The history of man
With our family research going further back than I ever anticipated, I have noticed three specific time periods that I am dealing with. In order to make the genealogy work in the best possible way, I have had to break it down into three seperate files for the time being, until I can link them up with a greater degree of accuracy. As with any genealogy, the further back you go, the more complicated it becomes. You run into things such as inter-marriages, illegitimate children, multiple marriages and so on and so forth.
The first time period that I am talking about is the recent past. Meaning, the last 500 years. This would be the time frame of 1500 to present. From 1780 and on, you can find census records of family easily online. Before that are church records that list births, marriages, and deaths.
The second time period is what is referred to as "Medieval Times" which covers the years of 500 A.D. to about 1500 A.D. which led to the birth of the Renaissance. This time period covers the Kings and Queens of Europe such as Charles the 1st ( a.k.a. Emperor Charlemagne), Sir William Wallace (Braveheart), King Longshanks, and of course William the Conqueror to name a very small few. This time period is the most interesting in my opinion, but it is also the most complex to deal with. Not only are you trying to reconcile multiple marriages, incest that produced children, and illigitimate children, but you also run into the problems of differing descendants of the same person. For example, one expert may say that Charlemagne only had 6 children and while another claims that he had 12 and the children's names differ from the first expert. On top of that, you are also dealing with the variations in the spellings of names. There is no difinitive spelling for any one person!
A good example of the confusion in the spellings would be with Charlemagne himself. He was not born with the name of Charlemagne. He was born with the name of Charles (or Karl) as I have seen in some books. Also, the people of this time period were not born with a number after their name, such as Louis the 1st, 2nd, 3rd and so on. Later generations added those numbers to trace the genealogies easier and keep track of people who had the same name.
The 3rd time period is the "Biblical Times" which encompass the time frame of about 4,000 B.C. to 500 A.D. Now, with this one it is hard to pinpoint exact years for the births of people. The only authoritative source I consider for this time period is the Bible. And the Bible does not tell you in what year Adam and Eve were created. That is left up to historians and scholars who put the date at about 4,000 B.C. From there, as you go through the names of the Bible, it does give you life-spans of certain people from Adam to Noah and Moses, on down to Jesus. In fact, the Bible tells you how old a person was when the had their child and how long they lived after the birth of that child.
The Bible is the one and only source that should be used for this time period. I have seen some people who use obvious works of fiction as fact and add mis-information to their genealogies. For example, with the recent written works on the supposed genealogy of Jesus. Books like "Holy Blood, Holy Grail" and "The Davinci Code" are works of fiction and should not be accepted as fact, but sadly, there are people out there who insist that Jesus Christ did marry Mary Magdalene and had children with her, but do not have one shred of proof for this other than a works of fiction.
As you can see, genealogy is like a giant puzzle where one piece can fit in multiple places and unless you have the best information possible, the picture will not be clear in the end. You will be left with a jumbled mess that doesn't make sense. There are very good books on certain genealogies out there, but they are like finding a needle in a hay stack. With so much wrong information being published online and in books, it is hard to find the best one, but you just need a little patience and you can find the right information that you are looking for.

