What evidence, if found, would falsify that claim?
I always go back to Adam and Eve, almost as a litmus test. If you can show that Adam and Eve were not real people that lived around 6,000 years ago that would go a long way toward falsifying the Bible. Perhaps that is why so much energy goes into trying to falsify that the people we read about were real. People like Adam, Abraham, Jacob, Moses, David and so on. The Bible would still have value as an allegory, but if these were not real people then the Bible would not have literal truth. For example no one questions the value of the book of Job, yet there is almost no historical context in the book of Job. The fact that the Bible has literal truth helps to substantiate the allegorical truth found in the Bible.
In Bible school we are taught that we teach the Bible one truth at a time. So for example look at the passage about the fig leaf in the story of Adam and Eve. Genesis 3:7 "
3:7 And the
eyes of them
both were
opened, and
they knew that they were
naked; and they
sewed fig leaves together, and made
themselves aprons." As Gerold Schroeder tells us: many many books are found in the library of our leading Universities that help to explain this passage. We see that their "eyes were opened". We see that they "knew they were naked" then they "sewed fig leaves together" and "made themselves aprons". So we have four points of discussion in this sentence.
Lets deal with: "they sewed leaves together". First of all we know that they had sewing needles LONG before 6,000 years ago. In fact they had three artifacts going back as far as 40,000 years: sewing needles, fishing hooks, fishing nets. We know that they were able to use the fiber from fig trees to make tread, then cloth and they sewed that cloth into clothing. In Africa today clothing made from a fig tree fiber is not very strong. This is more like paper and they make clothing that is more for a festival or a ceremony. It looks real pretty for a day or so but the early clothing did not last very long.
In Genesis 3:21 we see that: "The LORD God made garments of skin for Adam and his wife and clothed them". Now we see that Adam and Eve had more durable clothing than what they had back in Africa. We can see how Adam and Eve or their ancestors were able to go north out of Africa. It is easy to go east and west if you want to go from one biodiverse ecosystem to another system. Is it more difficult to go north or south because there is a difference in climate and the species must adapt to the difference in climate. Adam and Eve or the ancestors adapted to the colder ecosystem because they developed a way to make clothing out of animals skins. They then moved into an ecosystem that neanderthal dominated.
Now I talk about the way that God does things. In Exodus 23:29 we read: "But I will not drive them out in a single year, because the land would become desolate and the wild animals too numerous for you." We see that the process of one species replacing another species is slow and gradual. Deut 7:22 "The LORD your God will drive out those nations before you, little by little. You will not be allowed to eliminate them all at once, or the wild animals will multiply around you."
We clearly see that the Bible is literal truth. Not just a story that people tell, but a story that people tell about real people. A story that Science shows us is true. I have no problem with fiction, but the fact is that the Bible is a real story about real people. Of course this gets into the study of literature and that is a different class and a different book. People can know a lot about science but they may know very little about literature. They may only have their required freshman literature class. So they are not very qualified to understand literature and how to interpret it as a biography, autobiography or fiction. They are simply not trained to know the difference between fiction and nonfiction.
You and me have had discussion on how to balance catastrophism with gradualism. The Bible weighs in on this discussion with what looks more like gradualism. Yet I am sure I could come up with passages like Noah's flood that deals with catastrophism also. People who do not understand how to balance out these two theories may claim that there is a contradiction. You know that there is no contradiction when you properly understand the theories.