Cultural Leader and the Dynamics of Assimilation: Online Appendix By Thierry Verdier1 and Yves Zenou2

A

Online Appendix A: An alternative formulation of the payoff structure

Instead of the utilities (5), we can have an alternative (not normalized) formulation of the payoffs structure. They can be written as follows:   (  ) = (1 − ) +  +  

  (  ) = 

(A.1)

  (  ) =  +  +      (  ) = (1 − ) with parameters       0. Here the interpretation is the following. Actions  and  generate both market and non-market outcomes. This could be because action  is intrinsically less productive than action  Referring, for instance, to our example between religious Muslims and non-religious Muslims, it could be that certain religious practices (Ramadan fasting, praying, etc.) may be associated to productive inefficiencies of religious people as compared to non religious ones and that markets internalize partly such effects. For instance, Campante and Yanagizawa-Drott (2015) show that Ramadan fasting may have a significant negative effect on output growth in Muslim countries. Also, the Dinar 2011 Survey3 indicates a loss on average of two hours work per day during Ramadan. Alternatively the market outcome associated with action  can also be lower than the one associated to action  because of social discrimination related to individuals practicing action  (think about actions such as specific clothes like wearing a veil or a burqa) although such action would not induce per se any direct productivity loss. In such a case,  will be a measure of the extent of social discrimination or penalization associated to individuals choosing action . At the same time, depending on the cultural trait, actions  and  provide also different non-market outcomes. Specifically, an individual of type  taking action  receives a strictly 1

PSE and Ecole des Ponts ParisTech, PUC-Rio and CEPR. Email: [email protected]. Monash University, IFN and CEPR. Email: [email protected]. 3 see: http://www.dinarstandard.com/wp-content/uploads/2013/05/2011-Productivity-in-Ramadan-Report.pdf. 2

1

positive non-market benefit  +   while action  does not generate any positive nonmarket benefit. Conversely, an individual of type  taking action  receives a strictly positive non-market benefit +  while action  does not give her any positive non-market benefit. Obviously when  −  is positive, this payoff structure is equivalent to the one in (5) with  = −  0 and  =  +  0 and setting the utility normalization   (  ) =  and   (  ) = (1 − )  instead of zero. Note that under either payoff structure (5) or (A.1), with  −   0, clearly action  =  (resp.  = ) is the preferred action for individuals of type  =  (resp.  = ). It should be clear that all the results obtained in this paper will be the same under payoffs (5) or (A.1). In the main text, we will use payoffs (5) but we can interpret some policy results using payoffs (A.1) since they can give some insights on the productivity and discrimination of ethnic minorities. Indeed, if we consider Propositions 1 and 2, with payoffs (A.1), an alternative “integration” policy could also be to increase the opportunity cost  of the action linked to trait . This could be done, for instance, by increasing the market value  that the minority individuals can get when adopting the behavior corresponding to the “mainstream” culture. Although sometimes difficult to implement, repressive policies against social or economic discrimination or affirmative action policies promoting visible minorities may help achieve this outcome. Note, as well, that an increase in , the social discount or penalty factor associated to the action linked to trait  will also negatively affect the family incentives to transmit trait  in the minority population.

References [1] Campante, F. and D. Yanagizawa-Drott (2015), “Does religion affect economic growth and happiness? Evidence from Ramadan,” Quarterly Journal of Economics 130, 615-658.

2

B

B.1

Online Appendix B: Extensions of the benchmark case Online Appendix B.1: Non-rivalry of the community-specific public good

Consider now that the public good  =  of community  has some non-rivalry dimension so that individuals of type  also derive some benefits from to the provision of . An example of this is the organization of religious and cultural events that have positive recreative spillovers (fireworks, public entertainments, music shows, street marching, neighborhood parties) on individuals who do not necessarily actively participate, or personally share the cultural views of the cultural community that promotes specifically such events. A simple way to capture this feature is to modify the benchmark payoff specification (5) (with  = 0 as it is assumed in the main text) in the following way:   ( ) =  + ( +  )   ( ) =  

(B.1)

  ( ) =  +     ( ) =   where    ≥ 0 capture the extent of the spillover effect of the public good  when action  or action  is exerted. As before, individuals of type  obtain some specific benefit   associated with the public good, when they choose the preferred action (i.e. action ) associated to trait . On top of this, there is also a spillover effect   that is enjoyed by all individuals and which, eventually, depends on the nature of the action  ∈ { } that is chosen. It is natural to assume ∆ =  −  ≥ 0, that is the strength of the spillover of  is stronger for action  (the action that an individual of type  intrinsically prefers) than for action  (the action that an individual of type  intrinsically prefers). In other words, while the provision of the public good  produces some spillover effects beyond the strict boundaries of the community of individuals of type , these spillovers are still more effective when one undertakes the behavior preferred by such individuals. Moreover, we assume that ∆   , so that an individual with cultural trait  still always prefers to undertake action  even if this action is less “complementary” to the public good than action . It is then easy to see that the incentives to transmit the different cultural traits inside the families can be written as ∆  =   ( ) −   ( ) = ( + ∆)  +  3

and ∆  =   ( ) −   ( ) =  − ∆ Proceeding as for the benchmark model, the transmission of preferences can then be described by the following equation: £ ¡ ¢¤ •   =  (1 −  ) (1 −  ) [ + ( + ∆)  ] −   − ∆

or

£ ¤ •   =  (1 −  ) (1 −  ) ( +   ) −   + ∆

(B.2)

As in the benchmark model, we start in a long-run cultural situation when the leader is never active ( = 0), i.e. 0 = (0), where the initial fraction of individual with trait  is equal to the steady-state without a cultural leader, i.e. 0 =  ( +  ). Because of ¡ ¢ ∆   , the cultural steady state ∗  associated to the dynamics (B.2) with the full leader’s public good capacity  = , is always interior.4 Assuming again, for simplicity, that  =   = 1. Then, the program of the cultural leader of group  is given by: Z ∞ − (   −  )  max 0≤ ≤

0

£ ¤    =  (1 −  ) (1 −  ) ( +  ) −   + ∆ •

(B.3)

 0 = (0) is given

We proceed as for the benchmark model. After substitution of the control function, and using (B.2), we obtain: Ã " ¶#! µ  Z ∞ •    − ( +  )     −    −  − max  (1 −  ) (1 + ∆ −  ) 1 + ∆ −  0≤ ≤ 0     Now consider =

Z



"

# •    (1 −  ) (1 + ∆ −  )

Z

 (1 − ) (1 + ∆ − )

−

0

and denote the function  () as:  () =

0 4

Indeed

which is always less than 1

¡ ¢  + ∆ ∗  =    +  + 

4

We immediately have that 1 1 1 1 1 1 1 = − +  (1 −  ) (1 + ∆ −  ) (1 + ∆)  ∆ (1 −  ) ∆(1 + ∆) (1 + ∆ −  ) By integration, we obtain:  () =  +

1 1 1 ln  − ln(1 − ) + ln (1 + ∆ −  ) (1 + ∆) ∆ ∆(1 + ∆)

with  (0 ) = 0. Integration by parts then leads to: Z





  =   (1 −  ) (1 + ∆ −  ) 0 Z ∞ £ − ¤∞ =   ( ) 0 +  −  ( ) 0 Z ∞ =  −  ( ) −

0

The optimal control problem (B.3) of the leader is therefore equivalent to

max 0≤ ≤

where

Z



− ( )

0

¸  − ( +  ) ( ) =   +  −  ( ) 1 + ∆ −  

Now observe that

0 () =   − 



( +  ) (1 + ∆) −   − 2  (1 −  ) (1 + ∆ −  ) (1 + ∆ −  )

Consider the function Φ () =

  2 +  (1 −  ) (1 + ∆ −  ) (1 + ∆ −  )

with  = ( +  ) (1 + ∆) −   0 Inspection of Φ () shows that it has the shape shown in Figures B1(a) and B1(b). [   1()  1() ] Formally, it satisfies the following properties: 5

