When The Big Bang Theory premiered on CBS in 2007, it was a much different series than it is now. Back then, the series focused mainly on Leonard Hofstadter and Penny, whose will they, won't they relationship fueled the sitcom's main storyline for the first couple of years.
Sheldon Cooper was the third pillar of the cast, and he rapidly became the star of the show. Two other main characters, Howard Wolowitz and Raj Koothrappalli, would round out the cast as the series focused on four geeky friends and their attractive neighbor.
However, as time went on, The Big Bang Theory's DNA changed. While it started out as a goofy series featuring the quirky lives of four scientists who are obsessed with comic books, video games and everything sci-fi, it changed into an ensemble comedy about love, friendship and adulthood.
At first, the series originally counted five main cast members: four male characters and one female lead. Therefore, during its early years, The Big Bang Theory's gaze was heavily one-sided. However, as the main characters started to evolve and grow, so too did the show. With the arrival of Bernadette Rostenkowski (Melissa Rauch) and Amy Farrah Fowler (Mayim Bialik), the CBS sitcom received a tonal shift.
It wasn't just about a quirky group of male friends anymore. Now, on the other side of the hall, there were three women who had their own discussions and opinions on things. This not only brought a different gaze to the series, it opened up its story possibilities and allowed the characters to grow like never before.
Thanks to the inclusion of Amy and Bernadette, Penny evolved into a different character. She gained more depth, and she was given the chance to shine in a different, more human manner. What's more, Bernadette and Amy helped their respective boyfriends, Howard and Sheldon, grow. Thanks to their better halves, both characters' quirkiness was toned down and they were further humanized as their girlfriends helped them become better men.
Nowhere were the effects of the cast's expansion more clear than in the series' opening credits. At first, the Big Bang Theory credits ended with a shot of Leonard, Sheldon, Penny, Raj and Howard eating dinner. However, as stars Melissa Rauch and Mayim Bialik became series regulars, the shot was changed to add the two women into the diner scene. It's a small note that only lasts a second, but it spoke volumes about the series' tonal shift.
After that, the cast grew even bigger: Kevin Sussman, who plays comic store owner Stuart Bloom, became a series regular and an integral part of The Big Bang Theory family. While they are never shown onscreen, Howard and Bernadette had two children that once again changed the dynamic of the show.
After its first few seasons, The Big Bang Theory didn't just give two of its main characters girlfriends, it opened itself up to the female gaze and became a better show because of it. Not only did it become more balanced, it reinvented itself into an ensemble show that mixed and matched characters however it chose. Suddenly, it wasn't about the cute neighbor across the hall anymore. It was about supporting one another through all the changes that life brings.
The "Big Bang" theory is the scientific answer to the birth of the universe. It started as a singular point, but an explosion caused an expansion and created the cosmos. In retrospect, it appears as if this was the perfect title for CBS' hit sitcom. It started out with a core, but it soon exploded and expanded to include more characters that helped flesh it out to become something else entirely -- something even better.
The Big Bang Theory airs Thursdays at 8 p.m. ET/PT on CBS, and will conclude with an hour-long series finale on May 16. The series stars Jim Parsons, Johnny Galecki, Kaley Cuoco, Mayim Bialik, Kunal Nayyar, Simon Helberg and Melissa Rauch.