My previous post mentioned the new findings regarding Denisova admixture in Homo sapiens, and the two theories proposed to explain how Denisovan DNA spread between Austronesians and East Asians - Native Americans.
I believe that sooner or later we will find out that the elusive Denisovans are no others than Homo erectus. And I base my suspicions on two facts:
Erectus were alive in South East Asia about 40 kya. This was proved by Yokoyama Y, Falguères C, Sémah F, Jacob T and Grün R, in their paper (2008) Gamma-ray spectrometric dating of late Homo erectus skulls from Ngandong and Sambungmacan, Central Java, Indonesia. J Hum Evol. 2008 Aug;55(2):274-7. doi: 10.1016/j.jhevol.2008.01.006. Epub 2008 May 14., the team concluded that: "we establish[ed] minimum age estimates of around 40ka, with an upper age limit of around 60 to 70ka. This means that the Homo erectus of Java very likely survived the Toba eruption and may have been contemporaneous with the earliest Homo sapiens in Southeast Asia and Australasia..
The 400 ky Sima de los Huesos remains from Spain also hint at this. The mtDNA of the remains from this Spanish site was sequenced and found to be closer to Denisovan mtDNA than to Neanderthal ⁄ Human mtDNA. This is quite hard to explain: how did Denisovans get more of this mtDNA than the Neanderthals did considering that Denisovans are located in Altai while Neandertals are located in between Spain and Altai? The authors offer 4 explanations, and I believe that their fourth is correct: bold font is mine 
A fourth possible scenario is that gene flow from another hominin population brought the Denisova-like mtDNA into the Sima de los Huesos population or its ancestors. Such a hominin group might have also contributed mtDNA to the Densiovans in Asia. Based on the fossil record, more than one evolutionary lineage may have existed in Europe during the Middle Pleistocene. Several fossils have been found in Europe as well as in Africa and Asia that are close in time to Sima de los Huesos but do not exhibit clear Neanderthal traits. These fossils are often grouped into H. heidelbergensis, a taxon that is difficult to define, particularly with regard to whether the Sima de los Huesos hominins should be included. Furthermore, there may have been relict populations of still earlier hominins, notably those classified as Homo antecessor, which share some morphological traits with Asian Homo erectus and have been found just a few hundred metres away from Sima de los Huesos in Gran Dolina.
Home erectus left Africa (or maybe even originated out of Africa, in Asia from H. Habilis who had migrated earlier, and some of them returned to Africa later, generating the African erectus.) 1.8 Mya. They had plenty of time to move across Eurasia, fromm Indonesia to China to, why not?, Spain. Surely they originated more "modern" versions as time passed, the Homo antecessor and later H. heidelbergensis could be some of them. As well as Denisovans.
Maybe they even marched all the way to the New World.
Later, when modern H. sapiens moved into their territories they admixed, in varying degrees. This admixture must depend on the population ratios of migrants and residents. We have therefore a high content of Denisovan gene flow in Austronesia, and also in East Asia and the New World. But they may have been the result of separate admixture events.
Orthodoxy requires that the Humans marching into America be the result of a split that took place in Asia. And if these future Amerindians were the only ones to enter America, then they had to admix with Denisovans in Asia. But neat theories are not the way Nature works. The history of our genetic makeup is much more complex. And it may involve admixture in the New World, both with Neandertals and Denisovans
 Matthias Meyer, Qiaomei Fu, ,et al., A mitochondrial genome sequence of a hominin from Sima de los Huesos, Nature 505, 403–406 (16 January 2014) doi:10.1038/nature12788
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