When they discuss the Out of Africa (OOA) theory, scholars use DNA samples taken from contemporary, modern, existing populations, and add some (very few) ancient DNA samples to the dataset. However, are we certain that the modern genetic landscape reflects events that happened 60,000 to 100,000 years ago (60-100 ky)? And, more importantly, how old are these "ancient" DNA samples, belonging to ancestral humans.
DNA decays as time passes, the chemical bonds in the molecule break down due to the action of water, oxygen, temperature, and the pH of the soil in which the remains were preserved. So, we have relatively few samples of ancient modern human DNA. These "oldest" ones are: the Ust'-Ishim DNA from a man who lived in what is now western Siberia, Russia, around 45 ky ago. This is the very oldest of all specimens. The oldest East Asian sample is from Tianyuan, China, close to modern Beijing, roughly 39 to 42 ky old. In Europe proper, the sample from Czechia known as Zlatý kůň which are said to be 45 ky old (more on its age below). But, what about Africa, the purported cradle of mankind? The oldest DNA sequenced in Africa is roughly 18,000 years old, and comes from the Mlambalasi site, in Tanzania (source), the dates are not direct radiocarbon ones, but "...well constrained to the Late Pleistocene based on multiple indirect dates" Not so old after all!
Why is this relevant? The importance of ancient samples is that these people harbor, at least in Eurasia, Neanderthal admixture, at higher levels than current populations (as they were closer in time to the admixture event, and also, because depuration of harmful introgressed alleles hadn't had much time to take place). They also carry signals that were lost in later populations. But, in the case of Africa, we are lacking really old DNA, so all arguments about "diversity", "divergence" and distinctness are based on modern, living Africans. These contemporary people could have undergone admixture events with archaics, suffered selective adaptation, accelerated mutation rates over the past 45 ky, that altered their genetic makeup, so current comparisons may be misleading.
A look at the really ancient DNA in Eurasia
Eurasia has provided several samples older than 35,000 years and the DNA extracted from these individuals has paint a complicated migration process out of Africa. I can only imagine what surprises really ancient DNA samples from Africa would reveal.
A five-year-old paper, published by Prüfer K, Posth C, Yu H, et al., titled A genome sequence from a modern human skull over 45,000 years old from Zlatý kůň in Czechia (Nat Ecol Evol. 2021 Jun;5(6):820-825. doi: 10.1038/s41559-021-01443-x. Epub 2021 Apr 7. PMID: 33828249; PMCID: PMC8175239)🔓, reports the genetic makeup of the oldest European modern humans. Of course, as with all genetic publications, the Out Of Africa event is taken for granted and buttressed by each additional paper (even when there is no direct link between OOA and the study in question).
In this sense, this paper explains that "Modern humans expanded into Eurasia more than 40,000 years ago following their dispersal out of Africa. These Eurasians carried ~2–3% Neanderthal ancestry in their genomes, originating from admixture with Neanderthals that took place sometime between 50,000 and 60,000 years ago, probably in the Middle East. In Europe, the modern human expansion preceded the disappearance of Neanderthals from the fossil record by 3,000–5,000 years." In one streak they constrain the date of human expansion into Europe and Asia to 40 ky ago, and limit the admixture with Neanderthals to the Levant, ~50-60 ky before they expanded across Eurasia.
Interstingly this woman from Zlatý kůň "...belonged to a population that appears to have contributed genetically neither to later Europeans nor to Asians". A lineage that became extinct.
In this, she wasn't alone. The Ust'-Ishim person has no direct descent among contemporary Eurasians. This lineage also died out.
Another population, identifided by three individuals 42,580 to 45,930 years old, discovered in Bacho Kiru Cave, Bulgaria didn't contribute to the later European populations either, however they "are more closely related to present-day and ancient populations in East Asia and the Americas than to later west Eurasian populations." (Hajdinjak, 2021). They shared alleles with Oase 1, ancient Siberians, Native Americans, and the Far Eastern, 40,000 year-old Tianyuan man from China (who also shared his alleles with other populations: Amerindians and modern Asians).
This suggests a pan-Eurasian population of modern humans, spanning the continent from the Balkans to Eastern China (Oase 1, Tianyuan and Bacho Kiru are samples from it) with high levels of Neanderthal ancestry as we will see below.
The authors discuss the levels of Neanderthal introgression in Zlatý kůň and note that even though it is found at ~3%, similar to other specimens, like Ust'-Ishim (Note, however, that an old specimen from Europe, Oase 1, 40,000 years old, has two to three times those levels: 6 to 9% Neanderthal admixture) these are longer chunks, so they take this to signify that these segments didn't have time to break down into smaller segments (they are longer than those found in similar-aged Ust'-Ishim). This fact leads them to conclude that "... this individual from Zlatý kůň is one of the earliest Eurasian inhabitants following the expansion out of Africa". As you can see, this assumes OOA is a fact. Let's get some details.
