Why do Asian jawlines tend to more often have a downward angle to them? (photos)

I've seen it more often in Asian people, but also in Caucasians. The main difference being that usually the Caucasians with the downward angle are just underdeveloped. I noticed it is more common in Asians even when they have well developed faces. My jawline does it even though it is well developed, and it seems to be common on my mother's side of the family.

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