The Genealogical Adam and Eve

by S. Joshua Swamidass

  Figure 6.1. Several examples of isolation are considered. The strongest case is for the isolation of Tasmania, but even this is not definitive.

  Looking at any small portion of the genome, populations can seem isolated. Looking at whole genomes, however, we usually see intermixing with other populations. Likewise, more genetic information from neighboring populations often reveals evidence of mixing. The more we look, the more evidence of mixing we find.

  GEOGRAPHIC ISOLATION IS NOT GENEALOGICAL

  The geographic isolation of some populations merit special discussion (fig. 6.1). For example, the Americas, Australia, Tasmania, Hawaii, and Easter Island seem to be, at first glance, isolated for very long periods of time in the past.

  At first, the geographic isolation of the Americas seems insurmountable. It was thought that migration to the Americas was contingent on an intermittently open land bridge in Beringia or seafaring technology to cross the Pacific Ocean. Evidence, however, suggests continuous immigration in boats along a costal route and another route through the Aleutian Islands.13 Even if immigration ebbed at times, genealogical isolation would require zero successful migrants to the Americas for centuries and millennia. Even if we find genetically isolated populations in the Americas, it does not follow that the Americas were genealogically isolated too.

  Likewise, Australia is often offered as definitive evidence against recent common ancestors. Rising seas submerged land bridges across the world, making it more difficult to cross from Southeast Asia to Australia and separating Tasmania from Australia. For this reason, we might expect Australia to be genealogically isolated.14

  The initial colonization of Australia adds important information. Land bridges never extended all the way to Australia. The last stretch required crossing a fifty- to one-hundred-kilometer-wide body of water. Until the arrival of Homo sapiens about forty to sixty thousand years ago, this final gap was not crossed. It is thought that boats or rafts might have been a unique capability of Homo sapiens, at least in this region, and were used to cross the strait in order to colonize Australia.15 Similar seafaring feats enabled Homo sapiens to migrate to unexpected places for at least one hundred thousand years.16 This is evidence that ancient Homo sapiens were capable of crossing large bodies of water. In this case, the genetic data settles the debate. A 2013 genetic study uncovered evidence that about four thousand years ago there was “substantial gene flow between the Indian populations and Australia, well before European contact, contrary to the prevailing view that there was no contact between Australia and the rest of the world.”17 The authors note, “This is also approximately when changes in tool technology, food processing, and the dingo appear in the Australian archaeological record, suggesting that these may be related to the migration from India.”

  It is possible that the iconic dingoes of Australia arrived on Indian ships, just thousands of years ago. With evidence of large-scale mixing, we expect there were numerous migrations too small to detect both before and after this major event four thousand years ago.18 The geographic isolation of Australia, therefore, is not evidence of genealogical isolation.

  Tasmania is a large island in the present day, and it presents the strongest case for genealogical isolation. It was settled tens of thousands of years ago, while it was connected to Australia by a large land bridge that was submerged by rising seas by about fourteen thousand years ago, and difficult to cross by about ten thousand.19 As evidence of this difficulty, dingoes came to Australia four thousand years ago, but to Tasmania much later. There, nonetheless, remain several habitable islands between Tasmania and Australia. Using these islands as a broken bridge, the crossing might still be possible, though difficult, perhaps with the same sort of boats that enabled colonization of Australia in the first place. The real question is if the barriers prevented all mixing. Even if mixing was limited to rare events, universal ancestors arise. For this reason, we cannot know for sure if and when small amounts of migration took place to Tasmania. The oral tradition of Aborigines, to this day, retains ten-millennia-old memories of when the seas rose.20 They would have known that Tasmania existed across the strait, for example, four thousand years ago. It seems reasonable to wonder if at least one boat managed the crossing every century or so. In this case, I grant that skepticism is reasonable, and informed scientists might disagree. We cannot say for sure, nonetheless, one way or another. Future work, however, could settle the question. The remains of dingoes in Tasmania, if dated to 3,000 years ago, for example, would demonstrate there was exchange across the strait. Whole-genome studies of ancient DNA from Tasmanians, also, could demonstrate migration from Australia, perhaps against expectation. Right now, however, evidence does not tell us for sure.

  The most remote islands—like Hawaii, Easter Island, and the most eastern end of Polynesia—are very difficult and dangerous to find without modern technology. For this reason, these islands are key bottlenecks that push back estimates of the most recent ancestor of all present-day humans.21 However, these islands were colonized within the last couple thousand years or so.22 They are not, therefore, relevant to universal ancestors more ancient than about six thousand years ago.

  In any case, absence of positive evidence for migration does not demonstrate isolation. Alongside the limitations of genetic studies, rising seas limit the archaeological evidence of migration in the distant past. From about sixteen to seven thousand years ago, seas rose about 120 meters, submerging very large coastal areas across the globe.23 As the seas rose, they erased much of the archaeological evidence for migration and early settlements.24 Colonization in paleo-historic times might have been in boats, along coasts and rivers, enabling rapid dispersal over long distances.25 This dual problem of costal dispersion and submerged evidence limits our understanding of the most geographically isolated areas. Moreover, for universal ancestors ten thousand years or more ancient, most of the land bridges would be still passable for thousands of years. During this time, Australia, Tasmania, and the Americas would all be easier to access. If ancestry of nearly everyone is sufficient, a far more recent date is plausible.

