Social Behaviour
How biology and learned experience shape attraction, aggression, attachment, social support, and the evolutionary logic behind mating and altruism.
Human social behavior runs on a mix of biology and learned experience: what draws people together, what triggers aggression, how a child bonds with a caregiver, how people support one another, and why evolution favors mating strategies and even self-sacrificing acts. This article covers the mechanisms behind attraction, aggression, attachment, social support, and the evolutionary logic of social behavior — mating systems, mate choice, altruism, game theory, and inclusive fitness.
Key Takeaways
Attraction is driven by similarity, self-disclosure, reciprocity, and proximity (via the mere exposure effect), along with physical factors like symmetry and body proportion.
Aggression is shaped by the amygdala (increases it), the prefrontal cortex (decreases it), testosterone (increases it), and Berkowitz's cognitive neoassociation model, which links negative emotional states to aggressive responses.
Attachment, per Ainsworth's Strange Situation, comes in four styles: secure (caregiver preference, consistent comfort-seeking), avoidant (no preference, no distress), ambivalent (distress with inconsistent response), and disorganized (no clear pattern, associated with abuse).
Social support has five types — emotional, esteem, material/tangible, informational, and network — and higher support is linked to better mental and physical health outcomes.
Foraging behavior is governed partly by the hypothalamus (lateral promotes hunger, ventromedial promotes satiety) and partly by genetics, cognition, and social learning.
Mating systems (monogamy, polygyny, polyandry, promiscuity) and mate choice mechanisms (phenotypic benefits, sensory bias, Fisherian/runaway selection, indicator traits, genetic compatibility) explain how and why particular traits and relationship structures evolve.
Altruism, per Batson's empathy-altruism hypothesis, may be driven by genuine empathy rather than self-interest, though this remains debated against cost-benefit accounts.
Game theory and Maynard Smith's evolutionary stable strategy (illustrated by the Hawk-Dove game) explain social strategy in terms of four outcomes: altruism, cooperation, spite, and selfishness.
Inclusive fitness (Hamilton) measures success by including the reproductive success of relatives, explaining how altruistic and self-sacrificing behavior can still improve a species' overall fitness.
Attraction
Interpersonal attraction is the phenomenon of individuals liking each other. It's shaped by several factors:
Similarity — people tend to be attracted to others with similar attitudes, intelligence, education, height, age, religion, appearance, and socioeconomic status. This is partly a matter of convenience: it's easier to spend time with people who enjoy similar things.
Self-disclosure — sharing one's fears, thoughts, and goals with another person. When met with non-judgmental empathy, self-disclosure deepens attraction and friendship. It has to be reciprocated, though — one-sided disclosure can come across as someone being taken advantage of.
Reciprocity — captured by reciprocal liking: people like others better when they believe those others like them.
Proximity — being physically close to someone increases the likelihood of friendship forming, partly through convenience (it's easier to talk and make plans with people nearby). This connects to the mere exposure effect (also called the familiarity effect): people prefer stimuli they've been exposed to more frequently, so simply being around someone repeatedly tends to increase liking.
Appearance plays a role too — facial symmetry is linked to attractiveness, and people also tend to be drawn to body proportions that approximate the golden ratio (1.618:1).
Attraction doesn't always require similarity. Sometimes opposing qualities attract — the "opposites attract" pattern — because people are drawn to have their own values and choices validated by another person (for example, a nurturer pairing with someone who craves nurturing). Even these relationships tend to work only when the pair still shares some fundamental similarities underneath the surface difference.
Aggression
Aggression is behavior that intends to cause harm or increase social dominance. It can take the form of physical actions or verbal/nonverbal communication, and it's most often settled by threat alone, without actual bodily harm. Aggression offers protection against perceived and real threats, and from an evolutionary standpoint, it could be a deciding factor in whether an organism passes on its genes.
Several biological components are linked to aggressive behavior:
Amygdala — the brain structure responsible for associating stimuli with their corresponding rewards or punishments, and for signaling whether something is a threat. When the amygdala is activated, aggression increases.
Prefrontal cortex — a higher-order brain structure that exerts some control over the amygdala, tending to tone down emotional reactivity. Lower prefrontal cortex activity is linked to increased aggressive behavior.
Testosterone — higher levels are linked to more aggressive behavior, which may help explain why men are generally more aggressive than women.
