In the Figure above we can see frequency of words mentioned in different seasons of the The Big Bang Theory. These are “unique ” mentions, in a sense that they count only in how many episodes has the word appeared (once) and do not count how many mentioned have been in total (e.g. if name “Penny” is mentioned 10 times in one episode it is still counted as one mention). All of the lines have been normalized in respect to the season 1. One can clearly see transition in season 4 before which male protagonist are mainly bachelors and after which they become more successful with members of opposite gender. Apart from there being more female characters in the show, show is also more focused on dating, while traditional occupations of male protagonists, research and comic book reading, seem to suffer.
(see also interesting discussion that has developed on reddit)