by Dr. Hugh Ross and Sam Conner
A new discovery about a genetic phenomenon called "heteroplasmy" revises the date for our oldest female ancestor, Eve.(1) Previous research on mitochondrial DNA (the DNA present in organelles outside the cell's nucleus) fixed the earliest date for Eve at 150,000 years ago.(2) (Other sciences will have to supply a minimum date). This latest discovery recalibrates the earliest date down to one much closer to the rough biblical date of 12,000 to 60,000 years ago.(3)
Mitochondrial DNA (mDNA) can be used as an evolutionary clock because it passes from one generation to the next through the mother only. A child's mDNA could differ from his or her mother's only if a mutation occurred. Thus, if we measure the differences in mDNA among living humans (easily available) and compare this degree of diversity against an ancient, well-dated mDNA sample (typically unavailable), we can determine the human mDNA mutation rate. If we know this rate, we can calculate how much time has passed since certain human populations diverged. We can even estimate the date for the first woman from whom we are all descended.
The mDNA mutation rate most researchers have used in their calculations and estimates is one mutation every 300 to 600 generations (one every 6,000 to 12,000 years, assuming a generation = 20 years). Some scientists, including me, suspected this rate would need significant adjustment because it was deduced partly from the assumption that humans and chimpanzees descended (according to traditional Darwinist principles) from a common ape-like creature fossil-dated as 5 million years old. This rate was used to date Eve at 150,000 years ago or less.
With the fall of communism in Russia, researchers gained the opportunity to use mDNA testing on the genetically isolated family of the czars. In 1992, as they studied the remains of Nicholas II (the last Russian czar) and his family, they were stunned to find that the czar carried two different mDNA sequences and his brother also carried two, the same two. Apparently, the czar and his brother both inherited these same two different mDNA sequences from their mother. Each son manifested the phenomenon labeled "heteroplasmy."
Geneticists had previously thought heteroplasmy occurred rarely. However, this finding prompted additional studies on the families of missing soldiers (later found), on the Amish, and on other groups. These studies indicate that heteroplasmy occurs in 10 to 20 percent of all humans.(4) This degree of heteroplasmy suggests a mutation rate for mDNA of roughly one every 40 generations (one every 800 years), a rate 7 to 15 times faster than the old rate. This adjusted rate would yield a date for the mitochondrial Eve of just 10,000 to 20,000 years ago.
However, such a recent range of dates for Eve conflicts with sound archeological evidence for human immigration to Europe and Australia 30,000 years ago. Consequently, mDNA research was expanded to include other populations, most notable a set of Swedish families and residents of the island of Tristan da Cunha (in the Atlantic Ocean). These studies showed a lower percentage of heteroplasmy and, when averaged with the results from the earlier studies, indicated a mutation rate of one per 60 generations (one in about 1200 years).(5) With this adjustment, the mitochondrial date for Eve would be consistent with the archeological date.
Another study indicates that further refinements are needed. Research on the earliest American settlers show a factor of three difference between the archeological date and the old mDNA date (the date assigned before the heteroplasmy discovery).(5) In other words, the more accurate earliest date for Eve may be about one-third the 150,000 year date initially proposed, or 50,000 years ago, still compatible with the biblical and archeological dates.
As we learn more about genetics and about possible changes through time in the mDNA mutation rate, these dates will surely be adjusted. But we have some assurance, at least, that they are in the ballpark and increasingly consistent. Movement toward greater accuracy and consistency gives both scientists and apologists a thrill.
|1.||Hugh Ross, "The Mother of Mankind," Facts & Faith, v. 2, v. 1 (1987), pp. 1-2.|
|2.||Patricia Kahn and Ann Gibbons, "DNA From an Extinct Human," Science, 277 (1997), p. 177.|
|3.||Hugh Ross, "Searching for Adam," Facts & Faith, v. 10, n. 1 (1996), p. 4.|
|4.||Ann Gibbons, "Calibrating the Mitochondrial Clock," Science, 279 (1998), p. 28.|
|5.||Ann Gibbons, p. 29.|