> This sentence in the introduction assumes a level of choice on the part of the mammals that is pervasive in the article but never substantiated or even formal

> This sentence in the introduction assumes a level of choice on the part of the mammals that is pervasive in the article but never substantiated or even formalized to the point of a testable hypothesis. The field here is evolutionary biology, and specifically the area of parental investment and applications of game theory. It is very common in that area to talk about "choice" etc. while not meaning anything conscious. For example, it is acceptable to say that genes "want" to propagate copies of themselves, but of course this is just shorthand for something very different. In the field, this is not misunderstood, it is the norm. > The study found that gender bias in birth rates can affect the number of grandchildren. No, the point was that they found that gender bias in birth rates appeared to be not entirely random (50-50) and weighted towards what generates an optimal number of grandchildren. That exactly supports a hypothesis that has been around for decades that through female choice (again, choice is not meant in the sense that I can choose what to eat for lunch), animals can affect gender birth ratios in order to maximize the number of grandchildren. (Here you can see the connection to game theory.) It is very hard to study that empirically, which is why this study is receiving a lot of attention - after decades, it is among the first to actually give measurements. > nor do I accept their statement that the study taking place in a zoo means that their findings are somehow more likely to be present in the wild. That would require a different experiment on its own. This is indeed a weakness in their methodology, and surely being debated heavily.