The bilingual brain revisited: A comment on Hagen (2008)

From the book : Evolutionary Psychology 6 issue 1 : 182-185.
L.K.
Hagen (2008; Evolutionary Psychology, 6, 43-63) proposes that effortless first acquisition compared to more difficult second language acquisition provides evidence that the monolinguistic nature of our ancestral social environments implies a near-constant state of intergroup conflict.
I argue to the contrary that the capacity to acquire multiple languages simultaneously in childhood without decrement to first language acquisition suggests that there was selection pressure for multilingualism.
I further argue that this cognitive capacity is evidence for an ancestral environment in which distinct groups commingled (e.g., through long-term trading and marriage relationships) in relative security.