Where does the concept of yichus (meaning that the person descends from something akin to "good stock") come from? How is it judged?
Note: I am not asking about the halachic concept that a man must check the lineage of a potential wife, nor am I asking about the term used in kiddushin's "asara yuchsin" or even the idea that a man should strive to marry the daughter of a talmud chacham. I am asking about the term as it is commonly used today. For example "That boy is a catch! He has good "yichus".