Question: I have been taking a class on The History and Reliability of the Bible, where we recently discussed the subject of Noah and the Ark. I have gone back and forth before on whether the flood was a regional one, perhaps partly because of a statement made to me by a member of my biological family.  My biological brother Dan once stated to me that "There wouldn’t have been enough genetic diversity in Noah’s family to have started the entire human race all over again." He then explained to me that there needs to be a certain amount of genes to keep humans from inbreeding. I don’t remember the numbers he was giving me. Hopefully this is enough information.  How does this resonate to you, as scientists, and as disciples?  Thanks for your time,Ben Daugherty from the Denver Church of Christ Answer:  There is a fair amount of truth in the contention of your brother, although he is overstating his case just a bit.   First of all, he is wrong in stating that the human race could not continue with the genetic diversity of eight people, including a father, mother, three sons and, presumably, three unrelated daughters.   It is true that marriage between cousins brings a slight added risk, but some have exaggerated this risk.  The greatest risk, by far, is marrying siblings.   In any case, there have been a number of examples of quite small groups of people landing on an island and, through rather tight interbreeding, successfully populating that island.  So, his statement about Noah’s family being unable to restart the human race is simply not true.   However, with regard to genetic diversity, he may have a good point.   Actually, humans are relatively undiverse in their gene pool when compared to most other animals.  The diversity among dogs is vastly larger, as we can see from their different breeds.  This is (at least according to geneticists) because their common ancestor is much, much older.  The evidence (not proof, but reasonable evidence) is that human genetic diversity can be explained by somewhere around 100,000 years of “evolution.”   There is very strong evidence of a genetic bottleneck in the not very distant past for human beings.   Biologists have estimated that, based on the y chromosome, we are all (ie all males!) related to a single “Adamic y-chrosome” about 70,000  years ago.  Similarly, we all inherit our mitochondria from our mothers.  It has been estimated that all human mitochondria can be traced back to a single woman “Eve” about 130,000 years ago.    The mitochondrial Eve age and y-chromosome Adam ages are close enough that it is not wild speculation to think of these as evidence of a single ancestor or pair of ancesters about 100,000 years ago. Of course, virtually no one will claim that the flood in Genesis 7 happened 100,000 years ago.  That being the case, your brother is probably right that there is not sufficient time from the flood until now to explain the genetic diversity of human beings, at least according to the best current scientific estimates.  If we allow for at least five completely unrelated people (Noah, his wife and the three daughers), the case becomes actually quite a bit less difficult, but I will still concede that the question is not without difficulty. So, what is the explanation of the evidence?   My answer is that I am not sure.  I have various theories, but few hard and fast conclusions.   Personally, I find the local flood theory to be weak.   What would keep this flood confined to a small local area?   The words in Genesis 7 and 8 (all, every, all, all, every, all, all, all,…) certainly seems to imply more than a local flood.  I would not be dogmatic about this, but I find the local flood explanation to not work well.  Another possibility is that the flood had a world-wide impact of some sort but that not literally all of the species in South America, North America or Australia were destroyed.  In any case, I assume that the flood in Genesis 7,8 was of miraculous origin and that a lot of water was involved. I wish I had “the” answer, but I do not.   My belief in the flood in the time of Noah is based principally on faith in the reliability of the Bible.   I do not know when this flood happened, and the Bible does not answer this question.  For all I know, it might have been 10,000 years ago, although I doubt it.  As to whether random mutation and evolution from just the eight on the ark could explain the full genetic diversity today, I do not know, but I will admit that this question deserves an answer.   Might some humans have survived in pockets elsewhere?   Might this have been a local flood?   Given that there were at least five unrelated people on the ark, might this be sufficient to explain the current human genetic diversity?   I believe this is the least likely explanation of the three, but I am not in a position to rule th
is out. I am afraid that this is where I will leave you.  Feel free to ask me more specific questions. John Oakes, PhD