  THE ANCIENT DNA REVOLUTION

  The study of ancient DNA promises to revolutionize our knowledge of human history. In 2018, the book Who We Are and How We Got Here was authored by David Reich, one of the leading scientists in this area.26 The review of his book in Nature puts it well:

  What his and other labs are uncovering is the tremendous degree to which populations globally are blended, repeatedly, over generations. Gone is the family tree spreading from Africa over the world, with each branch and twig representing a new population that never touches others. What has been revealed is something much more complex and exciting: populations that split and re-form, change under selective pressures, move, exchange ideas, overthrow one another.27

  We sit at the beginning of this revolution. Thousands of ancient genomes have been sequenced already, but not yet analyzed or published. In another decade, we will know far more about who we are and where we came from. We will see in increasing detail how we are connected to one another. If the pattern continues, the evidence for populations and mixing in the past will grow.

  Ancient DNA is presenting us with mysteries and puzzles, even as it shows we are more connected than we imagined. In 2018, several ancient genomes from across America were analyzed and published. In this study, one individual from about ten thousand years ago in South America showed evidence of mixing with populations in Australia.28 None of the genomes to the north showed any evidence of this mixing event, and scientists are not sure how this happened. This presents a puzzle to solve in the coming years. We are just beginning to understand the complexity of human history.

  Were any populations totally genealogically isolated for thousands of years? These are honest questions and objections, but our understanding of the past is being reworked. A major realignment in our understanding of human history is being guided by a tidal wave of genetic data. What seemed like reasonable conclusions o
f isolation in prior decades are much less plausible now. As we learn more about the past, long-term isolation seems less and less likely. Were there any human populations isolated for tens of thousands of years? Perhaps with the exception of Tasmania, certain conclusions of long-term and total isolation increasingly seem like mythology. Even in the case of Tasmania we do not know for sure one way or another.

  Figure 6.2. Digging into the details, universal ancestry poses a dilemma of two universal absolutes. Either (left) there were populations with absolutely no mixing for thousands of years, or (right) there were absolutely no populations that were totally genealogically isolated. Genealogy is outside the genetic streetlight, so we may never know definitively from evidence alone. Depending on the theology adopted, this may not matter.

  CAUGHT BETWEEN TWO NEGATIVES

  We do not have a way of definitively demonstrating genealogical isolation. Looking across all the genetic data, what if we found a population that really was genetically isolated for tens of thousands of years? Even this would not be evidence that they were genealogically isolated. Initially, there was hope that genetics might determine if and when populations were genealogically isolated.29 However, genetic data cannot detect low levels of migration in the distant past.30 Genetic isolation, therefore, does not demonstrate genealogic isolation.

  The most likely consequence of rare interbreeding is genetically isolated populations that are not genealogically isolated. Remember, genealogic isolation is broken with a single successful dispersal event. Consequently, to demonstrate genealogical isolation, one has to prove that absolutely zero successful immigration has taken place over thousands of years. Most genealogical ancestors, however, do not leave any genetic evidence in their descendants.31 Most of the DNA that is passed on is not identifiable DNA, and is, therefore, unobservable in genetic data. This is not a low-probability loophole. Genetic information is unable to rule out genealogical relationships in the distant past. It is, therefore, not able to demonstrate genealogical isolation.

  For any multimillennium period in our distant past, were any populations genealogically isolated? Evidence is mounting for interbreeding everywhere. Will we ever know for sure that there were never genealogically isolated populations? Answering either yes or no requires making one of two absolute negative claims, each of which is difficult to substantiate. We just do not have the evidence required to definitively determine which answer is correct.

  On one hand, answering, “Yes, there were genealogically isolated populations” requires asserting there was zero successful migration or intermixing for thousands of years. This negative is not possible to demonstrate with evidence from either genetic or archaeological data. Those skeptical of the yes answer can posit at least a tiny amount of migration and intermixing, which would undetectably break genealogical isolation.

  On the other hand, answering, “No, there were no genealogically isolated populations” requires asserting that there were zero populations that were isolated for thousands of years. This negative requires comprehensive knowledge of all populations in our distant past. Those skeptical of the no can posit that somewhere, somehow an isolated population existed.

  We are faced, therefore, with a dilemma between two claims that are difficult, if not impossible, to substantiate. Absolute negatives, of either sort, are nearly impossible to demonstrate with evidence. What are we to do in situations like this? At the very least, reaching the limits of the evidence, there is flexibility in the scientific account.

