Mitochondrial DNA and a bouquet of bones is the way to Eve’s heart and to the origins of anatomically modern humans. Or, how to be right when you’re wrong…
1. Introducing Eve…
Today, Rebecca L. Cann is a professor in the Department of Cell and Molecular Biology at the University of Hawai’i at Manoa. Back in 1987, a year after she had joined the faculty at the Honolulu campus of UH, her paper on the genetics of human origins was finally published. Her paper suffered a contentious two-year incubation at the prestigious British journal, Nature, because it totally up-ended the field of paleoanthropology – the study of human origins. Most all the eminent silverbacks in the field fought the paper, fiercely. Yet now, Cann’s paper forms the basis of the most widely held scientific view – that all living humans descended from a small population in southern Africa a couple hundred thousand years ago. Specifically, the paper by Cann et al. said “these mitochondrial DNAs stem from one woman who … lived about 200,000 years ago, probably in Africa”. That one woman was commonly called African Eve or Mitochondrial Eve by the popular press.
Cann’s paper triggered academic battles that raged for decades. Her hypothesis was given various names including Out of Africa, Recent African Origin, or Replacement Theory (because of the implication that modern humans migrated globally from Africa and replaced all the local and more ancient hominids like the Neanderthal). Scornfully, it was also called Out of Eden.
The Out of Africa hypothesis was controversial for several reasons. The biggest reason for the fuss was because it completely contradicted the prevailing majority view at the time: that humans evolved continuously over millions of years in small regional groups scattered across several continents. This was called the Multiregional Evolution hypothesis. The Eurocentric anthropologists of the time refused to acknowledge the African origin of modern humans which was even suggested by the fossil record at the time.
Today the paleoanthropology battleground has shifted to what happened after modern humans left Africa around 100 thousand years ago.
For now, we will focus on how Eve came about with the help of these little cellular organelles called mitochondria.
But there are several other important themes in our story: like remaining steadfast when your data support you on the important ideas while conceding the lesser points; that there is a thin line between being steadfast when you are right versus when you are wrong and that we often can’t tell the difference.
2. Evolution and evolutionary trees…
In the 1870s, Othniel Charles Marsh was a professor and paleontologist at Yale University who was fighting off Native Americans, meeting with their Chiefs, and tramping through the wild frontiers of the American West. He was driven to find fossils, and among many of his classic discoveries like Triceratops and Stegosaurus, Marsh also uncovered a complete series of fossils that beautifully traced the evolution of the horse. Marsh published his fossil history of the horse, which included a classic illustration of the serial changes in the equine forefoot.
Marsh made many contributions to our understanding of evolution through paleontology. His success with the horse was spectacular and influenced scientists such as English biologist Thomas H. Huxley. Huxley had his conversion moment after meeting with Marsh to review his fossil horses and shortly after gave an important lecture on evolution in New York City. Unfortunately, Marsh’s linear model of evolution was too successful in capturing the public and academic imagination, unfortunate for being so wrong.
We’ve all seen museum displays or magazine illustrations showing similar series of skeletons, purporting to show the evolution of an animal, perhaps from a fox-sized four-toed equine ancestor to the single-hooved magnificence of the modern Percheron or the elegance of the Arabian.
These linear displays are wrong on many levels, and it might be best to illustrate just one type of error with a simple drawing. Let’s take the horse skeletons from above and draw a couple of hypothetical evolutionary or phylogenetic trees which summarize their evolutionary relationships.
The tree on the left suggests a straight-line direct ancestral relationship with each earlier fossil. The branched tree on the right shows a much more complex relationship, with most skeletons representing part of an extinct lineage (each skeleton is at the same height in the timeline, but placed differently in each hypothetical evolutionary tree).
Evolution is messy and never proceeds in a straight line as typical museum displays imply and as the left tree shows. Most of the fossils we unearth are not direct ancestors of modern species and are instead likely to be part of an extinct lineage. The highly-branched evolutionary tree is a better, though still imperfect, model of the biological past.
