During the summer of 2001, the sports world was rocked by a scandal when Little League officials discovered that pitcher Danny Almonte was 14 years old, not 12, as his falsified birth certificate indicated.
A few days earlier, Almonte had electrified the sports world by pitching a perfect game in the Little League World Series, striking out 16 batters. The next day, he pitched a one-hit shut out, throwing the baseball at speeds that topped 77 mph. ESPN coverage focused attention on Almonte’s accomplishments, heralded by many as among the greatest sports performances of all time. Sadly, his fame turned into notoriety just days later when officials learned that he was too old to be eligible for Little League baseball.
Recently, anthropologists have become embroiled in a similar—though not as scandalous—controversy about the age of mitochondrial Eve and Y chromosomal Adam.1 This controversy has implications about the mode and timing of humanity’s origin and directly impacts the scientific credibility of the biblical account of human origins. Though scientists are far from discovering humanity’s “birth certificate,” new work on mitochondrial DNA’s mutation rate helps bring resolution to this issue and, in doing so, provides affirmation of Scripture.2
As I described in my book Who Was Adam?, one of the most significant developments in human origins research has been molecular anthropology (the use of genetic variability among people around the world as a way to understand the origin and early history of humanity). DNA contains the blueprint needed to build each human being; it is also the molecule of inheritance. For example, mutation-generated structural variants of the DNA molecule can be passed on to the next generation. Anthropologists focus their attention on these variants.
Mutations yield a variety of DNA molecules (called genetic variants) within a given population as that population grows. When people migrate around the world, causing the original group to fragment, each of the resulting subpopulations’ genetic variability takes on its own distinct character.
Molecular anthropologists take advantage of this process. They characterize the origin and spread of humanity by cataloging the genetic variants from people around the world. The type of variants—the similarity and differences in the DNA structures—can be used to determine different populations’ historical relationships. Ultimately, genetic similarities and differences can be used to trace all populations back to a single ancestral group.
The extent of the differences in DNA molecules can also be used to estimate when different groups diverged from each other and even when the ancestral group lived. This technique, known as molecular clock analysis, bears similarity to calculating the time it takes to travel a certain distance in an automobile. If the speed is known, then the time it takes to travel to the specified destination can be easily calculated using the formula:
Time = Distance / Speed
In a like manner, if the extent of the differences between the genetic material of two populations and the mutation rate are known, then the time at which the two populations diverged can be calculated as follows:
Time = Number of Genetic Differences / Mutation Rate
For example, if DNA isolated from two populations that immediately share the same ancestral group differs in 100 locations and the mutation rate is 1 mutation per location per year, then the two populations diverged from each other 100 years ago.
Molecular Anthropology and the Biblical Account of Human Origins
Characterization of mitochondrial DNA variants (which trace humanity’s maternal lineage) and Y chromosomal variants (which trace humanity’s paternal lineage) indicate that human beings originated in a single location (East Africa, close to where theologians believe the Garden of Eden was located) from a small population. Additionally, the maternal and paternal lineages trace back to a single ancestral sequence for mitochondrial DNA and Y chromosomal DNA, respectively.
In Who Was Adam?, we note the remarkable agreement between the data from molecular anthropology and the biblical creation accounts. We suggest that the ancestral mitochondrial and Y chromosomal sequences correspond to a primordial couple, the biblical Adam and Eve. Skeptics and Christians who prefer an evolutionary origin of humanity have challenged our interpretation. However, in a recent article, I defend our proposal based on new advances in population genetics and work from conservation biology.
When Did Mitochondrial Eve Live?
Scientists refer to the mitochondrial sequence ancestral for all humanity as mitochondrial Eve. (Again, I argue that mitochondrial Eve is indeed the biblical Eve.) As of 2005, some of the initial studies indicated that mitochondrial Eve traced her origin to between 150,000 and 250,000 years ago (see Who Was Adam?). One of the most comprehensive studies compared the entire mitochondrial genome from 53 people around the world and estimated the date for mitochondrial Eve at 171,000 ± 50,000 years ago.
In 2009, a research group challenged these dates, questioning the validity of the assumptions employed to establish the mitochondrial DNA mutation rate.3 They pointed out that the mutation rate used in most studies relies on genetic comparisons between humans and chimpanzees. (This comparison assumes that humans and chimps share a common evolutionary ancestor, a notion that I reject.) To establish an average mutation rate for humans, scientists take the average number of genetic differences between human and chimpanzee mitochondrial DNA and assume that humans and chimps diverged from their shared ancestor around 6 million years ago.
The research group complains that using this mutation rate produces results that contradict the dates for events in human history derived from the fossil and archeological records. They believe this discrepancy stems from several factors. First, evolutionary biologists don’t know when the human-chimp ancestor lived. (Again, for the record, I dispute the evolutionary connection between humans and chimpanzees.) Secondly, the mutation rate is not constant through time, and can also vary based on geographical location. Finally, the mutation rate varies from region-to-region in the mitochondrial genome.
Thus, the group determined a new mutation rate for mitochondrial DNA, taking these factors into account and using well-established dates from the fossil and archeological record to calibrate the mitochondrial DNA molecular clock. Their date for mitochondrial Eve comes in close to 108,000 years ago.
