Anthropology & the Replacement Hypothesis
Mitochondrial Eve debuted January 1988, when Newsweek’s cover depicted “The Search for Adam and Eve” (Tierney 1988), reporting on a paper entitled Mitochondrial DNA and human evolution (Cann et al. 1987). The research purported all contemporary humans could be traced to relatively recent African origins, maybe even with a common mother. This mother became known as Mitochondrial Eve or African Eve. This research spurred the idea of a “replacement hypothesis.”
The Mitochondrial Eve model postulated all contemporary humans derived from a lineage of anatomically modern humans, evolved in Africa around 150,000 years ago and then spreading all over the world. They named this the replacement hypothesis or out-of-Africa II because these anatomically modern humans seemed to have fully replaced the earlier populations who had migrated from Africa about 1.8 million years ago, such as the Neandertals and Homo erectus populations in Asia. The replacement hypothesis and Mitochondrial Eve left little or no room for interbreeding, claiming no genetic evidence for contributions from Neandertals or other early hominids.
Initially anthropologists resisted a model derived purely from genetic evidence. Anthropologists studied fossils, and favored a model that emphasized gene flow and interconnection across the hominid species range. Known as the “multiregional model,” it was first proposed in 1946 by Franz Weidenreich, and then later developed and defended by Milford Wolpoff. In this model, early hominids and anatomically modern humans are all part of a single interbreeding species, with evolution occurring across the range (see Templeton’s Genetics and Recent Human Evolution 2007:1509 and previous section Denisovans, Neandertals, Archaics as Human Races).
Weidenreich’s 1946 book, Apes, Giants, and Man, also has a devastating critique of racial classification with regard to so-called racial “purity.” The critique is sometimes hidden under prose and photos that might seem race-centered to contemporary readers, but the text clearly demonstrates interconnectedness and how racial typologies are impossible–which would make sense under a properly-understood multiregional framework (see blog-post Race is a Social Construction for more on anthropology’s homegrown critique of race–long before the genetic evidence).
However, after initial resistance, scientific consensus and most anthropologists shifted toward the replacement hypothesis and Mitochondrial Eve. The replacement hypothesis became dominant in textbook models of human evolution, while Mitochondrial Eve nearly became a pop icon. Most students either never learned about the multiregional model, or if they did it was an impoverished and inaccurate version of it. “The out-of-Africa replacement hypothesis became the model of human evolution, particularly in undergraduate textbooks and the popular science literature” (Templeton 2007:1508). Ironically, the replacement hypothesis replaced all other accounts.
There were a number of reasons why anthropologists gravitated to the replacement hypothesis and embraced Mitochondrial Eve:
Mitochondrial Eve Won Scientific Consensus
Following the original research, more studies seemed to disprove any genetic connection between contemporary humans and Neandertal or other archaic groups. The genetic evidence seemed more dazzling, more precise, and more computational than messing with fossils. As Robert N. Proctor observed, in an insightful and quite funny 2003 overview, “it seems pretty clear that the Out-of-Africanists are winning the field. Multiregionalists have no technical wonder comparable to sequencing, and the original mitochondrial evidence has been joined by other evidence” (Three Roots of Human Recency, 225).
Mitochondrial Eve Slays Dreaded Candelabra
Since the 1960s anthropology has been haunted by the candelabra model proposed by anthropologist Carleton Coon. The candelabra hypothesis asserts Homo erectus dispersed from Africa about 1.8 million years ago, and then Homo sapiens evolved separately in Asia, Africa, and Europe. This model is scientifically wrong but persists in popular imagination and supports racist thinking. Many anthropologists were eager to fully excise and deny the candelabra model–the out-of-Africa replacement hypothesis through Mitochondrial Eve offered a simple way to dispense with an unfortunately persistent idea.
