Kuhlwilm, M. et al., Ancient gene flow from early modern humans into Eastern Neanderthals. Nature, doi:10.1038/nature16544 (2015).
Prehistory, the Universe, and Everything
Study confirms that Flores hominins are not Homo sapiens
Since their headline-making discovery in 2003, the diminutive hominins from the Indonesian island of Flores have been generally accepted to be a distinctive human species, Homo floresiensis. Popularly referred to as ‘hobbits’, they are widely believed that they owe their small size to a phenomenon known as ‘insular dwarfism’. In the absence of dangerous predators and in a habitat where food is scarce, it was suggested that they ‘downsized’ from their ancestral condition as evolution favoured smaller, less ‘gas-guzzling’ individuals. The ancestral species is often claimed to be Homo erectus, but claims have also been made for more primitive hominins such as Homo habilis or even Australopithecus.
Not everybody accepted that Homo floresiensis was a new human species and among the sceptics was the late Teuku Jacob, an Indonesian anthropologist who claimed that the ‘hobbits’ were modern humans affected by a developmental disorder known as microcephaly. Some years after Jacob’s death, his former colleagues revived the theory, this time claiming that Homo floresiensis were modern humans suffering from Down syndrome.
A newly-published study describes the investigation of the cranial bones of the partial female skeleton LB 1 (popularly and perhaps inevitably known as ‘Flo’). A series of high-resolution scans were taken using an X-ray CT scanner. Comparative scans were also taken of microcephalic specimens used in earlier studies of LB 1. The scans were used to study the bone thickness distribution of the cranial vault and internal bone composition and structure. Cranial vault thickness (CVT) can be diagnostic of a hominin species attribution, and it was found to be thick for LB 1 in absolute terms and even more so in relative terms when the small cranial size is taken into account. By contrast, microcephalic skulls of modern humans are thinner than those of humans unaffected by the condition. It was found that Flo had suffered from a condition known as bilateral hyperostosis frontalis interna, and bore the healed scar of a head injury, but there was nothing to indicate that she had suffered from any developmental disorders of the type suggested by Jacob or his former colleagues.
The researchers showed that LB 1 displays characteristics related to the distribution of bone thickness and arrangements of cranial structures that are primitive traits for hominins, differing from the derived condition of modern humans. This was not seen with the microcephalic skulls.
The study thus rules out the possibility that LB 1 can be assigned to Homo sapiens, but leaves the issue of its true affinities unresolved.
Balzeau, A. & Charlier, P., What do cranial bones of LB1 tell us about Homo floresiensis? Journal of Human Evolution 93, 12-24 (2016).
Fossils recovered at ‘Cradle of Humankind’ site
Sterkfontein is a set of limestone caves near Krugersdorp, South Africa. It is one of the most important hominin fossil-bearing sites in the world and finds include the female australopithecine Mrs Ples, discovered in 1947 and recently voted No.95 in a list of 100 Great South Africans. Sterkfontein has yielded stone tools in addition to hominin fossils and it is now part of the Cradle of Humankind, a World Heritage Site named by UNESCO in 1999. Most of the finds have been made in Members 4 and 5 of the cave’s sedimentary sequence, but rather less well known is the large underground chamber known as Milner Hall.
It is from Milner Hall that the discovery is reported of a hominin adult upper right molar (M1) tooth and a proximal phalanx finger bone, probably from a left hand. The chamber has previously yielded only stone tools, and association with these suggests that the fossils are 2.18 million years old.
The tooth is broadly closer to Homo than to Australopithecus or Paranthropus. It most closely resembles the Olduvai OH 6 first molar assigned to Homo habilis and a first molar assigned to the recently-proposed Homo naledi. The shape and size of the tooth’s cusps align it to early Homo.
The finger bone is larger and more robust than that of any hominin so far discovered in South Africa. It resembles the Olduvai Homo habilis fossil OH 7, but is much larger. It is markedly curved, within the range of Australopithecus afarensis and suggesting adaptation for tree-climbing, but it lacks other features associated with arborealism, such as a strongly developed flexor apparatus and a mediolaterally expanded diaphysis; these features are present in A. afarensis, Homo habilis and present-day chimpanzees. The finger bone possesses an enigmatic mixture of primitive, derived and unique characteristics. It is not clear whether or not it belonged to the same individual and its taxonomic affinities are at this stage uncertain.
Stratford, D., Heaton, J., Pickering, T., Caruana, M. & Shadrach, K., First hominin fossils from Milner Hall, Sterkfontein, South Africa. Journal of Human Evolution 91, 167-173 (2016).