The Australian Aborigines may not be just descendants of first settlers

Just realized. The Science paper has some interesting dates which allows us to make the above inference.

– Separation between Europeans and East Asians 25-38 thousand years before present.

– Gene flow between proto-East Asians and proto-Australians before the Native Americans diverged from the former 15 thousand years before the present.

– A conservative first landing in Australia 40-45 thousand years before the present.

The Native American result, where they share some derived variants unique to East Eurasians (mutations which emerged after the separation from West Eurasians) with Aborigines, pegs a minimum date of admixture ~15,000 years ago. But, obviously the admixture had to occur after the divergence of West and East Eurasians. Let’s say ~30,000 years ago. Even assuming that the gene flow between East Eurasians and proto-Australians occurred immediately after the separation 38,000 ago, there were anatomically modern humans in Australia for thousands of years already! The implication is that the first Australians by necessity can not have contributed in totality the ancestry of modern Aborigines. The AJHG paper gives a 50:50 estimate for the ratio of proto-Australian and the Andaman Islander/Malaysian-Negrito related population. We don’t need to be certain of the exact value to assume that numbers like this imply considerable admixture above trace levels.

Of all the dates I’m probably most confident about the archaeological ones about the settlement of Australia by anatomically modern humans. 46,000 years ago the megafauna started going extinct. That’s an immediate tell that humans have been let into the garden.

Out of Africa onward to Wallacea


There are two interesting and related papers out today which I want to review really quickly, in particular in relation to the results (as opposed to the guts of the methods). Taken together they do change our perception of how the world was settled by anatomically modern humans, and if the findings are found to be valid via replication (I think this is likely, in at least some parts) I was clearly wrong and misled others in assertions I made earlier on this weblog (more on that later). The first paper is somewhat easier to parse because it is in some ways a follow up on the paper from 2010 which documented admixture into Near Oceanian (Melanesian + Australian Aboriginal) populations from a distant hominin lineage, the Denisovans.

In this paper in The American Journal of Human Genetics they extend their geographic coverage. Denisova Admixture and the First Modern Human Dispersals into Southeast Asia and Oceania:

It has recently been shown that ancestors of New Guineans and Bougainville Islanders have inherited a proportion of their ancestry from Denisovans, an archaic hominin group from Siberia. However, only a sparse sampling of populations from Southeast Asia and Oceania were analyzed. Here, we quantify Denisova admixture in 33 additional populations from Asia and Oceania. Aboriginal Australians, Near Oceanians, Polynesians, Fijians, east Indonesians, and Mamanwa (a “Negrito” group from the Philippines) have all inherited genetic material from Denisovans, but mainland East Asians, western Indonesians, Jehai (a Negrito group from Malaysia), and Onge (a Negrito group from the Andaman Islands) have not. These results indicate that Denisova gene flow occurred into the common ancestors of New Guineans, Australians, and Mamanwa but not into the ancestors of the Jehai and Onge and suggest that relatives of present-day East Asians were not in Southeast Asia when the Denisova gene flow occurred. Our finding that descendants of the earliest inhabitants of Southeast Asia do not all harbor Denisova admixture is inconsistent with a history in which the Denisova interbreeding occurred in mainland Asia and then spread over Southeast Asia, leading to all its earliest modern human inhabitants. Instead, the data can be most parsimoniously explained if the Denisova gene flow occurred in Southeast Asia itself. Thus, archaic Denisovans must have lived over an extraordinarily broad geographic and ecological range, from Siberia to tropical Asia.

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God is intuitive

Update: An ungated version of the paper.

I used to spend a lot more time talking about cognitive science of religion on this weblog. It was an interest of mine, but I’ve come to a general resolution of what I think on this topic, and so I don’t spend much time discussing it. But in the comments below there was a lot of fast & furious accusation, often out of ignorance. I personally find that a little strange. I’ve been involved in freethought organizations in the past, and so have some acquaintance with “professional atheists.” Additionally, I’ve also been a participant and observer of the internet freethought websites since the mid-1990s (yes, I remember when alt.atheism was relevant!). In other words, I know of whom I speak (and I am not completely unsympathetic to their role in the broader ecology of ideas).

But the bigger issue is a cognitive model of how religiosity emerges. Luckily for me a paper came out which speaks to many of the points which I alluded to, Divine intuition: Cognitive style influences belief in God:

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40 hits in 40 years

I’m not very interested in music compared to the average person. But I’m curious about changing tastes in music over time, because it’s part of our cultural fabric. Since I lack real “thick” knowledge in this domain, I started to think of crutches to allow me to get a slice of perception as a function of time. So what I did was look at all the top songs by year since 1970, and found them on YouTube. I created a “playlist” which I could listen to all at once.

