PtERV 1 a fact that marks the difference between humans and African apes

In a previous post, I mentioned the strange virus that infected all African great apes, but didn't affect humans, it is known as PtERV 1.

PtERV 1 is an endogenous retrovirus found in chimpanzees (Pan troglodyte). And it gets its name from the initials of Pan troglodyte endogenous retrovirus (PtERV).

Let's first explain what it is.

Retroviruses are a type of virus (an example is HIV, that causes AIDS) that instead of store their genetic information as RNA. They differ from other virus because when a retrovirus infects a cell, it uses a special enzyme called reverse transcriptase to convert its RNA into DNA (hence its name "retro", from this reverse transcription). This DNA is then inserted into the host's DNA strand, and the cell reads it as if it was its own. In this way the cell makes copies of the virus, propagating it.

When a retrovirus is inserted into a cell that later becomes an egg or sperm, it can be passed on, within the cell's DNA, into the next generation, who inherit it as part of their genetic material. This is known as an "endogenous retrovirus" because it comes from within, inherited. The acronym ERV applies to Endogenous Retrovirus.

Humans carry ERVs in their genes, the outcome of ancient infections in our distant ancestral monkey relatives around 25 million years ago. But we don't carry the PtERV 1 variant. Neither do orangutans. The insertions are only found in African apes like gorillas, baboons, macaques, and chimpanzees.

Research (see Yohn, et al., 2005) reported that an ancient retrovirus infected "ancestral gorilla and chimpanzee lineages 3–4 million years ago", after humans had split from the lineage of chimpanzees. The infection took place at the same time, leading to very similar insertions into the genomes of gorillas and chimpanzees. PtERV 1 is also found in baboons and macaques, but there are differences between their genetics, suggesting a later infection ~1.5 million years ago, and by slightly mutated retrovirus.

We don't know which retrovirus caused this infection but it is likely a gammaretrovirus (there is no known gammaretrovirus that infects humans) and it shares roughly half of its genome with virus linked to leukemia in cats and rats (feline leukemia and murine leukemia viruses). The authors suggest that the infection was caused by a "retrovirus [that] was introduced into the great ape lineages by horizontal transmission, perhaps from contact with an ancient Old World monkey species."

Why didn't humans, or our Homo ancestors (H. habilis, H. erectus, etc.) become infected within Africa, as the virus spread among all other African apes and many Asian ones? Why were the orangutan and other Asian apes preserved from the infection?

• Not infected: humans, orangutan, siamang, and white-handed gibbon.
• Infected: African. Gorilla, bonobo, chimpanzee, Abyssinian black-and-white colobus monkey, olive baboon, gelada baboon, Hamadryas baboon, drill, mona, Black crested mangabey.
  Asian monkeys: rhesus macaque (South, Central, and SE Asia), Japanese macaque (Snow monkey), Sichuan snub-nosed monkey (Central China), Long-tailed macaque (SE Asia), Tibetan macaque, gelada baboon, , lion tailed monkey (India), Celebes macaque (Indonesia), Myanmar snub-nosed monkey (Myanmar and South China)



The following image, from Abu Eed, et al., 2025 (Fig. 7) shows in red, the monkey species infected with PtERV-1, in black, those that are not infected.







The paper speculates that the gorillas and chimpanzees were probably more susceptible, or that our Homo ancestors were resistant or immune (so were the Asian orangutans). Though, the orangutans lived far from Africa and distance could have preserved them, isolated from infection.




An interesting option is that "the lineage that ultimately gave rise to humans did not occupy the same habitat as the ancestral chimpanzee and gorilla lineages. An excursion by early hominids to Eurasia during the time that PTERV1 infected African great apes and then a return to Africa would explain this phylogenetic inconsistency." Or, may I add, if Homo originated in Asia, and evolved there, it may have entered Africa hundreds of thousands of years later, even millions, once the retroviral infection and its source had vanished. This would have protected them from infection. But, it does not explain why equally distant Asian monkeys caught it!




Since Into Africa or Out of Eurasia theories are not favored by mainstream scholars, the paper also suggests that population structure could have somehow preserved our ancestors from infection. But this explanation would require very large populations of humans and orangutans in comparison to those of gorillas and chimpanzees, which is unlikely.




Another option is considered briefly but quickly dismissed "the PTERV1 phylogenetic tree is inconsistent with the generally accepted species tree for primates, suggesting a horizontal transmission as opposed to a vertical transmission from a common ape ancestor.An alternative explanation may be that the primate phylogeny is grossly incorrect, as has been proposed by a minority of anthropologists [29]. This seems unlikely in light of the extensive molecular evolutionary data that have been collected over the last few years [5,25] that clearly place orangutan as the outgroup species to the human–chimpanzee–gorilla clade and Old World monkeys as an outgroup to the human/ape lineage."




The "antropologist" cited as [29] is: Schwartz JH. The evolutionary relationships of man and orang-utans. Nature. 1984;308:501–505. doi: 10.1038/308501a0. [DOI] [PubMed] [Google Scholar]




Comments




The most parsimonious explanation is that humans and our Homo ancestors evolved in Asia, in a region that was isolated from the infection. Orangutans may be closer to us, as suggested by Schwartz than chimpanzees. They too lived isolated from the other apes that caught it, or, maybe they share with humans some protecting factor.