Historically we have always tried to understand human origins by the fossil record, just like O.C. Marsh. However, there are numerous problems with using only fossils to draw our human phylogenetic tree.
One problem is hominid fossils are sporadic, fragmentary, and rare. We are often lucky to have a part of a skull and nothing else. We are thus left with a very incomplete record of our evolutionary history. Imagine trying to reconstruct your own detailed personal family tree using only a yearbook from one uncle on your maternal side, a marriage certificate from a distant aunt on the paternal side, and a fragmentary war record from a possible great grandfather – and that’s it. You know you cannot reconstruct the richness of a few generations of your own family history from such incomplete records. Yet paleontologists attempt to do this for millions of years of our evolutionary history with just a few thousand partial hominid fossils.
Another problem is the uncertainty in geological dating methods or in dating specific fossil specimens. Imagine for our family history we are unable to clearly set the dates of the yearbook, the marriage certificate, or the war record, so the uncle might really be a cousin or a great-uncle, etc.
Yet another problem is the size and shape of fossil bones are insufficient to prove an evolutionary relationship. Just like a yearbook is insufficient proof that the person in the photograph is your uncle.
Our classical reliance on fossils is fundamentally flawed and can only lead to significant errors in our family tree. Modern evolutionary biology uses molecular and genetic tools as well as fossils to build more accurate phylogenetic trees, and to overturn old prejudices.
3. Using molecular clocks to build evolutionary trees…
In 1958, Emile Zuckerkandl, a former refugee from Nazi Germany, applied to Linus Pauling at the California Institute of Technology for a research position. Zuckerkandl learned chemistry in Pauling’s lab, and applied that new knowledge to analyzing hemoglobin (an oxygen-carrying protein) from a variety of primates and other animals. Zuckerkandl and Pauling noticed the amount of variation in the sequence of amino acids (which are the building blocks of proteins) was related to evolutionary distance between the species. This led to their seminal 1965 paper which started the field of molecular evolution. The image above is a figure from their paper showing a phylogenetic tree based on hemoglobin sequences.
Almost a decade later in 1967, Allan C. Wilson and his graduate student Vincent M. Sarich published a paper on the rate of evolution of the protein albumin in primates. Wilson was a New Zealand farm boy who became a prominent biochemistry professor at Berkeley, and made a career of doing things differently. Wilson and Sarich used a novel method of inferring evolutionary change by measuring the binding strength of antibodies to albumin. The pair of species with stronger antibody binding is more closely related than the pair with weaker binding. As with Zuckerkandl and Pauling’s results using hemoglobin amino acid sequence, Sarich and Wilson found the strength of antibody binding to albumin varied in lock step with hypothesized evolutionary distance. Remember Allan Wilson’s name since he plays a central role in this story.
The next year in 1968, Motoo Kimura, at the National Institute of Genetics in Japan, published a short but important Nature paper which for the first time calculated a genetic mutation rate based on molecular sequences, and proposed the neutrality hypothesis, which said most mutations don’t make noticeable changes in a gene (like the spelling change between color and colour don’t change the meaning of the word). That, and a constant rate of evolutionary change, meant biological molecules could act as an evolutionary clock.
By 1977, the concept of a molecular clock had been established. The focus now centered around efforts by Allan Wilson and others to calibrate and validate molecular clocks with fossil and other evidence. Molecular evolutionary biology really flourished from here.
Since then, there has been an explosion in the number and variety of biological molecules (such as proteins, RNA, and DNA) used as clocks to infer evolutionary relationships. There are many reasons for this expansion of molecular clocks. A very practical reason is whether a given molecule is present in the relevant species (for example, bacteria do not have the hemoglobin used by Zuckerkandl and Pauling, or the albumin used by Sarich and Wilson).
