What is the purpose of describing who is son of who? In many excerpts of the Bible one can find an extended description of a person and his respective descendents. What's the purpose of this? Is it supposed to give an idea of how much time passed between two important facts? Is it supposed to preserve the origin of man? The genealogic tree is a lot more objective than most of the facts narrated in the sacred book. There must be a good reason for this.

Genesis, 5:21-24


  21 When Enoch had lived 65 years, he became the father of Methuselah. 22 After he became the father of Methuselah, Enoch walked faithfully with God 300 years and had other sons and daughters. 23 Altogether, Enoch lived a total of 365 years. 24 Enoch walked faithfully with God; then he was no more, because God took him away.
In many cultures, genealogy roots a person in who they are. By saying, "so and so is the son of so and so," you are establishing an identity.  As the old saying goes, "we don't want nobody nobody sent."

In the specific case of Genesis 5 &amp; 10 (sometimes called "the Table of Nations"), however, there is a very interesting theological point being made.  Namely, the Israelites were a nobody.

In many creation myths, the creation myth is set up in such a way as to highlight the fact that the culture that came up with it has pre-eminence amongst the peoples. In Babylonian myths, for example, the Mesopotamians were the firstborn among creation. In Egyptian creation myths, the same holds true, and the pattern is repeated in many places.

What is different about Genesis is that Abraham is kind of a nobody. He's not always the firstborn of the firstborn of the firstborn.  He's just another guy in creation.

What makes him different is that God chose him to say, "through you I will bless all nations."  The Jewish scriptures are remarkable in their lack of ethnocentricity.  As you state, these genealogies are very objective in their fact taking stance.