It could be argued that the listing of Lamech’s four children by his two wives, and their crediting as “ancestors” of those who practice various callings, is ultimately meaningless. Even if their children intermarried with the descendants of Seth, in the end, through the bottleneck of Noah, they would still be the ancestors of all human beings.
However, perhaps this is the meaning that can be found in the passage. Although throughout history there have been clans and guilds that have restricted certain trades to their own members, and even talents such as music that seem to have a genetic component, there is no “natural” reason why an aptitude should not show up in any given individual, regardless of bloodline. Indeed, even if these men, and one woman, who according to the midrash was a singer, had no blood descendants, as the originators of their callings they are the ancestors of all who followed them. As the Talmud points out, a teacher is, in a sense, a parent to his or her students.
Another aspect of this genealogy that drives home the idea that biology is not destiny is the fact that these are said to be the descendants of Cain, the first murderer, who was cursed by God. Even their father Lamech is known for nothing but his song of vengeance and perhaps as the first polygamist. Yet this bloodline makes considerable contributions to human civilization. Cain himself does so in his founding of the first city, although even today cities are seen as a mixed blessing at best!
Finally, the midrash brings the descendants of Cain and those of Seth together at the end of this first period of primeval history by making Naamah the wife of Noah, thus making all of humanity one family, as it was at the beginning.