Tuesday, 29 September 2009

Out of Europe?

Three weeks ago, I criticised the “quality” papers (the “Daily Telegraph” was an exception) for running a story based on a two-year-old paper about Homo georgicus as fresh news and for hyperbolic headlines about “rewriting the history of man”. True to form, the media have now completely missed out on an article published in Nature which does – if its conclusions are correct – have a substantial bearing on how we view the path of human evolution. The paper appeared in the 3 September edition of the journal, but due to a postal service that would be considered a disgrace in Somalia, it has only just reached me.

The paper entitled “The oldest hand-axes” in Europe is by Gary R. Scott and Luis Gibert of the Berkeley Geochronology Center, Berkeley, CA. It reports the re-dating of Acheulean hand-axes from Solana del Zamborino and Estrecho del Quipar, both in south eastern Spain. Both sites were previously considered to be among the younger Acheulean sites on the Iberian Peninsula. An age of approx 200ky assumed for Solana was based on its well-developed Acheulean technology. However Scott & Gibert reported revised dates of 0.9mya and 0.76mya for Solana del Zamborino and Estrecho del Quipar respectively, based on magnetic polarity considerations (Scott & Gilbert, 2009).

The oldest Acheulean hand-axes are around 1.65my old, from West Turkana in Kenya and by 1.4mya their usage was fairly widespread in Africa so on the face of it the fact that hand-axes had reached Spain by 0.9mya is hardly earth-shattering, albeit interesting. However while Acheulean hand-axes were once described as displaying a “variable sameness” that strikes “even enthusiasts as monotonous”, later hand-axes do appear to be more refined than earlier ones, which tend to be much thicker, less extensively trimmed and less symmetrical. The “evolved Mode 2” technology is not seen in the archaeological record in Africa until after 600,000 years ago, 300,000 years after its appearance in Spain.

The significance of this is that while even the earlier hand-axes probably represented a cognitive advance over that required to produce the early Oldowan tools, the later hand-axes possess three-dimensional symmetry that may imply a further cognitive advance as the tool would have had to be viewed and rotated through the mind’s eye while it yet remained a block of un-worked stone (Klein, 2005). The date of 600,000 years ago coincides with the first appearance in the fossil record of Homo heidelbergensis, which while slightly smaller-brained than a modern human, was considerably better endowed in that department than its supposed ancestor, Homo erectus. Homo heidelbergensis (or archaic Homo sapiens as it was known until fairly recently) is believed to be the common ancestor of both modern humans and the Neanderthals. Its bigger brain may have helped it to master the harsh conditions in Europe, which was periodically affected by episodes of glaciation. It could also have been responsible for the refinement in hand-axe making technology.

One problem is that there is no obvious evolutionary cause for this expansion in brain size if we accept, as is generally assumed, that Homo heidelbergensis evolved in Africa. The earliest human species, Homo habilis, possessed a larger brain than the australopithecines it is supposed to have evolved from. Its appearance coincides with the start of the present series of ice ages, 2.6 million years ago. Similarly Homo erectus – which also represented a cognitive step-up from its predecessor – appeared around 1.8-1.7mya during a further deterioration in the climate. But no such event seems to signal the appearance of Homo heidelbergensis.

While it would be a mistake to think there is agreement on the matter, a widely-held view is that Homo heidelbergensis evolved in Africa and migrated into Europe. The European deme eventually became the Neanderthals while the stay-at-home African deme eventually became Homo sapiens. Homo heidelbergensis was not the first human species to colonise Europe, but it was the first to stay there and reach more northerly places such as England and Germany. Previous migrants seem to have eventually been extinguished such as Homo antecessor, known from Level TD6 of the Gran Dolina cave, Atapuerca, Spain or back-migrants from Asia, en route back into Africa such as Homo cepranensis, known from a single skull found near Ceprano, Italy. The technology of the TD6 people was pre-Acheulean, that of the Ceprano people unknown. Both “species” were probably Homo erectus (broadly defined) and they were in Europe at about the same time as the makers of the Solana tools.

If it is the case that a) the re-dating is correct and, b) the “2g Acheulian” Solana tools were beyond the capabilities of Homo erectus then another human species must have made them. One possibility is Homo antecessor, but the problem is that while this species is said to have been larger-brained than “standard” Homo erectus (Bermudez de Castro, Arsuaga, Carbonell, Rosas, Martınez, & Mosquera, 1997) it lacked even the older-style Acheulean tools (Carbonell, et al., 2008), though we cannot rule out the possibility that these might at some stage come to light.

A more radical possibility is that a Homo erectus group equipped with Acheulean technology migrated into Europe and – unlike other migrants – managed to adapt to the harsher conditions. These provided the selective pressure for brain expansion and the migrant population eventually evolved into Homo heidelbergensis which then ranged far and wide throughout Eurasia, eventually evolving into the Neanderthals. But one group moved back into Africa and eventually became Homo sapiens. Thus the immediate ancestors of modern humans were actually a species of European origin rather than African.

© Christopher Seddon 2009
Bermudez de Castro, J., Arsuaga, J., Carbonell, E., Rosas, A., Martınez, I., & Mosquera, M. (1997). A Hominid from the Lower Pleistocene of Atapuerca, Spain: Possible Ancestor to Neandertals and Modern Humans. Science , 276, 1392-1395.
Carbonell, E., Bermudez de Castro, J., Pares, J., Perez-Gonzalez, A., Cuenca-Bescos, G., Olle, A., et al. (2008). The first hominin of Europe. Nature , 452, 465-470.
Klein, R. (2005). Hominin Dispersals in the Old World. In C. Scarre, The Human Past (pp. 84-123).
Scott, G., & Gibert, L. (2009). The oldest hand-axes in Europe. Nature , 461, 82-85.

