Although the ingredients used to make soap have changed over the years, the chemical process which creates soap has not. Basically oils and fats are combined with an alkali to create a reaction (saponification) which produces soap and glycerin. The quality of the ingredients you use has a significant effect on the final product.
A theory exists that prehistoric cavemen may have been aware of a crude form of soap. Cavemen typically roasted their meat over open wood fires. The fat from the meat would drip into the fire, mix with the ash (an alkali) and after a good rain, voila--you have foaming bubbles coming out of your campfire. Whether or not they realized the usefulness of this reaction is not known, but it is an interesting theory.
The first records of soap indicate that the Babylonians were making it around 2800 B.C. However these first soaps were thought to be used for cleaning textiles and fabric rather than the body. Soap for bathing the body seems to be credited to both the Romans and the Celtics who may have both independently discovered the benefits of hygiene around the beginning of the second century.
Soapmaking dramatically progressed around the 8th century in Italy, Spain and the southern parts of France when soapmakers began making soap from olive oil. These soaps were clearly superior for bathing and washing compared to those made elsewhere, and the result was a lively trade with Northern Europe.
In the 19th century, Louis Pasteur confirmed the benefits of personal hygiene thereby increasing the demand for soap. Later during the same century an English marketing wiz named Andrew Pears helped define soap as a cosmetic aid which made it's users "beautiful". Bathing came back into fashion and the demand for soap was higher than ever before.
Today, soap is as much a part of life as air and water, and there are many different types available. Unlike our ancestors, we are more fortunate to have so many more choices of what we elect to use on our skin.
So choose wisely and enjoy!