Behavioral Evolution and Kin Selection, Life History Evolution, Human Evolution

Evolution of eusociality

Highly organized social systems with reproductive division of labor (ants, bees, termites). Significance: Explained by kin selection (Hamilton's rule).

Spite

Behavior costly to self, harmful to other. Significance: Rare; requires kin discrimination.

Altruism

Behavior costly to self, beneficial to other. Significance: Evolves via kin selection or reciprocity.

Selfishness

Behavior benefits self, costs others. Significance: Default expectation from natural selection.

Mutual benefit (mutualism)

Both parties benefit (e.g., pollination). Significance: Common in nature.

Kin selection

Selection favoring altruism toward relatives. Significance: Explains eusociality and family-based cooperation.

Inclusive fitness

Total fitness including personal reproduction plus effects on relatives' reproduction (weighted by relatedness). Significance: Hamilton's rule predicts altruism when benefit to relatives × relatedness > cost to self.

Hamilton's rule

Altruism evolves when Br – C > 0 (Benefit × relatedness – Cost > 0). Significance: Kin selection theory.

Haplodiploidy hypothesis and eusociality

In Hymenoptera (ants, bees), females are more related to sisters (0.75) than to own daughters (0.5). Significance: Proposed explanation for eusociality evolution (though not universal).

Parental investment

Resources parents give to offspring. Significance: Trade-offs with future reproduction; basis of sexual selection theory.

Infanticide

Killing young, often by males to bring females into estrus. Significance: Example of sexual conflict.

Siblicide

Sibling killing, often due to limited resources. Significance: Example of kin conflict despite relatedness.

Parent-offspring conflict

Offspring want more resources than parents selected to give (optimal offspring vs. parental perspective differs). Significance: Conflict despite relatedness.

Genetic hitchhiking

Beneficial allele sweeps linked neutral/deleterious alleles to fixation. Significance: Reduces diversity at linked sites.

Trade-offs

Improvement in one trait causes decline in another (e.g., reproduction vs. survival). Significance: Constraints prevent perfection.

Evolutionary or physiological constraints

Lack of genetic variation, pleiotropy, or developmental limits blocking optimal adaptation. Significance: Explains why not all traits are perfect.

Senescence

Biological aging; decline in function with age. Significance: Evolves because selection weakens after reproduction.

Evolution of aging

Aging evolves due to declining selection with age (mutation accumulation and antagonistic pleiotropy). Significance: Not programmed death; byproduct of selection.

Rate of living theory

Aging from accumulated oxidative damage; higher metabolism = shorter lifespan. Significance: Predicts trade-off between metabolic rate and longevity.

Cancer risk and aging

Cancer risk increases with age due to accumulation of somatic mutations. Significance: Multimorbidity in aging.

Evolutionary theory of aging

Aging results from weaker selection on late-life traits. Significance: Combines mutation accumulation and antagonistic pleiotropy.

Mutation accumulation hypothesis

Deleterious mutations with late-life effects accumulate because selection is weak against them. Significance: One explanation for aging.

Pleiotropy

One gene affects multiple traits. Significance: Basis of antagonistic pleiotropy hypothesis of aging.

Alleles with early benefits and late costs

Antagonistic pleiotropy: allele increases early fitness but causes late-life decline. Significance: Explains evolution of aging.

Evolutionary explanation to menopause

Females stop reproducing to invest in existing offspring and grandchildren. Significance: Trade-off between continued reproduction and helping kin.

Grandmother hypothesis

Postmenopausal women help raise grandchildren, increasing inclusive fitness. Significance: Explains human longevity beyond reproduction.

Lack's hypothesis

Clutch size evolves to maximize number of surviving offspring. Significance: Optimal clutch size balances offspring number vs. survival.

Clutch size and survival in birds

Larger clutches produce more offspring, but each offspring has lower survival (trade-off). Significance: Supports Lack's hypothesis.

Selection on offspring size versus number

Trade-off: many small offspring vs. few large offspring. Significance: Optimal strategy depends on environment.

Optimal foraging hypothesis

Animals maximize energy intake per unit time foraging. Significance: Predicts diet choice and foraging behavior.

Evolution and the flu

Influenza virus evolves rapidly (antigenic drift), requiring new vaccines annually. Significance: Real-time evolution affecting human health.

Immune system and disease evolution

Pathogens evolve to evade immune detection (immune evasion). Significance: Arms race between host immunity and pathogen.

Antibiotic resistance

Bacteria evolve resistance to antibiotics via natural selection. Significance: Major public health crisis.

Evolutionary origin of disease

Many disease-causing traits evolved for other functions or are byproducts. Significance: Understanding evolution informs treatment.

Virulence

Damage pathogen inflicts on host. Significance: Evolves to maximize transmission (trade-off hypothesis).

Coincidental hypothesis

Virulence in humans is accidental byproduct of adaptation to other hosts (e.g., tetanus in soil). Significance: Not all virulence is adaptive in current host.

Shortsighted evolution hypothesis

Pathogen evolves within-host traits that increase replication but decrease transmission. Significance: Within-host selection can be maladaptive for spread.