() First, lim→0 Φ () = +∞ and lim →1 Φ () = +∞. () Second, there is a unique value b ∈ (0 1) such that Φ () is decreasing for  ∈ (0 b) and increasing for  ∈ (b   1), reaching therefore its minimum at Φ (b  ).  0 From () and (), it follows that, for   Φ (b ), then  ()  0 and () is decreasing £ ¤ for  ∈ (0 1)  In particular () is continuous and decreasing for  ∈ 0  ∗ () . On the other hand, for    Φ (b ), then there exist  and  with 0    b    1, such that 0 ()  0 for  ∈ (0  ) ∪ (  1) and 0 ()  0 for  ∈ (   ). Therefore, () has a local minimum at  and a local maximum at  . The shape of the function () is displayed in Figure B2 and it can be seen that it has the same shape as in the benchmark model (see Figure 1). Thus, one can apply the MRAP method of Spence and Starrett (1975) in exactly the same way. The results are qualitatively similar to those described in Proposition 1 where now  = Φ (b ). In other words, the  optimal decision of the amount of public good  provided by the leader is described by Proposition 1. Note, in particular, that when ∆ = 0 (i.e.  =  so that the strength of the spillovers is the same for both communities), we obtain exactly the results described in Proposition 1. In that case, the externality of the public good is not associated to one particular action Therefore, the incentives to transmit one trait do not depend on it. It is also immediate to see that an increase in ∆, the complementarity between the public good and the optimal behavior (i.e. action ) of cultural trait , shifts up the marginal benefit 0 () and shifts down the minimum marginal cost Φ (b  ). This makes it more likely for the cultural leader to be active and supply the public good  . Indeed, it will be profitable for the leader to supply  at a lower minimum threshold  of cultural rents, and at a lower minimum size b∗ of the initial fraction of the population 0 . In words, an increase in the difference between the strength of spillovers between the two communities shifts up the marginal benefit for the cultural leader of providing the public good  and shifts down the minimum marginal cost. This implies that the cultural leader is more likely to be active when the spillover benefits of the public good  are more specific to individuals from his own group. This also suggests that, if the leader can select to some extent the characteristics of the public good he wants to provide, he will choose a good that generates more “community-specific” spillover effects, which implies that the results will be closer to that of our benchmark model. [   2 ]

6

B.2

Online Appendix B.2: The leader maximizes socialization rents

We may consider that the objective function of the leader interacts with the socialization efforts of members of her community. More specifically, consider the case where the leader’s preferences are such that she maximizes the following rents (using (14) and assuming for simplicity that  =   = 1):   =  (1 −  )( +  ) These rents are just the fraction of the population of type  times the optimal effort of type− parents. In other words, the objective function of the leader is now given by: R ∞ −  (  −  ) . Note first that, after substitution of the control function, using 0 (9), we obtain: # " •    (1 − )( +  ) = (1 − ) + (1 − ) −  + (1 − )2 (1 − ) •

 =   + (1 − ) 2 

The objective function   −  of the leader can now be written as: # " • •     (1 − )( +  ) −  = 2  + − −  + (1 − ) (1 − )2 (1 − ) •



    + +  −  =   − 2 (1 − ) (1 − ) (1 − ) 2 

Therefore, the leader maximizes the following function: " # Z ∞ • •      −  2  − + +  −   (1 − ) (1 − )2 (1 − ) 0 Noting that

(B.4)

1 1 1 1 = + + 2 (1 − )  1 −  (1 − )2 •

and integration by parts of the term with   in (B.4) provides that the optimal control problem of the cultural leader is then equivalent to the following program (up to a constant): Z ∞ max  − ( ) 0≤  ≤

0

7

where ( ) =

2 

It is easily verified that:

µ

  +  −  log(1 −  ) −  1 − 

−  log

µ

 1 − 



¸ ∙   +   −  ( ) = 2  + 1 −   (1 −  )2 

0

This can be rewritten as



¤ £  (1 −  )2 0 ( ) = 22 (1 −  )2  +  (1 −  ) −   +  

Note that  (1 −  )2 0 ( ) is a function that is the difference between two terms Φ ( ) = £ ¤ 22 (1 −  )2  +  (1 −  ) and Γ ( ) =   +   . It is easy to see that the function Φ ( ) is increasing in  if and only if  ∈ [0 12], reaching therefore its maximum at  Φ (12) = 14 ( 2 +h) andi such that Φ (0) = Φ (1) = 0 While Γ ( ) is linear increasing in  with Γ (12) =   +

 2

. From this it follows easily that:

1 , 4

() for   one has 0 ( ) = Φ ( ) − Γ ( )  0 for all  ∈ [0 1] while () for  ≤ 14 there are two values  and  with  ≤ 12 ≤  and such that 0  ( ) ≤ 0 for  ∈ [0  ] ∪ [  1] and 0 ( ) ≥ 0 for  ∈ [   ]. Hence for  ≥ 14 ( ) is always decreasing in  ∈ [0 1] while for   14 ( ) has a local minimum at  and a local maximum at  . The function ( ) takes therefore the same shape as in Figure 1, and the analysis of the optimal degree of cultural participation of the leader is very similar to the benchmark case where the leader is maximizing a rent proportional to the size of her group.

B.3

Online Appendix B.3: The leader of type  maximizes the utility of the population of type 

We may consider that the objective function of the leader is to maximize the expected utility of individuals of the same type (i.e. of type ). In that case, instead of (12), the leader will maximize the following function (normalizing  = 1 and  = 1): Z ∞ − [ ( +  ) −  ]  max  0≤  ≤

0

£ ¤   =  (1 −  ) (1 −  ) ( +  ) −   •

 0 = (0) given

Note first that, using (9), we obtain: 



   −  = 2 + (1 −  )  (1 −  ) 8

By substituting  in the control function, the objective function is given by: •



  2   −   +  −  + ( ) = 2 2 (1 −  ) (1 −  ) (1 −  )  (1 −  ) ( − )  ( − ) •   + =  +  (1 −  )  (1 −  )2 Therefore, the leader maximizes the following function: ∙ ¸ Z ∞ ( − )  ( − ) • −   +       + (1 −  )  (1 −  )2 0

(B.5)

It is easily verified that ( − )   1− − + 2 = −  1 −  (1 −  )2  (1 −  ) •

Then integration by parts of the term with  in (B.5) provides easily that, up to some constant, our optimal control problem collapses to Z ∞ − ( ) max  0≤  ≤

where

0

¢ ¡  ¶ µ 2   +     +       − −  log ( ) =   + (1 −  ) (1 −  ) 1 − 

Let us study ( ). We have:

¢ ¡   (2 −  ) +    +   −  ( ) = (1 −  )2  (1 −  )2 0

and thus

¢ ¡  £ ¤    +   (1 −  )2 0 ( ) =   (2 −  ) +  −  Note that (1 −  )2 0 ( ) is a function that is the difference between two terms Ω ( ) = (+  )   (2 −  ) +  and Θ ( ) = . It is easy to see that the function Ω ( ) is increasing  for all  ∈ [0 1], and such that Φ (0) = , Φ (1) =  +  . Moreover, Θ ( ) is a decreasing £ ¤ in  with Θ (0) = +∞ and Θ(1) =   +  . From this it follows easily that, given that   1, there exists a unique value  ∈ ]0 1[ such that 0 ( ) ≤ 0 if and only if  ≤  . £  ¤ Hence ( ) is having a minimum at  with (0) = (1) = +∞. For  ∈ (0) ( ) , the function ( ) takes the shape as in Figure 1, and it is easy to see that the analysis of the optimal degree of cultural participation of the leader is very similar to the benchmark case where the leader is maximizing a rent proportional to the size of her group.

9

C

Online Appendix C: Club Good with community members’ contributions

In the benchmark model, we assumed that the cultural leader was financing himself the cost of the provision of the group-specific public good  =  . This could be justified if, for example, the leader is a foreign power that has a clear objective of building up a group of individuals favorable to its specific religious or political positions. An interesting example of this is the case in Kosovo of clerics funded by money from Saudi Arabia to promote the emergence of radical Islamic communities promoting active members for ISIS (New York Times article ‘How Kosovo was Turned into Fertile Ground for ISIS’ May 22, 2016). While in the case of a foreign power, the contribution and possibly the choice of public goods comes from outside the group, in many cases the financing of the public good comes from contributions collected on members of the community. In this Appendix, we extend the benchmark model to capture these features. Consider now that the public good  is financed by a contribution   ∈ [0  ] on community members. The utility functions of the different individuals are now by the following payoffs:   ( ) =   −  

  ( ) = 0

(C.1)

  ( ) = 0   ( ) = 0 −   where, for simplicity,  =  = 0. Note that taking action  corresponds to participating in the club activity of group  and therefore to pay the contribution   associated to this participation. Clearly individuals of type  have a valuation   of the club activity, which is increasing in  while individuals of type  do not value this club good. As a consequence, the optimal action  of individuals of type  will be action  =  when    −   ≥ 0, and action  =  otherwise. The optimal action  of individuals of type  will always be action  =  (non participation to the club good). The incentives to transmit the different cultural traits inside the families can then be written as ∆  =   (  ) −   (  ) = max {  −    0} and ∆  =   (  ) −   (  ) = 1 (  −   )   where 1() is the indicator function such that 1() = 1 when  ≥ 0 and 1() = 0 otherwise. 10

The budget constraint of the good  at time  can be written as  =  

(C.2)

Thus 

∆ =



max

½

¾ µ  ¶     − 1 0 and ∆ = 1  − 1   

(C.3)

To avoid non-trivial dynamics, assume that  =     1 (otherwise participation in the club good will never be optimal). Proceeding as in the benchmark model, the transmission of preferences can be described by the following equation: •

 =  (1 −  ) [(1 −  ) max { − 1 0} −  1 ( − 1)] We consider the case when 0  1 so that the size of the community is large enough to induce some club participation initially at least from a static point of view. First, note that, whenever 0  1, for all contribution  ≥ 0, the induced cultural dynamics of the community is such that  ≥ 1. Indeed, the cultural dynamics is given by: ( 0 when   1 •  = (C.4)   (1 −  ) [(1 −  ) − 1] when  ≥ 1 The steady states for 0  1 do not depend on  , which only affects the speed of conver• gence. When   4, we always have    0 for all  ∈ [1 1) as long as   0. Therefore, if   0, for all , then  converges towards 1 from above (the steady state  = 1 is unstable). Otherwise, when 0 = 0 at some time 0 , then the dynamics stops at 0  1. When   4, there are three steady states for the cultural dynamics: min , max and 1 such that 1  min  max  1 and only max is stable. In such a case, if   0 at all time, then the system converges to 1 when 0 ∈ [1 min ] and to max when 0  min . Whenever  = 0, the system stops at some value 0  1. In the sequel, we consider that   4 so that the utility of the club good is high enough relative to its costs, which implies that a positive active community can eventually be sustained in the long run at some value max  1. We have the following result: Proposition C1: Assume that   4 and 0  1, where  =    1. () When 0 ∈ (1 e), the cultural leader does not produce the club good  and the size  of the cultural group  remains stationary at  = 0 for all . 11

() When 0 ∈ (e   min ), then the cultural leader produces the club good  with the maximum contribution rate  and stops the production of the club good at some 0 such that 0 = e. The size  of the cultural group  decreases from 0 to e and then stays stationary at  = e for all  ≥ 0 . () When 0 ∈ (min  max ), then the cultural leader produces the club good  at all  with the maximum contribution rate  . The size  of the cultural group  grows and converges towards the steady-state lim→∞  = max . Proof of Proposition C1: The cultural leader maximizes a discounted sum of an average of some cultural rents proportional to the size of the community of type , i.e.    , and the sum of the utility of the members of the community  (   ) =    + (1 − ) max {  −   0} =    + (1 − )  max { − 1 0}

The intertemporal payoff of the leader is given by: Z ∞ −  (   ) 0

Obviously  (   )

=

(



   and   = 0 

  + (1 −



 ( −1) ) (1−  ) [(1− ) −1]

when

  1

when  ≥ 1 and   0

Define the functions: ( − 1) 1 for  ≥ 1 1 −  [(1 − ) − 1] Z ()  () =

() =

1

It is easily verified that () = where

   + + 1 −  max −   − min

 [( − 1) max − 1]  [( − 1) min − 1]  = max − min max − min 1 and   0,   0 and   0 (as −1  min  max for   4). Hence (  −  ln(1 − ) −  ln (max − ) +  ln(min − )) for  ∈ (1 min )  () =  −  ln(1 − ) −  ln (max − ) +  ln( − min ) for  ∈ (min  max )  = (1 − )   =

12

This implies that lim  () = −∞ lim +  () = −∞ and

→min −

→min

lim

→max −

 () = +∞

Moreover, because of the sign of () on the interval [1 max ],  () is decreasing on the interval  ∈ (1 min ) and increasing on the interval  ∈ (min  max ). Moreover there is a unique   ∈ (min  max ) such that  ( ) = 0. Consider now the integral: " • # Z ∞ (  − 1)    = (1 − ) −  (1 −  ) [(1 −  ) − 1]  0 Integration by parts gives:  = (1 − )

Z





−  ( )

0 Z ∞ £ − ¤∞ = (1 − )   ( ) 0 + (1 − ) −  ( ) 0 Z ∞ h i − = (1 − ) lim   ( ) −  (0 ) + (1 − ) −  ( ) →∞

0

Note that, for 0  min ,  ∈ (1 0 ) and  ( ) is absolutely bounded and lim→∞ −  ( ) = 0. Now, for 0  min , two cases can occur: Either () there exists a  such that   = 0 and the cultural dynamics stop. Then again lim→∞   max . Therefore  ( ) is again absolutely bounded and lim→∞ −  ( ) = 0. Or ()   0 for all . Then, lim→∞  = max , and lim  ( ) ∼ lim − log (max −  ) = +∞

→∞

→∞

However, we have lim→∞ −  ( ) = 0. Indeed denote () = −− log (max −  ). Then, •

 − () = −() +  max −  •



() + () = −  (1 −  ) ( − min ) Thus Z



0

∙ ¸ Z •  () + ()   

0



 (1 −  ) ( − min )  

As a result, ( )  (0) + 13

1 (max − min ) 4

1 (max − min ) 4

and lim →∞ ( ) = 0. From this, we also conclude that lim −  ( ) ∼  lim () = 0

→∞

→∞

Thus, for all initial conditions 0  1, the intertemporal payoff of the cultural leader can be rewritten as Z ∞ Z ∞ −    [  + (1 − )  ( − 1)]  = −     +  0 0 Z ∞ = − [   + (1 − ) ( )]  0

Thus the problem of the cultural leader collapses to Z ∞ − ( ) max 

(C.5)

0

where () =    + (1 − )  () This function is such that 0 () =   + (1 − ) () Denote ∆ () =   (1 − ) [(1 − ) − 1] + (1 − ) ( − 1) Then 0 () =

−∆ () (1 − ) [1 − (1 − )]

As we know, when   4, the function   Θ () = (1 − ) [1 − (1 − )] has three zeros: min  max and 1 such that 1  min  max  1. Moreover, Θ () is positive for  ∈ [1 min ] ∪ [max  1] (as Θ (1)  0 and Θ0 (1)  0) and negative for  ∈ (min  max ). Also, it is straightforward to see that Θ0 ()  0 for  ∈ [1 min ]. Given that for all   ≥ 0 and 0 ∈ [1 max ], the cultural dynamics  remains into the interval [1 max ], we can restrict ourselves to consider the optimal trajectories in this support. It is then a simple matter to see that there exists a unique value e ∈ (1 min ) such that ∆ () ≶ 0 if  ≶ e

