Thursday, 7 August 2014

Is Homo floresiensis a valid species?

New papers revive ‘hobbit’ controversy

The announcement in 2003 that dwarf hominins had been discovered at Liang Bua Cave on the Indonesian island of Flores was one of the major news stories of that year. The type specimen, LB1, a female inevitably dubbed ‘Flo’ had lived had lived just 18,000 years ago at a time when all archaic hominins were believed to be long extinct. Estimated to have been around thirty years old at the time of her death, ‘Flo’ stood just 1.06 m (3 ft. 6 in.) tall, weighed 16 and 36 kg (35 and 79 lb), and had an estimated cranial capacity of just 380 cc, comparable to that of an australopithecine.

Rapidly dubbed the ‘hobbit people’ on the grounds of their diminutive stature, the hominins were recognised as a new human species, Homo floresiensis. It was suggested that in the absence of natural enemies on an island where food is fairly scarce, ‘Flo’s’ people had undergone a process known as insular dwarfism, where smaller individuals are positively selected for and over several generations, the entire population ‘downsizes’.
Not everybody accepted this explanation. In 2006, the late Teuku Jacob claimed that Flo was a modern human of Australomelanesian extraction, who had suffered from a developmental disorder leading to a smaller brain known as microcephaly. Jacob found little support for his views and was also criticised for allegedly damaging the specimens while they were on loan to him from the Indonesian National Archaeological Research Center.

The controversy had been revived by the publication of two companion papers in the journal PNAS. Two of the authors of these new papers were also involved with Jacob’s original study. The first paper, Henneberg, et al (2014), argues that Flo was suffering from Down syndrome. This can result in atavism, where developmental characteristics of an earlier ancestral condition appear alongside undisrupted characteristics. This pattern could explain what has been otherwise interpreted as a mosaic of primitive and derived features. As a teratological specimen, the authors note that LB1 is not eligible to be designated the type specimen of a new species.

In the second paper, Eckhardt, et al (2014) suggest that based on an examination of the Flores specimens made in 2005, both the stature and brain size of LB1 have been underestimated. LB1, they argue, possessed abnormalities such as craniofacial asymmetry and a thigh bone disproportionately short in relation to its other long bones. Such abnormalities are indicative of Down syndrome and a number of other developmental conditions.

1. Jacob, T. et al., Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: Population affinities and pathological abnormalities. PNAS 103 (36), 13421–13426 (2006).
2. Henneberg, M., Eckhardt, R., Chavanaves, S. & Hsüc, K., Evolved developmental homeostasis disturbed in LB1 from Flores, Indonesia, denotes Down syndrome and not diagnostic traits of the invalid species Homo floresiensis. PNAS (Early Edition) (2014).
3. Eckhardt, R., Henneberg, M., Weller, A. & Hsüc, K., Rare events in earth history include the LB1 human skeleton from Flores, Indonesia, as a developmental singularity, not a unique taxon. PNAS (Early Edition) (2014).

Links (all papers are open access):
Jacob, et al
Henneberg, et al
Eckhardt, et al

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