Many molecular clocks are based on the divergence between human beings and chimpanzees. In my previous post I mentioned the calculation method and how it is used to work out the age of a "most recent common ancetstor", based on genetic divergence (mutations), and mutation rates (μ). I pointed out the variability of these μ, today we will look into the age estimations for the most recent common ancestors of humans and chimpanzees, all calculated using genetic molecular clocks, except for the work of Sarich and Wilson back in 1967.
Yes, as expected, there is a wide dispersion of values, frm 4.1 to 13 million years!
This is a summary of the different dates provided by studies over the course of the past 59 years, dates given in million years ago (Ma):
- 5 Ma (Sarich and Wilson, 1967). Used immunological data (albumins and antiserums) in apes and humans.
- 2.7 ± 0.6 Ma (Hasegawa M, Kishino H, Yano T., 1985). They used the mtDNA molecular clock to calculate their dates.
- 5 - 7 Ma (Galina V Glazko, Masatoshi Nei, 2003). Different calibration points, phylogenetic trees, and use of multiple genes and nuclear protein.
- <6.3 Ma (Nick Patterson, Daniel J. Richter, Sante Gnerre, Eric S. Lander & David Reich, 2006). They analized 20 M base pairs of DNA.
- 4.1 ± 0.4 Ma. Speciation time, the MRCA is older. (Asger Hobolth, Ole F Christensen, Thomas Mailund, Mikkel H Schierup, 2007). Used a model comparing ape-human autosomal DNA.
- 7 - 8 Ma K.E. Langergraber,K. Prüfer, et al., 2012. This team measured generation times in wild chimpanzees, used human mutation rate per generation and calculated the split date.
- 12.1 Ma (Priya Moorjani, Carlos Eduardo G. Amorim, Peter F. Arndt, and Molly Przeworski, 2016). Employed autosomal data but of CpG transitions and considered variable mutation rates.
- 7.4 Ma (Schrago and Voloch, 2013). Stepwise analyses of genetic and molecular datasets covering anthropoids.
- 13 Ma (11 to 17 Ma) (Venn et al., 2014). Considers the high mutation rate in male chimpanzees, and assumes it has always been so.
- 6.6 Ma (Guy Amster, Guy Sella, 2016). Modified mutation rates using sex-specific life histories (onset of puberty, generation times in both sexes, and how they changed over millions of years)
- 5.5 - 6.3 Ma (DongAhn Yoo, et al., 2025). They only used segments that could be aligned (ape-human DNA is very diverged) in an incomplete lineage sorting (ILS).
I like the ones that consider variable mutation rates (see my previous post), because it seems more realistic.
No fossils
The main problem is that there are no fossils of the ancestor of humans and chimpanzees. There are other ape fossils which have been dated, in Africa and Eurasia, but the exact relationship with the common ancestor of chimps and humans is the subject of intense debate in scholarly circles.
Reasons for not finding fossils: it is not easy to work in Africa, with the common civil wars, warlords, corruption, lack of access to potential sites, funding issues, and also excuse that the tropical African environment isn't the best to create fossils (It baffles me how Java man was discovered in a tropical setting in Asia!)
There are over 6000 fossils of hominins and 31 species (Foley and Lahr, 2024) but just a handful of ape fossils. There are some like the Ororrin, the Sahelanthropus and the Ardipithecus that could belong (or not) to the clade leading to chimps and humans. But Foley and Lahr write that "These groups may be entirely different, representing taxa that belong to none of the extant hominine lineages or they may belong to an early form of African ape, which... overlapped geographically with later hominins." Clearly, the situation is complex and unresolved.
Previously I posted about Miocene (a period spanning 23 to 5-3 Ma) apes found in Europe and Western Asia, and the lack of fossils from Africa suggesting an Eurasian origin for them followed by a migration into Africa as climate turned worse in their homeland. There are some African fossils dating back to the Miocene epoch the oldest date back to the early Miocene (16 to 22 Ma), in Kenya and Uganda, too far from the split of Chimps and Humans to be relevant for our post.
