Updated: Jul 29, 2019
There are as many theories about why many human cultures developed shame about our bodies. They range from evolutionary theory, which suggests that because humans live in primarily monogamous relationships, we have evolved a sense of shame so as to not tempt ourselves into extra marital sexual activities. Most of these theories ignore some basic facts, like, for example, most people are not actually very monogamous. Furthermore, science suggests that body shame is more culture than biology. There are, and have been, many societies were naked bodies have been or are celebrated. Rather than considering bodies taboo some cultures embrace and honor them.
I believe there are many explanations for Western society's prudish attitude about our bodies, which came into being largely with the rise of Judeo-Christian religion, which has largely taught that humans were somehow above or separate from other animals and nature. Human bodies, sex and sexuality link us unmistakably to all other living creatures. They show and demonstrate our animal nature. They prove we are of nature not above and separate from it.
That's my current theory at least. Tell me what you think in the comments!