Genetic Model Identifies Paranthropus boisei as Vector For Transmission of Herpes Virus

CNN (usual caveats) reports on a study that identifies Paranthropus boisei as the likely transmission vector of genital HSV-1.  From the story:

Herpes has been around a long time, to say the least.

Ancient chimpanzees genetically passed oral herpes (herpes simplex 1, or HSV-1) to the earliest humans millions of years ago when our lineage split. And we almost missed out on catching that other scourge, genital herpes (HSV-2) -- almost. Unlike HSV-1, HSV-2 didn't make the leap to early humans on its own.

Unfortunately for modern humans, millions of years ago, an early human ancestor was in the right place at the right time to catch HSV-2. And it might not have happened if it weren't for that meddling hominin species Paranthropus boisei, according to a new study in the journal Virus Evolution.

Why Paranthropus boisei, you ask? After all, P. boisei was not even on the main line of human evolution, coexisting with all manner of early Homo species at the same time, who likely out-competed them into extinction.  From the article, which is highly technical:

Paranthropus boisei would have been well placed to act as an intermediate host for HSV2. It most likely contracted the infection through hunting or more likely scavenging infected ancestral-chimpanzee meat. Processing (with or without tools) and consumption of raw meat would act as a simple path for ChHV1 to have crossed into P.boisei via open cuts or sores. Tropical refugia during hot dry periods may have driven chimpanzees into higher concentrations in certain areas, driving them into contact and competition with P.boisei and H.habilis as the margins of tropical forest blended into more open savannah-like habitats (Julier et al. 2017). Violent confrontation or hunting/scavenging and butchery practices would have provided a viable path of transmission for HSV2. Homo habilis remains have been recovered from the same layers as stone tools and bones carrying evidence of butchery, supporting a possible transmission–through-hunting/scavenging hypothesis for the initial anc-chimp to H.habilis transmission (Clarke 2012). Paranthropus aethiopicus, P. boisei, and P. robustus are associated with the Oldowan stone tool complex (De Heinzelin et al. 1999), and P.boisei explicitly with butchery (Domínguez-Rodrigo et al. 2013) lending support to the hypothesis that bushmeat hunting/scavenging and butchery may have led to the initial transmission of HSV2 to the hominins.

The entire exercise is very mathematical and relies on somewhat limited evidence of P. boisei behavior. It is, nonetheless, intriguing since it posits considerable interaction between the various hominin groups. 

Here is a mugshot of one of the perpetrators, the Zinj skull from Olduvai Gorge, found in 1959. 

Modern Hand Digit at 1.84 Mya

A story in Lab Equipment has spotlighted new evidence that modern human morphology was present in early hominins at 1.84 million years ago.  From the story:

“The new Olduvai fossil represents the earliest known hominin hand bone with (modern human-like) appearance,” they wrote. “Our results, along with the archaeological record, reveal that instead of following an orderly trend, eventually culminating in the modern human condition, some ‘primitive’ hand bone morphologies persisted side-by-side with (modern human-like) hand bone morphologies well after the first appearance of stone tools and zooarchaeological evidence of their use for butchery by at least (2.6 million years ago).”

This makes sense. Evolution happens at the trait level, not the species level. There are numerous examples of some traits becoming more modern over time, while some retained archaic dimensions.What is not clear is whether or not it is from early Homo or Australopithecus (Paranthropus) boisei.  If it is from Paranthropus, then the modern morphology extends back at least to the point where the later diversification of australopithecines occurred, between 2.5 and 3.0 mya and, perhaps, longer. 

New Hominin Species Coeval with Au. afarensis

A new hominin has been announced by Haile-Selassie and colleagues.  Here is the abstract from the Nature paper¹:

Middle Pliocene hominin species diversity has been a subject of debate over the past two decades, particularly after the naming of Australopithecus bahrelghazali and Kenyanthropus platyops in addition to the well-known species Australopithecus afarensis. Further analyses continue to support the proposal that several hominin species co-existed during this time period. Here we recognize a new hominin species (Australopithecus deyiremeda sp. nov.) from 3.3–3.5-million-year-old deposits in the Woranso–Mille study area, central Afar, Ethiopia. The new species from Woranso–Mille shows that there were at least two contemporaneous hominin species living in the Afar region of Ethiopia between 3.3 and 3.5million years ago, and further confirms early hominin taxonomic diversity in eastern Africa during the Middle Pliocene epoch. The morphology of Au. deyiremeda also reinforces concerns related to dentognathic (that is, jaws and teeth) homoplasy in Plio–Pleistocene hominins, and shows that some dentognathic features traditionally associated with Paranthropus and Homo appeared in the fossil record earlier than previously thought.

The Washington Post has a write-up of the new find, which they glibly refer to as “An Ethel for Lucy.” Rachel Feltman:

Haile-Selassie and his co-authors believe the find should encourage reexamination of other possible instances of pre-Homo cohabitation.  Two other species have been proposed as living at the same time as Australopithecus afarensis -- Australopithecus bahrelghazali and Kenyanthropus platyops -- but both remain controversial, with some scientists saying they aren't different enough from A. afarensis to constitute a new species. And in a previous expedition, Haile-Selassie himself found a partial foot that he believed was from the same time period -- but not the same species -- as Lucy. Unlike the jaw reported in Nature, the foot didn't provide enough evidence to name a new species.

