Cooperation and Altruism: Study Notes
Course Logistics and Upcoming Schedule
Today's Lecture: Cooperation and Altruism.
Later Today (Data Analysis Lab):
At least one person per group must bring a laptop with R and RStudio already downloaded.
Prepare by having some ideas for analysis; research possible methods online to maximize lab time for questions.
Next Week:
Thursday: Tutorial for Test 2.
Friday: Actual Test 2 (similar format to Test 1).
Practice questions for Test 2 will be provided on Friday.
Learning Objectives
Understand the concepts of cooperation and altruism.
Differentiate between cooperation and altruism.
Identify examples of cooperative and altruistic behaviors.
Explain how these behaviors evolve and are selected for by natural selection.
Introduction to Cooperation and Altruism
All animals exhibit some form of social awareness, being aware of other animals.
Cooperation is more complex than mere social awareness and only evolves if it is beneficial to the individual doing the cooperating.
Key Questions regarding cooperative behavior:
Who benefits? (Individual, group, species?)
How do they get this benefit?
When do they get the benefit?
Different types of cooperative/altruistic behaviors provide different answers to these questions.
Defining Cooperation and Altruism
Cooperative Behavior:
Involves a mutually beneficial interaction between individuals.
Both individuals receive a benefit, and there is generally no significant cost to either party.
Individuals are basically helping each other with shared interests.
Altruism:
A behavior performed to increase another individual's fitness.
Critically, there is a cost to the individual performing the altruistic act.
Costs can be energetic (e.g., expending energy to help), time-related (e.g., time spent helping rather than feeding oneself), or other forms of diverted resources.
The Puzzle of Altruism: The existence of altruism (where an individual incurs a cost for another's benefit) is puzzling from an evolutionary standpoint.
Genetic Basis and Natural Selection of Behavior
To explain behaviors like altruism, two fundamental assumptions related to population genetics are made:
Heritability: The behavior (e.g., altruism) must be heritable, meaning it is at least partially genetically fixed (though it can also be influenced by learning and environment). If not heritable, it cannot be passed to future generations and selected for.
Lifetime Reproductive Success: The genes controlling these adaptations must favor lifetime reproductive success. An individual must be able to reproduce successfully to pass on these genes.
Behaviors must pass the scrutiny of natural selection; if a behavior negatively impacts an individual's survival or reproduction, it will not persist.
The 'Selfish Gene' Concept: Natural selection primarily acts on individuals and their genes, not on the 'good of the species' or population.
While genes are not literally selfish, selection operates to maximize the replication of an individual's genes.
Therefore, any altruistic behavior must ultimately — directly or indirectly — provide some benefit to the actor's fitness or the propagation of their genetic material.
Degrees of Sociality
Sociality varies greatly across species, from simple awareness to complex societies.
No Altruism:
Solitary individuals or pairs: Only interacting during breeding season, with no cooperative activities (e.g., many solitary animals).
Aggregations: Individuals gather (e.g., at water holes), but primarily for competition over resources, not cooperation. They are in close proximity but not helping each other.
Cooperative Sociality:
Packs: Groups cooperate to achieve shared goals (e.g., wild dogs hunting together to predate larger species, sharing the rewards).
Societies:
Characterized by a division of labor (e.g., ants, bees where non-reproductive sisters assist the queen in reproduction and baby care, benefiting the group's overall fitness).
The evolution of sociality, cooperation, and altruism depends on various factors: habitat, reproduction, resource distribution, genetic relationships, and behavior types.
When, Who, and How: Questions for Cooperative Behavior
To understand cooperative behaviors and altruism, specific questions about their context and consequences are asked:
Who Benefits?
If only one party benefits significantly while the other receives little, it might be commensalism.
If one party benefits at a cost to the other, it is parasitism, not cooperation.
True cooperation requires both parties to derive some form of benefit.
How is the Benefit Passed?
Is it an individual benefit (directly to the actor)?
Is it a group benefit?
Is it a genetic benefit (transmission of shared genes)?
When is this Happening?
Is the benefit received immediately (now)?
Is the benefit received in the future?
Is the benefit to the actor or to their offspring?
Types of Cooperative and Altruistic Behaviors
There are three main types discussed, categorized by who benefits and when they benefit:
Mutualism (Individual Benefit, Now):
Both individuals benefit directly and immediately from the interaction.
Reciprocal Altruism (Individual Benefit, Future):
The actor incurs a cost now, expecting a benefit from the recipient in the future.
The benefit is to the individual, but it is delayed.
Kin Selection (Genetic Benefit, Future):
The actor incurs a cost, but helps related individuals.
The benefit is to the actor's genes (passed on through relatives), thus it's a future, indirect benefit.
Mutualism: Mutual Benefit to Individuals
Definition: Interactions where both individuals gain a direct, immediate benefit.
Requires common interests rather than competition for resources.
