 If both defect: punishment (P).

When repeated over time (iterated dilemma), the best strategy is Tit-for-Tat:

 Start by cooperating.

 Then mirror the other’s previous move.

This strategy is effective because it rewards cooperation, punishes defection, and is forgiving. It
reflects contingent reciprocity, meaning cooperation depends on how others behave (Trivers, 1985).

Cooperation Among Non-Human Species:

1. Vampire Bats:
Survival depends on regular blood meals. If a bat fails to feed, it may receive regurgitated blood from
a bat who has excess—but usually only if they’ve helped that individual in the past. This shows
memory-based reciprocal altruism. Starving bats are also more likely to return the favor later.

2. Chimpanzees:
Frans de Waal’s study revealed that alliances among chimpanzees serve strategic purposes. An old
alpha male, after losing dominance, allied with a younger male to regain access to mating
opportunities. Though he received fewer mates than before, it was better than none—showing how
cooperation enhances reproductive success.
Conclusion:

Reciprocal altruism resolves the evolutionary puzzle of cooperation among non-kin by framing it as
mutually beneficial exchange rather than pure self-sacrifice. Supported by theories, game models
like the prisoner’s dilemma, and evidence from both humans and animals, reciprocal altruism is a key
adaptive strategy in the evolution of cooperation.

U3-D
Cognitive Adaptations for Social Exchange
Social exchange, including acts of cooperation and reciprocal altruism, has been critical for human
survival and social functioning. However, the risk of cheating—receiving benefits without
reciprocating—poses a challenge. Evolutionary psychologists propose that humans have evolved
specific cognitive adaptations to manage and sustain reciprocal relationships.

1. Social Contract Theory (Cosmides & Tooby)

This theory suggests that humans have evolved mental mechanisms to detect violations of social
contracts—essentially, to identify cheaters in cooperative exchanges. These adaptations help ensure
fairness and stability in social interactions.

2. Five Key Cognitive Mechanisms for Social Exchange

1. Individual Recognition:
Humans can easily distinguish others, which is essential for remembering past interactions
and reciprocating or withholding cooperation based on prior behavior.

2. Memory for Social Interactions:

Keeping track of who helped or cheated allows people to engage in contingent reciprocity—
helping only those who have helped in the past.

3. Communication of Needs and Intentions:

Effective social exchange depends on expressing expectations, dissatisfaction, and
boundaries, which helps manage cooperation and discourage exploitation.

4. Understanding Others’ Needs and Value:

Accurately assessing another person’s needs helps tailor help effectively, increasing the
chances of reciprocation and strengthening alliances.

5. Cost-Benefit Calculation:
Humans can generalize and compute the worth of various exchanged items (food, favors,
protection), aiding decisions about when and with whom to cooperate.

3. Cheater Detection and Logical Reasoning

Humans are better at solving social contract problems than abstract logic problems. For instance, in
the Wason card selection task, people perform poorly on logical versions but excel when the task is
framed as a social contract (e.g., verifying age and alcohol consumption), highlighting evolved
specialization in social reasoning.

4. Memory for Cheaters and Altruists

Humans have enhanced memory for individuals who cheat, as avoiding them is critical for survival.
Interestingly, people can also detect genuine altruists, often through subtle cues like facial
expressions (e.g., authentic smiles vs. contempt).

5. Costly Signaling and Banker’s Paradox

Helping others also serves as a form of costly signaling—altruism broadcasts resource availability
and trustworthiness, which can attract allies and mates. The Banker’s Paradox further explains that
individuals who are temporarily needy but reliable and irreplaceable are more likely to be helped.

Conclusion

Humans possess evolved cognitive systems tailored for detecting fairness, assessing social value, and
managing cooperative exchanges. These adaptations support the maintenance of reciprocal altruism
and protect against exploitation, ensuring the long-term benefits of social cooperation.