Mitochondrial Eve Allied Anthropology with Lewontin and Gould
As noted in the section on Race Revival–Attacking Anthropology, the work of geneticist Richard Lewontin was very helpful for arguing against the genetic separation of human groups. Lewontin and especially Stephen Jay Gould explicitly embraced the replacement hypothesis. Many anthropologists had already promoted Gould’s open-ended view of evolution. Mitochondrial Eve helped cement the alliance.
Anthropology Likes Africa
Some of the best anthropology documents human and natural richness in Africa. But for the rest of the world, Africa gets ignored, misrepresented, left off the map. Afflicted by poverty, inequality, military conflicts, and HIV-AIDS, sub-Saharan Africa has been sadly omitted from a globalizing world, seen as a hopeless basket case. By stressing the out-of-Africa replacement hypothesis, anthropologists could re-assert African primacy, contributing to ideas that “we are all African” or that everyone is indigenous to Africa. As Proctor notes, “Some people seem to like the fact that we are all ‘Africans under the skin’” (2003:225).
In 2010 the tide turned. An innocuously-titled study A Draft Sequence of the Neandertal Genome documented Neandertal contributions to contemporary humans (Green et al. 2010). Then, perhaps even more dramatically, researchers found that the archaic human remains found in Denisova Cave in Siberia also found some genetic match in contemporary humans (Reich et al. 2010; Zimmer 2010). Homo sapiens interbred with both Neandertals and Denisovans, and the results show up in contemporary genome sequences. “‘It’s hard to explain how good I feel about this,’ says Wolpoff, who says that seeing complete replacement falsified twice in 1 year was beyond his wildest expectations. ‘It was a good year’” (Gibbons 2011:393-4, A New View Of the Birth of Homo sapiens). Of course, these studies do not prove a lot of interbreeding–it took some very sophisticated techniques to demonstrate any interbreeding at all–but the idea of no contribution from Neandertals, or that archaic populations are entirely separate species from modern humans, is no longer defensible. And as of 2012, the admixture findings continue to come in, with archaic African DNA from a “mystery group” entering the picture.
These findings will take some time to filter into the textbooks, Genetic anthropologist John Hawks wrote in 2011 that “a large-scale reorganization of the science of human origins is upon us.” However, “the shifting landscape has caught many geneticists off their footing” (Population structure within Africa).
Or as Libby Cowgill put it:
In introductory classes to biological anthropology, both instructors and the authors of numerous textbooks have been tempted to present the origin of modern humans as two equally plausible, mutually exclusive evolutionary scenarios: the Out of Africa hypothesis and the Multiregional Evolution hypothesis. These models can be expressed succinctly on a single PowerPoint slide, have historically been both suggested and supported by influential scholars in the field, and can be massively simplified for undergraduate consumption and, hopefully, comprehension. The good news is this: we can stop doing this now. The bad news is that a more current representation of the consensus that most researchers have reached is likely to be more complex and convoluted. In addition, it can likely only be represented by models of human evolution destined to befuddle introductory students everywhere, complete with multiple slides, wandering migration arrows, question marks, and unapologetic blank spaces. (One Year in Biological Anthropology: Species, Integration, and Boundaries in 2010, 214)
The 2010-2012 studies could have been a boon to anthropology if we had defended the multiregional model, but they now put some standard anthropological accounts in an awkward position. Embracing the replacement hypothesis and Mitochondrial Eve–without further developing the multiregional model–leaves anthropology needing to reconfigure a response.
In retrospect, embracing the replacement hypothesis and Mitochondrial Eve was very problematic for anthropology. Although these problems should have been more obvious earlier, they are painfully clear in 2012:
Talking about Mitochondrial Eve was not good for promoting evolution
This aspect may not be on the map for those who are debating scientific hypotheses, but I grew up with people who used the 1988 Newsweek Mitochondrial Eve cover to assert that scientists were going to eventually come around and prove the Biblical account of divine creation. Again, this may seem strange to those steeped in DNA sequencing, but the part about hominid and Homo sapien evolution is the most difficult for many people to swallow. Talking about any kind of Eve, even a Mitochondrial Eve, does not help. Moreover, the acrimonious debate let a lot of people tune out, contributing to an idea that scientists simply have no idea what was going on. The brilliant parody Anthropologists Trace Human Origins Back To One Large Goat (2011) in The Onion captures how many people view these debates, and see also the teaching materials in the blog-post Living with Darwin.