Kunimatsu, 2007 reported an ape from the Late Miocene epoch, named Nakalipithecus nakayamai, its remains were unearthed in Kenya and it "could be close to the last common ancestor of the extant African apes and humans." It was the size of female gorillas and orangutans. The authors dated it to 9.8-9.88 Ma.
Also in 2007, Suwa et al., reported another finding, some teeth with a gorilla-like appearane which were assigned to a new species, Chororapithecus abyssinicus from Chorora, Ethiopia. This great ape was dated to 8 Ma. It is possible that it is related to N. nakayamai.
The Sahelanthropus tchadensis, reported by Brunet et al., 2002, and 2005, was named for the Sahel region of Chad lived 7 Ma. Leg bones and a skull were recovered. We don't know if it is an ancestor of chimpancees and humans or just a separate branch like the Gorillas.
Orrorin lived in Kenya some 6 Ma. It was first described as closer to humans, but later studies placed it close to australopithecines. Almecija et al., (2013) place it as "intermediate between Miocene apes and australopiths".
The Ardipithecus ramidus seems to have evolved after humans and chimpancees separated (4.4 Ma). Partial remains have been recovered in the Afar region of Ethiopia, and it seems to have been adapted to living in the trees, and was also bipedal but not very efficient walking on two feet. It was the size of a chimp, and had a brain equivalent to theirs too. They may have split from the ancestor of the hominini tribe that encompasses humans and chimpancees and not be a direct human ancestor.
Much more recent are chimpanzee fossils, the very first! unearthed by McBrearty and Jablonski (2005) in Kenya, Eastern Africa, far from their current distribution in Central and Western Africa. They lived close to a hominin species, but they are relatively close in time to us, around 545-284 ky old.
Eurasian origin
Finally, I must mention Frances A. M. Mansfield and Mario Vaneechoutte (2024) who propose a Eurasian origin for Chimpancees and Gorillas, this is an unorthodox and thought provoking point of view. I highlighted their comments on Chimpancees.
"While the established paradigm of human evolution asserts that the lineages leading to the extant great apes and Homo arose in Africa, the large number of fossil discoveries from Europe in recent decades support arguments for a European origin of the Hominidae (all great apes) and plausibly, also a European common ancestor of the Homininae (African great apes, Australopithecus species, and the genus Homo).
Meanwhile, a lack of consensus remains regarding the phylogenetic placement of australopithecine fossil species in Africa, with substantial evidence indicating that some of them may align more closely to extant African great apes than to Homo. Based on a novel interpretation of existing fossil, genetic, paleogeographic and paleoclimatic evidence, this paper aims to put forward a new hypothesis regarding the separate divergences of Gorilla, Pan, and Homo.
We support existing arguments that the last common ancestor of African great apes and Homo may have lived in Europe in the late Miocene, and we put forward a new hypothesis as to where, when, and why the separate lineages may have started to diverge. Extreme conditions during the Vallesian Crisis (11.6-8.0 Ma) and the Messinian Salinity Crisis (6.0-5.3 Ma) may have forced separate branches of European hominids to migrate out of the Mediterranean region.
We argue that the lineages leading to Gorilla and Pan independently migrated into Africa, while the lineage leading to Homo went in another direction. Thereafter, the Zanclean Megaflood (5.3 Ma) —which caused the Mediterranean to refill very quickly— may have cut off the migration route between Eurasia and Africa at the Sinai Peninsula, isolating a small population (the putative Homo lineage) on the Arabian Peninsula / Red Sea coast during a period of hyperaridity. The other group (Pan lineage) crossed into Africa, where it subsequently diversified into various species of Australopithecus."
