One of my friends' got this one for his Group Discussion topic--"Men should wear Bangles and Mangalsutra". This kicked off my search on origin of mangalsutra. Following is what I came across in one of the articles---
Historically, the custom of tying a mangalsutra, the auspicious emblem or cord, on the wedding day, appears to have become popular only after the 6th century AD. Before this, a yellow protective cord known as 'kankanabandhana' was tied around the wrists of the bride and the groom to signal their commitment to marriage.
The mangalsutra is considered a talisman to ward off the evil eye. The black colour of the beads is said to absorb all negative vibrations before they can reach the bride and her family. The stringing together of the beads into one thread has its significance as well. Just as each bead contributes to making a beautiful necklace, so does the woman have to blend and integrate into the new family after marriage.
I personally think everything was initiated for a noble cause or because of some scientific reason but it later evolved into something which became a bonding for women or started to be seen like one. For example, sindoor was meant to keep women's temper in control, now more and more women are giving up flaunting sindoor. Most interestingly, all jwelleries have relevance in their scientific outcome. If we say that men should wear mangalsutra and bangles, it sound like nothing else but a feminist statement. before we say so, we should ask why men need to do so? just because over the years women had been made to do so?