Matthew 1:2-26 and 1 Chronicles 9:39-44

Its only really in modern history that people have developed the mindset of life is what you make it, in many generations past who you where and what you were like was very influenced by who your family was. If you could prove you were from a certain family of people then that would immediately prestige in the community where you live. As a result many Jews would know a long way back into their family tree just from memory and any record of there family trees would be precious and very well kept. They would either be meticulously copied after several years or if you were rich enough then you would have it engraved in metal plates so that they would last a very long time.