A study in 2012 challenged this revised date, claiming that mitochondrial Eve lived between 250,000 and 300,000 years ago.4 Researchers reached this conclusion based on a much slower mitochondrial DNA mutation rate derived from a comparison of genome sequences from humans living today.
I question the validity of this approach to estimate mutation rate because it fails to take into account the stochastic (random) nature of molecular clocks. These clocks are not metronomic (mechanically regular). Therefore, mutation rates cannot be reliably determined by comparing the genomes of contemporaries or by comparing the genomes of several generations of people in the same family. They must be determined over much more significant time frames.
A study just published (in 2013) takes this concern into account. The researchers calibrated the mitochondrial DNA clock using genomes recovered through ancient DNA analysis from the fossil remains of 10 humans that span about 40,000 years. (The remains’ dates were determined using reliable carbon-14 methods.) Using this calibration—which is likely the most accurate—the researchers concluded that mitochondrial Eve lived around 157,000 ± 40,000 years ago.5
When Did Y Chromosome Adam Live?
As of 2005, when Who Was Adam? was published, the most comprehensive analyses of Y chromosome variants returned a date for Y chromosomal Adam between 50,000 to 60,000 years ago, much more recent than mitochondrial Eve’s date. Two studies, conducted in 2011 and 2013, made use of a larger portion of the Y chromosome and rare Y chromosome variants to estimate dates of 142,000 ± 16,000 and between 101,000 and 115,000 years ago, respectively.6 The results of these most recent studies of Y chromosomal Adam fall in line with the best, most recent dates for mitochondrial Eve.
Another study published in 2013, created a bit of a stir when its authors reported a date for Y chromosomal Adam between 237,000 and 581,000 years ago, most likely with the age for Adam at 338,000 years.7 (To hear a description of this study and its implications listen to the March 7, 2013, episode of our podcast, Science News Flash.) This study’s date for Y chromosomal Adam is about 200,000 years earlier than the first appearance of modern humans in the fossil record and, on this basis alone, raises questions about the result’s validity.
Careful examination of this study’s approach to calculating the date of Y chromosomal Adam reveals that the mutation rate employed by the investigators to calibrate the molecular clock was slower than that used in previous studies. If they used the same mutation rate as everyone else, their estimated date for Y chromosomal Adam would be closer to 209,000 years ago.
The researchers based the mutation rate they used on whole genome sequence comparisons of people living today. As pointed out in our discussion of mitochondrial DNA, this type of calibration is probably invalid. Based on the best and most recent analysis of Y chromosome variants, it appears that the date for Y chromosomal Adam is between 100,000 and 200,000 years ago, not 50,000 to 60,000 years ago.
Comparisons of the Dates for Mitochondrial Eve and Y Chromosomal Adam
When Who Was Adam? was written, a large discrepancy existed between the dates for mitochondrial Eve (150,000 to 250,000 years ago) and Y chromosomal Adam (50,000 to 60,000 years ago). Now, based on better estimates of mutation rates for mitochondrial DNA, use of larger regions of the Y chromosome, and inclusion of rare Y chromosome variants, the dates for mitochondrial Eve and Y chromosomal Adam converge around 150,000 years ago.
This convergence is in line with estimates of humanity’s origin from the fossil record (between 200,000 and 100,000 years ago) and also comports fairly well with the archaeological record that places the first evidence for symbolism (which I take as a reflection of God’s image in humans) between 70,000 and 80,000 years ago. (Click here to read my recent article about the archaeological record and humanity’s origin.)
There is no real reason to think that the dates for mitochondrial Eve and Y chromosomal Adam conflict with the biblical account of human origins. In effect, Scripture is silent about when God created Adam and Eve—just as it’s silent about when God created the earth. Though some people are tempted to use the genealogies in Genesis 5 and 11 to calculate the time of Adam and Eve’s creation (usually resulting in a date about 6,000 years ago), the best scholarship rejects this approach.
Many biblical scholars point out that these genealogies are theological constructs. The author never intended them to be used to calculate or estimate the date for human origins. Instead, these lists are communicating key theological points, highlighting patriarchs of importance in the lineage of Adam to Noah and Noah to Abraham, respectively.
On the other hand, dates derived from molecular clock analysis are best understood as estimates hampered by much imprecision. Calibrating molecular clocks is extremely difficult. The best way to determine mutation rates is still unclear. Even if the mutation rate is known, molecular clock analysis is still remarkably imprecise; typical uncertainties are on the order of ± 50,000 years.
While the exact dates for mitochondrial Eve and Y chromosomal Adam may never be precisely known, the agreement between molecular clock analysis and the dates from the human fossil and archaeological records is remarkable and stands as one of the most significant accomplishments of modern science. To put it simply, molecular anthropology supports a recent origin of humanity from a small population near where theologians think the Garden of Eden was located and traceable back to single ancestral sequences for mitochondrial and Y chromosomal DNA. This is significant in light of the biblical account of humanity’s origin. There is no scandal. There is no controversy. The scientific and biblical stories of human origins harmonize quite well.