I think we have good reason to doubt.
Historicity
There is actually no evidence external to the Bible to even corroborate the existence of Abraham, Isaac, or Jacob, let alone the historicity of the stories. The stories are set in a time period that pre-dates the invention of the Hebrew language by many hundreds of years, and they were probably transmitted orally for quite some time.
Theories abound concerning the "historical" Abraham as well as his legendary character and mythical significance. The discovery of the name Abi-ramu (Abram) on Babylonian contracts from about 2000 B.C.E. shows at least that the story of Abram's "Chaldean" origins is plausible.
Source
It seems that many believers have some difficulty distinguishing between something that is plausible and actual history. I suspect it is an artifact of black-and-white thinking, common to many fundamentalist believers, and also the idea that so long as one can construct a hypothetical scenario supporting the Bible, then it's as good as proven. If this is the way you normally approach apologetics, then you might want to consider whether you'd accept the same line of reasoning in defence of a view you disagree with, for example another religion.
This detail about the origins of the name "Abram" may be enough to satisfy the most credulous of believers, but it in no way confirms the historicity of the stories in any detail. Just as with the stories about Jesus, perhaps there was a real person behind the legend, but to what extent we may never know. Many believers will be happy to take the stories of Abraham, Isaac, and Jacob on (blind) faith, but those of us who are more interested in truth (and therefore evidence) should be willing to accept a great deal of uncertainty, and admit that there's not a lot we have to go on. I accept that this sword cuts both ways.
There is, however, one particular detail in the story that has been falsified in recent years.
Did Abraham and his family ride on camels?
Camels are mentioned as pack animals in the biblical stories of Abraham, Joseph, and Jacob. But archaeologists have shown that camels were not domesticated in the Land of Israel until centuries after the Age of the Patriarchs (2000-1500 BCE). In addition to challenging the Bible's historicity, this anachronism is direct proof that the text was compiled well after the events it describes.
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The Documentary Hypothesis
The traditional view of the Bible, and the one probably still held by most Christadelphians, is that Moses wrote the first 5 books of the Old Testament, known as the Torah (or Pentateuch). However, at least since the 17th century, and probably earlier, many biblical scholars have questioned this view. The view that has emerged instead is known as the Documentary Hypothesis.
In biblical scholarship, the documentary hypothesis proposes that the Pentateuch (also called the Torah, or first five books of the Hebrew Bible) was not literally revealed by God to Moses, but represents a composite account from several later documents. Four basic sources are identified in the theory, designated as "J" (Yahwist), "E" (Elohist), "P" (Priestly), and "D" (Deuteronomic), usually dated from the ninth or tenth through the fifth centuries B.C.E. Although the hypothesis had many antecedents, it reached its mature expression in the late nineteenth century through the work of Karl Heinrich Graf and Julius Wellhausen and is thus also referred to as the Graf-Wellhausen hypothesis.
The documentary hypothesis has been refined and criticized by later writers, but its basic outline remains widely accepted by contemporary biblical scholars.
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Perhaps the most obvious signs that the first 5 books of the Bible were edited over time are the insertions of material that could only have been known by, or could only make sense to, an author writing much later.
Some examples are listed below (all Bible quotations are from the NET):
"At that time the Canaanites were in the land"
Genesis 12:6 (suggesting the Canaanites were not in the land at the time of writing)
"that is why the name of the city has been Beer Sheba to this day"
Genesis 26:33
"That is why to this day the Israelites do not eat the sinew which is attached to the socket of the hip, because he struck the socket of Jacob’s hip near the attached sinew"
Genesis 32:32
"Jacob set up a marker over her grave; it is the Marker of Rachel’s Grave to this day"
Genesis 35:20
"So Joseph made it a statute, which is in effect to this day throughout the land of Egypt: One-fifth belongs to Pharaoh. Only the land of the priests did not become Pharaoh’s."
Genesis 47:26
"no one knows his exact burial place to this very day"
Deut 34:6
Even the mere existence of the account of Moses death demands that Moses at least did not write that part, and some scholars have noted that there is no difference in style between the account of Moses' death and the rest of the book of Deuteronomy.
Other reasons for positing multiple sources for the Torah include differences in writing style, contradictory accounts of various events, differences in the titles of God, differences in emphasis surrounding the law, and differences in theology.
I cannot hope to cover the Documentary Hypothesis in any great detail here, and I encourage you to do more reading on the subject. The hypothesis has not remained constant and there is still much discussion and debate over specific details, but the basic outline is still widely accepted.
The important points to learn from it are that the Torah was compiled from multiple earlier sources, from different authors, probably written and redacted over hundreds of years, and most likely "finalised" sometime in the 5th century BCE, following the return from Babylon. The earliest copy we have of the Torah is in the Dead Sea Scrolls, which are dated to around the second century BCE or possibly later.
Authorship
As my quote above says, the Torah is believed to have been written between the 10th and 5th centuries BCE, although it's possible it contained material from before the 10th century as well. For example, the "song of the sea" in Exodus 15, is written in a style of Hebrew much older than the rest of the Exodus text, and was possibly preserved in oral form.
Given the relatively late date of writing for most of these books, it is therefore obvious that Moses could not have written them, and if Moses did not write them, then the idea that God dictated them to Moses is also false.
Or perhaps you think Moses or God authored the sources that the later scribes edited and pieced together to make the books of the Torah. Why would God have people write down his message and then not accurately preserve it? Of course, this argument also applies to the New Testament, but I'll get to that in a later article.
And lastly, if God had inspired the later scribes who brought the various sources together, why would God need to inspire people to edit material from earlier (human) sources? Or maybe you think God inspired both the earlier sources and the editing process. Why not just get it right on the first draft?
Conclusion
The Documentary Hypothesis clearly points to a very human process of writing and redacting material over centuries. This is the most obvious and the most likely explanation. Anyone who wishes to claim there was any divine inspiration going on must first falsify this view. That is, they must demonstrate that it was not purely a human process. Mere plausibility or consistency with divine inspiration is not enough, because the "human origins" hypothesis is sufficient to explain all of the available evidence on its own, and it is simpler.
So once again the evidence we have points strongly towards the Bible having human origins.
Next Article: The Exodus