Common in relatives but can also occur within and among species.
Examples of Mutualism Within Species
Grooming:
Seen in species like Japanese macaques and zebras.
Benefits: Removal of parasites (immediate physical relief) and strengthening of social bonds (studies show well-groomed individuals are involved in fewer aggressive encounters).
Both partners directly benefit during the act.
Pack Hunting:
Example: Wild dogs hunting together.
Cooperation allows a pack of smaller individuals to successfully predate larger prey than any individual could alone.
All participants share in the reward (food).
Shared Vigilance:
Individuals in a group take turns being vigilant while others feed, reducing the cost of vigilance for any single individual.
Benefits: Increases the average feeding rate of the group and decreases the average vigilance time needed per individual.
This is a direct, immediate benefit to each individual in the group.
Examples of Mutualism Between Species
Cleaner Organisms:
Fish, birds, or crabs clean parasites or debris from other species (e.g., cleaner fish removing algae from a sea turtle).
Benefits: The cleaner gets food, and the cleaned animal is relieved of parasites or heavy loads.
Ants and Aphids:
Aphids feed on plant sap and excrete a sugary 'honeydew' that ants consume.
Benefits: Aphids provide food for ants; ants, being aggressive, protect the aphids from predators.
Mongooses and Hornbills:
Mongooses are skilled at finding insects but vulnerable to aerial predators when foraging.
Hornbills are less efficient at finding insects but are good at spotting predators due to their aerial vantage point.
Benefits: Mongooses forage while hornbills watch for danger. Hornbills issue alarm calls, and mongooses hide. They may share the collected insects.
Cautionary Tale: The Oxpeckers
Initial Assumption: For a long time, oxpeckers were thought to have a mutualistic relationship with African game animals (e.g., giraffes, zebras) by removing ticks and parasites.
Research Findings: A study compared tick loads on animals with and without oxpeckers.
Result: No significant difference in tick loads, suggesting oxpeckers were not effectively cleaning parasites.
Instead, oxpeckers were observed feeding on blood from wounds and earwax.
Animals with oxpeckers had more open wounds (likely caused or exacerbated by the birds) and less earwax.
Conclusion: The relationship was not mutualistic; oxpeckers were parasitic, gaining personal benefit at a cost (wounds, earwax loss) to the mammals. This highlights the importance of empirical testing over assumption.
Kin Selection: Helping Relatives for Genetic Benefit
Definition: Altruistic behavior directed towards genetically related individuals.
Concept: While the actor incurs a cost, helping relatives increases the likelihood of shared genes being passed to the next generation.
Fitness:
Direct Fitness: Achieved by raising one's own offspring.
Indirect Fitness: Achieved by helping family members reproduce, thereby aiding the propagation of shared genetic material.
Examples:
Social Insects (e.g., Bees, Ants): Sterile sisters help the queen reproduce, effectively passing on a high proportion of their shared genes.
Birds (e.g., Morehens): Sub-adult helpers assist the breeding mother in raising offspring, gaining experience and increasing their future reproductive success if they have been helpers in the past, while enhancing the genetic output of close relatives.
Naked Mole Rats: Exhibit a complex social structure with a queen and numerous workers/followers, often highly related, contributing to the colony's success without reproducing themselves.
Hamilton's Rule (Br > C): A mathematical model explaining when altruism towards kin is favored by natural selection.
B = Benefit to the recipient (measured in extra offspring produced by the recipient due to the altruistic act).
r = Coefficient of Relatedness (the proportion of genes shared between the altruist and the recipient, ranging from 0 to 1).
C = Cost to the altruist (measured in offspring the altruist foregoes by performing the altruistic act).
Altruism is favored when the benefit to the recipient, weighted by the degree of relatedness, outweighs the cost to the altruist. The product of B and r must be greater than C.
Calculating the Coefficient of Relatedness (r)
The coefficient of relatedness (r) represents the probability that a gene in one individual is an identical copy, by descent, of a gene in another individual.
Formula: r = \sum (0.5)^L (where L is the number of 'steps' or genetic links in each unique path connecting two individuals, and the sum is across all such paths).
Each step (e.g., parent to offspring) contributes \times 0.5 probability of sharing a specific gene.
Examples:
Half-siblings (share one parent):
Path: Altruist \rightarrow Mother \rightarrow Half-sibling.
Steps (L): 2
r = (0.5)^2 = 0.25 (or one-quarter related).
Full Siblings (share both parents):
Path 1: Altruist \rightarrow Mother \rightarrow Full-sibling.
Path 2: Altruist \rightarrow Father \rightarrow Full-sibling.
Steps (L) for each path: 2
r = (0.5)^2 + (0.5)^2 = 0.25 + 0.25 = 0.5 (or one-half related).
