If you look up this Wikipedia article on head flattening and other ‘cranial modifications’, cultures around the world have practiced this for pretty much the Anthro 101 class explanations you’d expect – group identification (tied to social class or tribe or some such). In the Pacific NW, many tribes practiced head flattening. Newborns were subjected to practices to shape their foreheads into a ‘flat’ upward sloping shape. On the OR coast, the Alsea people were the southern most tribe to practice this.
A handful of Siuslaws were recalled to have flattened heads, and they all had Alsea relatives so presumably it was done by Alsea mothers who had intermarried at Siuslaw. Siuslaw people, for whatever reason, had not taken up the practice regularly on their own.
Lottie Evanoff recalled at Yachats that Alsea kids teased the Coos and Lower Umpqua kids by calling them ‘seal heads’. I take it as a compliment – seals are cute! In return, Lottie called them dllaqi xwiluxw – Hanis for bread head (ie, flat head).
I have not found anywhere that anyone asked Alseas why they flattened their heads. Maybe anthropologists assumed it was to distinguish themselves from slaves. Chinooks kidnapped or bought Indians from the south that did not practice head flattening. The assumption may have been, well it was to distinguish their own tribe from slaves. That was likely a factor, but apparently not the only one.
Lottie told this story about her Alsea acquaintence John Albert (who worked with JP Harrington at about the same time as Lottie did). She said, “John Albert had flat head. His mother tried to flatten his daughter’s head. He removed sandbags and told her don’t do that. His mom said yes, you want to have it looking ugly when she has head like a seal.
It’s supposed head flattening makes you look upward. John Albert said his mom would spoil the daughter’s looks….
The Alsea Indians used to say the unflattened head Coos Indians were ‘looking down.’. John Albert said he wanted his daughter to be looking down, not up.
So, the Alseas once thought it helped people to ‘look up’, perhaps to be more spiritual and/or moral people. An interesting explanation from the culture as to the meaning of the practice.
All in all though, I think we south coast seal-headed types managed fine without the fancy foreheads.