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, 275 (1640), 1287-96

Are the Small Human-Like Fossils Found on Flores Human Endemic Cretins?

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Are the Small Human-Like Fossils Found on Flores Human Endemic Cretins?

Peter J Obendorf et al. Proc Biol Sci.

Abstract

Fossils from Liang Bua (LB) on Flores, Indonesia, including a nearly complete skeleton (LB1) dated to 18kyr BP, were assigned to a new species, Homo floresiensis. We hypothesize that these individuals are myxoedematous endemic (ME) cretins, part of an inland population of (mostly unaffected) Homo sapiens. ME cretins are born without a functioning thyroid; their congenital hypothyroidism leads to severe dwarfism and reduced brain size, but less severe mental retardation and motor disability than neurological endemic cretins. We show that the fossils display many signs of congenital hypothyroidism, including enlarged pituitary fossa, and that distinctive primitive features of LB1 such as the double rooted lower premolar and the primitive wrist morphology are consistent with the hypothesis. We find that the null hypothesis (that LB1 is not a cretin) is rejected by the pituitary fossa size of LB1, and by multivariate analyses of cranial measures. We show that critical environmental factors were potentially present on Flores, how remains of cretins but not of unaffected individuals could be preserved in caves, and that extant oral traditions may provide a record of cretinism.

Figures

Figure 1
Figure 1
(ac) Plots of the first three PCs from nine cranial measures, size adjusted, show LB1 grouping with cretins (n=5) and not with microcephalics (n=3) or normal modern humans. All are H. sapiens except Kabwe (H. heidelbergensis), Mrs Ples (A. africanus) and Nariokotome (Homo erectus (sensu lato)). These PCs explain 64.8% of the variance (37.2, 15.8 and 11.8%). Residual correlation with size is in the electronic supplementary material, figure S8 and the component matrix is in the electronic supplementary material, table S8.
Figure 2
Figure 2
(ac) Plots of the first three PCs from nine cranial measures, size adjusted, show LB1 grouping with cretins (n=5) and not with microcephalics (n=3) or normal modern humans. All are H. sapiens except Kabwe (H. heidelbergensis), Mrs Ples (A. africanus) and Nariokotome (Homo erectus (sensu lato)). These PCs explain 76.0% of the variance (40.1, 24.3 and 11.6%). The component matrix is in the electronic supplementary material, table S9.
Figure 3
Figure 3
Plots of the discriminant functions 1 and 2 for three groups (modern humans, microcephalics and cretins) and unassigned individuals. (a) Modern human group is from 28 populations including Andaman Islanders (n=2523). (b) Modern human group is Andaman islanders only (n=69). In each case, these functions correctly classify all modern humans, and all cretins (n=5) but not all microcephalics (n=3), and assign LB1 to the group of cretins (posterior probability p>0.999). Numerical results are in the electronic supplementary material, tables S10 and S11.

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