MCAT Callout — Amygdala vs. prefrontal cortex in aggression: these two structures pull aggression in opposite directions. The amygdala flags threats and increases aggression when activated. The prefrontal cortex regulates the amygdala and decreases aggression — so lower prefrontal cortex activity (less regulation) is associated with more aggressive behavior, not less. If a vignette describes reduced prefrontal cortex function, expect increased aggression as the outcome.
Psychologist Leonard Berkowitz's cognitive neoassociation model offers a cognitive explanation: a person is more likely to respond to others aggressively whenever they're feeling negative emotions — being tired, sick, frustrated, or in pain all raise the likelihood of an aggressive response. Exposure to violent behavior also correlates with an increase in aggressive behavior, as demonstrated by the classic Bobo doll experiment.
Attachment
Attachment is the emotional bond between a caregiver and a child, and its development begins during infancy. Children are most sensitive to this need during the first six months to two years of life, when they require a consistent caregiver to develop appropriately. Psychologist Mary Ainsworth's "Strange Situation" procedure — observing how infants respond to a caregiver's departure and return — is the classic method for classifying attachment into four styles.
Secure attachment — the child has a consistent caregiver and is able to go out and explore, knowing they have a secure base to return to. The child trusts the caregiver will be there for comfort and prefers the caregiver over all others. The child is upset when the caregiver departs and is comforted by the caregiver's return. This is a vital aspect of children's social development; children with the other three attachment types can show deficits in social skills.
Avoidant attachment — results when the caregiver has little or no response to a distressed child. The child shows no preference between a stranger and the caregiver, and shows little or no distress when the caregiver leaves and little or no relief when the caregiver returns.
Ambivalent attachment — the caregiver has an inconsistent response to a child's distress. The child is unable to form a secure base since they can't consistently rely on the caregiver's response. The child is very distressed when separated from the caregiver but shows a mixed response when the caregiver returns — sometimes called anxious ambivalent attachment, since the child stays anxious about the caregiver's reliability.
Disorganized attachment — shows no clear pattern of behavior in response to the caregiver's absence or presence. The child shows a mixture of behaviors — avoidance or resistance, seeming dazed, frozen, or confused, or repetitive behaviors like rocking. This style is often associated with erratic behavior and social withdrawal by the caregiver, and it's a red flag for abuse.
MCAT Callout — Telling the four attachment styles apart: the fastest way to sort a vignette is to check two things — is there a caregiver preference, and is the behavior pattern consistent? Secure attachment has a clear preference and a consistent, comfort-seeking pattern. Avoidant attachment has no preference and no distress either way. Ambivalent attachment has distress at separation but an inconsistent, mixed response at return. Disorganized attachment has no discernible pattern at all — a grab bag of avoidance, freezing, and repetitive behavior, and it's the type most associated with caregiver abuse.
Social Support
Social support is the perception or reality that one is cared for by a social network. It's present at all times but is most pronounced when someone suffers a personal or family tragedy. There are five recognized types:
Emotional support — listening, affirming, and empathizing with someone's feelings.
Esteem support — similar to emotional support, but focused more on affirming a person's qualities and skills, attempting to bolster their confidence by reminding them of what they're good at.
Material or tangible support — any type of financial or material contribution to another person, such as making a meal for a friend or donating money.
Informational support — providing information that helps someone, such as a doctor explaining a diagnosis, treatment options, and the risks and benefits of those options.
Network support — the type of support that gives a person a sense of belonging, shown physically (like hugging) or through gestures, group activities, and shared experiences.
Social support offers real health benefits. It helps reduce psychological distress like anxiety and depression — people with low support show higher levels of major mental disorders, alcohol and drug use, and suicidal thoughts. It also improves physical health: people with low social support have a higher mortality risk from diseases like diabetes, cardiovascular disease, and cancer, while people with high social support are less likely to catch colds and recover faster when they do.
Social Behavior and Evolutionary Fitness
Foraging
Foraging is the behavior of seeking out and eating food, driven by biological, psychological, and social influences. Biologically, hunger is driven by a complex pathway involving both neurotransmitters and hormones, controlled by the hypothalamus: the lateral hypothalamus promotes hunger, while the ventromedial hypothalamus promotes satiety. Certain genes play a role in foraging behavior — some species forage together, while others forage solitarily — and cognitive skills like spatial awareness, memory, and decision-making all affect foraging success. In group foraging, the behavior is primarily learned; young animals observe others to learn how to find and consume food.
Mating and Mate Choice
A mating system is the organization of a group's sexual behavior:
Monogamy — an exclusive mating relationship.