Thursday, 10 September 2009

Bad Science!

While browsing the Independent website yesterday evening I saw this article at the top of the Most Viewed list. An article entitled A skull that that rewrites the history of man is an attention-getter. But when I read the article by Science Editor Steve Connor and this accompanying piece also by Mr Connor I was frankly astounded. The first of the fossil remains in question were discovered near the medieval Georgian town of Dmanisi in 1991 (when Georgia was still a part of the Soviet Union). They were attributed to a new species, Homo georgicus, in a 2002 article in the journal Science (Vekua et al, 2002). Moreover the article is free to download to anybody and does not require a subscription to the journal.

Yet nowhere in either of Mr Connor’s articles does he mention that Homo georgicus has been in the public domain for so long. I’ve read both pretty carefully and they imply that this is a brand new discovery. Furthermore, both the Independent articles are dated 9 September 2009. It does sometimes happen that an old article will feature in a website’s “most viewed” list; this is not the case here.

Turning to the articles themselves, the content leaves a lot to be desired. They are full of phrases such as “conventional view of evolution” and “simple view” which (it is implied) has been overturned by the discovery of the Dmanisi remains. This is utter nonsense. Just about the only thing physical anthropologists ever agree on is to disagree! There is no “simple view” of human evolution that has begun to “unravel”. Rather the view is based on a jigsaw puzzle with pieces that have gradually been added, beginning in the 19th Century with the discovery of the Neanderthals and Java Man.

The “simple view” that Mr Connor alludes to is that Homo habilis evolved from a gracile australopithecine species, possibly A. afrarensis (“Lucy”); Homo erectus evolved from H. habilis and migrated into Eurasia, and that Homo sapiens and the Neanderthals both evolved from Homo erectus via an intermediate form sometimes known as Archaic Homo sapiens. This is a first order approximation that nobody has ever seriously believed represented the true picture.

Homo georgicus is probably an early form of Homo ergaster (“African Homo erectus”). We know that very soon after the appearance of H. ergaster in Africa, Homo erectus shows up in Java. There are two possible interpretations; firstly H. georgicus left Africa and died out, with Asian H. erectus arising from a subsequent migration of H. ergaster from Africa. The second – more likely – possibility is that Homo georgicus carried on into Asia and evolved into Homo erectus. It is more likely because it explains the puzzling absence of the characteristic H. erectus (sensu lato) teardrop-shaped Acheulian handaxes from East Asia. This problem was first noted by the US archaeologist Hallam Movius in 1948. One possible explanation is that the ancestors of the East Asian Homo erectus left Africa before the Acheulian handaxes were invented. This view is supported by the Dmanisi remains, which were found in association with stone tools of the earlier Oldowan type.

Homo georgicus is another piece in the fascinating jigsaw of human evolution, but it doesn’t “rewrite” anything. To suggest otherwise is quite simply bad science and to present a 7 year old article in Science as if it were a new discovery is even worse journalism.

It appears that I have singled out the Independent unfairly, becuse both the Times and the Guardian also ran the same story. The Times does at least make it clear the discovery happened a while ago, though why three of the UK's four quality newspapers should choose to report on the Dmanasi hominins now is a complete mystery. It also turns out that the Daily Telegraph ran the same story just under two years ago.

Incredibly even Richard Dawkins website is carrying a link - via Twitter and Fox News - to the Times article. While I am fairly certain Prof. Dawkins is not personally responsible for everything on his site, this is a little surprising! I have to say that I wish Prof. Dawkins - as the country's leading populariser of science - would devote as much time and energy to combating this kind of "bad science" as he does to opposing creationism, which anybody with a brain larger than Homo georgicus knows is utter nonsense anyway.

UPDATE 16 Sept 2009
It now turns out that David Lordkipanidze, who has headed up the Dmanisi investigation for some years, was speaking to an audience at the British Science Festival in Guildford. No new information was being presented and indeed Prof. Lordkipanidze's most recent paper on the subject appeared 2 years ago (this was the story carried by the Telegraph in September 2007). The newspapers should really have made these facts clear rather than presenting them as fresh news. Nowhere did I see the words "speaking yesterday at the British Science Festival in Guildford" which would have explained everything.

© Christopher Seddon 2009

Gabunia, L., de Lumley, M.-A., Vekua, A., Lordkipanidze, D., & de Lumley, H. (2002). Découverte d'un nouvel hominidé à Dmanissi (Transcaucasie, Géorgie). C.R. Palévol. , 1, 243–253 .
Gabunia, L., Vekua, A., Lordkipanidze, D., Swisher, C., Ferring, R., Justus, A., et al. (2000). Earliest Pleistocene Hominid Cranial Remains from Dmanisi,Republic of Georgia: Taxonomy, Geological Setting, and Age. Science , 228, 1019-1025.
Klein, R. (2005). Hominin Dispersals in the Old World. In C. Scarre, The Human Past (pp. 84-123).
Lordkipanidze, D., Jashashvili, T., Vekua, A., Ponce de Leon, M., Zollikofer, C., Rightmire, C., et al. (2007). Postcranial evidence from early Homo from Dmanisi, Georgia. Nature , 449, 305-310.
Lordkipanidze, D., Vekua, A., Ferring, R., Rightmire, G., Zollikofer, C., Ponce de León, M., et al. (2006). A Fourth Hominin Skull From Dmanisi, Georgia. The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology , 288A, 1146–1157.
Vekua, A., Lordkipanidze, D., Rightmire, P., Agusti, J., Ferring, R., Maisuradze, G., et al. (2002). A New Skull of Early Homo from Dmanisi, Georgia. Science , 297, 85-89.