The most important reason to look at a wide range of molecules is to ensure the truth of the story each molecule tells us about evolutionary relationships – like the police or a reporter cross-checking multiple witnesses of an event. We need to look at multiple molecules when building a phylogenetic tree.
Critical developments in molecular evolution since the 1970s included the statistical and computational methods used to create evolutionary trees, and to statistically test their validity.
Today, molecular clocks are one of the standard tools we use to draw phylogenetic trees, and are as important to our understanding of evolution as fossils. We need both molecules and bones to understand our evolutionary history and the relationships among our biological family.
4. Building molecular clocks with mitochondrial DNA…
In Wilson’s molecular clock graph above, the evolutionary timescale is in the tens to hundreds of millions of years. For such long times, the slope of genetic or protein changes is sufficient to give good time resolution as seen in the graph. Those changes, however, are too slow if we want to look at short evolutionary times, less than a few million years. Imagine using a clock with only an hour hand to measure your time in a 50-meter sprint. The hour hand moves too slowly to measure short races accurately, just as protein changes are too slow to measure short evolutionary times.
This is where mitochondria come in. Mitochondria are the powerplants of the cell, using oxygen to burn fuels to yield a cellular energy currency called adenosine tri-phosphate (ATP). Billions of years ago mitochondria were originally free-living aerobic bacteria that were engulfed by the last common ancestor of all eukaryotic cells (cells with a nucleus). Now they reside symbiotically in all animal, plant, and fungal cells, as well as in ours. This is important for our story, since mitochondria come with their own DNA, separate from the DNA in our nucleus.
This makes mitochondria a very practical and useful source of DNA for molecular clocks. They are common organelles, easy to separate from other cellular components like the nucleus, and yield lots of mitochondrial DNA (mtDNA). Most importantly for our purposes, mtDNA mutates at a much faster rate than genomic or nuclear DNA (gDNA), and can be used for short evolutionary times. We can think of mtDNA as the seconds hand on our clock for timing evolutionary sprints, where gDNA is like the hours hand for timing ultra-marathons.
In most eukaryotes, the gDNA contains two copies of each chromosome (called diploid; we get one copy from each parent), and two copies of any gene may have different mutations. Furthermore, segments of chromosomes in gDNA often swap places in a process called homologous recombination. Those properties of gDNA significantly muddy the evolutionary clock.
Bacteria – and therefore mitochondria – have only one copy (called haploid) of their simpler and smaller chromosome. Even better, mitochondria are passed to their offspring only from the mother through her eggs. This makes tracking the path of mitochondria through evolution much easier.
In 1985, Masami Hasegawa, then at the Institute of Statistical Mathematics in Tokyo, Japan, published a paper with his colleagues which established a method for dating evolutionary events with a mtDNA molecular clock. The goal was to calculate a more precise date at which a hominid evolutionary branching event happened – only a short few million years ago.
Today, mtDNA is one of several very important molecules used to understand human evolution. But it is important to recognize the need to use mtDNA along with other molecules to get a true understanding of human evolution. Just as molecular clocks must be used alongside fossil evidence to create an accurate evolutionary tree, mtDNA must be used with other biological molecules to function well as a molecular clock.
5. Dating Eve…
Allan Wilson, who we met earlier developing evolutionary molecular clocks, was a full professor at the University of California Berkeley where he remained for his whole career. Rebecca Cann, whose paper revolutionized anthropology, got her Ph.D. under Wilson’s supervision at Berkeley. She was in Wilson’s lab for her post-doctoral training when she discovered Mitochondrial Eve and wrote her paper.
For her research with Wilson, Cann purified mtDNA from 145 placentas and two cell lines. The donors of the placentas covered a range of racial populations (20 Africans, 34 Asians, 46 Caucasians, 21 aboriginal Australians and 26 aboriginal New Guineans). She then digested the mtDNA using a set of restriction enzymes (RE). REs are enzymes made by bacteria to defend against viruses by cutting DNA at very specific, short sequences. Therefore, where an RE cuts tells you the sequence of the DNA at that cut site. If an RE cuts mtDNA in one person, but not in another, you can tell that there is a DNA sequence difference between the two.
