Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-96.255.242.119-20130716034511/@comment-11835613-20130716042519

I think Jeff Davis answered this question during the beginning of season 3. In one of the episodes, we will learn why some Alphas turn into full/semi wolf, while the others turn into more of humanoid beasts.

As of now, here is my assumption..... Derek Hale and Peter Hale belong to a family of Super Alphas (Perhaps they are a more vicious and powerful breed) that are actually more powerfull than other Alphas for some reason.

1) Jeff clearly stated in one of his Q&A sessions that Derek's mom was a powerful Alpha Werewolf. Maybe only the elders in a family can turn into a wolf. This explains the reason why Laura Hale (Elder Sister of Derek, defacto Alpha elder due to the family being killed in a fire and Peter, the oldest living member bed-ridden for 6 years due to burns) can turn into a full wolf, while Peter Hale (After he recovered from his burns) can turn into a wolf-like beast as he became an Alpha by killing Laura Hale. Derek couldn't shift into full/semi-wolf form because 1) In Season 2, he rarely shifts into full Alpha form and by the end of Season 2, Peter Hale comes back from the dead and actually absorbs a part of Derek's energy (Refer to the Lunatic episode (Worm Moon incident)) to resurrect himself.

2) Another reason could be that only an Alpha, who has killed one or more Alphas can acquire the power tp shape-shift into a full/semi-wolf.

Derek's mom perhaps was one such Alpha, who killed or ambushed several other Alphas to acquire the position. Laura Hale, being the only surviving eldest member (Before Derek Hale returned from Coma) took over the mantle of the Super Alpha. Derek Hale then killed Laura to get the Alpha powers to avenge the Hale family fire.

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