This is a paradox of genetics. DNA is a streetlight, revealing a great deal about close relationships between individuals in our immediate genealogical vicinity. DNA is also a telescope, revealing a great deal about ancient relationships between populations. However, DNA’s view into the past comes with tunnel vision. Genetic ancestry only traces a tiny fraction of genealogical relationships in the past. This is what causes its tunnel vision. We cannot see the genealogical history that is untraced by DNA. Most of our genealogical history is real, but invisible.
We can understand genetic relationships as a subset of our genealogical relationships. Genetic relationships are contained within genealogical relationships. This has two consequences.
1. Genealogical ancestry does not imply genetic ancestry. Consider a child’s father and grandfather. They both are fully the child’s genealogical ancestors. However, they are only partially the child’s genetic ancestors, approximately 1/2 and 1/4, respectively. The same is true of the child’s mother and grandmothers. Genetic ancestry continues to dilute each generation: 1/8, 1/16, 1/32 . . . to a number so small it is unlikely a descendent has any genetic material from most of their ancestors.8 The many genealogical ancestors that pass us no DNA are not our genetic ancestors.
2. Genetic ancestors are, usually, also genealogical ancestors. For example, Y-adam is the genetic ancestor of all living men, and he is also their genealogical ancestor. Similarly, Mt-eve is the genealogical ancestor of everyone across the earth. From these facts, some have correctly inferred that they were common ancestors of everyone alive today over one hundred thousand years ago.9
Genetic ancestors are usually genealogical ancestors too, but in biology, there are often exceptions. The human genome includes a specific type of DNA, transposable elements. Transposable elements arose initially from viruses that inserted their genetic material into the genomes of our distant ancestors. These ancient viruses are our genetic ancestors, contributing to our genetic inheritance. The viruses, however, are not our genealogical ancestors.10 For our purposes, this fact is not directly important, but it reminds us that genetic ancestry is not always what it seems.
Genetic and genealogical ancestry are distinct, but they are nonetheless related to one another. Genetic ancestry traces a tiny subset of our genealogical ancestry, conveying information to us now that we can study. In this way, genetic ancestry gives us a tunnel-vision view of genealogical relationships, like a streetlight and a telescope, revealing only a tiny fraction of our ancestral history.
MITOCHONDRIAL EVE AND Y-CHROMOSOMAL ADAM
Much confusion began in January of 1987, when a widely reported study in Nature heralded the discovery of “Mitochondrial Eve” (Mt-eve), estimating she lived about two hundred thousand years ago.11 The accompanying editorial was titled “Out of the Garden Eden.”12 Soon after, “Y-Chromosomal Adam” (Y-adam) was in the news. At the moment, the best estimates place him about two to three hundred thousand years ago.13 Linking a mundane finding with Adam and Eve was a brilliant publicity move. Mitochondrial Eve, “mother of all mothers,” and Y-Chromosomal Adam, “father of all fathers,” captured the imagination of the public. The problem, however, is that these terms are deeply misleading.
In the following figures (figs. 3.2, 3.3, 3.4) there are gray and black lines showing relationships between parents and children. All the lines together are the genealogical relationships, which are a dense web. The black lines are parts of the history traced out by genetic ancestry, of one sort or another. This gives a stark visual cue, as we try to understand what genetic ancestry tells us about our past (figs. 3.2A, 3.3A). In the recent past, genetic ancestry is dense, giving us a streetlight view of the immediate vicinity. In the ancient past, genetic ancestry is singular for each location of the genome, giving us a telescope view into the distant past, but with tunnel vision. Most of what happens in the population is not traced by DNA.
Does the existence of Mt-eve demonstrate that the total population of our ancestors dipped to a single couple? Some think the answer is yes, but this is not true. Even in a large population, an Mt-eve is expected to appear (fig. 3.2A). In the figure, for example, an Mt-eve appears, even though the total number of people each generation remains constant. This is not forced into the simulation that produced this graph. We expect Mt-eve to arise, even if our ancestral population never drops in size.
