Major Evolutionary Transitions Flashcards
What is social behaviour in evolutionary terms
Behaviour that directly impacts another individual and is thought to have evolved through natural selection
Do animals living in groups always cooperate
No. Group living doesn’t always mean cooperation
Give an example of animals living in groups which don’t cooperate
guillemots live in pairs despite appearing in groups
shoals of fish benefit individuals independently
Give an example of cooperation in bacteria
Bacteria may cooperate to break down food sources but also kill each other with toxins - cooperation with competition
What is special about slime mould fruiting bodies
They form by aggregation of individuals. Some cells die or become sterile stalks to raise spores - showing indirect benefits and division of labour
How does the Portuguese Man O’ War exhibit social behaviour
It’s made of zooids that function together. Once formed, they can’t survive independently - a new level of individual
How is termite society structured
Only the Queen and King reproduce, the rest are sterile workers - a form of eusociality with complete reproductive division of labour
Who introduced the idea of METs
John Maynard Smith - he viewed them as revolutions rather than gradual changes
What is a MET
A transformation where units that could previously replicate independently come together to form a new type of individual with higher level organisation
Give examples of major evolutionary transitions
Genes → Chromosomes → Genomes
Prokaryotes → Eukaryotic cell
Asexual → Sexual reproduction
Unicellular → Multicellular organisms
Solitary insects → Eusocial colonies
What does a MET typically involve
- Change in how information is transferred
- New level of individuality
- Mechanism to reduce internal conflict
What is a transition in individuality
When previously independent individuals form a cooperative group that functions as a new individual, and can no longer reproduce alone
What are the two stages of a transition to individuality
Solitary → Cooperative group
Group → New individual (higher level)
What two conditions favour cooperative group formation
Monogamy/Low promiscuity → High genetic relatedness (siblings r = 0.5)
Group benefits outweigh individual costs
What condition is needed for group transformation into a new indvidual
No selection within the group → requires reduced internal conflict
What are two key methods for reducing group conflict
Aligned genetic relatedness – through monogamy or clonality
Repression of competition – members become obligately interdependent
How does clonality help group transformation
All members are genetically identical, so competition is eliminated – doesn’t matter which cell reproduces
How does repression of competition help group transformation
Group members depend completely on each other, making group fitness > individual fitness
How does insect sociality evolve (mechanism of group formation)
Subsocial: Queen mates once → high r (siblings = offspring)
Semisocial: Siblings reproduce → r(nephews) < r(offspring)
What’s required for eusociality to evolve in insects
Strict monogamy in ancestors → maintains high relatedness
Can promiscuity come before eusociality
No. Promiscuity only evolves after eusociality has formed
Why is eusociality irreversible
Members are so interdependent they can no longer function or reproduce alone
When does obligate multicellularity evolve
Only in clonal group formations (e.g. cell division from a single ancestor)
What developmental feature is necessary for complex multicellularity
A single-cell stage (e.g. zygote) → maintains clonality and control