Using these enzymes Cann was able to make a map of the mtDNA, where they were cut by each RE. These maps showed Cann where the cuts (or therefore the sequences) were the same or different between each person. From these maps, Cann was able to calculate how much the sequences differed from person to person.
Cann then used software to automatically calculate a phylogenetic tree from the mtDNA maps, using the parsimony method. The parsimony method is based on something commonly known as Occam’s razor: the simplest theory requiring the least number of assumptions is the best explanation for a set of data. Applied to Cann’s phylogenetic trees, maximum parsimony says the tree requiring the least number of genetic changes to explain the current diversity is the best tree for a set of mtDNA sequences.
If there are few differences and many similarities in mtDNA, parsimony suggests a close relationship. The more differences in mtDNA, the more distant the relationship. In this way, one can gradually build up hypothetical trees representing the evolutionary relationships among the present people. The deepest branches representing the biggest sequence differences may be where the ancestral origins lie.
The mtDNA data and analysis inferred an African origin, and more importantly that all the modern mtDNA descended from a single African woman. Using an estimate for the rate of mutations, Cann also inferred the African common ancestor of modern mtDNA lived between 140 to 290 thousand years ago.
6. Barbarians at the gate...
Hordes of critics came pouring through every breach in the walls of Cann’s paper, taking pot shots at her and her boss Allan Wilson. Many of the leading anthropologists of the day were British men and Cann was an American woman. Anthropologists back then concentrated on fossils and associated cultural items like tools and weapons. Cann used molecular biology and biochemistry to step deep into their realm of inquiry.
But worst of all, she completely disagreed with every tenet of their field’s position on modern human origins. Cann said modern humans originated very recently, only 200 thousand years ago, in Africa, and then spread across the globe. The critics held firm that humans had been evolving gradually over 2 million years in many regions around multiple continents, across Europe and all the way into east Asia and south into Australia and down to Africa, developing their own regional differences.
The chief of the barbarians tearing at the walls was Milford Howell Wolpoff, a professor of anthropology at the University of Michigan since 1977 (a position he still holds today). Wolpoff was the chief and most vocal proponent of the Multiregional Hypothesis of human evolution, where he proposed that Homo erectus and H. ergaster migrated from Africa across the globe about 2 million years ago, and that modern humans evolved from local populations of these species over that time. He immediately attacked the Out of Africa hypothesis christening it “Out of Eden”, and continues attacking to this day.
In April, 1987, Robert B. Eckhardt of Pennsylvania State University wrote to Nature (wrongly) objecting that Cann et al. dismissed fossil evidence of regional evolution. In May 1987, Naruya Saitou and Keiichi Omotoo of the University of Tokyo also wrote a letter to Nature (correctly) complaining that mtDNA can be considered a single locus (like a single gene) and is insufficient to accurately reconstruct the human evolutionary tree.
Later that same year, Darlu and Tassy wrote letters to Nature as well as to Human Evolution and other journals, to rebut the claims for an African origin of modern humans. Several (valid) criticisms included that Wilson’s phylogenetic tree was not calibrated, had a small sample size, used African Americans to represent Africans, and objected to the midpoint method of constructing the tree.
Another important criticism from others was that Cann and Wilson used restriction fragments rather than the full sequence of mtDNA.
The criticisms came hard and fast and for years – and some of them were right. There were indeed weaknesses and holes in Cann’s analyses. The full mtDNA sequence is indeed better than using only RE fragment maps. Using other molecules in addition to mtDNA would have been better. Calibrating the tree is an important step in analyzing any molecular clock. And so on. Nonetheless, Cann et al. were ultimately right on their conclusions.
