Why did they invent toilet paper?
Prior to the use of toilet tissue, the standard personal cleansing methods were cloth or water (as in a bidet). Once sewerage systems were in general use, an affordable and disposable alternative was sought (bidets being expensive and cloth requiring cleaning and sanitizing). It had to be soft, and soluble in water to avoid clogging, but durable enough to avoid falling apart in use. Both criteria were eventually achieved.
