Phylogeny

The Emperor and King Penguins are the oldest current lineage of penguins, and kidnapping behavior as been observed in individuals of both species. The behavior, however, is not necessarily “old” as kidnapping does not appear to occur in the other species of penguins. It would seem more appropriate to view the kidnapping behavior as one deriving from the most recent ancestor of the King and Emperor Penguins, as opposed to originating with the predecessor of all penguins. "But wait," you may say. "Other species of birds, such as snow geese, have been known to kidnap chicks as well!" Well, headstrong nerd, it's likely that this behavior has evolved independently in several lineages, in an example of convergent evolution.