Human evolution; explaining hobbits, luzonensis, etc. (Introduction)

by David Turell , Saturday, April 13, 2024, 21:34 (16 days ago) @ David Turell

Who travelled where and evolved who is a mystery; an attempt to unravel:

https://www.newscientist.com/article/2426655-untangling-the-enigmatic-origins-of-the-hu...

"On 10 April 2019, our extended family got a bit bigger. A study in Nature reported the discovery of a new species of hominin called Homo luzonensis, from the Philippines. My colleague and fellow fossil enthusiast Colin Barras wrote about it for New Scientist.

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"That story almost surely involves a sea crossing. During the glacial periods, sea levels were lower because so much water was locked up in the ice caps. As a result, many places that are now islands, like Borneo and Sumatra, were connected to mainland Asia – forming a vast expanse of land called Sunda. However, it seems Luzon was always an island.

"The implication is that some population of hominins, wandering vaguely eastwards, made their way to Luzon – accidentally or on purpose. Isolated on the island, they evolved bodies different to those of other hominins, ultimately becoming the distinct species we call H. luzonensis.

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"First, Luzon has a tropical climate, so it’s unlikely ancient DNA has been preserved – and indeed, attempts to extract it from the H. luzonensis remains have been unsuccessful. This cuts off a key line of evidence.

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"Secondly, we only have one set of remains of H. luzonensis. This means we don’t know how long they lived on Luzon. A 2018 study found the earliest known hominin activity in the Philippines on Luzon, in the form of stone tools and butchered rhino bones. These artefacts were 709,000 years old. Conceivably the hominins involved were H. luzonensis or their direct ancestors, but no hominin bones were found so we have no way of knowing. The two findings could be completely unrelated.

"This means a wide variety of hominins are in the frame. One candidate is Homo erectus, which was living outside of Africa at least 1.8 million years ago and survived at Ngandong on Java until as recently as 108,000 years ago. It seems distinctly possible that some H. erectus made it to Luzon.

"Another possibility is the “hobbits”, Homo floresiensis, known from the island of Flores in Indonesia. It’s conceivable that some of them made it to Luzon and then became isolated there. However, there’s no sign of the hobbits outside of Flores. The timings also may not work: the hobbits probably lived on Flores between 190,000 and 50,000 years ago, so if H. luzonensis turns out to be older than that, the hobbits can’t be their ancestors.

"The third possibility is the Denisovans, whose remains have been found on mainland Asia in the Altai Mountains and Tibetan plateau. Today many people in island South-East Asia carry Denisovan DNA, suggesting the Denisovans roamed Sunda as well as what we now think of as the mainland. Intriguingly, a 2021 study found that groups called Ayta living on Luzon have the highest level of Denisovan ancestry in the world, hinting that the Denisovans visited the island. However, we have few confirmed Denisovan remains, so we don’t know how long they were around.

"Finally, there is the most dramatic possibility: that H. luzonensis is directly descended from an Australopithecus. These earlier hominins have only been found in Africa, but it’s conceivable that some of them did wander outside the continent. In the original 2019 study, the researchers described a number of attributes of the H. luzonensis remains that are not found in other Homo species but are found in Australopithecus.

"Two studies point to a link with H. erectus. In 2022, Détroit, Mijares and their colleagues published a study of H. luzonensis teeth. They compared the teeth with those of several other hominins. The crowns of the teeth were most like those of H. erectus in their external shape, while the internal structures were most similar to those of H. erectus and of hobbits. The team interpreted this to mean that both H. luzonensis and H. floresiensis were descended from H. erectus.

"In line with this, a 2023 study by an independent group argued that H. luzonensis and H. floresiensis are both similar enough to known H. erectus fossils, and separated enough in time, that we should not be unduly surprised by their existence. Put another way, there was plenty of time for H. erectus populations to evolve into these different forms.

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"The Australopithecus idea is clearly the most radical and therefore the one that excites me the most. Nevertheless, I’m wary of claiming that H. luzonensis is a direct descendant of an Australopithecus. Yes, the similarities are there, but evolution often throws up the same thing multiple times in different species: it’s called convergent evolution. I would want to see a lot more of the skeleton and a lot more similarities to Australopithecus.

"The other obvious issue is that we have plenty of evidence of H. erectus in South-East Asia, and no physical evidence of Australopithecus outside Africa. For that reason, I think H. erectus remains the most likely ancestor of H. luzonensis (although possibly via a Denisovan intermediate, if we assume Denisovans are descended from H. erectus)."

Comment: H. erectus certainly got around and arriving on these islands had enough time to fit into a "small island syndrome" development. Environment causes adaptations. A 300,000-year history ending up with a 25,000-year history in the Americas, wandering to the East.