My next post will look into Schwartz and his orangutan-human link.




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Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2026 by Austin Whittall © 

Chimp-Homo split in Eurasia?

Earlier this year, in my March 2nd post, I quoted Mansfield and Vaneechoutte, 2024 who put forward a new hypothesis about the split between Pan (chimpancees), Gorilla, and Homo. Instead of taking place in Africa, they argue that the split happened in Eurasia.

Since one of my recent posts dealt with the Chimpanzee-Human (Homo) spilt, assuming the orthodox view that it took place inside Africa, in today's post we will revisit the possibility of an Eurasian origin for the Homo genus.

Mansfield and Vaneechoutte's paper

In their article, Mansfield and Vaneechoutte elaborate on the lack of fossils inside Africa of a common ancestor for chimps, gorillas, and humans.

Focusing on the very early presence of apes in the Anatolia and the Balkans at 10 to 6 million years ago, they suggest that the closure of Gibraltar that led to the dissecation of the Mediterranean Sea (Messenian Salinity Event), and the very arid period that followed that event, forced the "separate branches of European hominids to migrate out of the Mediterranean region." This migration led the ancestors of gorillas and chimpanzees-bonobos across the dry seabed of the Mediterranean, from Greece, into Africa.

The authors believe that the ancestors of Gorilla and Pan entered Africa from Eurasia in two separate migratory events, and a third lineage, the one leading to Homo, and eventually to us, humans, moved in another direction into the Arabian Peninsula. There, these future Homo survived the hyperarid period that had forced them out of Europe.

Tectonic rifting led to thhe reopening of Gibraltar, and the vast Zanclean Megaflood that took place 5.3 million years ago modified the geography and cut-off potential routes of entry into Africa (like Sinai), by refilling the Mediterranean basin up, in just two years, and flooding the Sinai region and the Red Sea. Isolating the ancestors of Homo in a humid refuge in Arabia, isolated from all other apes.

The Pan lineage, of the chimpanzees and bonobos went deep into Africa and there, it split, with a branch evolving into the Australopithecines and the Paranthropus. These small-brained, small, primitive hominins are more adapted to a life in the trees than in the open savannas.

Homo, evolved, and produced the bigger, stronger, long-legged, brainier Homo erectus. This paper suggests that after the water levels dropped, coastal corridors and routes opened up, and these were used by erectus to walk westwards, into Africa, and east, crossing Eurasia from China and Indonesia, while the northern route through the Levant led to the Caucasus (Dmanisi) and Europe.

This theory was again put forward in a paper by Verhaegen, Munro, Bonne, Mansfield, & Vaneechoutte, 2026 (A hypothesis of ape and human evolution based on comparative biology and plate tectonics. Academia Biology, 4(2). https://doi.org/10.20935/AcadBiol8310) which is worth reading as it explains in detail the species, and gives a very good timeline for all these eventss.

Earlier, Böhme, 2017 had proposed an Eurasian origin of the Homo group and a Eurasian split between the ancestors of chimps and humans: suggesting that "the Pan-Homo split predated the Messinian and that the chimpanzee–human last common ancestor thrived in the Mediterranean region... major Miocene hominid radiations occurred outside Africa and endorse the hypothesis that the hominin clade arose in the Eastern Mediterranean."

However, these ideas are dismissed by mainstream scholars. I believe that the reason for this is that an African origin of Homo is crucial to the Out Of Africa theory.

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Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2026 by Austin Whittall © 

Evolution, divergence, chimps, bonobos, and humans

I often wonder why are chimpanzees and bonobos so similar to each other, at least on their external appearance, and seem to have evolved very slowly over the past two to three million years. Modern Humans, on the other hand, compared to our 3 million year old ancestors the Australopiths and Homo habilis are very different in our abilities and appearance.

Bonobos (Pan paniscus) are a species of ape that lives in the tropical rainforests of Western Africa in the Democratic Republic of the Congo (DRC). They are, together with the chimpanzees, the closest living relatives of human beings. The chimps, (Pan troglodytes) have a wider range in both territory and environment, from tropical jungles to savannas. They live in a wide swath across central Africa, from Guinea and Liberia on the Atlantic area of West Africa, through Mali, Sierra Leone, and across th heart of Africa (Habon, Congo, DRC, Cameroon, Ruanda, and Uganda) and into East Africa (Tanzania).

Chimpanzees and bonobos share a comon ancestor. They diverged into two distinct species between 2.5 and 1.5 million years ago. But, they don't seem to be all that different (on the outside).

It seems that, unlike humans, and our ancestors, they didn't admix with each other. The Congo River seems to have been a physical barrier that kept chimps and bonobos apart (Diogo, 2017).

According to Diogo, although bonobos and chimpanzees are different, the differences between them accumulated at a much lower rate than the differences that either species have with modern humans.

We grew apart, with us mutating faster than either of the Pan species: The rate vs. humans is over 2.5 times higher for the common chimpanzee and over 1.6 times higher for the bonobo, vs. their divergences between each other.

