Toward this end, recent advances in molecular genetics are quite provocative. As Hugh Ross and I discuss in Who Was Adam?, numerous studies indicate that humanity originated: (1) recently (around 100,000 years ago, plus or minus 20,000 years or so); (2) at a single location (East Africa)—close to where some Bible scholars think the Garden of Eden was located; and (3) from a small population
Moreover, analysis of mitochondrial DNA (which provides insight into the origin of the maternal lineage) indicates that humanity traces back to a single ancestral sequence that could be interpreted as a single woman. Likewise, characterization of Y-chromosomal DNA (which provides insight into the origin of the
paternal lineage) indicates that all men trace their origin back to a single ancestral sequence that could be interpreted as a single man.
These astounding results harmonize with a traditional reading of the biblical account of human origins, and suggest that Adam and Eve likely existed as real persons who gave rise to all of humanity.
But Did Adam and Eve Exist? Population Size
Others have challenged this interpretation, arguing that the genetic data shows that humanity arose from thousands of individuals, not two.1 The chief basis for this claim comes from estimates of the ancestral population size of humans based on genetic diversity.
It is possible to estimate the effective population size of any ancestral group from genetic diversity of present-day populations if the mutation rate is known. As discussed in Who Was Adam?, a number of these types of studies do indeed indicate that humans stem from a small population, on the
order of a few hundred to a few thousand.2
Skeptics of the traditional reading of the biblical account of human origins uncritically accept these results. They argue that the data indicate humanity experienced a genetic bottleneck, with the population collapsing to a relatively small number of individuals. Consequently humanity arose from the thousands of survivors, not a primeval pair.
Critics also point to other methods to model the size of the ancestral population that do not depend on mutations, but on other types of processes to generate genetic diversity.3 Studies employing these techniques also seem to indicate that humanity arose from population sizes on the order of a few thousand individuals.
What Was the Population Size, Really?
In the face of this challenge, it is important to recognize that population sizes generated by these methods are merely estimates, not hard and fast values. The reason: the mathematical models are highly idealized, generating differing estimates based on a number of factors. As a case in point consider two studies discussed in Who Was Adam? One, reported in 2003 by a Russian and U.S. research team, examined DNA sequence elements called short tandem repeats at 377 locations in the human genome for 1,056 individuals that represented 52 population groups. On the basis of this analysis, they concluded that humanity originated from a single point of origin (apparently Africa), from a small population (~2,000 or less) between 71,000 and 142,000 years ago.4 Although this conclusion was consistent with that of an earlier study of short tandem repeats, the population size estimate from the earlier study was around 500 individuals.5 The reason for the difference (of about 1,500) was due to a varying sample size and number of locations in the human genome that were studied.
Did humanity originate from a single pair? Even though population estimates reveal that humanity originated from several hundred to several thousand individuals based on mathematical models, it could well be the case that these models overestimate the original numbers for the first humans.
And it is important to note that an origin of humanity from a small population is consistent with the existence of a historical Adam and Eve who gave rise to all of humanity. After their creation the biblical text teaches that they procreated––having many sons and daughters (Genesis 5:4). Given the limitations of the methods, could it be that the population estimates are reporting on the population structure of humans some time after their creation, when the population would have been small, on the order of a few thousand? Additionally, skeptics who claim that humanity came from thousands of individuals and not two assume that Adam and Eve were genetically identical. Yet, there is no hint of that idea in Scripture. When Eve is created, God takes material from Adam’s side and rebuilds (bānâ in the original Hebrew) it. Part of this process could have involved the introduction of genetic differences into Eve’s genome that made Adam and Eve genetically heterogeneous.
As with the mouflon sheep, if natural selection drove an increase in genetic diversity in humans, then the estimates of the original population sizes of humanity would be artificially high.
We All Like Sheep?
In 2007 a research team reported on the genetic diversity of wild mouflon sheep on one of the islands that are part of the Kerguelen sub-Antarctic archipelago.6 This group of sheep provided researchers with an unprecedented opportunity to study the effects of population dynamics on genetic diversity in small populations.
In 1957 a male and female yearling were placed onto Haute Island (an island in the Kerguelen Archipelago). These two sheep were taken from a captive population in France. By the beginning of the 1970s, the number had grown to 100 individuals and peaked at 700 sheep in 1977. Since that time the population has fluctuated in a cyclical manner between 250 and 700 members. Given that the population began with only two individuals (the founder effect), has experienced cyclical changes in the population size, and was isolated on an island, the researchers expected very low genetic diversity (measured as heterozygosity).
Using mathematical models, the heterozygosity of a population can be computed at any point in time from the heterozygosity of the ancestral population (which was known for the original mouflon pair) and the original population size. What the researchers discovered, however, when they measured this quantity directly for the sheep on Haute Island was that it exceeded the predictions made by the models by up to a factor of 4. In other words, the models underestimated the genetic diversity of the actual population.
The researchers explained this discrepancy by speculating that natural selection drives the increase in genetic diversity, since an increase in genetic variability increases the survivability of the population.
Consequently, if these same models were used to estimate the effective sizes of the ancestral population from the measured genetic diversity at any point in time, they would have overestimated the original population size as much larger than two individuals.
Lastly, the primary reason to think that humanity arose from a single pair does not rest on population estimates, but the fact that the Y-chromosomal and mitochondrial DNA sequences sampled from humans alive today trace back to single ancestral sequences. Again, these can be understood as reflecting an origin from a single man and single woman.
One Lucky Mother, One Lucky Father?
Even though the genetic data traces humanity’s origin back to a single woman and man, evolutionary biologists are quick to assert that mitochondrial Eve and Y-chromosomal Adam were not the first humans. Rather, according to them, many “Eves” and “Adams” existed.7 Accordingly, mitochondrial Eve and Y-chromosomal Adam were the lucky ones whose genetic material just happened to survive. The genetic lines of the other first humans were lost over time.
While this explanation is not out of the realm of possibility, it is highly contrived. It would work if only a few of the first humans reproduced, or were allowed to reproduce. If the data is simply taken at face value, the biblical model is the more parsimonious explanation.
Even though evolutionary biologists offer ways to explain away the implications of the human population genetic data, these explanations—entrenched in naturalism—are not necessarily superior to an interpretation that fully squares with the biblical account. The scientific case for the biblical Adam and Eve stands firm.