There was some support for the “African Eve” conclusion right after Cann’s 1987 paper was published.
For example, Stringer and Andrews wrote a paper in 1988 explaining the two competing hypotheses for the origin of modern humans. The Multiregional hypothesis had modern humans evolve from Homo erectus and ergaster over 2 million years in diverse locales scattered across several continents. Periodic cross breeding allowed a single modern species to evolve from such diverse groups. Such a model predicted that each population should have significant genetic differences between groups (like Asians and Europeans), and less differences within a group. Stringer and Andrews noted that the Out of Africa hypothesis (Cann’s paper) predicted that genetic differences within a group should be larger than differences between population groups. They pointed out that genetic analysis confirmed Cann’s hypothesis. Furthermore, they noted that fossil evidence also supported a single African origin of modern humans.
7. Buttressing the walls...
Four years after the first Eve paper by Cann et al., Wilson’s team published a follow up paper in the journal Science in 1991 with Linda Vigilant as the lead author.
Today, Linda Vigilant is married to Svante Paabo, a Swedish evolutionary geneticist famous for sequencing the entire Neanderthal genome. They both currently work at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. In the 1980s, Paabo was secretly studying and writing about the DNA of Egyptian mummies, fearing what his Ph.D. advisor would say. Paabo was supposed to be studying virus DNA for his thesis. But he was fascinated with the idea of getting DNA from ancient mummies and sequencing them. Paabo then learned that a team at Berkeley had sequenced DNA fragments from an extinct horse called a quagga, sampling a hide from the National History Museum of Mainz, Germany. The leader of the quagga sequencing team was Allan Wilson. Paabo published his mummy DNA paper, which became the cover article in Nature, and then moved to Berkeley to work for Wilson. Paabo and Vigilant met in Berkeley at the time, but did not marry until the late 1990s after they had moved to Leipzig.
The focus of Vigilant’s paper was to present data on the mtDNA sequences from 189 individuals including 121 Africans from across five regions of Africa. Many of the criticisms of the 1987 Cann et al. paper were specifically addressed by Vigilant: in the new paper she established a rate of evolution, calibrated their molecular clock with chimpanzee mtDNA, used native Africans instead of African Americans, used full mtDNA sequences rather than RE digest maps, and applied rigorous statistical tests.
Furthermore, Vigilant and team used a new and more powerful computer program to generate the new tree. The program, Phylogenetic Analysis Using Parsimony or PAUP was written by David Swofford then at the Illinois Natural History Survey in Champaign Illinois.
Vigilant’s paper confirmed both the African origin of modern humans and the age of the common mtDNA ancestor at approximately 200 thousand years, as in the 1987 paper.
Vigilant’s paper was published in September of 1991. Wilson had died of leukemia in July of that year. He was 56 years old.
8. Savages circle ‘round the wagons…
The new posthumous efforts by Wilson’s lab did not dampen the critics.
In January 1992, Alan Templeton published a letter in Science, the same journal that published Vigilant’s paper. Templeton reported that he re-analyzed the same mtDNA sequence dataset used by Vigilant et al. and got a different tree. The key argument was that Vigilant only did a single run of the program PAUP to generate her tree, and entered the data in a sequential order. Templeton argued that many runs of the program with randomized entry of the data was necessary to generate better and more accurate trees.
In the same letters section of Science, another group also wrote a dissenting letter which was signed by Blair Hedges, Sudhir Kumar, Koichiro Tamura, and most importantly, by Mark Stoneking. Stoneking was co-author of both papers by Cann and Vigilant, and had been a Ph.D. student and post-doc in Wilson’s lab.
Mark Stoneking is currently Group Leader at the Max Planck Institute for Evolutionary Anthropology in Leipzig, the same group where Vigilant works with her husband Paabo. Since Stoneking co-authored both Wilson Lab papers on Mitochondrial Eve, his apparent recantation caused the popular media to celebrate the death of Mitochondrial Eve.
