Wednesday, 10 April 2019

Human Evolution News - Another New Species?

Callao Cave, Luzon, Philippines. Home of Homo uzonensis.
New species of ancient human discovered in the Philippines: Homo luzonensis

The wonderful human evolutionary story that only a few days ago became a little more complicated with the discovery of two more 'Denisovans' in Papua-New Guinea, just got even more complicated with the announcement of yet another possible species of archaic hominins on the island of Luzon in the Philippines.

A combined French, Filipino and Australian team of archaeologists led by Florent Détroit of Département Homme & Environnement, Muséum National d’Histoire Naturelle, Paris, France have discovered twelve more fragments of hominin bones and teeth to add to the metatarsal bone found in 2007 and dated to 67,000 years ago. These recent finds of two more toe bones along with seven teeth, two finger bones, and part of a femur, are from the same stratigraphic layer as the earlier find and come from at least three individuals.

Five of the seven teeth attributed to Homo luzonensis. The teeth have small sizes and relatively simple shapes, but one premolar has three roots, which is uncommon among modern humans.

Photo credit: © Callao Cave Archaeology Project
Their discovery is published in Nature today, regrettably behind a paywall.

The bones and teeth show a mosaic of primitive and advanced feature, for example the teeth are small and simple (a 'modern' feature) but an upper premolar has three roots (A more primitive feature). One foot bone shows similarities to those of 'Lucy', the Australopithecus afarensis that lived in East Africa some 3,000,000 years ago. This mosaic of feature, together with the small size has prompted the team to propose this is a newly-discovered hominin which is neither Homo erectus or H. floresiensis (the 'Hobbit'). They have named it H. luzonensis.

The biological significance of this find is that it is the third example of hominin remains being found east of the Wallace Line which was assumed to be a barrier to migration of terrestrial species because the lack of land bridges and adverse ocean currents would have prevented chance migration. The Wallace Line is named after the biologist Alfred Russel Wallace who co-presented the idea of evolution by natural selection to the Linnaean Society with Charles Darwin.

Like H. floresiensis this hominin is assumed to have evolved from H. erectus, an African species that is believed to have migrated via a coastal route to South and southeast Asia and up into Central Asia. H. erectus is believed to the the ancestor of both H. neanderthalensis and H. sapiens as well as H. floresiensis and now maybe H. luzonensis.

A picture is now beginning to emerge of an early dispersal out of Africa of an archaic human that had mastered seafaring. This early human then diversified and spread across Asia and maybe into Europe. These were replaced by a second wave of anatomically modern humans coming out of Africa some 40,000 years ago to interbreed with and displace the descendants of the earlier migrants, leaving just modern H. sapiens as the sole survivor.

Given that this new species is believed to have lived between 50,000 and 67,000 years ago at least, and given the relatively recent age of H. naledi in South Africa and the possible new Denisovan relatives in Papua-New Guinea, this give the distinct possibility that as many as ten and maybe more species of Homo coexisted in various parts of the world, maybe interbreeding when they came into contact.

Reference:
Détroit, F., Mijares, A.S., Corny, J., Daver, G., Zanolli, C., Dizon, E., Robles, E., Grün, R., and Piper, P.J. (2019).
A new species of Homo from the Late Pleistocene of the Philippines.
Nature
568, 181–186. doi:10.1038/s41586-019-1067-9.







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