Polygamy — a male having exclusive relationships with multiple females (polygyny) or a female having exclusive relationships with multiple males (polyandry).
Promiscuity — members of one sex mating with any member of the opposite sex, without exclusivity.
Most animal species maintain one dominant mating system. Human mating behavior is highly influenced by both social and biological factors, and humans also form formal relationships that correspond to their mate choice.
Mate choice, or intersexual selection, is the selection of a mate based on attraction. Mate bias describes how choosy members of a species are while selecting a mate — an evolutionary mechanism aimed at increasing the fitness of the species. Mate choice may carry direct benefits (material advantage, protection, or emotional support) or indirect benefits (promoting better survival in offspring).
Mechanisms of Mate Choice
Several mechanisms explain why particular traits become attractive to potential mates:
Phenotypic benefits — observable traits that make a potential mate more attractive, usually because they indicate increased production and survival of offspring.
Sensory bias — the development of a trait to match a preexisting preference that already exists in the population.
Fisherian or runaway selection — a positive feedback mechanism in which a trait that has no effect, or even a negative effect, on survival becomes progressively more exaggerated over time. Once a trait is deemed sexually desirable, it's more likely to be passed on, which increases the likelihood that the trait continues being passed on — the bright plumage of a peacock is the classic example.
Indicator traits — traits that signify an organism's overall good health and well-being, increasing the trait's attractiveness to mates. These traits may or may not be genetic in origin — for example, female cats are more attracted to males with clean, shiny coats.
Genetic compatibility — the creation of mate pairs with complementary genetics when combined. This provides a mechanism for reducing the frequency of recessive genetic disorders in a population, since attraction to mates with starkly different genetic makeups reduces the probability of offspring being homozygous for a disease-carrying allele.
MCAT Callout — Fisherian selection vs. indicator traits: both mechanisms explain why a trait becomes attractive, but for different reasons. Fisherian (runaway) selection is feedback-driven — the trait becomes exaggerated simply because it's desirable, independent of (or even despite) its actual survival value. Indicator traits are the opposite: they're attractive precisely because they're an honest signal of real health or fitness. A peacock's tail (Fisherian) and a shiny, healthy coat (indicator trait) illustrate the difference.
Altruism
Altruism is a form of helping behavior in which the person's intent is to benefit someone else at some cost to themselves. It can be motivated by pure selflessness, but it can also be motivated by egoism or an ulterior motive like public recognition. Empathy is the ability to vicariously experience the emotions of another person, and psychologist Daniel Batson's empathy-altruism hypothesis holds that an individual helps another person when they feel empathy for that person, regardless of the personal cost — a heavily debated theory for the connection between empathy and altruism. More recent theories suggest that an individual will only help another person when the benefits outweigh the costs to themselves.
Game Theory
Game theory attempts to explain decision-making behavior. It originated in economics and mathematics as a way to predict interactions based on characteristics like strategy, winning and losing, rewards and punishments, and profits and costs. In biology, game payoff refers to fitness.
John Maynard Smith's concept of an evolutionary stable strategy (ESS) describes a strategy that, once adopted by a given population in a specific environment, natural selection will prevent alternative strategies from arising. Strategies are inherited traits passed along by the population, and the object of the "game" is to become more fit than competitors. The classic example is the Hawk-Dove game, which shows that two different strategies can coexist as evolutionary stable strategies within the same population.
Due to social influences, there are four possible alternatives to direct competition:
Altruism — the donor provides a benefit to the recipient at a cost to themselves.
Cooperation — both the donor and recipient benefit by cooperating.
Spite — both the donor and recipient are negatively impacted.
Selfishness — the donor benefits while the recipient is negatively impacted.
MCAT Callout — Sorting the four game-theory outcomes: treat this as a simple 2x2 of who gains and who loses. Both gain: cooperation. Both lose: spite. Donor loses, recipient gains: altruism. Donor gains, recipient loses: selfishness. Matching a vignette to one of these four labels is just identifying which party benefits and which pays a cost.
Inclusive Fitness
Inclusive fitness, a concept developed by W. D. Hamilton, is a measure of an organism's success in the population. It's based on the number of offspring, the organism's success in supporting those offspring, and the offspring's own ability to then support others — not just the raw number of viable offspring, but the benefits certain behaviors provide to the population at large.
