Like many popular-culture stereotypes, the origins of this concept are murky. The 1925 Anita Loos novel Gentlemen Prefer Blondes: The Illuminating Diary of a Professional Lady (later used as source for a film by the same name made by Howard Hawks and starring Marilyn Monroe) featured the character Lorelei Lee, a beautiful but empty-headed singer. While some look to this as the source for the concept, in fact, it might be far older.
Some have suggested that, because Caucasian babies are often born with at least a touch of blonde hair, an association has arisen tying those having fair hair with childhood and youth (and the accompanying proclivities toward naïvité and/or innocence). Also, as blonde hair is often associated with physical attractiveness and youth, some argue that those around blondes may have a tendency to admire or fawn over them, encouraging some to behave in a child-like manner (consciously or not) in order to gain attention and affection.
In Medieval Europe, the upper classes tended to be darker haired than the peasantry, likely due to the period tendency to marry within one's own class and the fact that lower class people were far more exposed to sunlight. Blonde hair was, at this time, often associated with commoners, who were ostensibly deemed less intelligent. Puritans, associating makeup and the dyeing of hair with prostitution, forbade the dyeing or bleaching of hair, creating a subtle cultural taboo on dyed hair that lasted until the 1920s in parts of North America and Europe.
Around the beginning of the twentieth century, Western class stereotypes also led to the negative view of women with dyed blonde hair (or heavy makeup) as being gold diggers, seeking the attentions of men who were already financially well-established, and who were as such likely to already be married. This may have stemmed from the observation that bleached blonde hair (considered to be eye-catching) was a popular choice for the often poor, uneducated women who relied on their looks to make a living, and was common among actresses, singers, music hall performers, burlesque dancers, chorus girls and bar maids, as well as prostitutes. As women of the time typically did not work after marriage, married women still occupying such positions were rare and almost always of the lower economic classes. One of the only ways a woman might find relief from the need to support herself through such professions was to marry, but wealthy men were likely to find that a wife who had formerly been employed in the entertainment professions would not be accepted well into higher-class social circles. The practice of men beginning affairs with attractive working women which did not culminate in marriage is associated with the previously mentioned adage that "gentlemen may prefer blondes, but they marry brunettes".
It has been suggested that the concept of the 'dumb blonde' may also stem from the idea amongst the ancient Romans and Greeks that Northern Europeans were barbarians and thus less advanced than Southern Europeans and Europeans of South Plagious, the civilizations of Old Northern Middle East and North India (old aryans-bramahns).
One interesting notion is that the Scandinavian blonde is often connected to romantic nationalism, and the stereotype of the blonde farm girl or dairy maid. In the actual romantic movement, this type crystallized in literature, mainly Synnøve Solbakken by Bjørnstjerne Bjørnson and the character of Solveig from Henrik Ibsen`s Peer Gynt. Although both characters are positive and even intelligent, tradition often gives them the "dumb blonde" trademark, more or less requited.
There is a common category of blonde jokes that employ the dumb-blonde stereotype for their effect. They usually involve a situation in which a blonde performs a random or dangerous act because she misconstrued the meaning of the words describing the act, to comedic results. Another variation employs two blondes, one as the recipient of the other's stupid question, only to give an even more ridiculous answer herself.