Indeed, at  = 1, one has ∆ (1) = −  Θ (1)  0 and ∆ () = (1 − ) ( − 1) − Θ ()  0 for all  ∈ (min  max ). Moreover, in the interval (1 min ), ∆0 () = (1 − )  − Θ0 ()  0 14

Therefore there exists a unique e ∈ (1 min ) such that ∆ () ≶ 0 if  ≶ e. From this, we conclude that 0 () is positive for  ∈ [1 e], negative for  ∈ [e ; min ] and 0  () is again positive for  ∈ (min  max ). This implies that () has one local optimum e in the interval[1 min ()] and is increasing from −∞ to +∞ in the interval (min  max ). The shape of the function () is displayed in Figure C1. [   1 ] We have two cases: () 0 ∈ (1 min ). Then, we know that, for all ,  ∈ [1 0 ]. Indeed as long as   0 (the club good is active), then  is decreasing in  and therefore  ∈ [1 0 ] and if there exists some time [0  1 ] such that  = 0, then  = 0  0 for all time  ∈ [0  1 ]  Thus again  ∈ [1 0 ]. From this, it follows that the function ( ) is continuous and bounded at all  ∈ [0 +∞). A simple application of the MRAP provides then results () and () stated in Proposition C1. () 0 ∈ (min  max ), then for all ,  ∈ [0  max ),  is weakly increasing sequence in . Moreover, the function () is increasing in  ∈ [0  max ) from (0 ) towards +∞. Then, the optimal solution to (C.5) is to choose a dynamic path ( )=0∞ such that we again go as fast as possible towards lim→∞  = max with  =  at all time. Indeed, take any other ¡ 0 ¢ dynamic path (0 )≥1 with an associated contribution rate sequence   ∈(0∞) satisfying 0

(C.4) and denote the first interval  ∈ (1  2 ) such that      Also denote  () = (1 − ) [(1 − ) − 1] and () =

Z

  ()

1

() is a well defined function for  ∈ (0  max )  increasing in  as  () is positive in the interval (0  max ). Given the definition of 1 , for  ≤ 1 , we have  = 0 . Then, integrating (C.4) along the dynamic path (0 )≥1 , gives, for all   1 , 0

Z

1

 =  ()

Z

0

  

1

Z

1

  =

Z

  ()

1

Thus, for all   1 (0 )  ( ) and therefore 0   . Given that () is increasing in  in

15

the interval (0  max ), we also have that (0 )  ( ) for   1 . As a consequence Z ∞ Z 1 Z ∞ − 0 − 0  ( ) =  ( ) + − (0 ) 0  0 Z 1 Z 1∞ = − ( ) + − (0 )  0 Z 1 Z 1∞  − ( ) + − ( ) 1 Z0 ∞ − ( ) = 0

and the intertemporal value for the cultural leader of the dynamic path (0 ) induced by the ¡ 0 ¢ fee sequence   is dominated by the path ( ) induced by ( ) =  . Again the cultural leader wants to approach the steady state max as fast as possible and we obtain result () stated in Proposition C1. Let us summarize the findings of this section. We demonstrate that the results in terms of dynamics are similar to that of the benchmark case. Specifically, in Proposition C1, we show that there is a minimum threshold value e of the initial population 0 of individuals of type , such that, beyond this threshold, the leader will become active and supply the good . Different from the case with external financing though, it could be that the active provision of  might not be sufficient to allow the community of individuals with trait  to increase its size. The reason is that the amount of good  provided at each period  now depends on the total contributions collected by the group and, therefore, on the fraction  of individuals of type . More precisely, the provision of the club good  generates immediate benefits to individuals of type  who consume it. As it triggers a difference of consumption between the two cultural traits, it also induces paternalistic parents of both types ( and ) to increase their socialization effort in order to transmit their own trait to their children. Now, the incentive ∆  to transmit trait  is related to the net consumption benefit of the club good ( − 1)  for an individual of type  (where  =    1). ∆  therefore depends positively on the fraction  of individuals contributing to the club good. On the other hand, the socialization incentive ∆  to transmit the other trait depends on the access fee  to the club good, which is the cost perceived by a paternalistic parent of type  who does not value the club good  and expects his child with preference  to pay  to access this good. When  is low enough (but larger than 1), ∆  is small compared to ∆  . As a consequence, parents of type  socialize less their children than parents of type  and, therefore, the cultural dynamics lead to a reduction of the fraction  of individuals with trait  in the population. 16

In part () of Proposition C1, we show that when the initial value 0 ∈ (1 e), the leader does not produce the club good  and the size of the group stays at  = 0 , for all . It is easily verified that when   1, the consumption value of the club good becomes positive for individuals of type . Therefore, a fully myopic leader, who cares about the welfare of his community members, would always produce the club good  as soon as   1. However, as soon as the leader becomes forward looking, the leader knows that, starting at 0 ∈ (1 e), there are too few individuals of type  to finance the good  and that, eventually,  will decrease and end up at 1 in steady state. This is going to reduce dynamically its rents    . Also, the consumption value ( − 1)  of the club good to community members is positive but quite small along the transition path from 0 to 1. As a result, contrary to the myopic case, it is optimal for the forward-looking leader to remain inactive and to never produce the good . Consider now the case where the group starts with a fraction 0 slightly above the threshold e (part () of Proposition C1 with 0 ∈ (e   min )). Although the value of 0 is still not high enough to trigger some positive cultural dynamics of  , the discounted intertemporal consumption value of the club good for individuals of type  is now high enough that it may compensate for the loss of cultural rents that the leader incurs along the transition path from 0 to 1. In that case, the cultural leader will provide the club good . However, the level of club good that the community can finance is not sufficient to permit the diffusion of trait  in the population. The leader, therefore, remains active and provides the public good only for a finite amount of time. The population of individuals of type  declines and consumes  up to the moment where its per capita provision cost is too high compared to its benefit. At this stage, the cultural leader ceases to supply the public good and the cultural dynamic process stops. Finally, when the initial fraction 0 is much larger than the threshold e (part () of Proposition C1 with 0 ∈ (min  max )), then the cultural leader provides the public good at the maximum possible rate of individual contribution, and this promotes the diffusion of the cultural trait  to a higher long-run steady state level. This is because the leader anticipates that there are enough individuals of type  to finance the good  and that  will increase until it reaches its maximum value.

D D.1

Online Appendix D: Direct socialization of leaders Direct socialization of the leader

In the benchmark model, we assumed the following cultural transmission process. All children, born without defined cultural traits, are first exposed to their parent’s trait (direct 17

vertical socialization) and, if not directly socialized, are subject to outside socialization. The latter is such that the child is matched to a passive role model randomly chosen from the society. The active role model, i.e. the leader, affects this cultural transmission only indirectly through her choice of the public good  , which, in turn, impacts on   (  ) =  +  , the utility of a type− individual taking action . The utility   (  ) directly affects  , the parent ’s effort in transmitting her trait. In this section, we consider a model where the leader directly affects the cultural transmission mechanism. For this we amend our previous framework in the following way. Specifically we now assume that children are first exposed to their parent ’s trait (with probability  ) but, when this fails, the child is subject to outside socialization so that, with probability , she is directly exposed to the leader (of trait ) while, with probability 1 − , the child is matched to a passive role model randomly chosen in the society (i.e. she adopts trait  with probability   ). D.1.1

The model with one leader

In this new transmission mechanism, we can write the transition probabilities, for all   ∈ { }, as follows:   =  + (1 −  ) [ + (1 − )  ]   = (1 −  ) (1 − ) (1 −  )   =  + (1 −  ) (1 − ) (1 −  )   = (1 −  ) [ + (1 − )  ] Observe that, in these transition probabilities, we assume that, once a child is exposed to a leader, she automatically adopts trait . The cultural dynamics of  is then given by: +1 =    + (1 −  )  =  [ + (1 −  ) [ + (1 − )  ]] + (1 −  )(1 −  ) [ + (1 − )  ] As a result, instead of (6), the continuous-time dynamics version of this equation is now given by: ¢ ¡ •  = (1 −  ) 1 −  [ (1 −  ) +  ] −  (1 −  ) (1 −  ) (1 − )