‘”African Eve” Backers Beat a Retreat’ crowed one editorial headline in the top-tier journal Science, where Vigilant published her paper.
Another powerful criticism came from David Swofford, the author of the PAUP software used to create the phylogenetic tree in the Vigilant et al. paper. Swofford joined two top Harvard researchers David Maddison and Maryellen Ruvolo in a paper that echoed Templeton, in saying that many randomized runs were necessary to get the best results from his software.
Other critics came pouring out of the woodwork in papers by Takahata in 1991, Nei in 1992, Langaney et al., in 1992, and many, many more.
There were some supportive papers as well, such as by Klein in 1992, Deacon in 1992, and Tamura and Nei in 1993. And bizarrely, Stoneking wrote supportively of Vigilant’s results after publicly denouncing them a few months earlier.
An important paper was published by Stanley H. Ambrose in 1998 in the Journal of Human Evolution. Ambrose showed that a six-year long volcanic winter caused by the super-eruption of Toba, Sumatra caused a population crash and a genetic bottleneck, and may have accounted for such a low overall human genetic diversity. This helped to explain how modern humans originating in Africa, isolated into small groups by the volcanic winter, could have differentiated so quickly into modern races.
The papers that came out of Wilson's lab in 1987 and 1991 were indeed flawed and many of the critics were technically correct in calling out the errors. Furthermore, Wilson’s Lab did the right thing in addressing many of the criticisms. Despite the imperfect nature of the original paper and even the improved second paper, Wilson and his colleagues were correct in the most important points of their research: that modern humans originated in a small region of southern Africa approximately 200 thousand years ago, and spread across the African continent and then the globe.
We can ask: how it is that Wilson could have remained so steadfast in his convictions and research efforts amid such pointed and competent criticism? Was it merely pig-headed stubbornness? Or was it a rationally informed and defensible minority position? Here is how I view it. I interpret all the negative criticism of Wilson’s work as essentially saying: Wilson’s flawed analysis added a large amount of noise and uncertainty making it impossible to draw conclusions. But I believe Wilson was able to maintain his course because the mtDNA signal was strong enough to cut through the excess noise. Yes there was noise, yet he could still draw conclusions. The tremendous differences in the African mtDNA was so much greater than the variation in all other populations, it was like a beacon to Wilson’s team. Africa was the origin.
An analogy might be identifying the position of the sun and stars in the sky. In this analogy Wilson made a single measurement during a cloudy day, and reported the position of the sun and stars. His critics correctly pointed out that Wilson should have made multiple measurements, on clear days and clear nights using a calibrated device. But Wilson was correct about the position of the sun because its signal was strong enough to cut through the clouds. Meanwhile, Wilson’s critics made the more fundamental error of throwing the baby out with the bathwater.
This view also puts Stoneking’s multiple apparent reversals into perspective. Stoneking could co-author both Cann and Vigilant papers from the Wilson Lab, yet months later concede with critics, in writing, that certain points of their analysis could have been done better. Because on those points the critics were right. And then a few months later he could publish another paper supporting the core claims of a recent African origin of modern humans, because the sun burned its beacon through the clouds. Because on the most important points, Wilson and his team were right.
9. Where are we with Eve today…
Starting with a paper by Wainscoat et al. in the journal Nature in 1986, independent studies on human gDNA accumulated in support of the Out of Africa mtDNA studies by Wilson’s group. These are the other molecules needed to improve the molecular clock, which Wilson's team should have included.
Dating methods improved especially starting in the mid 1980s. Thermoluminescence dating in particular proved to be key in dating artifacts and sediment associated with modern human fossils and showed that African human fossils were older than humans outside Africa.
