Romance Through The Ages
There are many stories about how romance novels started, but it's often suggested that the letters of Abelard and Heloise were the start of the genre. As a story theme, romance pervades all genres. The need for romance has been so ingrained that Hollywood films often include gratituous romances due to the belief that including them is the only way to attract female audiences (it's not, but studio executive don't get that).
Though Harlequin Romances date back to approximately 1949 (Harlequin Enterprises Ltd via Wikipedia), romance novels moved outside the niche mindset in the 1970s with the advent of the so-called bodice ripper titles of Kathleen Woodiwiss and sexy (for their time) works of Rosemary Rogers.
The modern romance novel effectively mirrors the lives of today's woman, focusing on issues such as fertility, divorced, blended families, job versus family life, the glass ceiling, and, of course, romantic relationships in the modern era -- the challenges that face everyone.
The diversity of reading tastes is reflected in the breadth of the romance fiction market. Romance novels focus on a wide range of topics from modern Christian life to outer space. Authors reflect this divergent interest -- in addition to writing fiction, romance authors also enjoy careers including law, medicine, home, astrophysics, academia, politics, and piloting airliners.