(D.1)

Let us now study the program of the leader. The program of the leader can now be written as: Z ∞ max − (   − )  0≤≤1 0 ¡ ¢ • (D.2)    = (1 −  ) 1 −  [ (1 −  ) +  ] −  (1 −  ) (1 −  ) (1 − ) 18

Observe that, compared to (13), the objective function of the leader has changed since she now chooses , her influence in the society and not the public good  as in the previous section. Solving this program is quite complicated. Thus, we assume that the choice  of parent  is exogenous. When  = 0, this, however, leads to very simple dynamics converging to the corner solutions  = 0 when    and to  = 1 when    . These situations of pure homogenous populations may prevent the application of the MRAP approach for the maximization problem.5 Therefore, to avoid such situations and to replicate the idea that with endogenous family socialization rates (and cultural substituability) there is always some long-run cultural heterogeneity (with and without leader intervention), we approximate the constant parent socialization rates by a frequency dependent socialization rate in the following way: (  for   1 −   () = 0 for  ≥ 1 −  (  for     () = 0 for  ≤  With such socialization rates, it is easily verified that the cultural dynamics without leader intervention converge respectively to the interior steady states  when    and 1 −  when    . For   0, we can then apply our MRAP approach as the associated function () is bounded on the interval [ 1 − ]. We can then recover the insights of optimal leader intervention in the standard case when  → 0. With these modified socialization rates and starting with some initial population frequency  (0) ∈ ] 1 − [, the cultural dynamic system is again given by (D.1). As in Section 3, we have the following result: Lemma D1 () Assume that  =  = . Then, up to some constant, the optimal control problem (D.2) is equivalent to: Z ∞

max

0≤≤1

− ( )

0

where

( ) =    +

 log (1 −  ) (1 − )

() Assume that  6=  . Then, up to some constant, the optimal control problem (13) is equivalent to: Z ∞ − ( ) max 0≤≤1

5

0

The function () may become unbounded as one approaches  = 0 or  = 1.

19

where " ¢ ¡  ¢# ¡     −  −  −      1 −     − log ( ) =    + [ (1 −  ) + (1 −  ) (1 −  )] (1 −  ) 1 −  Proof of Lemma D1: Observe that, from (D.1), we easily obtain: ¡ ¢ •   −  (1 −  )  −  = (1 −  ) [ (1 −  ) + (1 −  ) (1 −  )]

(D.3)

Therefore, we have:    − 

¡  ¢ •  −        − =   + [ (1 −  ) + (1 −  ) (1 −  )] (1 −  ) [ (1 −  ) + (1 −  ) (1 −  )] As a result, the program (D.2) can be written as: µ ¶ ¡  ¢      +   −    max 0≤≤1 0 [ (1 −  ) + (1 −  ) (1 −  )] Ã ! Z ∞ •   − − max 0≤≤1 0 (1 −  ) [ (1 −  ) + (1 −  ) (1 −  )] Z



−

Observe that 1 (1 −  ) [ (1 − + (1 −  ) (1 −  )] ¢ ¡   −  1 = − (1 −  ) (1 −  ) [1 −  −  ( −  )] (1 −  )  )

Thus Ã

! •   −  ) + (1 −  ) (1 −  )] (1 −  ) [ (1 −     0 ¢Z ∞ ¡  Z ∞ • •  −    1 − −    −  = (1 −  ) 0 (1 −  ) (1 −  ) 0 1 −  −  ( −  ) Z



which after integration provides " ¡ ¢# ∙ ¸ Z ∞ 1 −  −   −  1 − 0  1 −  log log + (1 −  ) 1 −  − 0 ( −  ) (1 −  ) 0 1 −  20

As a result, the objective function of the leader to be maximized can be written as: Z Z ∞ ¡  ¢ ∞ −  −        +   −    [ (1 −  ) + (1 −  ) (1 −  )] 0 0 " ¡ ¢# ∙ ¸ Z ∞ 1 −  −   −   1 − 0  − −  log log −      (1 −  ) 1 −  − 0 ( −  ) (1 −  ) 0 1 −  () Assume that  =  = . This objective function simplifies to: ¶ µ ¶ µ Z ∞ Z ∞ 1 − 0   1− −  −  log −     − log (1 − ) 1 −  (1 − ) 1 −   0 ∙ ¸ Z0 ∞   = −    + log (1 −  )  − log (1 − 0 ) (1 − ) (1 − ) 0  Hence, up to some constant (here − (1−) log (1 − 0 )), our optimal control problem collapses to Z ∞ max − ( ) 0≤≤1

0

where

( ) =    +

 log (1 −  ) (1 − )

() Assume now that  6=  . This objective function can be written as: ( " ¢ ¡  ¢ #) ¡  Z ∞    −  −  −      1 −      −    + − log  ) + (1 −  ) (1 −  )] ) [ (1 −  (1 −  1 −    0 ∙ ¸ 1 − 0  log − (1 −  ) 1 −  − 0 ( −  ) ∙ ¸ 1−0  Hence, up to some constant (here − (1− ) log 1− −  − ), our optimal control prob) 0( lem collapses to Z ∞ − ( ) max 0≤≤1

0

where

" ¢ ¡  ¢# ¡     −  −  −    1 −       ( ) =    + − log [ (1 −  ) + (1 −  ) (1 −  )] (1 −  ) 1 −  This completes the proof of this lemma.

21

D.1.2

Equilibrium and dynamics

Let us first consider the case when  =  = . The objective function () is depicted in Figure D1 when     (1 − ). It reaches a maximum at ∗ = 1 −  [  (1 − )] so that, when    ∗ , () is increasing while, when   ∗ , () is decreasing. When     (1 − ), then the function () is always decreasing. [   1 ] The dynamics is relatively simple in that case. Notice, first, that the cultural dynamics can be written as: •

 = (1 −  ) (1 − ) [ (1 −  ) +  ] −  (1 −  ) (1 − ) (1 − ) = (1 − ) (1 −  ) 

for  ∈ ] 1 − [

Hence for given initial conditions  (0) ∈ ]0 1[, the fraction of  increases in the population as long as   0 Conversely, given that parental socialization is symmetric, the population stays at any value of  where it is as soon as  = 0. Now, when     (1 − ), and given some initial conditions  (0) ∈ ]0 1[, it is optimal for the leader to remain inactive at all time so that  ∗ = 0. The population stays therefore at this initial value (0). When     (1 − ), (0)  ∗ , given that  can only be positive and trigger a further increase in the fraction , the optimal strategy of the leader is again to remain inactive with  ∗ = 0 and to stay at this initial value  (0)  When, however, (0)   ∗ , then it pays for the leader to be active up to the point when she reaches  ∗ . Hence, as long as  remains below  ∗ , the leader provides full biased cultural influence at  = 1. Then at some finite time  , the dynamics of  imply that the population reaches the targeted fraction  ∗ . At this time  , the leader stops her cultural influence and chooses to remain inactive at  ∗ = 0. Indeed, when  =  = , the parent’s effort of each type of families is the same. Thus, for     (1 − ), the gain for the leader to act on  is too small and therefore she stays inactive ( ∗ = 0). The time pattern of cultural influence for this case is illustrated in Figure D2. [   2 ] Consider now the case when  6=  . The study of the shape of the function ( ) now depends on whether parental socialization rates of the leader’s type (i.e. type ) is large enough compared to those of parents of the other type . Specifically, we have the following result: Lemma D2: Assume that ∆ =  −  6= 0 and that the leader is sufficiently patient, i.e.  is less than 1 −  . 22