Age of Zlatý kůň
When the remains of this woman were found, they were estimated to be 30,000 years old based on faunal remains and stratigraphy. However, radiocarbon dating gave much younger dates!: "direct radiocarbon dating resulted in a much younger date of ~15 ka (12,870 ± 70 years bp; GrA-13696)... In an attempt to clarify [its] ... age... , we radiocarbon dated a cranial bone fragment, resulting in a significantly older date of ~27 ka (23,080 ± 80 years bp; MAMS-36077)... A third date, ... produced a younger date of ~19 ka (15,537 ± 65 years bp; OxA-38602)." These young dates were attributed to contamination so they tried another method and tested an amino acid (hydroxyproline) from the bone collagen. It gave them a similar (young) date of ~34 ka (29,650 ± 650 years bp; OxA-38022). Finally (seeking something to provide a really older date) the authors used a phylogenetic tree by comparing the mt DNA from the Zlatý kůň woman, and assigned it to haplogroup N and comparing it to mtDNA from the Bacho Kiro site in Bulgaria (43 to 47 ky old) they reckoned that this fossil was roughly 43,000 years old (31.5–52.6 ky). It had to fit, by hook or by crook. So they got the old date they were looking for.
The Neanderthal "twist" to obtain an even older age
The oldest samples of DNA with Neanderthal admixture in Eurasia are, the Oase 1 (40 ky), Ust'-Ishim (45 ky), and this Zlatý kůň ("45 ky"). The level of Neanderthal introgression in other old remains from Eurasia are around 3%. All, except one, Oase 1 who lived 40,000 years ago, had a very high Neanderthal component. The authors try to explain this fact away: "Oase 1 carried more Neanderthal ancestry (6–9%) than other modern human genomes sequenced to date, owing to admixture with Neanderthals that occurred within the six generations before the individual lived."
The paper reporting Oase 1 gave (see Table 5) its average Neanderthal content as 7.11%, Ust'-Ishim as 3.08%, Kostenki 14 as 2.18% (Romania, 37 ky old), The Bacho Kiro ubduvudyaks carried 3.8%, 3.4%, and 3.0% respectively. Finally, Tianyuan, in China carried 4% to 5% (Yang, 2022) of Neanderthal alleles.
Compared with these, the 3.2% of the Zlatý kůň is normal and there is nothing unusual about it. So the authors tried another track.
They found that "Zlatý k&367;&328; shares more alleles with Asians than with Europeans." Which is not unusual all of these ancient Europeans are part of a pan-Eurasian population. But they explain it differently: modern Europeans originated in a "deeply divergent out-of-Africa lineage referred to as basal Eurasian" found mainly in the Caucasus, Levant and Anatolia. While all ancient European specimens don't carry any traces of this lineage.
Basal Eurasians
This population somehow did not admix with Neanderthals, and later replaced all of the ancient populations (those carrying high Neanderthal admixture).
The Basal Eurasian ancestry is strange; it carries "... little if any Neanderthal admixture and... separated from other non-African lineages prior to their separation from each other" (Lazaridis, 2016) because they split "from other Eurasians before the latter received Neanderthal gene flow" (Feldman, 2019)
So there is a population that left Africa and never mixed with Neanderthals (Basal Eurasians), one that moved into Europe and Asia, all the way to China (Zlatý kůň, Ust'-Ishim, Oase 1, etc.) mixing with Neanderthals, but they did so before the rest of the Out of African population moved east and north into Eurasia. Complicated scenario.
The authors argue, based on their data, that "Zlatý kůň falls basal to the split of the European and Asian populations... This suggests that Zlatý kůň was part of a population that split earlier from the population that later gave rise to Ust’-Ishim and other Eurasian populations."
The longer vs. shorter "chunks" of Neanderthal DNA found in Zlatý kůň is used as an argument to support its older age, and closeness to the Neanderthal introgression, but there are factors that could cut the admixed DNA into smaller pieces beyond recombination caused by the passage of successive generations. For instance, natural selection could have maintained long segments in Zlatý kůň because they provided an adaptative advantage, or these people were part of a larger population, which reduced the impact of genetic drift and segment shortening.
Veller, 2023 notes that demography also influences recombination (shortening of introgressed segments), populations don't admix in an instantaneous pulse, they mate over time, and mates are not randomly assigned, they may be chosen (non-randomly, or "assortative mating) and this reduces recombination's effects and the purging, or loss of introgressed segments. Choosing a mate with similar ancestry adds introgressed segments to the mix, reducing recombination and segment shortening. This effect could have acted among the people at Zlatý kůň preserving longer segments and causing the impression that they are older, when, in fact, they are not.
Comments
Out of Africa is painted as a simple migration that caused loss of genetic diversity due to founder effect and bottlenecks followed by admixing with Denisovans in the East, and Neanderthals in the West. As we have seen, this picture is oversimplified. The intermingling of ancient Eurasian lineages and modern humans were complex, with extinctions of local populations (this paper adds that the replacement of the original Eurasians by the Basal Eurasians was probably due to a massive volcanic event c.39 kya that altered the environment in Europe, the Campanian eruption, in Naples, Italy).
Africa, on the other hand has few, and very recent DNA samples. The discovery and analysis of older samples will surely make us rethink the Out of Africa theory and the origin of moden humans.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2025by Austin Whittall ©
