1. Prisoner’s Dilemma as a model of cooperation and individuality
How does this “game” represent what we see in life?
Steeves & Farr, UA, EEB, Michod Lab

2. Review Prisoners Dilemma review
Prisoner’s dilemma (PD) is a game about cooperating and defecting
To cooperate you are going to agree to help each other, but your “reward” is not the highest it could be.
There is always a temptation to “cheat” or defect, thus giving you the max reward possible.
Steeves & Farr, UA, EEB, Michod Lab

3. Prisoners Dilemma matrix each # = the # of days in ISS
COPY MATRIX IN NOTES:
Player 2
Say nothing +
COOPERATE
“He did it” -
DEFECT
2 days
“Reward”
10 days
“Sucker”
0 days
“Temptation”
5 days
“Punishment”
Payoff to player 1
Player 1
Steeves & Farr, UA, EEB, Michod Lab

4. PD strategy? Does it pay to be a “cheater” and always defect guilt?
YES! No matter what your partner does, you are better off to cheat.
Say nothing +
COOPERATE
“He did it” -
DEFECT
2 days
“Reward”
10 days
“Sucker”
0 days
“Temptation”
5 days
“Punishment”
Payoff to player 1
Compare R to T (Player 1 payoff if Player 2 cooperates)
Compare S to P (Player 1 payoff if Player 2 defects)
Steeves & Farr, UA, EEB, Michod Lab

5. PD strategy? Does it pay to cooperate? For a single iteration, NO!
No matter what your partner does, you are always better off to cheat
Steeves & Farr, UA, EEB, Michod Lab

6. PD strategy? Does it pay to cooperate?
For multiple iterations, it depends:
You are both better off if you both cooperate
So it may be better to cooperate if this will convince your partner to do the same
No one strategy always wins; it depends on your partner’s strategy
One good option is “Tit-for-Tat”: Do unto others as they do unto you
Lots of other strategies are summarized at Students can try these out or invent their own strategies. The point here is that there is no one best strategy; most strategies do well against some and poorly against others.
Steeves & Farr, UA, EEB, Michod Lab

7. Steeves & Farr, UA, EEB, Michod Lab

8. How does this relate to life?
Cooperation is a critical part of any transition in individuality
Prokaryote  eukaryote
Single-celled  multicellular
Individuals  societies
Steeves & Farr, UA, EEB, Michod Lab

9. Prokaryote  eukaryote
We can think of eukaryotes as cells within cells.
Eukaryotic cells have specialized structures that do specific jobs.
Mitochondria - provides energy
Nucleus - hold DNA
Golgi - transports proteins
Etc…
Mitochondria were once free-living bacteria!
Steeves & Farr, UA, EEB, Michod Lab

10. Prokaryote  eukaryote
The organelles within a eukaryotic cell cooperate in order to DO SOMETHING TOGETHER THAT THEY COULD NOT DO ALONE
I.e. the nucleus could not do alone all the jobs of the Golgi, lysosomes, mitochondria, ribosomes, etc. do.
To function efficiently, the “symbiotic” mitochondria must cooperate with the “host” cell
Steeves & Farr, UA, EEB, Michod Lab

11. Cooperation The eukaryotic cell mimics what we see in our own bodies.
The billions of cells in our bodies are specialized to do certain jobs
Blood cells carry nutrients and oxygen
Immune system to fight infection and foreign invaders
Nervous system to communicate through the body
Reproductive cells to pass on our genetic info
Steeves & Farr, UA, EEB, Michod Lab

12. Cooperation
We can also extend this theory process of cooperation to society
We as people usually work or belong to a larger organization.
As a teacher I work for a school district
Other jobs: administrator, counselor, support staff, janitor
Each is specialized to do his or her own job.
Specialization makes us more efficient.
Does this mean the organization is an individual?
Steeves & Farr, UA, EEB, Michod Lab

13. Cooperation Lots of single-celled organisms are still around.
These cells do fine; in fact, there are many more of them than there are of us.
This shows that different strategies work in different environments – just as in the prisoner’s dilemma.
Steeves & Farr, UA, EEB, Michod Lab

14. Cooperation
Volvox
Slime molds
Steeves & Farr, UA, EEB, Michod Lab

15. Cooperation
We will be using Chlamydomonas (Chlamy) and Volvox green algae to draw comparisons from.
Volvox is a differentiated, multicellular organism (like us).
There are also many other examples that show what we see in these algae.
Steeves & Farr, UA, EEB, Michod Lab

16. Altruism
Sometimes we give up our own reproductive abilities, like the worker bees or somatic cells in Volvox, so that we can help our close relatives reproduce.
This is called altruism!
Steeves & Farr, UA, EEB, Michod Lab

17. Kin selection
Altruism is often explained by the theory of kin selection
By helping our relatives, or kin, reproduce, individuals ensure that some of their own genes are passed on
For example, siblings share half of their genes, parents and children half, and cousins 1/8
How do the cells in our bodies, Volvox cells and bumble bees represent these theories of sociality, kin selection, and altruism?
For more information on kin selection and its role in promoting altruism, see West Eberhard MJ The evolution of social behavior by kin selection. Quarterly Review of Biology 50:1-34. (
For information specifically about eusociality, see Queller DC and Strassmann JE Kin selection and social insects. BioScience 48: (
Steeves & Farr, UA, EEB, Michod Lab

18. Volvox Very small dots are somatic cells.
Specialized for movement
Larger cells within the cell are germ (reproductive) cells.
All they do is produce more Volvox
The “daughter” colonies will incubate within the “mother” cell…mother cell will EXPLODE and release daughter cells when ready.
Ultimate Altruism!
Steeves & Farr, UA, EEB, Michod Lab

19. Bumble bees Bees are said to be a “eusocial” insect
They do their specialized job to benefit the overall group
Could we call the hive an individual?
We are an individual...our workers would be all the cells in our body except for our sex cells.
Steeves & Farr, UA, EEB, Michod Lab

20. Other examples of cooperation
Ants (do the same as bees)
Cyclists!
Two riders who alternate leading so the back rider gets the benefits of the front rider blocking the wind
The back rider could cheat by staying back and then blowing by front rider to win the race!
Naked mole rats!!!
Eusocial shrimp?!?
For more information about eusocial shrimp, see DUFFY, J. EMMETT; MORRISON, CHERYL L. & RÍOS, RUBÉN (2000): Multiple Origins of Eusociality among Sponge-dwelling Shrimps (Synalpheus). Evolution 54(2): (pdf:
Steeves & Farr, UA, EEB, Michod Lab

21. Other examples of cooperation
“Helper fish” - small fish clean larger fish..but have temptation to take big chunk out of big fish!
High School wrestling!
Try to get to lower weight bracket
Opponent does same
Both suffer from loss in strength and athleticism
Everyone would be better off if everyone competed in their “natural” weight class, but each wrestler has the temptation to “defect”.
Steeves & Farr, UA, EEB, Michod Lab