Is Mt-eve unique, the only “mother of all mothers?” Some think the answer is yes, but this is not true. She is not unique. Mt-eve’s mother and maternal grandmother, for example, are also universal ancestors in the same way as she is. Mt-eve is only the most recent of a long lineage of woman that are also “mother of all mothers” (fig. 3.2B). Note, her paternal grandmother (mother of her father) is not a universal ancestor by way of mitochondrial DNA, but she is a universal genealogical ancestor.
Is Mt-eve the genetic ancestor of everyone in the past too? Some think the answer is yes, but this is not true. She is expected to be the genetic ancestor of everyone alive today. Going back each generation, she would be the genetic ancestor of fewer and fewer people (fig. 3.2C). This fact comes with a nonintuitive consequence. As time progresses, the set of people comprising “everyone alive today” changes each generation, and this change causes the identity of Mt-eve to change too. For this reason, Mt-eve does not remain the same person as time progresses. The Mt-eve of everyone alive today is a different person than the Mt-eve of, for example, everyone alive 2,000 or 10,000 years ago.
The same analysis applies to Y-adam, “father of all fathers,” tracing DNA inherited only from father to sons. Does his existence demonstrate there was a dip in our ancestral population size? No, it does not (fig. 3.3A). Is he unique, the only “father of all fathers?” No, he is merely the most recent of many, and there is a long lineage of universal genetic ancestors stretching into the past (fig. 3.3B). Is he father of everyone in the past? No, he is only the father of all men living today (fig. 3.3C); the Y-adam of everyone, for example, 2,000 years ago is a different person.
Even in a population that genetically arises from a single couple, without people outside the Garden, it is extremely unlikely that Mt-eve and Y-adam are the progenitor couple (fig. 3.4B). This last point answers a common objection. Some contend that the analysis assumes that we arise from a larger population, and removing this assumption would change the analysis. This contention is false. Even if we all arose from a single couple, without people outside the Garden, all the same patterns are observed.
Figure 3.2. Mitochondrial Eve (Mt-eve) is the most recent genetic ancestor of all mitochondrial DNA in the present-day population. The diagrams show a population of individuals over time, with parents connected to children. Mt-eve is circled where all mitochondrial lineages converge. (A) The history of all present-day mitochondria is highlighted. The presence of Mt-eve does not indicate a small population, because we expect to find an Mt-eve even when there is a large population. (B) Mt-eve is not the unique ancestor of all mitochondria. The other universal ancestors of all present-day mitochondria are marked. (C) All the individuals that inherit their mitochondrial DNA from Mt-eve are marked. Even just one generation back in time, Mt-eve is no longer the ancestor of everyone.
Could Mt-eve and Y-adam have lived at the same time, and been a paired couple? The chances of this are exceedingly unlikely, whether we arise from a population (fig. 3.4A) or from a single couple (fig. 3.4B). First, they would have to live in the same time period. Within that time period, they would also have to be a paired couple. These conclusions are not assumptions in the modeling and are visible patterns, whether or not the whole population genetically arises from a single couple.
Figure 3.3. Y-Chromosomal Adam (Y-adam) is the most recent genetic ancestor of all Y-chromosomes observed in populations today. The diagrams show a population of individuals over time, with parents connected to children. (A) The history of all present-day Y-chromosomes is highlighted, with Y-adam marked with a square. The presence of Y-adam does not indicate a sma
ll population, because we expect to find a Y-adam even when there is a large population. (B) All men in Y-adam’s patrilineal lineage are also universal ancestors of all present-day mitochondria and marked. Y-adam is not the unique common ancestor of all Y-chromosomes; there are others. (C) The individuals that inherit their Y-chromosomes from Y-adam are marked. Even just one generation back in time, Y-Chromosomal Adam is no longer the ancestor of everyone. Y-Chromosomal Adam is only the genetic ancestor of men, and just one generation back, he is no longer the universal common ancestor of everyone.