The authors note that "Upon reviewing the descriptions of presumed hominin fossils from Africa from the late Miocene to the early Pleistocene (from Sahelanthropus tchadensis, ~7.0 Ma, through H. habilis, ~2.31–1.65 Ma) one finds, contrary to expectation, that many of the earlier species tend to display a number of presumed derived features, while later species often display more presumed primitive features.... Meanwhile, detailed analyses of Australopithecus fossils reveal that, other than features related to bipedalism, they tend to display many characters more similar to great apes than to humans... Finally, most students of paleoanthropology agree that the earliest Homo erectus/H. ergaster fossil specimens bear marked dissimilarities with any presumed Australopithecus ancestor, which makes it difficult to establish any direct transition or relationship between the two groups."
The Retrovirus
The paper also mentions the strange case of retroviral genes (originating in a virus) that entered the genome of all African primates except Homo (us and our ancestors), this introgressed region known as Pan troglodytes endogenous retrovirus 1 (PTERV1), which is completely absent from the human genome. PtERV-1 is believed to have ocurred 3 to 4 million years ago when the retrovirus infected chimpanzees and gorillas.
The paper states that "This strongly indicates that our ancestors were most probably not even in Africa during the Pliocene (Benveniste and Todaro 1976, Polavarapu et al. 2006), but this is rarely commented upon, and attempts to explain how Homo ancestors may have managed to evade viruses that affected all other extant African apes have proved inconclusive (Kaiser et al. 2007, PerezCaballero et al. 2008). The most parsimonious explanation is that our ancestors were not in Africa during the middle Pliocene and may instead have evolved in “an ecological niche that physically separated them from the source of the infectious PtERV1 virus” (Kaiser et al. 2007b)." They made a good point!
The paper argues the following (a long quote, but worth the while reading it); LCA is the Last Common Ancestor:
"We propose that the species representing the LCA of humans and chimpanzees formed part of a continuous migration of fauna from southern Eurasia to northern Africa during the Messinian, between 5.9–5.3 Ma, via Anatolia and across the northern Sinai region of the Arabian Peninsula. Ultimately, a small group of individuals, ancestral to Homo, may have been cut off and separated from other hominids, ancestral to Pan, when, at 5.33 Ma, the Zanclean flood refilled the Mediterranean and submerged the land bridge between the African and Arabian plates, at which point the connection between the two continents was lost. This date would be consistent with the majority of genetic analyses for the timing of the Pan/Homo divergence. The lineage that made it to the African continent—eventually leading to the Pan lineage—may have migrated south along the African Red Sea and/or Nile River valley and continued southward at Afar, following the many substantial waterways and lakes along the East African Rift Valley and Coastal Forest. This may explain why existing fossil evidence fails to demonstrate a clear progression from primitive/ape-like features towards more derived/human-like features, and why there is no obvious progression from quadrupedalism towards bipedalism in the australopithecines...
We suggest that, unlike the ancestors of australopithecines and extant African apes, the proto-human group remained isolated on the Arabian Peninsula. Between 5.6 and 3.3 Ma, the Arabian Peninsula went through a stage of hyperaridity (Böhme 2021), so any species trapped there would have been isolated between the Red Sea and a lifeless desert—an impenetrable barrier... Unfortunately, there is no fossil evidence to support this scenario... Moreover, the Arabian Peninsula presents a location from where a new genus, Homo, could migrate coastally in multiple directions (Africa to the west, Dmanisi, Georgia to the north, Pakistan, China and Indonesia to the east) only once sea levels fell again in the early Pleistocene, thereby giving rise to multiple variations of Homo erectus/ergaster."
Closing Comments
In this post we have mentioned the wide range and variable dates for the last common ancestor shared by human beings and chimpanzees, which is the outcome of the variability of mutation rate values mentioned in my previous post. We also described the lack of fossils in Africa that could help clearly define the transition between Miocene apes and the first homo individuals. Both genetic and archaeological-paleontological finds offer weak backing to the African origin of our ancestors.
I notice, time and time again, an effort to "fit" or "adapt" findings to the accepted timelines and chronologies, and to support the African origin of the great apes. Perhaps Mansfield and Vaneechoutte are on the right track, and their hypothesis explains the early Georgian fossils at Dmanisi.
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