Unarmed Combat: Str Damage Multiplier?

[tmaaas]

For an unarmed attack is the melee damage modifier equal to the character's STR mod or 1.5 * STR mod?

I know in the Monster Manual melee 'natural attacks' get 1.5 * STR mod added, but I didn't think this applied to player character races. But I can't find any explicit reference stating this, so I thought I'd ask.

 

[CRGreathouse]

Str mod. It's a light weapon.