We know little of the Mael-Num, as with many of the species of the Sentient Milieu. Along with the Ur-Quan they were mentally enslaved by the Dnyarri and carried out genocides against other members of the Sentient Milieu.
After the Dnyarri slave revolt and the first doctrinal enforcements agains the Faz and Yuptar, the Kohr-Ah came to the homeworld of the Mael-Num, the last free race the Ur-Quan where aware of, with the intent of destroying it. The Mael-Num asked the Kohr-Ah why they had come to destroy them, and so sincere was the question that the Kohr-Ah were given pause. In that hesitation, the Kzer-Za arrived with the intent to enslave the Mael-Num.
The two Ur-Quan subraces fought, and thus began the first Doctrinal War. During the long battle, the Mael-Num escaped to places unknown. It is reasonable to assume that, were either species of Ur-Quan to discover the Mael-Num's hiding place, they would make great efforts to correct their millenia old oversight.
Given that the Kohr-Ah refer to them as "one-eyed creatures", and the similarity of their names, it is suspected that the Mael-Num are the ancestors of the Melnorme. (This assumption has been acknowledged true by Paul Reiche III and Fred Ford in the October 1998 IRC chat.)