Anthropology denied a richer, home-grown model of human evolution
The replacement hypothesis and Mitochondrial Eve offer a simple model of human evolution. It is easy to explain, and it eliminates the candelabra justification for race-thinking. Multiregional evolution is more complex and difficult to diagram. There is more room for misinterpretation. However, as Alan Templeton convincingly explains:
Weidenreich (1946) argued that regional populations could display differences, and some local differences could persist through time in the same locality, but there is no assumption of independent, parallel evolution. Instead, humanity consists of a single evolutionary lineage with no subbranches because humanity’s geographically dispersed populations were and are interconnected by gene flow and lines of recent, not ancient, common descent due to this gene flow. (2007:1509).
Moreover, by embracing the replacement hypothesis and Mitochondrial Eve, anthropology went along with the trend of reducing all biological evolution to genetics. Anthropology had fossil evidence and forms of analysis different from the dazzle of genetic computation. What genetic computation cannot deliver is the full range of the evolutionary process, where evolutionary change can occur with or without genetic modification. As Tim Ingold has theorized:
Much genetic change occurs without any corollary on the level of form or behaviour; conversely, significant morphological or behavioural transformation may occur without any corresponding changes in the genome. We have seen that since organisms, in their activities, can modify the conditions of development for successor generations, developmental systems–and the capacities specified therein–can go on evolving without requiring any genetic change at all. Nowhere is this more evident than in the evolution of our own kind. (2000:385)
Indeed, by changing the conditions of the environment for later migrations, those early migrants from Africa were contributing to the evolutionary selection process.
The replacement hypothesis looks like colonization and domination
The replacement hypothesis is perhaps less racially charged than the candelabra model, but the idea that anatomically modern humans set out from Africa and then replaced all other populations is one of colonization and domination. Advocates for replacement have been quick to say replacement could occur without any warfare or interaction–it may only depend on a small difference in reproductive success–but it is nevertheless congruent with ideas of dominance and subjugation:
It is striking how accurately this [out-of-Africa] hypothesis mirrors the story of global colonial conquest by White Europeans so much favoured by Darwin and his contemporaries. The story may have been turned upside down, but the structure is the same: one dominant race, equipped with superior intelligence, supersedes the rest. (Ingold 2006:278)
Or, as Proctor noted the rhetoric on both sides:
The different rhetorical strategies used by replacement versus multiregionalist theorists are interesting in this context, given that each side has tried, at various points, to accuse the opposing camp of being more racist. Out-of-Africanists have accused multiregionalists of exaggerating racial divisions (conceived as going back as far as a million years in some candelabra models); multiregionalists in turn have accused Out-of-Africa advocates of implying a total and perhaps violent (genocide-like?) replacement of H. erectus (or Neanderthals) by H. sapiens. (Proctor 2003:224-5)
Stephen Jay Gould seriously distorted the multiregional model
The original authors of the Mitochondrial Eve research in 1987 lumped Wolpoff and Weidenreich’s model together with the candelabra model from Coon. Textbooks perpetuated this error, portraying multiregional evolution as candelabra with some gene flow. “There is no doubt that Cann et al. (1987) equated multiregional evolution to Coon’s model of parallel evolution of isolated archaic populations. . . . However, as is clear from Weidenreich (1946) and many subsequent papers by Wolpoff and his associates, parallel evolution was never part of the multiregional model, much less its core” (Templeton 2007:1510).