() When ∆  − 1− , we have: 2 −∆  (1) If   1− ,the function () has a unique maximum at  =  ∈ (0 1);  (2) If   −∆ , the function () is decreasing for all  ∈ [0 1]. 1− 1− such that: () When ∆  − 2 , there exists a threshold   −∆ 1− −∆  (1) If   1− ,the function () has a unique maximum at  =  ∈ (0 1);  (1) If     −∆ , there exist  and  such that the function () is 1− decreasing for  ∈ [0  ] ∪ [  1] and increasing for  ∈ [ ;  ];  (3) If   , the function () is decreasing in  ∈ [0 1]. Proof of Lemma D2: The function ( ) now takes the following form: " ¢ ¡ ¢# ¡ 1 −  −   −    −     ( ) =   + − log [ (1 −  ) + (1 −  ) (1 −  )] (1 −  ) 1 −  and differentiation provides ¢ ¡   −  (1 −  )  0   ( ) =  + − 2 [1 −  −  ( −  )] [1 −  ] [1 −  −  ( −  )] £ ¡ ¡ ¢¤2 ¢ Now denote Λ () = 0 ( ) 1 −  −   −  (1 −  ) and pose ∆ =  −  . Then Λ () writes as Λ () =   Φ() − Υ () with ¤2 £ Φ() = 1 −  − ∆ (1 − ) ¢ ¡ Υ () =  1 −  − ∆ − ∆(1 −  )(1 − )

The function Υ () is a linear function of  with Υ (0) = ( − ∆)(1 −  ) and Υ (1) = (1 −  )  0. Its slope is ∆(1 −  − ). We assume that the discount is small enough that  is less than 1 −  . Therefore the function Υ () is increasing in  if and only if ∆  0 £ ¤2 The function Φ() = 1 −  − ∆ (1 − ) is such that £ ¤ £ ¤2 Φ0 () = −2∆ 1 −  − ∆ (1 − ) − 1 −  − ∆ £ ¤£ ¤ = − 1 −  − ∆ 2∆ (1 − ) + 1 −  − ∆ ¤£ ¤ £ = − 1 −  − ∆ 1 −  + 2∆ − 3∆

Therefore the function Φ() is decreasing in  when ∆  0 It is also decreasing in  when ∆  0 and 1 −  + 2∆  0. On the other hand when 1 −  + 2∆  0 and ∆  0, £ ¤  then Φ() is increasing in  if and only if  ∈ 0   with  = 23 + 1− . Moreover 3∆ £ ¤  2 Φ(0) = 1 −   0, Φ(1) = 0.  () Assume first that ∆  0. Then when   −∆) , there exists a unique  such 1− that Λ () is positive if and only if  ∈ [0  ] and the function () has a unique maximum 23



at  =  . When  ≤ −∆ , Λ () is always negative for all  and the function () is 1− decreasing in  ∈ [0 1]. () Suppose now that ∆  0. and 1 −  + 2∆  0. Then Φ() is decreasing in  Moreover it is easy to see that Φ00 ()  0 . Υ () is also linear decreasing in . Again it is easy  to see that when   −∆ , there exists a unique  such that Λ () is positive if and only 1−  if  ∈ [0  ] and the function () has a unique maximum at  =  . When  ≤ −∆ , 1− Λ () is always negative for all  and the function () is decreasing in  ∈ [0 1]. () Suppose now that ∆  0. and 1 −  + 2∆  0. Φ() is increasing in  if and £ ¤ only if  ∈ 0    Denote Φ = Φ(  ) the maximum of Φ(). Υ () is linear decreasing  in . . When   −∆ , it is easy to see that as before there exists a unique  such that 1− Λ () is positive if and only if  ∈ [0  ] and the function () has a unique maximum at   =  . When   −∆ , the function Φ() is decreasing in  Moreover it is easy to see 1− 

)   . that Φ00 ()  0 if and only if  ≤  = 13 + 2(1− 3∆ The shape of the functions Φ() and   Υ () is depicted in Figure D3 (when  and Figure D4 (  ≤ −∆ ). 1−

 



−∆ ) 1−

[   3  4 ] 

one has   Υ (0) = Φ(0) while   Υ (1)  0 = Φ(1) There As can be seen at  = −∆ 1−  is therefore a unique intersection at a point  . By continuity , a decrease of  from −∆ leads to an upward shift of the function   Υ (). The function   Υ () crosses then 1− ¡ ¢ ¡ ¢ two times the function Φ() at the two points   and   which are respectively  decreasing and increasing functions of  ). From this it follows that the function Λ () is £ ¡ ¢ ¡   ¢¤ £ ¡  ¢¤ £ ¡   ¢ ¤ positive for  ∈   ;   and negative for  ∈ 0   ∪    1 . It follows immediately that in such case the function () has a unique minimum at  =  and a local maximum at  =  .  Keeping on decreasing further the parameter  leads the two points  and  to con¢ ¡ verge by continuity to the tangent point   ∈  ;  between   Υ () and Φ(). When  is further decreased below the value  such that   =  ()  the curve   Υ () is always  above the curve Φ ()  From this Λ () is always negative for all  and the function () is decreasing in  ∈ [0 1]  This completes the proof of this lemma. Again assume that without leader intervention, the dynamics of culture have converged towards their steady states (0) =  when ∆  0 or (0) = 1 −  when ∆  0. Then we have the following proposition: Proposition D1: Assume that ∆ =  −  6= 0 and that the leader is sufficiently patient, i.e.  is less than 1 −  . For any  small enough, we have: 24

() When ∆  0 and (0) = 1 − , then the leader never socializes, i.e.  ∗ = 0 and the cultural dynamics stay at (0) = 1 − . () When ∆  0 and (0) = , then we have:  (1) If   −∆ , the leader chooses to fully socialize  ∗ = 1 up to to some finite 1− time  for which  ( ) =  and then, for    , to socialize at the interior rate ∗ =

− ∆ (1 −  ) −  ∆

The cultural dynamics then stay at the interior steady state  .  (2) If   −∆ , the leader never socializes,  ∗ = 0, and the cultural dynamics 1− stay at (0) = . Proof of Proposition D1: We have seen that, for ∆ =  −  6= 0 and for the leader sufficiently patient (i.e.  less than 1 − ), the shape of the function () is given by Lemma D2. Then it is easy to have the following result:  () Consider first that ∆  0 and (0) = 1 −  When   −∆ and for  small enough 1− 1 −    . Therefore any positive value of  would only increase further  and reduce the value of the function () Therefore the leader should stay at  (0) = 1 −  and choose   ∗ = 0. When   −∆ , the function () is decreasing for all values of . Therefore 1− again the leader should stay at  (0) = 1 −  and choose  ∗ = 0. () Consider now that ∆  0 and (0) =  . then:  (1) when   −∆ , the function () has again a global maximum at  =  . As 1− a consequence given that    , the leader chooses optimally his MRAP towards  with full socialization  ∗ = 1 up to some finite time  at which  ( ) =  . Then for    the leader maintains the cultural dynamics at  =  with an interior socialization rate  such · that  = 0, namely: − ∆ ∗ = (1 −  ) −  ∆ The cultural dynamics then stay at the interior steady state  .  (2) When  ∈] −∆ [, there exists  and  such that the function () is decreasing 1− for  ∈ [0  ] ∪ [  1] and increasing for  ∈ [ ;  ]. For  small enough (i.e.    ) , the intertemporal value  () = () is larger than ( ) , and therefore is larger than any  other dynamic path that converges monotonically from (0) to  . It is then optimal for the leader to stay at  =  with  ∗ = 0.  (3) when   , the function () is decreasing in  ∈ [0 1]. Hence again the leader never socializes,  ∗ = 0. and the cultural dynamics stay at (0) = . Intuitively, Proposition D1 provides very similar results to the case where the cultural leader is not directly participating into the socialization process of her trait (benchmark 25

