Grooming Model (1)

 

 

 

Grooming means “cleaning your body from dirt or parasites”.

The problem of birds is that they can groom all their body except the head, so

they need cooperation to groom each other.

 

Storchevoy M. A. Corporate Social Responsibility. 2013

Topic 3. Where Do Norms Come From?

 

 

Optimal Degree of Virtue

Grooming Model (2)

 

 

S S SS S S

S

S S S SS S S

 

 

Sucker is the bird who grooms everyone even if it is not paid back. If the whole population consists from

S S S SS S

S S S S

Suckers, the Sucker is ESS (evolutionary stable strategy).

 

 

S S SS S S

S

S S S SS S S

 

 

If the population of Suckers is invaded by a Cheat

(accepts grooming but never pays back), the Sucker is

S S C S S S

S S S S

no longer ESS.

 

 

C C CC C C

C

C C C CC C C

 

Soon, all Suckers will be driven extinct, and the whole population will consist from Cheats, slowly dying from

C C C CC C

C C C C

parasites….

 

 

Storchevoy M. A. Corporate Social Responsibility. 2013

Topic 3. Where Do Norms Come From?

 

 

Optimal Degree of Virtue

Grooming Model (3)

 

 

 

S S S

S SS S

 

The Grudge is the bird who has a good memory and

G

S G S G

S

S S

G S S S SS S S S

never groom another bird who once refused to pay

back. If there are some Grudges in the population of

Cheats, both strategies are ESS.

 

 

 

S S S

S SS S

G

S G S G

S

S S

G S C C S

If Cheats invade the population of Suckers and Grudges,

only Grudges is ESS.

S S C S

 

 

 

G G G

G GG G

 

 

First, all Suckers will go extinct. Then all Cheats will go

G

G G G G

G G

 

extinct. The Grudges are ESS survivors.

G

G G G G G