(This is from a reply to a FaceBook acquaintance's post.)
I once had this possibility suggested to my mind, that it would be reasonable to assume that the lifespans mentioned in the Bible for Adam and certain of his descendants made sense in month counts instead of years.
I considered it – for all of about the hour or two of reading that it took to ascertain that it does not fit with certain important details of the lives of the patriarchs.
I felt a certain kind of disappointment, because it would make the Book of Genesis more "reasonable", and provide a defense from friends who disparaged the scriptures for being "unreasonable". But friends who insist that the Bible is unreasonable will not be placated by merely making the lifespans fit better with our experience in the modern world.
The scriptures do not need to be that kind of reasonable. God is capable of doing things we don't understand. Nature herself does lots of things we only pretend to understand.
If we think about reasonability, we must think about what the world was like back then. The world would not have had all the pollutions society has imposed on it since men started building cities. Adam and Eve, if we can trust the scriptures at all, would have had nearly perfect genetic material, undamaged by pollutions or mutations. Long lifespans would, on the contrary, be reasonable.
We know that modern humans can live to over a hundred. Without disease, accident, or war and other such violence, we can easily well exceed a hundred. Japan, for example, has several tens of thousands of people over the age of 100, many of them still out working their farms.
Adam and his righteous descendants were taught many things from on high, it is only reasonable to expect that they were taught how to take care of their health. It is very reasonable to expect lifespans well over a hundred. Given the healthy conditions, it is not particularly reasonable to expect lifespans over 200. When we see things in such light, hundreds of years is not at all unreasonable, and nearly a thousand certainly isn't too much of a stretch.
