Shampoo ain't netchural

Washing hair with shampoo is not a natural act it would seem.  How long has humanity had soap and chandlers, let alone hair soap?  Shampoo is just soap modified specifically for hair.

Given this, why does it feel so unnatural for me to go without washing my hair?  I can't stand the way my head feels after a day without washing.  It's grimy and itchy.  I hate it.