[malsme]

It is probably a strange thing to say (i.e. common knowledge for others), but it only recently occurred to me that people develop a standard pose for photos. If you look at a family album or say Facebook or Flickr, and scroll through historic photos, the most "photogenic" people look almost identical. Those people will face in a certain direction with the same shape of smile and posture, it's almost freaky how identical they are! So it's obviously a practised/fake thing, that some learn to do while others remain oblivious. Back then, this concept would not have existed.

[justincormack]

Early photos had very long exposures, with clamps used to hold people still. That may have set the expected look for a long time later.