Stephen Jay Gould never understood the multiregional model, and he repeatedly and unfairly jabbed at the model and at Wolpoff:
Multiregional evolution should be labeled iconoclastic, if not a bit bizarre. How could a new species evolve in lockstep parallelism from three ancestral populations spread over more than half the globe? (Gould 2002 cited in Templeton 2007:1510)
By allying with Gould, anthropology did not defend one of our own from unfair characterizations. (See blog-post Mismeasuring Gould in “The Mismeasure of Science.”)
Out-of-Africa became Escape-from-Africa
Anthropologists may have hoped the out-of-Africa hypothesis with a Mitochondrial Eve in Africa would bring much-needed attention to sub-Saharan Africa, as a celebrated cradle of humanity. It did not. Instead, people began to imply that leaving Africa was a good thing. “I call this ‘Out-of-Africa: Thank God!’ to point to the presumption that hominids became human in the process of leaving Africa–a slight that seems always unintentional, yet is surprisingly common. . . . Leaving Africa has become a troubling focus of a great deal of research and popular celebration” (Proctor 2003:225-226).
In 2011 New York Times reporter Nicholas Wade raised this slight to an insult, writing about “when and how modern humans escaped from their ancestral homeland” (Tools Suggest Earlier Human Exit From Africa). Modern humans did not escape! There were migrations out of Africa, within Africa, and people also migrated back into Africa.
Extreme versions of Mitochondrial Eve and the replacement hypothesis are gone. It is time to recapture the complexities of anthropological models. It is time to go back to Wolpoff’s statement from the 1988 Newsweek article: “we have a long history of people constantly mixing with one another and cooperating with one another and evolving into one great family.”
2017: More Homo sapien Surprises
In June 2017, Carl Zimmer reports that Oldest Fossils of Homo Sapiens Found in Morocco, Altering History of Our Species. Indeed, this re-setting of the clock–with Anatomically Modern Humans debuting in Morocco around 300,000 years ago–should be yet another blow to the Mitochondrial Eve ideas. However, it should very much support that the first modern humans originate in Africa. Of particular interest is the idea that “our species may have been evolving as a network of groups spread across the [African] continent.” Again, this should support a re-examination of the multi-regional trellis model of human evolution.
For more updates, see:
- 2018: At the very end of this post for the section titled “Out-of-Africa became Escape-from-Africa” I discussed one of the problematic aspects of Mitochondrial Eve and the replacement hypothesis. In January 2018, I asked for support Dr. Holly Dunsworth as she took on the overtones from news reports on how Modern humans left Africa much earlier:
For anyone looking on and wondering: Not only is “exodus” unscientific but it belongs in and supports the very real racial/racist narrative out there in the world where human origins is explained as if “modern humans” had to get the hell “Out of Africa.” We have to do better. https://t.co/GQ6cuuP3DV
— Holly Dunsworth (@HollyDunsworth) January 26, 2018
The quote from Robert N. Proctor’s Three Roots of Human Recency (2003) remains relevant: “I call this ‘Out-of-Africa: Thank God!’ to point to the presumption that hominids became human in the process of leaving Africa–a slight that seems always unintentional, yet is surprisingly common. . . . Leaving Africa has become a troubling focus of a great deal of research and popular celebration” (Proctor 2003:225-226).
- Kathleen Fuller, Pathological Science and mtEve (September 2012; and see comment below)
- Jonathan Marks, My Ancestors, Myself (November 2012)
- Carl Zimmer, Interbreeding With Neanderthals (March 2013)
- Daniel Stolte, Human Y chromosome much older than previously thought (March 2013)
- Alan R. Templeton, Revolutionizing the “Out of Africa” Story (April 2013)
To cite: Antrosio, Jason, 2013. More Mothers than Mitochondrial Eve. Living Anthropologically, https://www.livinganthropologically.com/biological-anthropology/mitochondrial-eve/. Last updated 26 January 2018.
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