Monday, April 24, 2017

65,000 Years Of Beringia In Maps

The linked post shows images of how Beringia looked on a map at regular intervals over the last 65,000 years. The land bridge was more long lived than usually recognized.

Saturday, April 22, 2017

Hobbits Are Not Dwarf H. Erectus

Most people had already rejected the theory that H. florensiensis (Hobbits) were diseased humans. But, this new physical anthropology study rules out the possibility that they are derived from H. erectus, because their bones show more primitive and basal features.

The is notable because it also largely rules out the theory that Hobbits are a subtype of Denisovans or H. heidelbergensis. Instead, it seems likely that they left Africa before or contemporaneously with H. erectus and are closer to H. habilis than any other known species of Homo.
The most comprehensive study on the bones of Homo floresiensis, a species of tiny human discovered on the Indonesian island of Flores in 2003, has found that they most likely evolved from an ancestor in Africa and not from Homo erectus as has been widely believed. The study by The Australian National University (ANU) found Homo floresiensis, dubbed "the hobbits" due to their small stature, were most likely a sister species of Homo habilis -- one of the earliest known species of human found in Africa 1.75 million years ago. 
Data from the study concluded there was no evidence for the popular theory that Homo floresiensis evolved from the much larger Homo erectus, the only other early hominid known to have lived in the region with fossils discovered on the Indonesian mainland of Java. . . .
Homo floresiensis is known to have lived on Flores until as recently as 54,000 years ago.
The study was the result of an Australian Research Council grant in 2010 that enabled the researchers to explore where the newly-found species fits in the human evolutionary tree. 
Where previous research had focused mostly on the skull and lower jaw, this study used 133 data points ranging across the skull, jaws, teeth, arms, legs and shoulders. 
Dr Argue said none of the data supported the theory that Homo floresiensis evolved from Homo erectus. 
"We looked at whether Homo floresiensis could be descended from Homo erectus," she said. 
"We found that if you try and link them on the family tree, you get a very unsupported result. All the tests say it doesn't fit -- it's just not a viable theory." 
Dr Argue said this was supported by the fact that in many features, such as the structure of the jaw, Homo floresiensis was more primitive than Homo erectus. 
"Logically, it would be hard to understand how you could have that regression -- why would the jaw of Homo erectus evolve back to the primitive condition we see in Homo floresiensis?" 
Dr Argue said the analyses could also support the theory that Homo floresiensis could have branched off earlier in the timeline, more than 1.75 million years ago. 
"If this was the case Homo floresiensis would have evolved before the earliest Homo habilis, which would make it very archaic indeed," she said. 
Professor Mike Lee of Flinders University and the South Australian Museum, used statistical modeling to analyse the data. 
"When we did the analysis there was really clear support for the relationship with Homo habilis. Homo floresiensis occupied a very primitive position on the human evolutionary tree," Professor Lee said. 
"We can be 99 per cent sure it's not related to Homo erectus and nearly 100 per cent chance it isn't a malformed Homo sapiens," Professor Lee said.
From Science News.
Although the diminutive Homo floresiensis has been known for a decade, its phylogenetic status remains highly contentious. A broad range of potential explanations for the evolution of this species has been explored. One view is that H. floresiensis is derived from Asian Homo erectus that arrived on Flores and subsequently evolved a smaller body size, perhaps to survive the constrained resources they faced in a new island environment. Fossil remains of H. erectus, well known from Java, have not yet been discovered on Flores. The second hypothesis is that H. floresiensis is directly descended from an early Homo lineage with roots in Africa, such as Homo habilis; the third is that it is Homo sapiens with pathology. 
We use parsimony and Bayesian phylogenetic methods to test these hypotheses. Our phylogenetic data build upon those characters previously presented in support of these hypotheses by broadening the range of traits to include the crania, mandibles, dentition, and postcrania of Homo and Australopithecus. 
The new data and analyses support the hypothesis that H. floresiensis is an early Homo lineage: H. floresiensis is sister either to H. habilis alone or to a clade consisting of at least H. habilis, H. erectus, Homo ergaster, and H. sapiens. A close phylogenetic relationship between H. floresiensis and H. erectus or H. sapiens can be rejected; furthermore, most of the traits separating H. floresiensis from H. sapiens are not readily attributable to pathology (e.g., Down syndrome). The results suggest H. floresiensis is a long-surviving relict of an early (>1.75 Ma) hominin lineage and a hitherto unknown migration out of Africa, and not a recent derivative of either H. erectus or H. sapiens.
Debbie Argue, Colin P. Groves, Michael S.Y. Lee, William L. Jungers. "The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters." Journal of Human Evolution (April 2017).

UPDATE April 24, 2017:
The [Hobbit] skull was astonishingly small: around just 400 cubic centimetres. This was a good 200cc less than the cranial capacity of any fossils then included in our our genus, Homo. Just for comparison, your brain will measure somewhere between 1,000 and 2,000cc. . . . Earlier Homo erectus specimens were known from east and South-East Asia. Perhaps, suggested some researchers, the Flores hominin was an offshoot of Homo erectus, and had undergone “island dwarfing”. Other experts were not so sure; the anatomy of Homo floresiensis seemed too primitive. . . .The shape of the pelvis and the proportions of the limbs looked primitive – reminiscent of australopithecines, or the earliest of human species, Homo habilis, from around 2-3m years ago. But those hominins only ever lived in Africa … as far as we know. . . .

The Flores hominins were, more clearly than ever, rooted deep in that tree: they could not be descendants of Homo erectus. They came from something more primitive – a close cousin of Homo habilis. But what was an ancient-looking hominin like this doing in Indonesia? 
In the most widely accepted model of human evolution today, the first emergence of hominins out of Africa involved Homo erectus, and happened some time after 2m years ago. But Homo floresiensis raises the tantalising possibility of an earlier expansion of hominins – who were probably not-quite-Homo – out of Africa. 
We know, from reconstructions of ancient climate and geography that it certainly would have been possible for hominins to emerge from Africa as far back as 3m years ago. In fact, other large mammal species – including elephants – did just that.
From The Conversation. Another discussion at the same site notes that a different study found a fit with H. Erectus that this study rejects.

The link on the words "climate and geography" above is to the following review article (whose abstract, unfortunately offers more tease than substance).
The past decade has seen the Pliocene and Pleistocene fossil hominin record enriched by the addition of at least ten new taxa, including the Early Pleistocene, small-brained hominins from Dmanisi, Georgia, and the diminutive Late Pleistocene Homo floresiensis from Flores, Indonesia. At the same time, Asia's earliest hominin presence has been extended up to 1.8 Myr ago, hundreds of thousands of years earlier than previously envisaged. Nevertheless, the preferred explanation for the first appearance of hominins outside Africa has remained virtually unchanged. We show here that it is time to develop alternatives to one of palaeoanthropology's most basic paradigms: ‘Out of Africa 1’.
Robin Dennell and Wil Roebroeks, "An Asian perspective on early human dispersal from Africa", 438 Nature 1099-1104 (December 22, 2005).

Meanwhile the brain of H. Naledi is called tiny but advanced.