On Sociological Images, David Pickett is tracing the history of gendering in Lego toys, from the early efforts to produce girl-sets and boy-sets before 1988, to the full-blown gendering watershed attending the release of the Pirates minifigs, which had definite "girl" and "boy" characters. It all went downhill from there, too. He's got two parts posted, with more to come. It's engrossing stuff.
This pioneering pirate was the first in a long line of token females in otherwise male-dominated action-centric themes. The imbalanced ratio of masculine to feminine minifigs persists today, though it has lessened over time. I have seen several different numbers for this ratio, so I decided to do my own count. I gave TLG the benefit of the doubt and counted as gender neutral any minifigs lacking definitely masculine (facial hair) or feminine (lipstick, eyelashes, cleveage) traits, even when LEGO marketing materials clearly delineate them as male or female.
The following graphs represent masculine minifigs in blue, feminine minifigs in red, and gender neutral minifigs in gray. I have also calculated the masculine to feminine ratio (m/f ratio). Ideally this should be 1, indicating that there are equal number of masculine and feminine figures. This chart shows the aggreagate across all themes for the five key years between 1989 and 1999. The m/f ratio for this data is 3.74 (which is a lot better than the initial 13.5 it starts at in 1989, but not exactly something to celebrate).
The trend to unrepresent feminine figures in the main LEGO product line is mirrored by a tendency to overrepresent them in the "girls only" lines. LEGO released four major "girls only" themes through this time period: Paradisa, Belville, Scala Dolls, and Clikits. Here's a quick run down of the "girls only" themes: