Kissing as a romantic or intimate practice is believed to have originated in the Indian subcontinent around 1500 BC, with some evidence suggesting it could date back to as early as 2500 BC in ancient Mesopotamia (modern-day Iraq and Syria). Ancient texts from India like the Sanskrit epic Mahabharata and the Kama Sutra mention kissing. The custom spread beyond South Asia to regions like Greece and Rome around the time of Alexander the Great's conquests in 326 BC. Archaeological findings, such as inscriptions on Mesopotamian clay tablets dating back about 4,500 years, also provide the earliest documented evidence of kissing. Additionally, genetic studies suggest that Neanderthals and early modern humans might have exchanged saliva through lip kissing over 100,000 years ago. However, kissing is not universal across all human cultures, being common in about 46% of surveyed cultures worldwide, especially in the Middle East, Asia, Europe, and North America.