Cooperation, partners, and culture · quick reference
Genes, organisms, groups, partners
“What is selection acting on?” has no slogan-sized universal answer. Track variation, transmission, and reproductive differences at the scale relevant to the case.
Short version: evolutionary change can be counted at several levels. Ask what is passed on, who leaves descendants, and whether partners reproduce together often enough to act as a unit.
Gene talk is bookkeeping, not psychology
A “selfish gene” does not want anything. Gene-centered models ask which inherited variants increase in copies through their effects in bodies and environments. Phenotypes still arise through development; genes are causally important without being tiny agents or complete blueprints.
Cooperation can face opposing selection
Suppose cooperators pay a cost that benefits their group. Within each group, non-cooperators may reproduce faster. Yet groups rich in cooperators may survive or found more groups. The total change depends on both components. Kin selection and multilevel selection can sometimes partition the same mathematics differently; the biological work is measuring assortment, relatedness, conflict, and reproduction—not choosing a tribal slogan.
Mini-game · two levels
In every colony, selfish cells divide 10% faster. Colonies with mostly cooperative cells produce three times as many daughter colonies. Which statement is warranted?
Major transitions make new individuals
Evolution repeatedly joined previously independent units: genes into chromosomes, cells into eukaryotic cells, cells into multicellular organisms, and organisms into some eusocial colonies. Cooperation is not enough. A new higher-level individual needs shared reproduction and ways to keep internal cheaters from taking over—for example, reproductive bottlenecks, policing, or partners usually passing on together.
Endosymbiosis is central, not fringe. Mitochondria and plastids descend from bacteria incorporated into ancestral cells. Evolution can innovate by merger and integration as well as by branching modification.
Microbiomes: phenotype partner ≠ automatic individual
Microbes can shape host nutrition, immunity, and development. A host plus microbes is ecologically useful as a holobiont. Calling host and microbes one evolutionary individual requires more evidence: do they usually pass to descendants together, differ in combined reproductive success, and keep internal conflict under control? Many microbes arrive from the environment and evolve on different timescales.
Evidence check
A gut bacterium improves host digestion but is reacquired from soil every generation and also spreads between host species. What can we safely say?
Culture is another transmission system
Socially learned skills, norms, and technologies vary, persist, recombine, and spread vertically, horizontally, or obliquely. Cultural evolution is not “a second genome”: copying can be intentional and rapid. But population models help. Dairying altered environments and diets; selection independently increased lactase persistence in several populations—a clear gene–culture feedback.
Read both sides
- Queller (2000), relatedness and major transitionsHow cooperation and conflict connect to new levels of individuality.
- Okasha (2006), Evolution and the Levels of SelectionExpert synthesis of the conceptual and mathematical issues.
- Tishkoff et al. (2006), “Convergent adaptation of human lactase persistence in Africa and Europe”Primary genomic evidence for convergent gene–culture coevolution.
- Bordenstein & Theis (2015), the strong holobiont caseRead alongside the critique below.
- Moran & Sloan (2015), “The Hologenome Concept: Helpful or Hollow?”A model pair for learning from a live dispute.