From the post:
As some of you have no doubt noticed, we haven't said much about half-elves and half-orcs except to confirm that they'll be part of the Pathfinder Playtest. Of all of the ancestry choices in Pathfinder, these were two of the trickiest to design. With the way that the feats are structured, it would be easy enough to just list the feats from both parents (plus some unique options), but that quickly led to cherry-picking the best of both. Moreover, that approach didn't address the base statistics of the ancestry that are very important to overall balance, such as starting hit points and speed.
In the end, we decided to make both half-elves and half-orcs an addition to the human ancestry. You start by selecting human, then take the corresponding heritage feat to represent your diverse ancestry.