In 2000, Sally McBrearty and Alison Brooks put a stake in the heart of the multiregional hypothesis of anatomically modern humans, placing our origins firmly in Africa. The multiregionalists argued that modern human behaviors arose suddenly and almost simultaneously throughout the Old World around 40-50 thousand years ago. McBrearty and Brooks showed that the same evidence of modern human behaviors were also found in Africa, but tens of thousands of years before the Old World. This mirrored the findings of modern human fossils in Africa over a hundred thousand years before they arrived in the Old World.
Other reviews agreed that both anatomical and behavioral modernity in humans originated in Africa and that modern humans only migrated to the rest of the world after they were established in their home continent.
In 2007, Andrea Manica et al. reported on their work where they made 37 different measurements of 4,666 male skulls. These skulls represented 105 global populations. The goal of this work was to definitively and statistically distinguish between the single-origin hypothesis (Cann et al. and Vigilant et al.) and the multiregional hypothesis (Wolpoff et al.). The analytical methods were the same as for the genetic data, but the skull measurements were input into the software instead. The skull measurements strongly supported a single African origin for modern humans, and failed to find even a second origin, firmly denying the multiregional hypothesis.
In 2008 a review in the journal Nature by J. H. Relethford moved the debate forward. Relethford emphasized all the evidence for a Recent African Origin of anatomically modern humans. Modern humans, he said, then expanded out of Africa into the Old World. The debate, he said, was now about what happened next. Did modern humans extinguish and replace the archaic humans, such as Neanderthals? Or did some genetic mixture happen?
In 2016, a wide-ranging review by Chris Stringer in Philosophical Transactions B also discussed modifications to the Recent African Origin model. Emerging data showed gene flow between Neanderthal, Denisovan, and H. sapiens outside of Africa. The date of human origin was again placed firmly at 200 thousand years ago, as in Wilson’s original papers.
More controversies were on the horizon. A 2017 Nature paper by Hulin et al. reported on the discovery of a new cache of apparently modern human fossils in Morocco, in a cave complex in Jebel Irhoud. Thermoluminescent dating established the fossils at about 315 thousand years old. The skulls had a mosaic of anatomically modern humans with more primitive features. The authors concluded that the evolutionary process leading to modern H. sapiens occurred over the whole African continent, not in a limited locale. This, ironically, is called the African Multiregional hypothesis, somewhat combining the two formerly diametrically opposed positions.
In October of 2019, a Nature paper by Chan et al. reported on mtDNA data, claiming the largest assembly of 1,217 mitogenomes (complete sequences of mtDNA) from modern southern Africans. Their conclusion was that anatomically modern humans originated in southern Africa where they remained for at least 70 thousand years until climate change forced the first migrations, first to the northeast, and then to the southwest.
In retrospect, after over three decades, we can see Wilson was right even though he was wrong. He and his team readily conceded where they were wrong, acknowledged their critics, amended their studies, and yet stuck to their hypothesis of our recent African origin. Eventually most of the paleoanthropology field converted to Wilson’s views, much like T.H. Huxley converted to O.C. Marshes views of evolution after seeing his fossil horse series.
We see a couple holdouts like Wolpoff, still defending multiregional evolution to this day. Some might dismiss them as cranks or racists. We have to remember, there is much more detail and complexity to the story of how the field of paleoanthropology converted to the Out of Africa hypothesis. Would any of us have been a Wilson or a Wolpoff in their place?
So where are we with Eve today?
Eve herself appears to have faded behind the clouds. More important is that the Sun burned through the same obscuring clouds, signaling Africa as the recent birthplace of modern humans. As we develop more fossil and genetic data, we learn that our evolution is even more complicated, like we learned that horse evolution is messier, bushier, than O.C. Marsh’s simple linear model. We carry within us small amounts of DNA from ancient hominids, evidence of infrequent but close relations with Neanderthals and Denisovans and perhaps others yet to be discovered, as we encountered them. So, the story of our origins continues to unfold with yet more and more complexity and beauty and wonder the deeper we look, like falling endlessly into a Mandelbrot set.
