The Genealogical Adam and Eve

by S. Joshua Swamidass

  There is a vast amount of genetic information in the past. Almost all of it was lost. Genealogical ancestry is a real feature of the world, connecting us physically, genetically, and biologically to our ancestors. We are not usually, however, genetically connected in a direct way to most our distant ancestors. The few ancestors in our past that passed us DNA were the lottery winners. Of course, whomever the source of our genome, the DNA we receive is nearly identical to DNA of other humans. For this reason, universal genealogical ancestors themselves, and much of the ancient migration that makes them possible, are unobservable in genetic data.

  GENETIC SCIENCE STILL STANDS

  Genealogical ancestry, therefore, is surprising. It works much differently than genetic ancestry (fig. 4.2). As surprising as this is, Henry Kendall reasoned correctly to most of these findings in 1888, coming very close to proposing a genealogical Adam and Eve himself.27 Before DNA was discovered, Kendall might even have predicted genetic ghosts.28 He correctly understood we were all one family, linked across the whole globe. His calculations, moreover, were almost correct, off by merely a factor of two.29 This seems like a very different story than that of genetics. None of these surprises in genealogies, however, contradict genetic science in any way. The problem is not genetic science itself, but the error of using genetic ancestry to answer a distinctly genealogical question. Genetic ancestry is not genealogy.

  It still appears Homo sapiens (1) shares ancestry with the great apes and (2) arose from a larger population that never dipped in size to a single couple. Nothing in genealogical science undermines these two conclusions. If Adam as an individual existed, the notorious problem of intermarriage of his descendants with one another is avoided; instead, their descendants mixed with a larger population of reproductively compatible beings. However, we would also count a particular couple called Adam and Eve as among our genealogical ancestors. They would be two people among those from whom we all descend, with theological or historical significance.

  If Adam was a particular individual in our past, what happened to the population “outside the Garden?”30 Their history is rightfully and carefully studied in genetics, archaeology and anthropology. We find strong evidence for large-scale population movements and intermixing in our ancient history. It is often said that our ancestors arose in Africa and spread across the globe, leaving some populations isolated for long periods of time. It is now clear that our ancestors remained linked by constant interbreeding as they spread. Yes, we spread from Africa, but also individuals or groups migrated in the opposite direction of the larger populations.31 We are just now beginning to uncover some of the complex history of intermixing across the globe.32

  What does genealogical science add to this account? The full story of human evolution is that of populations across the globe linked into a common evolutionary fate by pervasive interbreeding everywhere.33 We can now see the genealogical hypothesis is far more plausible than we might have first imagined. If Adam and Eve were real people, very quickly, in just thousands of years, their lineage would mix with everyone outside the Garden. Interbreeding across the globe links us both genetically and genealogically together. Chang and Olson’s conclusion to their landmark study is poetic:

  To the extent that ancestry is considered in genealogical rather than genetic terms, our findings suggest a remarkable proposition: no matter the languages we speak or the colour of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who laboured to build the Great Pyramid of Khufu.34

  We are all linked together in the recent past by genealogical ancestry. The human race is a single family, in a common story. Whatever our skin color, country of origin, ethnicity, or culture, we are all one family. We are one blood, one race, the human race.

  CHAPTER FIVE

  GENEALOGICAL ADAMS AND EVES

  UNIVERSAL GENEALOGICAL ANCESTORS of everyone alive arise as recently as a few thousand years ago. We can now begin to assess our hypothesis. Could Adam and Eve, ancestors of us all, have lived in the Middle East as recently as six thousand years ago? What are the ranges of times they could have lived? Already, it seems as if this may not be as ridiculous a hypothesis as we first imagined.

  Surprisingly, the distinction between genetic and genealogical ancestry in the 2004 Nature study went largely unnoticed in the theological conversation. David Opderbeck published a single blog article in 2010, noting the distinction between genetic and genealogical ancestry, supposing that universal ancestry from a recent Adam and Eve might be valuable to theology.1 Jon Garvey published the first of many blog articles in 2011, with his own reflections on how this distinction might be useful to theology.2 Later and independently, Kenneth Kemp, Gregg Davidson, and Andrew Loke intuited that genetic ancestry was not the whole story, making contributions to the theological conversation of their own.3 From time to time, the instinct to think beyond genetics would pop up, but this instinct was largely passed over. Often, these contributions were incorrectly dismissed as variations of polygenesis, a theory of origins often associated with racism.4 This rush to judgment prevented recognition and inquiry. Some authors during this time, for example, knew of Kemp, Opderbeck, and Garvey’s work but excluded mention of recent genealogical ancestry in their summaries of the field.5 Several scientific and theological objections were repeated, usually echoing objections against polygenesis. These objections, however, were rooted in deep misunderstanding of both science of ancestry and the monogenesis tradition. There was not yet a cohesive conceptual framework to bind these distinct contributions and insights together, so they were incorrectly lumped in with polygenesis. I will explain the depths of the error of this comparison in the next part of the book. As should be clear already, however, Olson and Kendall were both personally impressed by how universal genealogical ancestry demonstrates that polygenesis is false. The mythology of isolated races, nonetheless, remains strong. This mythology is, perhaps, one reason recent universal ancestry remains so counterintuitive.

