Tuesday, 16 February 2016

Flores ‘hobbits’ arose from an archaic human species

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).

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