model). Specifically, when families of type  are more successful in socializing their offsprings than families of type , the cultural leader does not enter into the process of socialization as her action is a pure substitute to the family socialization from members of her own community. More interestingly, when family socialization by individuals of trait  is lower than that of individuals of trait , then a cultural leader may enter actively into direct socialization when the relative value of the cultural rent    she derives from this socialization ¡ ¢ process is above a certain threshold (here ( − ∆)  1 −  ). Such leader will socialize to compensate for the lack of family socialization to her own trait and, by doing so, will induce a positive long-term fraction  of members of her own type. As in the previous section, the direct socialization effort of the leader will temporarily overshoot her long-run value. Indeed, for a finite period of time, the leader will provide a maximum socialization of  = 1. Then, after reaching the optimal population share of  , the leader will reduce the socialization effort to an intermediate value of  ∗  1 such that the system stays at  . Note that the leader is more likely to be active the more patient she is (i.e. the smaller is ), the smaller  (the family effort of the other group ) and the larger the difference −∆ =  −  between family socialization of types  and . Obviously, the emergence of a cultural leader for group  is also more likely to happen when the cost of direct socialization  is small. Our analysis thus suggests that, in the context of religious radical leaders (group ), they are likely to be active when, in the community, family socialization to the mainstream model is weak ( small) but still larger than family socialization for radicalism (∆  0). In such situation, when the cost of direct socialization is low (due, for example, to easier access to communication technologies), cultural leaders, supporting traits that would have otherwise disappeared (such as Muslim radicalization), have larger incentives to become active to countervail the natural tendency of the long-run assimilation of the ethnic population to the mainstream host culture. More generally, all these extensions of the benchmark model highlight the idea that, independently of the objective function of cultural leaders, the nature of the intervention process of the leader or the fact that the public good can be imperfectly excludable to outgroups, the qualitative nature of the dynamics of cultural integration crucially depend on the cultural substituability and internalization (complementarity) effects between centralized and decentralized channels of cultural transmission inside communities. The existence of these two types of effects then typically generate non-monotonic size effects, threshold and hysteresis effects, which are crucial determinants of these dynamics.

26

D.2

Competition between cultural leaders

In this section, we extend our framework of direct socialization of the leader to discuss the issue of competition between cultural leaders, for example, between a religious leader and the host-country institution. The transmission process is now as follows. First, parents of type  ∈ { } directly transmit their trait with probability  . To have a tractable setting, we assume that family socialization  is exogenous. Second, cultural influence outside the family depends on two types of role models. As before, there are passive role models with whom naive children can be randomly matched. With probability 1− , the child is matched with a passive role model randomly chosen in the society. In such case, she adopts trait  with probability   =  and trait  with probability   = 1 − . There are also specific role models (i.e. cultural leaders) who do interact strategically by choosing their socialization efforts, directly influencing cultural evolution in a way that favors their interests. It is clear that these two leaders will compete since their objectives are different, even opposite. To be more precise, with probability , the child will be exposed to a cultural leader of type  6= . She then gets socialized to trait  with probability Π (   ) and, with probability Π (   ) = 1 − Π (   ), she adopts the other trait  6= , where  and  are the socialization efforts of the leaders of type  and type , respectively. Observe that  reflects the relative importance of cultural leaders in the transmission process as compared to the rest of society. This is a technological parameter that may also reflect the importance of information technologies or the degree of centrality of the network of cultural socialization in society. For simplicity, we take a specific well-known contest function (Hirshleifer, 1989; Skaperdas, 1996; Konrad, 2009) given by: Π (   ) = 1 − Π (   ) =

  + 

(D.4)

This formulation captures the fact that cultural leaders are in competition with each other for cultural transmission. Therefore, for all   ∈ { }, the probability that a child from a family with trait  is socialized to trait  is now given by: ¡ ¢            =  + (1 −  )Π (   ) + (1 − )

¡ ¢           = (1 −  )Π (   ) + (1 − )(1 −  )

The dynamics of the fraction of the population with trait , can then be straightforwardly written as: ¡ ¢ ¡ ¢  =            + (1 −  )           +1 27

Thus, taking as before the notation   = 1−  =  and passing to continuous time dynamics, we obtain: ¡ ¤ ¢ £ •  =  (1 − ) (1 − )  −  +  (1 − )(1 −  )Π − (1 −  )(1 −   )

(D.5)

where Π ≡ Π (   ). We assume that cultural leaders enjoy the rents associated with the number of individuals who share their cultural traits in the population and therefore are ready to spend resources to affect the process of cultural evolution in society. Specifically, assume that the utility of a cultural leader of group  ∈ { } is given by: Z ∞ ¢  ¡   = −      −    0

where the leader’s cultural rents    (resp.   (1 − )) of type  (resp. ) increases with the size of her own group   =  (resp.   = 1−) and   (resp.   ) is the linear resource cost to compete for cultural socialization in the contest between leaders. This setting describes then a dynamic differential game of cultural influence between the two leaders. As it is wellknown, various equilibrium concepts can be used to analyze such games. In the following, we characterize the open-loop Nash equilibrium concept. Denote by  () and  () ∈ R+ ¢ ¡ some admissible socialization efforts of the leaders  and , and by    ()  () and ¢ ¡    ()  () the intertemporal values associated to these socialization efforts, i.e., Z ∞ ¢ ¤ ¡   £     ()  () = −    (    ) −   ()  0

¡ ¢   ()  () = 

Z

0



−



£  ¤  (1 − (    )) −   () 

where (    ) is the trajectory starting at 0 and satisfying the following differential equation: ¸ ∙ £  ¤   •      =  (1 −  ) (1 − )  −  +  (1 −  )(1 −  )  −  (1 −  )   +   +  (D.6) ∗ Definition D1: An open-loop Nash equilibrium (∗    ) is characterized by the following conditions:

¢ ¢ ¡ ¡   ∗ () ∗ () ≥    () ∗ () for all admissible  () 28

¢ ¢ ¡ ¡   ∗ () ∗ () ≥   ∗ ()  () for all admissible  () In the Online Appendix D.3, we characterize the solutions of the open-loop Nash equi∗ librium (∗    ) and show that a complete characterization of the equilibrium trajectory and socialization efforts of the two leaders is intractable. As a result, to obtain analytical results, we assume that  =  = , which means that the family (vertical) socialization is neutral in terms of cultural evolution so that both parents (of types  and ) provide the same constant socialization effort. In other words, we shut down the vertical socialization channel and focus on the oblique one by analyzing the influence of each type of leader on socialization when they compete with each other. In such a case, the conditions given in the Online Appendix D.3 collapse to much simpler conditions, which are:  (1 − ) •

∗

= 

2

(∗ +∗ ) ∗

− (1 − )

2

(∗ +∗ )

=  

 −   = − [  −  (1 − )] and lim→∞  −  = 0 • £ ¤     −   = − − −  (1 − ) and lim→∞  −  = 0 ´ ³ ∗ •  = (1 − ) ∗+∗ − 

(D.7)

where  and  are the associated adjoint variables to each leader. It follows immediately that the adjoint equilibrium variables jump immediately to their long-run values, given by:  =

 −   = ,   + (1 − )  + (1 − )

while the equilibrium socialization efforts of the two leaders are constant and equal to:   ∗ = − ∗  or equivalently ∙ ¸ ∗     + (1 − ) =    ∗    + (1 − )

(D.8)

This implies that the ratio of socialization efforts of the two cultural leaders will depend on the relative cost and benefit of providing socialization effort, on the relative discount rate or degree of patience and on , the relative importance of cultural leaders in the transmission process as compared to the rest of society. On can verify that the sign of the impact of  on ∗ ∗ is the same as  −  . In other words, if the cultural leader of type  is more (less) 29

patient than that of type , then the higher is the importance of leaders in the society, the higher (lower) is the effort of leader  compared to that of leader . We can then determine each socialization effort as follows: ¤ £     2  ( ) + (1 − ) (1 − )   ∗ = (D.9) {   [ + (1 − )] +    [ + (1 − )]}2 ∗

