system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What made us, so many years ago, just being naked be seen as being indecent?
gpt
While clothing began as a "tool" to keep us warm, it quickly developed a symbolic meaning far beyond this. For example, it distinguished tribes/groups/nations from one another and indicated social status, wealth, and personality. It still does this. 

In a society that developed cultural norms such as sexual restraint, monogamy, and other sexually normative social pressures, clothing became representative of these cultural factors. To not wear clothing was, in essence, to communicate a sexuality that was taboo.

Clothing as seen by the anthropologist is simply an outer representation of cultural beliefs. If a society believes in sexual restraint - taught by religions both modern an ancient but also common in non-religious societies (e.g. modern China) - then the clothing will represent these cultural norms. 


So in short, clothing became an expression of modesty and social pressures to conform and be accepted.