As noted with the Ledi jaw, there seems to be quite of a bit of morphological variability and experimentation going on at the Plio-Pleistocene boundary.   

¹Haile-Selassie, Y., Gibert, L., Melillo, S.M., Ryan, T.M., Alene, M., Deino, A., Levin, N.E., Scott, G., Saylor, B.Z. (2015) New species from Ethiopia further expands Middle Pliocene hominin diversity. Nature. 521(7553): 483-488.
http://dx.doi.org/10.1038/nature14448

New Dates For Little Foot Push It Back to Au. afarensis Time-Period

On the heels of the Ledi jaw dates for early Homo at 2.8 million years ago, and the corresponding tentative conclusion that only Au. afarensis could emerge as a possible ancestor for early Homo, to the exclusion of any of the other australopithecines, comes a redating of the Australopithecus specimen from the cave of Sterkfontein to 3.67 million years ago.  From the story in Science Daily:

Ronald Clarke, a professor in the Evolutionary Studies Institute at the University of the Witwatersrand who discovered the Little Foot skeleton, said the fossil represents Australopithecus prometheus, a species very different from its contemporary, Australopithecus afarensis, and with more similarities to the Paranthropus lineage.

“It demonstrates that the later hominids, for example, Australopithecus africanus and Paranthropus did not all have to have derived from Australopithecus afarensis,” he said. “We have only a small number of sites and we tend to base our evolutionary scenarios on the few fossils we have from those sites. This new date is a reminder that there could well have been many species of Australopithecus extending over a much wider area of Africa.”

So, what is Au. prometheus, exactly and how does it differ from the other australopithecines in the area?  From the paper by Granger, et al.¹:

This species was named on the basis of a parietooccipital fossil from Makapansgat23. It has been suggested22 that several other Sterkfontein and some Makapansgat specimens also belong in this species making Australopithecus africanus and A. prometheus contemporaries in the assemblages of Makapansgat Member 3 and Sterkfontein Member 4. A. prometheus differs from A. africanus in features including Paranthropus-like larger, bulbous-cusped cheek teeth, a longer, flatter face, incipient supraglabellar hollowing and a more vertical rounded occiput22. (Note that we use the term hominid in the traditional sense to include humans and their ancestral relatives but exclude the great apes.)

One of the raging debates in human palaeontological studies concerns whether or not the robust australopithecines, Au. robustus and Au. boisei, represent their own clade, Paranthropus. This perspective is based on traits that are shared to the exclusion of other australopithecine species.  Opponents of this view argue that quite a few of the traits that make up this clade are functional in nature, involving mostly the chewing complex, and that as such, Au. robustus and Au. boisei are  outgrowths of Au. africanus.

The story continues, quoting Ron Clarke:

“It demonstrates that the later hominids, for example, Australopithecus africanus and Paranthropus did not all have to have derived from Australopithecus afarensis," he said. “We have only a small number of sites and we tend to base our evolutionary scenarios on the few fossils we have from those sites. This new date is a reminder that there could well have been many species of Australopithecus extending over a much wider area of Africa.”

Hope so, because right now, here is how it looks:

• P. robustus (or Au. robustus) only in South Africa
• P. boisei (or Au. boisei) only in East Africa
• Early Homo only in East and Northeast Africa
• Au. africanus only in South Africa
• Ar. ramidus only in North East Africa
• Au. afarensis only in North East Africa

As Slim Pickens would say: “What in the Wide, Wide World of Sports is a-goin' on here?”

All of this sort of leads to the question of who the last common ancestor of humans and modern apes was.  All we have to go on is a badly crushed skull from the Sahel River area in Chad that is purported to be somewhere around 7 mya, but is, in reality, a surface find, and some hominin-looking post-cranial remains from the Tugen Hills, in Kenya that are dated to between 5.6 and 6.1 mya.  By the time we get to Ar. ramidus, at least facultative bipedalism is in place, although there are still quite a few ape-like traits.  What is not clear from the report by Granger et al, is how the morphology compares to earlier hominins.  For example, can the traits observed in Au. prometheus be derived from Ar. ramidus?  If so, then it still represents a possible precursor and something like Ar. ramidus gave rise to both the australopithecines and the paranthropines.  The fact that the discoverers are calling it Australopithecus suggests that it shares enough derived traits with the australopithecines as a whole to be called that.  If the traits cannot be derived from Ar. ramidus, then it raises the possibility that the paranthropines and Ar. ramidus share a common ancestor.  At this point, until some systematic analyses can be done, we simply don't know. 

Of course, all of this is contingent on the dates holding up.  The article gives a pretty good run-down on how isochron dating works and indicates that the dates are consistent with what would be expected given the deposition.   I am sure that more will come out about this very shortly.  Until then...

¹Darryl E. Granger, Ryan J. Gibbon, Kathleen Kuman, Ronald J. Clarke, Laurent Bruxelles, Marc W. Caffee. New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and Member 5 Oldowan. Nature, 2015