Before we consider examples of mosaic vc. concerted evolution, let us delve further into the “late-equals-large” itself.

Strictly speaking, this hypothesis is part of a new class of theories in evolutionary biology, called evolutionary developmental hypotheses (or evo-devo for short). In short, evolutionary developmental biology is exactly what its name shows: it is about the connection between evolutionary biology and developmental biology.
In the case at hand, what is important is not how the embryonic brain evolves, but how evolutionary changes in brain development produce differences between species. Briefly, the “late-equals-large” theory proposes that those brain regions which are “born” later during development tend to be bigger than regions which were born earlier; as such, if evolution changes the “birth schedule” of brain regions, then a change in the size of those regions will accompany the developmental alteration. Brain region size is important because, in general, larger regions tend to attract more axons from other regions, and tend to “invade” regions which were previously (in evolutionary history, that is) not innervated by it.

(For more on evolutionary and developmental modularity, see this entry on my other blog )