Theories of cooperation 2
True and Strong Altruism
Definition of Altruism:
Altruism is defined as “true altruism” when the cost to the altruist is greater than the individual's benefit.
Strong altruism is characterized by:
Cost (c) is greater than benefit (x), i.e., (x < c).
Weak altruism is characterized by:
Cost (c) is less than benefit (x), i.e., (x > c).
Concept of Cost:
Cost represents a decrease in lifetime personal reproductive fitness of the altruist.
Relatedness Factor:
Strong altruism can only evolve when relatedness is positive.
A high degree of relatedness between altruist and beneficiary increases the likelihood of altruistic behavior.
Benefit to Altruist:
Helping non-relatives may evolve if it provides feedback benefits to the actor's own reproduction.
Evolution of Altruism
Indirect Fitness Benefits:
Cooperation can be explained through indirect fitness benefits directed toward individuals carrying the cooperation gene.
Kin Selection Theory:
The empirical success of kin selection theory (inclusive fitness theory) contributed to the decline of traditional group selection theories.
New group selection models are now mathematically equivalent to kin selection theories.
Group selection can effectively operate if genetic differentiation exists between groups, meaning group members must be genetically more similar to their group than to those in other groups.
Key factors:
Limited dispersal leads to population viscosity and the potential for compatibility between kin selection and group selection.
Altruistic behaviors may evolve to improve group productivity when genetic similarities within groups enhance indirect fitness benefits.
Mechanisms Promoting Altruism's Evolution
Increased Relatedness:
Increased relatedness between interacting partners can arise in three ways:
Kin Discrimination:
Can involve phenotype matching where individuals recognize and preferentially interact with genetic relatives.
Limited Dispersal (Population Viscosity):
Leads to familiarity among relatives and enhances the chance of interacting with kin.
Green Beards:
An individual can recognize and help others who share the same gene but are not directly related.
The beneficiary of altruistic acts must have a higher probability of sharing genes with the altruist relative to random members of the population.
Discriminating Altruism:
Increased net fitness for altruists by ensuring that the benefit to the recipient outweighs the cost incurred by the altruist.
The Green Beard Effect
Phenotype and Gene Association:
A gene may result in a phenotype that allows carriers of the gene to identify each other, directing altruistic behavior towards fellow gene carriers.
Case Study:
Dictyostelium discoideum, a slime mold species, demonstrates this by selectively cooperating with other csa gene carriers to form fruiting bodies which accommodate only fellow carriers.
Kin Selection and Inclusive Fitness
Examples of Kin Selection:
Parental care is a prime example where natural selection favors individuals who maximize the transmission of their genes.
Inclusive fitness encompasses the genetic contributions made by the altruist to their relatives, not just direct descendants.
Common Ancestry and Relatedness:
Genetic relatedness can exist without recent common ancestry; relatedness is established whenever genes are correlated among individuals.
Correlation Coefficient (r):
A general correlation coefficient that illustrates the probability of altruists and recipients sharing genes, regardless of kinship.
Simplified Calculations in Altruism
Payoff Example:
Scenario: A rabbit encounters 9 carrots and consumes 4, achieving a total payoff of 8 units.
If a brother and friend are invited to share, the payoff is recalculated as follows:
Total Payoff = $(32)1 + (32)0.5 + (32)0 = 6 + 3 + 0 = 9$ (total payoff).
This demonstrates that even with reduced personal payoff, sharing maximizes genetic contribution.
Inclusive Fitness Concept
Inclusive Fitness Definition:
Inclusive fitness equals direct fitness (from an individual's actions) plus indirect fitness (impact on the reproductive success of relatives weighted by relatedness).
Mathematically, (br - c > 0):
$r$ = relatedness between helper and beneficiary.
$b$ = benefit from rearing additional offspring (recipient).
$c$ = cost incurred by the helper.
Hypothetical Alleles for Altruism
Gene Perspective:
Kin selection is often viewed from a gene-centric angle, where individuals act as vessels to ensure their genetic material is propagated.
Individuals maximize their inclusive fitness, leading altruistic behaviors to boost copies of altruistic genes in the population.
Hamilton’s Theory of Altruism
Partitioning Individual Fitness:
Hamilton posited methods to evaluate how altruistic genes could enhance the fitness of others, potentially at the altruist's cost.
He established a framework to assess total inclusive fitness by partitioning direct and indirect contributions resulting from social behaviors.
Link Between Inclusive Fitness and Group Selection
Altruism in Groups:
Genetic relatedness fosters group altruism that enhances group productivity.
Altruistic acts can stem from either inclusive fitness benefits or group selection logic, intertwining their concepts.
Strong altruism requires both genetic relatedness and cooperative benefits for it to manifest.
Selection at Colony-Level vs. Kin Selection
Weak Altruism:
Weak altruism can arise when helping behavior leads to benefits for both the altruist and other group members, while true altruism necessitates positive relatedness to survive.
Hamilton's Rule for Evaluation:
The assessment model includes evaluating rb = indirect fitness consequences and c = direct fitness consequences, asserting that (rB - c > 0) is critical for altruistic acts to be selected.
Calculation of Relatedness in Diploid Species
Coefficients of Relatedness:
Example includes multiple individuals (A, B, C) where:
Relatedness between A and B calculated as (0.5 imes 0.5) + 0 = 0.25.
Relatedness between B and C is calculated as: (0.5 imes 0.5) + (0.5 imes 0.5) = 0.5.
Full Sibling and Other Kin Relations:
Related coefficients are established for full sibs, uncles, cousins, and half-sibs with corresponding values.
Non-Calculate Need for Relatedness in Altruism
Instinctual Behavior:
Altruistic behavior occurs without active calculation of relatedness, evidenced by the fulfillment of Hamilton’s Rules which govern altruistic motivations.
Cues for relatedness can stem from population viscosity or kin discrimination.
Experimental Support for Kin Selection
Research Limitations:
It is challenging to manipulate altruistic behaviors and relatedness in experimental designs, but microorganisms allow such experiments.
Bacterial Evidence:
Studies on bacterial populations maintained altruistic traits (e.g., iron scavenging) confirming higher altruistic actions occur with elevated relatedness levels.
Estimating Benefits and Costs
Defining b and c:
Both terms represent changes in lifetime reproductive outcomes for altruists and recipients compared to scenarios without altruistic actions.
Example provided of Florida scrub jays where helpers increase fledgling survival, yielding a calculated b proportional to their nest contributions.
Maximizing Benefits in Cooperative Contexts
Discriminatory vs. Non-Discriminatory Help:
Cooperative behaviors are critically examined in context to benefit realization versus costs, suggesting helpers preferentially assist based on kin relationships aligned with kin selection theory.
Costs of Altruism Measurement
Difficulty in Quantifying Costs:
Cost assessments are convoluted as evidenced by hover wasps, where the queuing system represents direct fitness loss opportunities.
Parental Manipulation and Enforcement of Altruism
Definition:
Investigations suggest parental coercion creates altruism dynamics that may not appear altruistic on the surface but are fundamentally driven by genetic strategies to enhance progeny survival.
The role of enforcement in altruism is prominent in social insect studies, indicating a need to reassess altruism within the context of kin selection theory.