Peer review of: Wild primates copy higher-ranked individuals in a social transmission experiment (2020)


 
 

Reviewers' Comments: 
 
Reviewer #1: 
None 
 
Reviewer #2: 
Remarks to the Author: 
The authors have put a lot of effort into the revision. There is no doubt that NBDA (or the OADA) 
variant is a cool tool, and that the experiment is very smart. Yet, I still feel that there is room for 
improvement; specifically when it comes to convincing the reader that NBDA is the appropriate tool to 
model the acquisition of the different box opening techniques in the vervet monkeys. 
 
Showing that one model is better than another one is one thing, but showing how accurately the 
model fits the data is another. There is not sufficient information to judge this. Thus, the authors need 
to clearly spell out the numbers of learning events they modeled. Please provide the reader with a 
table with the important raw data that contain for each learning event how often a given subject had 
seen how many other subjects had used which technique prior to learning. 
 
It also remains unclear how the authors distinguish between social and asocial learning when an 
animal switches to the alternative technique: One of the key statements is that animals are 31 times 
faster to subsequently asocially learn the other option than individuals naïve to both options. Could 
the authors rule out that the individual had ever observed the alternative technique? And how can 
they be certain that this learning is now asocial? And did they include these events in the model for 
social learning? Again, I think this needs to be specified. 
 
In this context, I was happy to see that the authors now report the latencies, but how was latency 
determined? Are these the latencies from first having observed a subjects using option Y until using 
option Y? Is this actual time or time boxes being available? The latencies are very long: what does it 
tell us about the learning process if the latency can be up to 24 hours? More information is needed 
here. It would be helpful if the latencies were also reported in hours and minutes. 
 
In their rebuttal letter, the authors object that it would only be necessary to show [how many subjects 
had only seen one technique and then also used this technique] if they “were claiming that all vervets 
(save the innovators) learned by social transmission (copying), and/or that observation always leads 
to learning”. I think the authors are trying to evade a critical point here. Nobody assumes that 
learning can only be shown when all subjects acquired the technique socially. The critical point is 
whether the likelihood of using one option rather than another one depends on the social input, i.e. 
who and how many other subjects used that particular technique before. If the majority does learn it 
socially, everybody will be convinced, but if it is only half of the subjects, doubts will arise. To judge 
this, the authors should please provide the actual numbers and not force the reader to extract these 
data from the raw data files. 
 
It is impossible to judge the worthiness of the simulations because the information given is insufficient 
(rebuttal letter only). 
 
Furthermore, it is important to distinguish between the opportunity to learn and the actual rate of 
transmission. A rate of transmission can only be inferred once it is established that the subject indeed 
learns from the model(s). This semantic precision is necessary to avoid conflating the premise with the 
result. The authors write (line 179): The underlying assumption is that the rate of social transmission 
between individuals is proportional to the network connection between them; the more two individuals 
are connected (i.e. observe each other), the more opportunities they have to learn from each other. A 

parameter, s, is fitted to the data estimating the rate of transmission per unit of network connection, 
with representing the null hypothesis of only asocial learning.” 
 
In summary, this is certainly a potent method, but given the small number of events, and the lack of 
transparency in reporting, considerable doubts remain whether the dynamic network approach is 
indeed helpful to model the acquisition of box opening in vervets.