# Cooperation and Conflict

Psychology I · Ethology · https://tryals.app/learn/psychology-i/cooperation-and-conflict

## Hawk-Dove & Bourgeois

**Evolutionary game theory** analyzes interactions where your payoff depends on what others do. The **Hawk-Dove game** models conflict over a shared resource: Hawks always escalate and fight, while Doves display but retreat before injury.

Neither pure strategy is stable alone. Doves get invaded by Hawks, and Hawks pay heavy injury costs that let Doves thrive. The population settles at a mixed **Evolutionarily Stable Strategy (ESS)**: a strategy that, once common, cannot be beaten by any rare alternative.

$$\text{ESS: no rare strategy can invade}$$

In some species, the **Bourgeois** strategy emerges as the ESS instead: fight if you are the resource owner, retreat if you are the intruder.

## Prisoner's Dilemma & Tit-for-Tat

The **Prisoner's Dilemma** models cooperation between non-relatives. Mutual cooperation yields the best collective payoff, but each individual is tempted to **defect** for a higher personal payoff.

Robert Axelrod's computer tournaments found that a simple strategy—**Tit-for-Tat** (cooperate first, then mirror the partner's previous move)—outperformed complex rivals by being nice, retaliatory, forgiving, and clear.

| Feature | Hawk-Dove | Prisoner's Dilemma |
| --- | --- | --- |
| **Core Conflict** | Escalate vs Retreat | Cooperate vs Defect |
| **Best Solution** | Mixed ESS or Bourgeois | Tit-for-Tat |

> **Common pitfall:** Assuming the winning strategy must be cunning and deceptive. Transparent, reciprocal strategies that start cooperatively consistently outperform exploitative ones.

## Practice questions

6 of this lesson's 12 practice questions, with answers. The full set is in the app.

### 1. Select every statement that is TRUE about cooperation and conflict.

A. Once established, a stable strategy leaves no opening for a scarce newcomer.
B. A pure Dove population resists invasion by Hawks.
C. An all-Hawk population is stable and free of injury costs.
D. Two cooperators take more from the game than any other pairing.
E. A strategy can punish defection and still resume cooperating the moment the other side does.

**Answer:** A. Once established, a stable strategy leaves no opening for a scarce newcomer.; D. Two cooperators take more from the game than any other pairing.; E. A strategy can punish defection and still resume cooperating the moment the other side does.

**Why:** Best-collective-cooperation, Tit-for-Tat's traits, and the ESS definition are all true. An all-Hawk population suffers heavy injury costs (not injury-free), and a pure Dove population is invaded by Hawks - so those two are false.

Page: https://tryals.app/practice/psychology-i/cooperation-and-conflict/select-every-statement-that-is-true-about-cooperation-and-conflict

### 2. In Axelrod's tournament, Tit-for-Tat never once scored more points than the strategy it was playing against. It won the tournament outright. How can a strategy that never beats a single opponent finish first?

A. Because it beat most of the other strategies on average, despite losing the majority of individual matches.
B. Because it happened to be matched against copies of itself more often than the other strategies were.
C. Because the tournament awarded additional points for behaving cooperatively.
D. Because the tournament scored total points, not head-to-head wins.

**Answer:** D. Because the tournament scored total points, not head-to-head wins.

**Why:** The result looks paradoxical only if you assume the game is a contest between the two players. It is not zero-sum: Tit-for-Tat never defected first, so the most it could do was match a cooperator, which is a high score for both. The exploiters collected small advantages and then met each other, where both scored badly.

Page: https://tryals.app/practice/psychology-i/cooperation-and-conflict/in-axelrods-tournament-tit-for-tat-never-once-scored-more-points

### 3. A Tit-for-Tat player faces a partner who defects on round 1 but cooperates on round 2. Order what Tit-for-Tat does across the interaction.

**Answer:**

1. Round 1: Tit-for-Tat cooperates (it is 'nice' and opens with cooperation).
2. The partner defects on round 1.
3. Round 2: Tit-for-Tat retaliates by defecting, mirroring the partner's last move.
4. The partner cooperates on round 2.
5. Round 3: Tit-for-Tat forgives and returns to cooperation.

**Why:** Tit-for-Tat starts nice (cooperate), retaliates the round after a defection, and forgives as soon as the partner cooperates again. Being nice, retaliatory, and forgiving - in that behavioral order - is what made it win Axelrod's tournaments.

Page: https://tryals.app/practice/psychology-i/cooperation-and-conflict/a-tit-for-tat-player-faces-a-partner-who-defects-on-round-1-but

### 4. Sort each feature under the Hawk or the Dove strategy in the Hawk-Dove game.

**Answer:**

- Hawk: Always escalates and fights for the resource, Risks serious injury in a contest, Wins resources from a Dove without a fight
- Dove: Displays, then retreats rather than fight, Avoids injury but often yields the resource, Gets a share only when it meets another Dove

**Why:** Hawks always escalate, risk injury, and beat Doves without a fight; Doves display, retreat, avoid injury, and only gain when meeting other Doves. Escalation-and-risk versus display-and-retreat defines the two strategies.

Page: https://tryals.app/practice/psychology-i/cooperation-and-conflict/sort-each-feature-under-the-hawk-or-the-dove-strategy-in-the

### 5. Vampire bats regurgitate blood for roost-mates who failed to feed, including unrelated ones. What has to be true of their lives for this to be stable rather than exploitable?

A. They must be closely related, since altruism between non-relatives cannot persist
B. They must meet repeatedly and recognise individuals
C. They must have surplus blood, making the donation costless
D. They must be unable to detect who fed them, so cheating carries no advantage

**Answer:** B. They must meet repeatedly and recognise individuals

**Why:** Repetition plus recognition is what makes generosity safe: a stable roost means today's donor is next month's beggar, and a persistent taker gets refused. Take either condition away and the system collapses, which is why reciprocal altruism is found in long-lived social species and almost nowhere else.

Page: https://tryals.app/practice/psychology-i/cooperation-and-conflict/vampire-bats-regurgitate-blood-for-roost-mates-who-failed-to-feed

### 6. An all-Dove population is not evolutionarily stable, because a single Hawk introduced into it would win every contest without being injured and would spread.

**Answer:** True

**Why:** True. Among all Doves, a lone Hawk wins every contest without injury, so it out-reproduces the Doves and spreads - meaning all-Dove cannot be an ESS. This is why the population settles at a mixed equilibrium instead.

Page: https://tryals.app/practice/psychology-i/cooperation-and-conflict/an-all-dove-population-is-not-evolutionarily-stable-because-a-single