The Lineage of Joseph (and by extension, Jesus)
The first 16 versus (1.5%) of Matthew addressed the lineage of Jesus, or more specifically of Joseph. It is quite clear that the authors of this text are responding to an argument, namely that Jesus of Nazareth was not the Messiah predicted by earlier Jewish prophets. Although it seems somewhat awkward to a modern reader, it was important enough for them to devote, in painstaking detail, the first 1.5% of their text to this point, one that seems to be of questionable significance, since elsewhere in the text we are told that Joseph was not the father of Jesus, that his teenage wife was made pregnant by an angel. If Jesus has no DNA from Joseph, it seems unclear as to why Joseph's lineage should matter. David lived nearly a thousand years before Joseph, so it is likely that many Jews alive at the time would have descended from him anyway.
This is the first problem with Matthew. The lineage is moot, but it is also contradicted by the other Gospel that addresses Joseph's lineage in pain-staking detail. Matthew described 26 generations between Jesus; Luke describes 40. Assuming 25 years per generation, this implies an error of 350 years! More disturbingly, for those who would like to take these logical accounts literally, is that not a single name on the David-Joseph lineage of Matthew overlaps with the David-Joseph lineage of Luke. Clearly, they cannot both be right in the way we use the word right today.
Another problem with this lineage is that even if Joseph were Jesus's biological father, with 26 generations, Jesus would only have a relatedness of 0.00000149% to David.
Relatedness is an interesting concept that quantifies the probability of a given gene in one person being shared by another. Our relatedness to our parents is ½, meaning that there is a 50% probability of a given gene in our parents being in us. Put another way, half of either parent's genes, on average, are in us. Our relatedness to our siblings is also ½, by the way. At each generation, our relatedness is halved, so that our grandchildren will have a relatedness of ⅛ to us, and our great grandchildren 1/16 relatedness. Given the number of generations n that separate two people in a direct line of descent, our relatedness is 1 divided by 2 to the power of n. In only a few generations, our relatedness to a given ancestor quickly approaches that of our relatedness to anyone else in the human gene pool. If you are interested in more detail including an excellent excerpt from Richard Dawkin's classic The Selfish Gene, click here.
Biblical authors knew nothing about this, of course, and had the strange idea (shared by many primitive cultures) that all of a male's attributes (or right to rule) were inherited from his father's father's father's father... (with the mother a nameless breeding vehicle). Doubtless they never would have spent so much time and energy creating these completely non-overlapping genealogies in such detail if they knew that in the end - even if true - the proportion of Jesus's genes that would be shared with David would only be 1 in 67,108,864. Put another way, the probability that a gene of David made it through to Jesus would be less than one in 67 million.
Luke's 40 generation genealogy is even worse, of course: Jesus would share only one gene in 1,099,511,627,776 with David, or 1 in 1.1 trillion. Obviously, since we are all quite literally each other's cousins and quite a bit of interbreeding and outright incest occurs in our species, the background relatedness of any two strangers is much greater than 1 in a trillion, but the point is that by 40 generations, whatever genetic impact David would have on Jesus (or Joseph, to be more specific) would be no greater than that of anyone else on the planet. I am as related to David as Jesus was, as are all of us.