  In light of the 2004 Nature study, the genealogical hypothesis seems plausible now, but there are two remaining scientific gaps to bridge before we can be sure.

  First, we want Adam and Eve to be ancestors of, at least, everyone alive “to the ends of the earth” at some point in the past. The published literature, however, only considered the universal genealogical ancestry of everyone in present day. This literature demonstrates we have good reason to believe there were universal genealogical ancestors of everyone alive today. The most recent of these ancestors, however, would not be the ancestors of everyone alive, for example, in AD 1. How do we extrapolate these findings backward to consider universal ancestry at some date in the past?

  Second, the estimates so far are for the most recent of all universal ancestors. This is a tiny number of individuals, possibly in specific areas of the globe, and only arising at some narrow window of time in the past. It would be almost inconceivably lucky for Adam and Eve to be part of this tiny group of people. Nothing in our hypothesis, however, requires them to be the most recent. Instead, we just want them to be universal ancestors, not necessarily the most recent ones. Somehow, we want to know the time at which most people are universal ancestors of everyone at a later date. This is a more conservative approach than using the most recent date; it pushes any estimates we make of when Adam and Eve could have lived to more ancient times. The advantage of this approach, however, is that it gives us an estimate that does not rely on luck or miraculous intervention.

  These are the gaps I bridged in my contributions. In mid-2017, I put out the basic details of the genealogical hypothesis, first in an informal presentation, then in a book review in a theological journal. It became clear that the proposal was important for theology, but it needed further development. In March of 2018, I authored an article, “The Overlooked Science of Genealogical Ancestry,” in an interdisciplinary jou
rnal, Perspectives on Science and the Christian Faith.6 This paper shows how the findings of the 2004 Nature study can be extrapolated to test our hypothesis, bridging these last gaps. This analysis, accidentally, demonstrated that there would be no evidence against the de novo creation of Adam and Eve within a population. This, perhaps, was an even bigger surprise, as we soon explore.

  REQUIRED DESCENDANTS AT AD 1

  In scientific literature, we usually define universal ancestors with respect to everyone alive today. I extended this concept to consider all universal ancestors of a specified group of required descendants in the past. We define genealogical adams and genealogical eves as the people who each individually are a universal genealogical ancestor of this entire group. The “universal ancestors” we seek must be an ancestor of all the required descendants. Of course, the lineage of any particular universal ancestors would also include many more people than just the required descendants.

  How should we choose the required descendants? I can imagine several dates that might be theologically important. I use numbers rounded to millennia, because the precise dates would give the false impression of certainty. AD 1 is before the ministry of Jesus, and before Paul writes Romans. About 4,000 years ago, Genesis is compiled into its final form. About 6,500 years ago, the first cities arise. Perhaps we require that everyone alive at one of these points in time were all descendants of Adam and Eve. Alternatively, we could require ancestry at different dates in different regions. In this chapter, I choose the required descendants to be everyone alive at AD 1. For theological reasons, this seems to be the most recent date allowable, as I will explain in the next part of the book. Depending on when Adam and Eve are placed, it is possible that everyone descends from them long before AD 1.

  NO LUCK OR MIRACLES REQUIRED

  With respect to the required descendants chosen, we can estimate a range, which will stretch from a recent date into the distant past. The key task we have is to estimate the recent end of the range of dates that the universal ancestors appear.

  The recent end of the range is defined by three critical dates: (1) the most recent universal genealogical ancestor (MRUGA), (2) the nearly identical ancestor point (nearly IAP), and (3) the identical ancestor point (IAP). The most recent date is that of the MRUGA, the first point. Here, the first universal genealogical ancestors appear somewhere in the globe. The most ancient date is that of the IAP, the third point. Here, each one that leaves any ancestors is also a universal ancestor. The only people at this point who are not universal ancestors are those who leave no surviving descendants. Between these two dates is the nearly IAP, where nearly everyone alive (95–99 percent) who leaves ancestors is also a universal ancestor.

  Which of these three points in time is most important to us? At the nearly IAP most people across the globe are each individually ancestors of all the required descendants. In the simulations, these last 2–5 percent were people born in Australia and the Americas.7 At the nearly IAP, most people in Mesopotamia are universal ancestors. If Adam and Eve lived at this point in time, or any time more ancient, it would not take luck or miracles for them to be universal ancestors of everyone.