 =

¡ ¢2      [ + (1 − )] (1 − )

{   [ + (1 − )] +    [ + (1 − )]}2

(D.10)

The cultural dynamics (D.6) are now given by (when  =  = ): •

 = (1 − ) ( ∗ −  )

¡ ¢ where  ∗ = ∗  ∗ + ∗ is the long-run value of the fraction of individuals of type  and, using (D.9) and (D.10), is equal to: ¤ £     + (1 − ) ∗  =    (D.11)   [ + (1 − )] +    [ + (1 − )] Note that, in this case, the current-value Hamiltonian   (      ) (resp.   (      )) is the sum of a linear function in  and a strictly concave function in  (resp. in  ) and ¡ ¢ thus is jointly strictly concave in (  ) (resp.    ). Hence, given the other leader’s optimal socialization rate, the optimal control problem of each cultural leader satisfies the Magasarian sufficiency conditions and the necessary conditions (D.7) are also sufficient to characterize the Nash open-loop equilibrium. The phase diagram of the cultural evolution process is depicted in Figure D5, which immediately shows that the steady state ∗ is unique and stable. [   5 ] Proposition D2: The steady state interior equilibrium  ∗ is increasing in       and decreasing in       . Moreover, the sign of the impact of (1 − ) on  ∗ is the same as that of  −  , i.e. ∗ T 0 ⇔  T    [(1 − )] The steady-state equilibrium fraction of people of type  decreases with the cost and the discount factor  of the leader of type  and increases with the cost and the discount factor  of the leader of type . We have the opposite result for the benefit of leaders of type 30

 ∈ { }. A more surprising result is the impact of  and  on  ∗ , which depends on the relative discount rate (or degree of impatience) of the two leaders. Indeed, if the cultural leader of type  is less patient than the leader of type  (i.e.    ), then the higher is the importance of leaders in the society (), the higher is the fraction of individual of type  in the long-run equilibrium. The intuition for this result is as follow. When  increases (because of, say, technical progress in communication technologies), the competition between leaders is intensified and both socialization efforts  and  increase. However, the more patient leader (of type ) initially exerts a higher socialization effort  than the less patient leader of type . Given that the contest function features marginal decreasing returns in own influence effort, the more patient leader  is therefore increasing her socialization effort by less than the more impatient leader , in response to a higher value of . As a consequence, the relative socialization efforts ratio   tends to increase, leading to a higher relative socialization success of leader  compared to leader . The long run consequence of this is an increase in the steady-steady value ∗ of individuals with trait  in the population. Similarly, if the cultural leader of type  is less (more) patient than that of type , then the higher is the effort exerted by parents of both types in socializing their kids, i.e. higher , the lower (higher) is ∗ . Again, this is due to the cultural substituability effect between vertical and oblique socialization and its differential impact on the cultural leaders’ incentives to socialize depending on their degree of patience. Indeed, when  increases, there is less scope for leader influence and therefore less competition between cultural leaders. Since the less patient leader (say leader  when    ) is reducing more strongly her effort than the patient leader (because of the decreasing marginal returns of the contest function and the fact that she already invests less in socialization than the patient leader), then ∗ ∗ goes down. As a consequence leader  is relatively less successful at socializing members of the population to trait  and the long-run fraction ∗ of individuals of type  is reduced.

References [1] Hirshleifer, J. (1989), “Conflict and rent-seeking success functions: Ratio vs. difference models of relative success,” Public Choice 63, 101-112. [2] Konrad, K.A. (2009), Strategy and Dynamics in Contests, New York: Oxford University Press. [3] Skaperdas, S. (1996), “Contest success functions,” Economic Theory 7, 283-290. [4] Verdier, T. and Y. Zenou (2015), “The role of cultural leaders in the transmission of preferences,” Economics Letters 136, 158-161. 31

D.3

Characterization of the solutions of the open-loop Nash equi∗ librium (∗    )

∗ To characterize the solutions of the open-loop Nash equilibrium (∗    ), we need to provide the following current-value Hamiltoneans:

  (      ) =    −   ∙ µ ¡  ¢   +  (1 − ) (1 − )  −  +  (1 − )(1 −  )

   − (1 −  )  +   + 

¶¸

   − (1 −  )  +   + 

¶¸

  (      ) =   (1 − ) −   ∙ µ ¡  ¢   +  (1 − ) (1 − )  −  +  (1 − )(1 −  )

where  and  are the associated adjoint variables to each leader and the parental socialization efforts take the general form  =  ();  =  (). An open loop Nash equilibrium (∗ () ∗ ()) should then satisfy the following necessary conditions ∗ = arg max   (  ∗    )  

∗

 •

= arg max   (∗      ) 

  (∗  ∗    )   ∗  (  ∗    ) = − 

 −   = − • 

 −  



and lim  ()−  = 0 →∞



and lim  ()−  = 0 →∞

¡ ¢ •   =  (1 −  ) (1 − )  ( ) −  ( ) ∙ ¸ ∗ ∗     + (1 −  )(1 −  ( )) ∗ −  (1 −  ( )) ∗  + ∗  + ∗   or equivalently, £ ¤   (1 − )(1 −  ()) + (1 −  ())

∗  2 =  ∗ ∗ ( +  )

£ ¤ −  (1 − )(1 −  ()) + (1 −  ()) 

32

∗  2 =  ∗ ∗ ( +  )



 −   h i ) ( ¡  ¢ ∗ ∗        +  (1 − 2)) (1 − )  −  −  (1 −  ) ∗ +∗ + (1 −  ) ∗ +∗ = − − ¡ ¢ + · Θ  ∗  ∗ 

and lim  −  = 0 →∞



 −   h i ) ( ¡ ¢ ∗ ∗ −  +  (1 − 2)) (1 − )  −  −  (1 −  ) ∗+∗ + (1 −  ) ∗+∗ = − ¡ ¢ + · Θ  ∗  ∗ 

and lim  −  = 0 →∞ ¸ ∙ ¡  ¢ ∗ ∗ •        =  (1 −  ) (1 − )  −  +  (1 −  )(1 −  ) ∗ −  (1 −  ) ∗  + ∗  + ∗   ¡  ¢ denoting Θ     , the following function : ∙ ¸ ∙ ¸ ¡  ¢   0 0 + (1 − )  +  () 1 −   −  (1 − ) Θ     = −(1 − ) ())    +   + 

It should be clear that a complete characterization of the equilibrium trajectory and socialization efforts of the two leaders is intractable in this general case.

33



Figure B1(a):           <  W a q 

q

 q

Wa 0

 q

1



Figure B1(b):          >            W a q 

q

Wa  q

0

qL

 q

qH

1

Figure B2: The function R(q) with public good spillovers  R(q)



=

q



0 a  q case            <              

W



case            >              W a q 

Figure C1: The function R(q) R(q)

q min 0

1/  q

No club  Club good good cultural  No Dynamics decline

q max

Club good Cultural  decline

q

Figure D1: The function R(q) when the leader chooses  γ when R(q)

0



1

q 1

1

Figure D2:  The choice of  along the transition path when W a  c/1 − d and q0  q ∗  1

0

t T

Figure D3: Case when Wa c



−Δd 1−d b

q −Δd

c Wa

1−d b

0

q

qM

qC

qH

1

q

Figure D4: Case when

case

−Δd

Wa c

Wa c



−Δd 1−d b

case Wca  



c Wa

q

1−d b

0

qL

qT

qH

1

q

Figure D5 : Dynamics with leader competition



qt

1 − dq ∗

0

q



1

qt

Online Appendix

The optimal control problem (B.3) of the leader is therefore equivalent to max. 0≤Gt≤G / ∞. 0 e−ptR(qt)dt where. R(qt) = Waqt + c∙ ua − (ua + ub)qt. 1 + ∆λ − qt.

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