Another problem arises. Y-adam and Mt-eve only consider a tiny amount of the data available. Mt-eve is the most recent common genetic ancestor of mitochondrial DNA, about 0.0005% of the genome. Y-adam is the most recent common genetic ancestor of Y-chromosomal DNA, about 1.9% of the genome. What about the rest of the genome, more than 98% of it? Each part of the genome has a different genetic common ancestor, and the full set of data must be examined to understand when and where a genetic progenitor couple did or did not arise. Looking at all the data, if there are no people outside the Garden, Adam and Eve seem solidly ruled out by the data more recently than five hundred thousand years ago. Going back father, the evidence is weaker but still might rule out an Adam and Eve, if we are to understand them as genetic progenitors, without people outside the Garden.
For these reasons and more, Mt-eve and Y-adam are not the Adam and Eve of Scripture, even if there were no people outside the Garden. There is no reason to believe they are Adam and Eve, even if there actually is an ancient genetic progenitor couple (fig. 3.4B). Y-adam and Mt-eve are, in fact, highly effective publicity for an arcane detail of genetic history, even though this publicity is misleading. Even if we did arise genetically from a single couple, Mt-eve and Y-adam are not this progenitor couple. They are, instead, a pair of strangers, who most likely lived in different millennia, and whose identity changes as time passes. They are the people at which the genetic telescope is pointing, along with several other individuals, but there is no reason to think they are the Adam and Eve of Scripture.
Figure 3.4. Removing the large population assumption, nothing changes. In these simulations, we display the universal ancestors of all mitochondrial and Y-chromosomes. Whether we arise from a population (A) or a single couple (B), it is very unlikely for Y-adam and Mt-eve to be a paired couple at our origin. Other universal ancestors along each lineage, however, might be a paired couple in our past.
THE GENEALOGICAL HYPOTHESIS
The genealogical hypothesis is that Adam and Eve are universal genealogical ancestors. They need not be our genetic ancestors. This not an overly clever loophole derived from modern scientific understanding. Rather, genealogical ancestry is a return to a more traditional reading of Genesis, which cannot possibly be talking about DNA.
First, historical claims in theology are understood using the ordinary meanings of words, consistent with understanding long before modern science arose. Scripture discusses ancestry, often recording genealogies, but it is entirely silent about DNA. Ancient authors make no mention of the double helix, or of genomes.
Second, all claims about DNA and Adam and Eve that arise in theology, therefore, are inferences, not the direct claims of Scripture. The inference that Adam and Eve are our universal genetic ancestors depends on the assumption, often tacit, that there are no people outside the Garden. The genealogical hypothesis, however, starts from the opposite presumption, so the inference that Adam and Eve are our genetic ancestors is not valid. At the outset, we do not know if they are our genetic ancestors or not. Scripture does not tell us one way or another.
For these two reasons, the genealogical hypothesis states Adam and Eve are our universal genealogical ancestors, but not necessarily our universal genetic ancestors. If our purpose was to disprove the traditional account, we would gloss over the distinction between genetic and genealogical ancestry. In order to disprove a historical Adam and Eve, one recent book defines them as our genetic ancestors, passing DNA to us all.14 Traditionalists such as Wayne Grudem were quick to object; this is a strawman of their position.15 Adam and Eve need not be our genetic ancestors. Scripture and theology do not mention DNA. Genealogy matters in this theological question, not genetics. Insisting otherwise foists an anachronistic strawman on the text.
Important theological questions will arise about the people outside the Garden. Does Scripture or theology rule them out? What is the theological meaning of ancestry if it is not genetic? These questions, however, are not part of the scientific analysis; they will be considered later.
CHAPTER FOUR
ANCESTORS OF EVERYONE TODAY
UNDER OUR HYPOTHESIS, ADAM AND EVE must be the “ancestors of everyone” to “the ends of the earth” from at least AD 1 onward. Their offspring interbred with the people outside the Garden. Does the evidence constrain where or when they could have lived?