  WHEN UNIVERSAL LINEAGES ARISE

  Our first task is to start from the required descendants and work backward to determine when universal ancestors could have lived. Currently, the 2004 Nature study is the only published study that models migration, geographic barriers, and population structure. This study estimates when universal ancestors arise for all humans alive today. The first author also released an unpublished and unreviewed report with expanded results using a variety of parameters. These two studies represent the most realistic simulations of universality.8 Building confidence in the estimates, simulations results were consistent, even though all models used very low migration levels. The outliers with the longest estimates use unrealistically low migration across the entire map. The high immigration rate models still use very low immigration rates, but a MRUGA can arise in as little as two thousand years. Other simulations in the literature are less relevant because they neglect geographic constraints entirely or unrealistically restrict migration to only a few kilometers.9

  In this simulation, the MRUGA is estimated to arise three thousand years earlier than the required descendants.10 The IAP is estimated to about five thousand years earlier than the required descendants. The nearly IAP is likely closer to the MRUGA date than the IAP, perhaps close to three and a half thousand years.11 Taking a more conservative estimate, we will round up to four thousand years ago. For reference, this is approximately three times longer than analytic results assuming random mating.12 The barriers to mixing in the simulation, therefore, increases estimates over the theoretical results, but not by much.

  Figure 5.1. Estimating when universal ancestors arise. Universal genealogical ancestors first arise about three thousand years before the required descendants and extend back into the distant past. The estimated universal ancestors of all those alive at AD 1, six thousand years ago, and forty-five thousand years ago are displayed in cartooned pedigrees (top). The time axes are drawn approximately to scale, but width does not correlate with population size. Three dates define the recent end of the range (bottom): (1) the most recent universal genealogical ancestor (MRUGA) date, (2) nearly identical ancestor point (nearly IAP), and (3) the identical ancestor point (IAP).

  Though cautious, these estimates lead to surprising conclusions. For example, consider choosing all those alive in AD 1 (about two thousand years ago) as the required descendants. An estimate of the IAP is about seven thousand years ago, with a MRUGA at five thousand years ago. At the nearly IAP, estimated at 6,000 years ago, all farmers in Mesopotamia who left a reasonable number of grandchildren would each be universal ancestors of everyone alive in AD 1 (fig. 5.1). The reference to six thousand years, to be clear, is merely a consequence of the math (4 + 2 = 6) and should not be interpreted as a specific endorsement of dating Adam and Eve at this time. If they lived ten thousand years ago, or fifty thousand years ago, or five hundred thousand years ago, they also would be ancestors of everyone from AD 1 onwards, along with many people who lived before AD 1.

  Moreover, by using the simulation from the 2004 Nature study, we are making an acutely cautious estimate. Before AD 1, the most remote islands are not yet settled,13 the population was smaller than present day,14 and the simulation assumes very low levels of migration. All these deviations from reality increase the time to universal ancestry, biasing the estimate toward more ancient times.

  HOW QUICKLY DO ANCESTORS UNIVERSALIZE?

  Our second task is to understand how ancestry spreads from a particular genealogical adam and eve. This is the inverse of the first task, which started from the required descendants to estimate when genealogical adams and eves arise. Here, we start with a particular genealogical adam and eve, and endeavor to understand how their descendants spread out across the globe.

  Consider a specific genealogical adam and eve in the distant past. How long does it take them to become a universal ancestor of all those alive? How quickly does genealogical ancestry spread? How much time do we have to wait till they become universal ancestors? The estimates of the prior section guide us to the answer. It will take between three thousand and five thousand years for a specific ancestor to become a universal ancestor (fig. 5.2). The quickest time, three thousand years, corresponds the time to the MRUGA and applies to very few individuals who are lucky and ideally located. The longest time, five thousand years, corresponds to the time of the IAP and applies to very few, unlucky, and poorly located individuals, like those in the Americas or Australia. More likely, especially for those in central locations like the Middle East, the wait time is between four and three thousand years. A cautious estimate, therefore, of the wait time for typical individuals is four thousand years, even though a more accurate estimate might be 3,500 years.

  Remember, at four thousand years, everyone in the Middle East that leaves ancestors is a universal ancestor. It do
es not take luck or miracles for Adam and Eve, at this point, to be ancestors of everyone.

  Figure 5.2. Estimating the descendants of universal ancestors. Cartooned pedigrees show the estimated ancestors at the MRUGA, nearly IAP, and IAP points (top). Universal ancestors usually become universal in less than four thousand years, before the nearly IAP (bottom). The most likely time that universal ancestors first arise in a region is well before the nearly IAP, so most of the recent universal ancestors have pedigrees with dates about halfway between MRUGA (top left) and the nearly IAP (top middle) pedigrees. There are four eras to consider in relation to any specific universal ancestor. In the first era, there are only those before the ancestor. In the second era, there are many living alongside the descendants of the ancestor. In the third era, almost everyone is a descendant of the ancestor. Those outside the genealogical lineage are those in the most isolated populations. In the fourth era, everyone alive is a descendant of the ancestor.