Cousins (e.g., full cousin):
Path 1: Altruist \rightarrow Father \rightarrow Grandparent \rightarrow Uncle/Aunt \rightarrow Cousin.
Path 2: Altruist \rightarrow Father \rightarrow Grandparent \rightarrow Uncle/Aunt \rightarrow Cousin.
Steps (L) for each path: 4
r = (0.5)^4 + (0.5)^4 = 0.0625 + 0.0625 = 0.125 (or one-eighth related).
Implication: The higher the relatedness (r), the more beneficial it is (genetically) to perform altruistic acts towards that individual, as a larger proportion of shared genes are being passed on.
Application of Hamilton's Rule: Bird Example
Scenario: A bird (altruist) can raise 1 offspring on her own (C=1). Her sister (recipient) can raise 2 offspring without help, but could raise 5 offspring with the altruist's help. Thus, the sister gains 3 extra offspring due to the help (B=3).
Relatedness: Full siblings, so r = 0.5.
Calculation: Is Br > C?
(3 \times 0.5)>1
1.5 > 1
Conclusion: Since 1.5 is greater than 1, it is genetically beneficial for the sister to help, as the indirect genetic gain outweighs the direct cost of her own foregone reproduction.
Kin Recognition: Identifying Relatives
Importance: For kin selection to be effective, individuals must be able to identify their relatives to direct altruism appropriately.
Methods of Kin Recognition:
By Location:
Assumption: Any individual in proximity (e.g., in the same nest or territory) is related.
Vulnerability to Exploitation: Cuckoos, for example, lay eggs in other birds' nests; the host parents will raise the cuckoo chick believing it to be their own, even though it's unrelated.
By Association (Familiarity):
Assumption: Individuals that grow up together are kin.
Example: Humans generally do not accept marriage between adopted siblings, even if not genetically related, due to this ingrained association principle.
By Similarity (Phenotype Matching):
Individuals recognize kin based on similar phenotypic cues: looks, smells, sounds, or other shared characteristics.
Example: Ground squirrels 'kiss' by smelling each other's breath/odor (from specific glands) to identify relatives. Different family members have distinct odors.
Prairie Dog Alarm Calls: An Example of Kin Selection
Context: Prairie dogs use alarm calls to warn others of danger (e.g., predators).
Cost: The caller draws attention to itself, increasing its own risk of predation.
Study: Researchers compared alarm calling behavior between related and unrelated prairie dogs.
Finding: Related prairie dogs issued significantly more alarm calls than unrelated ones.
Interpretation: The cost to the individual caller is outweighed by the genetic benefit of protecting numerous relatives, who share a substantial portion of the caller's genes and can then reproduce, passing those genes on.
Reciprocal Altruism: 'You Scratch My Back, I'll Scratch Yours'
Definition: Altruistic behavior between unrelated individuals where the actor incurs a cost now, expecting a reciprocal benefit from the recipient at a later time.
Distinguishing from Mutualism: Benefits are not immediate for both parties.
Distinguishing from Kin Selection: Individuals are not genetically related.
Requirements for Evolution:
Individual Recognition: The actor must be able to recognize specific individuals they've interacted with in the past.
Memory of Past Interactions: The actor needs to remember who they helped and who helped them (or who cheated).
Frequent Interactions: Individuals must interact repeatedly for reciprocal exchanges to occur.
Commonality: Most common in sociable and cognitively advanced animals (e.g., birds, primates) that have the cognitive capacity for recognition and memory.
**Vulnerability to **Cheats: An individual might receive aid but never reciprocate, gaining benefit without cost.
If cheating is prevalent, reciprocal altruism would not evolve.
Mechanism to Counter Cheats: 'Keep Score':
Individuals typically remember who has helped them and who has cheated.
Refusal to aid cheats: If an individual consistently fails to reciprocate, others will stop helping them.
This behavioral strategy selects against cheating, making reciprocal altruism stable.
Game Theory and Social Decisions
Definition: The study of strategic decision-making in situations where the outcome for one player depends on the choices of others.
Relevance to Altruism: Helps understand how cooperation can arise and persist even when individual and collective interests might conflict.
Types of Games:
Zero-Sum Games: One player's gain equals another's loss (e.g., predator-prey interaction).
Non-Zero-Sum Games: Both players can win, or both can lose, or cooperate to gain from a third party (e.g., cooperative hunting against a prey animal).
The Prisoner's Dilemma
Scenario: Two suspects are arrested for a minor crime (e.g., stealing bread) and suspected of a major crime (e.g., bank robbery). Separated, they are offered a deal:
If you confess and implicate your partner, and your partner stays silent: You go free (0 years), your partner gets 8 years.
If your partner confesses and implicates you, and you stay silent: You get 8 years, your partner goes free.
If both confess: Both get 3 years (reduced sentence).
If both stay silent: Both get 1 year (for the minor crime).
The Dilemma: From an individual perspective, confessing is always the