Genesis 5 presents a chronological record of Patriarchal births and deaths from Adam to Noah’s Flood. The chronology is presented in such a way that if you had a starting date for Adam, you could set a date for each of the births and deaths. Genesis 11 continues the chronology from the end of the Flood to the birth of Abraham. (For a detailed study of Genesis 5 and 11 see my “Genesis Chronology and Egyptian King-Lists.”
The Septuagint is a Greek translation of the Hebrew text. The almost universally accepted consensus is that the work was begun in the Egyptian city of Alexandria during the reign of the Egyptian ruler Ptolemy II (283–246 B.C.E.) and was completed sometime in the second century B.C.E. Alexandria was a major center of intellectual activity. The Septuagint was the bible used by the authors of the Gospels.
While the Septuagint is based on some versions of the Hebrew books of the bible (there was no single official canonical version of any of the books of the bible at that time), there are many differences between it and the standard Masoretic text used by Jews and modern scholars. One significant difference is in the chronological record of Genesis 5.
In both the Hebrew and Greek texts, Genesis 5 tells you how old a patriarch was when he gave birth to a son, and how long he lived. The big change is that in the Septuagint, six of the births have been delayed for a century. The effect of this is to move the date of Creation six centuries earlier. There are also a couple of trivial changes to the date of Noah’s birth but the numbers involve only a couple of years and don’t affect the Flood date.
Also during the reign of Ptolemy II, an Egyptian priest named Manetho wrote a history of Egypt that included a chronological record of Egyptian dynasties down to the conquest of Egypt by Alexander the Great. In addition, not only does Manetho provide a chronology of Egyptian dynasties, but he also adds several thousand years of additional Egyptian civilization under the rule of various deities.
The work was apparently quite popular and widely distributed. Jews and Christians were both interested in it primarily because of its chronological record. Unfortunately, Manetho’s original text is lost to history and what has been preserved appears to be assorted badly garbled transmissions.
The first century Jewish historian Josephus had at least two copies and already he demonstrates variations in the source texts, pointing out differences between them. The third century Christian chronographer Africanus preserved an extracted but often inaccurate summary of Manetho’s dynastic history that served as a primary source for Egyptian chronology down to modern times. Eusebius, the fourth century Church historian, also preserved a version of a Manetho chronological summary that differs in many ways from the Africanus version.
To make a long story short, the preserved copies of Manetho present a much longer history of Egypt than is now accepted by modern scholars. Either Manetho produced a largely accurate chronology of Egypt that was badly distorted in the course of transmission or he erroneously produced an unacceptably longer history of Egypt than is borne out by the evidence.
In either case, this brings us to the problem. Manetho’s chronology shows a much longer history of civilization than the bible does, although much of it takes place in what we would think of a s a mythological era. We know this troubled the Christian writers because they try to reconcile Manetho’s long history with the biblical chronology in the Septuagint, which, as I explain in “Genesis Chronology and Egyptian King-Lists,” led them to come up with all sorts of theories to shorten the Manetho chronology. Among the tactics was to describe the years in the early long periods as the equivalent of months or seasons rather than full solar or lunar years.
Given the popularity of Manetho’s work and the environment in which the Septuagint was produced, I strongly suspect that these differences may have been known among the educated Jews of Egyptian Alexandria. To be more specific, the Jewish tradition based on the annual celebration of a New Year day, places the date of Creation at 3761 B.C.E. and the Flood at 2105 B.C.E. In Egypt, the First Dynasty came to power at about 3100 B.C.E. plus or minus 150 years. The first six dynasties, collectively referred to as The Old Kingdom, ruled for almost one thousand years bringing it close in time to the date of the Flood. Egypt had no great Universal Flood at the end of that time frame, and a large Egyptian kingdom continued to flourish in dynastic succession down to the time of Alexander the Great. The Septuagint changes push back the date of Creation to at least about 4360 B.C.E., with some additional time extensions based on exegetical interpretations of chronology throughout the bible.
I suggest, therefore, that in an attempt to provide some harmony between the Genesis and Egyptian chronological history, at some point in the transmission of the Septuagint, scribes altered the chronology of Genesis 5 in order to move the date of Creation to an earlier time.