Tuesday, 2 May 2017

(190) Australopithecus interbred with Homo sapiens?

Basic Dimension


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Fossils recovered from an old mine on a desolate mountain in Morocco have rocked one of the most enduring foundations of the human story: that Homo sapiens arose in a cradle of humankind in East Africa 200,000 years ago.
Archaeologists unearthed the bones of at least five people at Jebel Irhoud, a former barite mine 100km west of Marrakesh, in excavations that lasted years. They knew the remains were old, but were stunned when dating tests revealed that a tooth and stone tools found with the bones were about 300,000 years old.


So where does H. naledi fit within the overall picture of human evolution in Africa? It’s still unresolved. Berger et al. suggested three scenarios: First, H. naledi belongs to one of the lineages leading to H. habilis, H. rudolfensis, H. floresiensis, and A. sediba. Alternatively, H. naledi is younger - a sister lineage to the clade that contains H. erectus and the big-brained later hominins (including H. sapiens). The final scenario is that H. naledi is even younger still - a sister lineage to H. sapiens. Another possibility is that H. naledi is the result of hybridisation between two or more lineages, perhaps one related to humans and one related to Australopithecines.

(190) Australopithecus interbred with Homo sapiens?



The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa


New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of 222Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/–70 ka, whilst a minimum age scenario yields an average age of 200 +70/–61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.
DOI: http://dx.doi.org/10.7554/eLife.24231.001


How do you figure out a fossil’s age? (By John Hawks)

We applied six different methods. The most valuable of these were electron spin resonance (ESR) dating, and uranium-thorium (U-Th) dating. ESR relies on the fact that teeth contain tiny crystals, and the electron energy in these crystals is affected by natural radiation in the ground over long periods of time after fossils are buried. U-Th relies on the fact that water drips into caves and forms layers of calcite, which contain traces of uranium. The radioactive fraction of uranium decays into thorium slowly over time. So the proportion of thorium compared to uranium gives an estimate of the time since the calcite layers formed. One of these calcite deposits, called a flowstone, formed above the H. naledi fossils in the Dinaledi Chamber. That flowstone helps to establish the minimum age: the fossils must be older than the flowstone above them.



[Anyway, they definitely are half Australopithecus, which dates from 2.5 - 7 million years ago. This means half their genes are old and half are young. So, they still might have been evolved in the developmental stage of Rebirth. They likely survived for millions of years. Just learned Hominin subspecies do not change much in evolution after they are established.]

Well, it isn't it shocking that damned Homo naledi is not that old, not 2.3 million years but only 200-335 thousand years old. On the other hand it is quite amazing and in a way much more heuristic for the forming of new hypotheses about the human origin which now has become a complete mess.

It likely means up to 200.000 years genes of Australopiths could have mixed with Homo erectus (2 Ma; 900cc), I mean Homo sapiens (200 Ma; 1400cc). Imagine what would happen if we could mix with chimps?

Would the brain remain apelike together with trunk characteristics? And would our offspring have humanlike extremities? Extended arms, legs and feet? And what about teeth? Said differently, could Homo naledi have interbred with Homo sapiens?

I still think they had no fire in Dinaledi chamber, since nowhere have been found burned materials. 

So we have the choice to let Australopiths breed with later Hominins about 200.000 years ago, or we must accept Homo naledi has been evolved about 2.3 million years ago and has not changed over millions of years. Everything might be possible. Homo naledi might have regressed to Australopiths because of climbing into trees again. But that's highly unlikely because meanwhile they could defend themselves much better than earlier Australopiths.

So, what do we conclude? The latest findings are more shocking than when Homo naledi was dated at 2.3 million years ago. Now, our whole hominin lineage is proven to be a mess. That's great since from now on a lot of new theories will emerge in this heuristic labyrinth:


This work is licenced under a Creative Commons Attibution-Non Commercial-ShareAlike 4.0 International Licence.

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