One of the big design themes in Generation V is common descent, which is apparent from how many Pokémon parallel those of other generations, though most especially Generation I. Despite Unova being a long way away from Kanto and the other regions, many of its Pokémon show distinct similarities to those from the other regions.
Some are very obvious - Throh and Sawk quite obviously mirror Hitmonchan and Hitmonlee. On the other hand, some are less apparent - I've been thinking about Blitzle and its evolution, which based on zebras, and what struck me is that equids are very rare in the Pokémon world, with the last non-legendary example being the Ponyta line; perhaps adding credence to the idea that the two families are related is that Blitzle and its evolution learn Flame Charge, a curious move for Electric-types.
Of course, this isn't new - looking at Rhydon and Aggron, for example, it's easy to imagine that they branched off from each other at some point in their history.
Anyway, seeing as how I'm posting this, it's obvious I think you should do a piece on common descent and divergent evolution.