Genetic ancestry seems to place strong constraints on our answer. Our most recent common genetic ancestors, such as Y-Chromosome Adam and Mitochondrial Eve, are over one hundred thousand years in the past. It is a consequential error, however, to think that these ancient dates demonstrate that our common ancestors were only in the ancient past.1
If we mean ancestry in a genealogical sense, we find a different answer. Could a single couple be among the ancestors of all humans, in the recent past? The answer is yes. There are many universal genealogical ancestors in our past, each individually from whom we all descend. These genealogical adams and genealogical eves2 are likely to appear just thousands of years ago. They continue back until ancient times. Universal ancestors do not arise by luck or miracles. We expect them to arise everywhere. Two of them could be a particular couple in the Middle East, named Adam and Eve in Scripture and from whom we all descend.
What, then, is the science of genealogical ancestry? It is (paradoxically) a subfield of population genetics that studies how family trees, also termed “pedigrees,” interact with genetic ancestry. We cannot directly view genealogical relationships in the past, but we can sequence DNA. Understanding how genetics is shaped by genealogical relationships helps us determine what genetic data does and does not tell us about our past.
THE HISTORY OF GENEALOGICAL SCIENCE
In 1886, Henry Kendall syndicated an article, which he later expanded into a book, The Kinship of Men: An Argument from Pedigrees; or, Genealogy Viewed as a Science (1888).3 Using a series of mathematical arguments, Kendall’s analysis of genealogical ancestry was essentially correct. He mused about the theological, social, and political implications. Kendall argued all people of all races shared recent common ancestors, linking us into a single common race. His work, however, fell into obscurity, never entering the scientific literature. Somehow, Kendall’s insight was forgotten, only to be rediscovered over a century later.
In 1999, Joseph T. Chang published a paper in a journal of probability.4 In this paper, Chang presented the same surprising findings, this time with genetics in view. Common genealogical ancestors, it seems, appear much more recently than genetic ancestors. For the human population, genetic common ancestors arise over one hundred thousand years ago in the past. Genealogical common ancestors, however, were computed to arise as recently as just seven hundred years ago. Just a little bit further back, we all have the same set of ancestors.
The finding was so striking and surprising that the journal organized a discussion in response to the article.5 Everyone agreed that Chang’s math was based on a simplified model of the human population, without any geographical barriers or realistic barriers to interbreeding. The date at which universal ancestors arise would be further in the past. The basic premise of Chang’s conclusions, nonetheless, was correct. In 2004, Richard Dawkins explained Chang’s 1999 findings in The Ancestor’s Tale.6 He leaves out the estimate of when precisely a universal ancestor might arise, writing,
If we go sufficiently far back, everybody’s ancestors are shared. All your ancestors are mine, whoever you are, and all mine
are yours. Not just approximately but literally. This is one of those truths that turns out, on reflection, to need no new evidence.
A freelance science writer had already gone a step further. In 2002, Steve Olson authored Mapping Human History.7 Olson also referenced Chang’s work, but went a step further to claim that all of us, in actuality, shared a common ancestor just two to three thousand years ago. Chang’s original paper modeled a simplified model of the human population that may or may not apply to the real-world complexities of human history. Olson conjectured that these complexities did not change the result by much. Everyone across the globe related to ancestors just a couple thousand years in the past.
This reality was important to Olson. Recent universal ancestry affirmed the unity of all humankind. He argued, correctly, that much of what we understood of race was naive, an illusion not rooted in biology. Olson explains how dispelling the illusion came to alter his understanding of race:
Like many people, I used to divide humans into groups that I thought were fairly distinct, both as historical and as biological entities. Having written this book, I now realize just how closely related people really are. We sort people into categories and then try to justify those distinctions through biology. But the distinctions are in our heads, not in our genes.8
Science bears out Olson’s newfound understanding of race. The legitimacy of the specific date Olson put forward, however, was still uncertain. Chang’s work did not model human history well enough to be numerically accurate.
The Genealogical Adam and Eve Page 4