Remarkable difference, considering that we are said to share 98.7% of their genome with us (More on this "myth" further down).

Geographic range chimpanzees and bonobos. Adapted from Fig. 1 in Prüfer, 2012

Behavior-wise, bonobos and chimps are different. See Prüfer, 2012 and Wilson, 2021. Bonobos are more intensly sexual (and creative in that field too!), female dominated and less aggressive towards other bands; they retain the playful attitude of infancy even as they age. Chimpanzees are the opposite (aggressive males, hierarchical, competitive).

However, alpha bonobo males have more offspring than lower ranking ones, and even more than chimpanzee alphas, showing that even in matriarchal societies, there can be a polygynic bias.

Chimps use tools: stones to crack nuts, and wood spears to hunt monkeys or dig for roots. Bonobos don't. Chimps can kill their kin, bonobos don't

Based on these behaviors, it seems that modern humans share traits from both ape species.

Human-Chimp & Bonobo split date

I have always believed that the 6 million year (My) date assigned to the split between humans and Pan, is too recent (see this post). A recent study by Oliveira Coelho et al., 2026 (Parting ways: Pan-Homo divergence revisited) acknowledges that over the past decades, the date has been gradually pushed back "from ~ 6 Ma to ~ 8.5 Ma over the past 56 years" This is important because it impacts on the molecular clock, often gauged using this split date (take the genetic difference between Pan and us, and divide it by the time elapsed since we split, and you have the mutation rate. A more distant split implies a lower mutation rate).

However, fossils are not there! There is a gap in the fossil record spanning the period ~7 to 9 My ago.

Let's see what future research finds.

Similarity between Humans and Pan

A study by Yoo et al., 2024 (Complete sequencing of ape genomes) is quite clear that we are not 99% similar to them (highlight is mine): "The oft-quoted statistic of ~99% sequence identity between chimpanzee and human holds for most of the genome when considering single-nucleotide variants (SNVs) (Fig. 2b). However, comparisons of T2T genomes suggest a much more nuanced estimate. Examining the distribution of 1 Mbp aligned windows shows that the tail of that distribution is much longer with 12.5–27.3% of the genome failing to align or inconsistent with a simple 1-to-1 alignment, especially within centromeres, telomeres, acrocentric regions, and SDs." Structure and content don't seem to line up in the comparison leaving only a 87.5 to 72.7% similarity.

This is quite a spread, from 99% down to 72.7% is a big difference.

Interestingly, regarding the X to A ratio (mentioned in my previous post), Yoo et al., reported an extremely low value: "for the human–chimpanzee–bonobo ancestor (Ne=76,700, X-to-A ratio of 0.42)."

Are we descended from a common ancestor of chimps and bonobos? Or not at all?

We should bear in mind that when we compare humans with the Pan, we are looking at contemporary species, alive now. But we may be far more different from the last common ancestor (LCA) of both humans and chimpanzees-bonobos (Wilson). This LCA could be radically different from Pan and Homo.

The LCA also had a more Pan-like appearance than human. Sekhavati et al., 2025 analyzed the shape of human, hominin, and Pan feet, and found that it "supports the hypothesis of a Pan-like last common ancestor of humans and chimpanzees." Furthermore, the first purported ancestors of our human lineage "the Paranthropus and the Australopithecus africanus + Australopithecus sediba clades evolved arboreal characteristics, suggesting adaptations for arboreality." This is relevant as they are probably not our ancestors after all (more below).

In fact, the earliest human ancestors after the split, members of the Homo group, are probably misclassified as such; I am refering to the Homo habilis. Fortin, 2025 argues that they were added to the Homo group because Leakey argued that even though they had minute brains (only 600 cm³) they walked on two feet and made stone tools. Now, some scholars are having second thoughts. Habilis seems to be more similar to Australopiths than to Homo (see my post: Was Homo habilis a member of our Homo genus?) Even Homo rudolfensis should probably be removed from the Homo group.

In this regard Vaneechoutte et al., 2024 (see my post about his paper: Australopithecines are not our ancestors at all (says study)) wrote: "Instead of considering [Australopith] graciles as ancestral to Pan and robusts as ancestral to Gorilla, as suggested by Kleindienst et al., Verhaegen considered the eastern African australopithecines, such as A. afarensis (incl. Lucy) as well as P. boisei to be ancestral or closer to the genus Gorilla, and the South-African australopithecines, A. africanus (incl. the Taung child) and P. robustus, ancestral or closer to the genus Pan." Vaneechoutee argues that an Ardipithecus-like ancestor evolved into Australopiths, and these evolved into A. africanus and Paranthropus robustus, leading to Pan, and the A. afarensis and P. boisei leading to Gorilla. Humans did not split from Pan, instead they did so from the Adripithecus via an "unknown missing link" adding that "Australopithecines Are Possibly Not Hominins Because Our Ancestors May Not Have Been Present in Africa in between 4 and 3 Ma."

It is possible that Eurasian apes evolved into our ancestor, Homo erectus in Western Eurasia, and that these are the base of the homo lineage.

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Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2026 by Austin Whittall ©