A family of close relatives shares many of the same genes, so altruism within a family unit promotes the reproduction and survival of individuals with similar genomes. Similarly, an organism that sacrifices itself to protect the young of a larger group ensures the passing of genes to future generations even though that individual doesn't survive. Taken as a whole, inclusive fitness supports the idea that altruistic behavior can improve the fitness and success of a species as a whole, even when it comes at a cost to any one individual.
Why Social Behaviour Matters for the MCAT
MCAT questions on this material typically describe a scenario and ask you to identify the underlying mechanism or classify the behavior using the correct term:
Track which direction a structure or hormone pushes aggression. The amygdala and testosterone increase it; the prefrontal cortex decreases it (so lower prefrontal activity means more aggression).
Use caregiver preference and consistency of pattern to sort attachment styles. Secure has both; avoidant has neither; ambivalent has distress but an inconsistent response; disorganized has no pattern at all.
Match the type of help offered to the correct social support category. Listening (emotional), boosting confidence (esteem), money or goods (material/tangible), facts (informational), and belonging (network) are distinct categories even when a vignette blends more than one.
Separate mate choice mechanisms by their underlying logic, not just by the example given — Fisherian selection is feedback-driven regardless of survival value, while indicator traits and genetic compatibility are tied to genuine fitness benefits.
Use a gain/loss framework for game theory — cooperation (both gain), spite (both lose), altruism (donor loses), selfishness (donor gains) — rather than memorizing the four terms in isolation.
Common MCAT Mistakes
Assuming every attachment style produces distress at separation. Only secure and ambivalent attachment show clear distress when the caregiver leaves. Avoidant attachment shows little or no distress either way, and disorganized attachment shows no consistent pattern at all — distress alone doesn't identify the style; consistency of the response does.
Treating "lower prefrontal cortex activity" as protective against aggression. The prefrontal cortex normally suppresses amygdala-driven aggression, so reduced prefrontal activity means less regulation — and therefore more aggressive behavior, not less.
Confusing Fisherian (runaway) selection with indicator traits because both describe attractive physical features. The distinguishing question is whether the trait is attractive despite having no real survival value (Fisherian) or because it honestly signals real health or fitness (indicator trait).
Misreading game theory outcomes by focusing on the recipient only. All four outcomes (altruism, cooperation, spite, selfishness) have to be classified by what happens to both the donor and the recipient — a vignette mentioning only one party's gain or loss is incomplete for classification purposes.
MCAT-Style Concept Check
Question: In a wolf pack, one wolf gives a loud alarm call upon spotting an approaching predator, which draws the predator's attention toward the caller while allowing the rest of the pack to flee safely with no added risk to themselves. According to game theory's four social outcomes, this donor-recipient interaction is best classified as:
A) Cooperation, because the whole pack benefits from the warning.
B) Spite, because the caller and the rest of the pack are both put at risk.
C) Altruism, because the caller incurs a cost while the rest of the pack benefits at no cost to themselves.
D) Selfishness, because the caller benefits by drawing attention away from itself.
Answer: C
Explanation: Altruism describes an interaction where the donor (the calling wolf) incurs a cost — increased personal risk from drawing the predator's attention — while the recipient (the rest of the pack) benefits with no cost to themselves. Option A is incorrect because cooperation requires both parties to benefit; here only the pack benefits, and the caller pays a cost. Option B is incorrect because spite requires both parties to be harmed, but the rest of the pack is not harmed — they're helped. Option D is incorrect because selfishness requires the donor to benefit while the recipient is harmed, which is the reverse of what happens here.
FAQ
Does aggression always involve physical harm?
No. Aggression is behavior that intends to cause harm or increase social dominance, but it's most often settled by threat alone — through physical actions or verbal/nonverbal communication — without actual bodily harm occurring.
Can a child be securely attached to one caregiver and insecurely attached to another?
Attachment style is specific to a given caregiving relationship, since it depends on that particular caregiver's consistency of response — so a child's behavior can differ across relationships depending on how consistently each caregiver responds to their distress.
What's the difference between emotional support and esteem support?
Emotional support means listening to, affirming, and empathizing with someone's feelings in general. Esteem support is more specific: it focuses on affirming a person's particular qualities and skills to bolster their confidence, rather than simply acknowledging how they feel.
Does the empathy-altruism hypothesis mean all helping behavior is selfless?
No, it's a heavily debated theory. Batson's hypothesis holds that empathy alone can drive helping behavior regardless of personal cost, but more recent cost-benefit theories suggest people only help others when the benefits to themselves outweigh the costs.
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