  It is possible that we all descend from Adam and Eve. What then is the likelihood that Adam and Eve, six thousand years ago, in the Middle East, would become ancestors of everyone by AD 1? What about at ten thousand years ago? Or twelve thousand years ago? We do not have the evidence to know for sure. Without definitive evidence, some scientists might conclude that, for example, it is most likely that Tasmania was totally isolated between six and two thousand years ago. Even then, evidence does not demonstrate this definitively. It remains possible that a single boat each generation could have crossed the strait to break genealogical isolation. It is possible that further research, especially into ancient DNA, might falsify the hypothesis of isolation. At this time, however, we cannot evidentially demonstrate genealogical isolation with high certainty, nor can we demonstrate it false.

  THE GENEALOGICAL HYPOTHESIS

  What should we conclude at this impasse? There is a puzzle here, without definitive evidence to settle our questions. Making an “inference to the best explanation,”32 perhaps invoking Occam’s razor, we might conclude that mixing does not exist where there is no evidence of mixing. This seems reasonable, but ancient DNA is sparing with Occam’s razor.33 Over and over again, we are finding out that ancient history is more complex than the simplest explanations of limited data.

  Where evidence is sparse, as it is here, a better mode of reasoning might be hypothesis testing. Under this mode of reasoning, we can be sure that no evidence has definitively demonstrated genealogical isolation. Perhaps some populations are geographically and genetically isolated, according to current knowledge. This, however, is not strong evidence against a rare interbreeding event.

  More careful modeling or additional evidence might resolve some questions, at least in part. It might take a philosopher to untangle the epistemological knot. In the meantime, perhaps we describe universal ancestry of everyone at AD 1 as “likely under a disputed assumption,” if Adam and Eve lived six thousand years ago. The more ancient we move Adam and Eve back in history, the more certain we become they are universal ancestors. For example, if Adam and Eve lived ten thousand years ago, we might describe universal ancestry as “likely under a plausible assumption.” If they lived fifteen thousand years ago, perhaps it is just “very likely.”

  Either way, this scientific debate may be entirely ancillary to the theological questions at hand. Moving Adam and Eve slightly back in time overcomes most scientific objections. Theology does not make claims with scientific precision anyway, so nearly universal ancestry by AD 1 may be sufficient for the doctrine of monogenesis. Looming objections about human dignity and worth can be addressed in our theology of those outside the Garden. Whatever the outcome of remaining scientific debate, we can be certain that if Adam and Eve existed, then the vast majority of the earth’s population were their descendants long before AD 1. The scientific debate might continue on about a few exceptions to this rule, but this debate may be unresolvable with evidence. This technical debate, moreover, should not concern us as we move forward into theological reflection.

  CHAPTER SEVEN

  DIRECT AND MIRACULOUS CREATION

  ADAM AND EVE, ANCESTORS OF US ALL, could have lived as recently as six thousand years ago, in the Middle East. Perhaps we might prefer to understand them as living ten thousand years ago, to be more certain they are universal ancestors. Could they have been de novo created in a direct act of God? Is there any evidence against this part of the hypothesis?

  Paradoxically, Adam and Eve could have been created from the dust and a rib, without parents, and at the same time we all could also share common ancestry with the great apes. These two facts are not in conflict. There is no evidence against the de novo creation of Adam. Our genomes would appear as if we shared ancestry with the great apes, because we do. This evidence would not imply God was deceitful, because genomes would record the true story of everyone outside the Garden. The genetic evidence that we descend from Adam and Eve, however, would be lost long ago. For this reason, there is no genetic evidence for or against the de novo creation of Adam and Eve. As this conclusion became clear to the biologist Darrel Falk, he wrote with surprise,

  Science is silent on the question of Adam and Eve being ancestors of us all. It is even silent on the issue of whether Adam and Eve were created de novo. . . . One can’t pin the question of Adam and Eve on science anymore.1

  This, perhaps, is the most surprising finding of my 2017 and 2018 articles.2

  This finding is a secul
ar claim about evidence, which does not require belief in a de novo created Adam and Eve to affirm. For example, several atheist scientists participated in the workshops, and all agreed there was no evidence against a couple specially created within a larger population. They agreed with this evidential conclusion even though they personally do not think Adam and Eve were real, nor do they believe that God exists. In a public shift, moreover, evolutionary creationists at BioLogos changed their position, removing from their statement on Adam and Eve the incorrect claim,

  The de novo creation of Adam and Eve is not compatible with what scientists have found in God’s creation.3

  This shift comes as, over 2017 and 2018, several scientists connected with BioLogos independently and publicly agreed with me that there was no evidence for or against the de novo creation of Adam and Eve.4 Then, in 2019, Deborah Haarsma edited her response to Keller from 2017, removing the claim that there is no evidence against the de novo creation of Adam and Eve within a population.5 These BioLogos scientists do not affirm the de novo creation Adam and Eve, and have been arguing against it for decades. Evolutionary creationists still “dismiss” the traditional account, and still oppose it for theological reasons. It is notable, despite this dismissal, that they now acknowledge there is no evidence against the de novo creation of Adam and Eve.