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What atheism and autism may have in common

My post below on atheism and autism caused some confusion. I want to quickly clear up some issues in regards to the model which I had in mind implicitly. In short I’m convinced by the work of cognitive scientists of religion (see Religion Explained and In Gods We Trust) that belief in gods and spirits is intuitively plausible to most people. It does not follow from this that when you have an intuitive belief that that belief is unshakable. This explains the variation in levels of atheism across societies as well as shifts of views across one’s lifetime. But, it also explains why in pre-modern societies acceptance of supernatural entities is the null or default position, if not necessarily universal.

But what’s the basis for the idea that belief in gods is intuitive? To reduce a lot of results down to a few sentences, humans live in a universe of other actors, agents, which we preoccupy over greatly. Additionally, we can conceive of agents which aren’t present before us. In other words, the plausibility of supernatural narratives derives from our orientation toward populating the universe with social beings and agency. There’s a lot of evolutionary psychological models for why this phenotype is adaptive, but that’s not relevant to us here. The point is that religious beliefs and systems use these intuitions and impulses as atoms with which they can build up more complex cultural ideas.

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The words of the father

Over at A Replicated Typo they are talking about a short paper in Science, Mother Tongue and Y Chromosomes. In it Peter Forster and Colin Renfrew observe that “A correlation is emerging that suggests language change in an already-populated region may require a minimum proportion of immigrant males, as reflected in Y-chromosome DNA types.” But there’s a catch: they don’t calculate a correlation in the paper. Rather, they’re making a descriptive verbal observation. This observation seems plausible on the face of it. In addition to the examples offered, one can add the Latin American case, where mestizo populations tend to have European Y chromosomal profiles and indigenous mtDNA.

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Atheism as mental deviance

Tyler Cowen points me to a PDF, Religious Belief Systems of Persons with High Functioning Autism, which has some fascinating results on the religiosity (or lack thereof) of people with high functioning autism. I’ve seen speculation about the peculiar psychological profile of atheists before in the cognitive science literature, and there’s a fair amount of social psychological data on the different personality profile of atheists (e.g., more disagreeable). But there hasn’t been a lot of systematic investigation of the possibility that autistic individuals are more likely to be atheist because they lack a fully fleshed “theory of mind,” which would make supernatural agents, gods, more plausible.

You can read the whole paper yourself, but these two figures are the most important bits:

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Rational optimist or scientific racist?

I’m quite looking forward to Steven Pinker’s The Better Angels of Our Nature: Why Violence Has Declined. It’s coming out in three weeks, so expect to hear a lot more about it. That violence has declined is known outside of Pinker’s own work, and I try and spread this “good news” as much as I can. But I’ve always found it peculiar that some of the most pessimistic and skeptical individuals in regards to these data aren’t reactionaries pining for the ancient idyll, but self-styled progressives who seem to believe that we are fallen creatures. Many of the latter are clearly modern followers of Rousseau, previously discussed in The Blank Slate.

In any case, Jerry Coyne points me to a really strange aside in a review of Pinker’s book in The Guardian:

To be tagged as a credulous optimist is one thing, yet Pinker also risks being condemned as a scientific racist. His graphs on the incidence of murder show present-day tribal and hunter-gatherer cultures to be far more homicidal than even the most lethally armed developed nation, a fact that is bound to bring censure from those Pinker derides as the “anthropologists of peace”

If the reviewer is characterizing these “anthropologists of peace” correctly perhaps it’s a commentary on what modern anthropology has become. I’ll leave you with some charts….

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The end of "archaic" H. sapiens

The Pith: The Bushmen branch of the human family tree diverged ~130,000 years ago. The non-Africans branched off from the Africans ~50,000 years ago. The Europeans and East Asians diverged ~35,000 years ago.

One of the terms in paleoanthropology which can confuse is that of archaic Homo sapiens (AHS). This is in contrast to anatomically modern humans (AMH). A simple Out of Africa “recent-origin-with-replacement” model allowed to sidestep the semantic imprecision in tossing disparate populations into a generic category such as AHS (similarly, the term “animal” as opposed to “human” has some colloquial utility, but it’s not scientifically useful). But the possibility of admixture from archaic lineages in modern human populations forces us to grapple with the dichotomy between AHS and AMH, as modern humans may be a compound of these two categories (not to mention the idea of behaviorally modern humans, who are a subset of AMH).

I assume that fleshing out the details of a new paradigm which is both precise and accurate will be a project for the coming years. But before we move on we need to fix more sturdily our understanding of the genealogical relationships of contemporary human populations. Over the past few years there have been major strides in this domain, confirming the broad outline of a dominant African heritage for modern humans. Geneticists have moved from classical markers to SNP data, focusing on hundreds of thousands of genetic variants. But now they’re shifting to whole genome sequences, which with errors excepted encapsulate the totality of the lowest order aspect of human genetic variation.* Earlier this summer I reviewed a paper in Nature which was a foretaste, Inference of human population history from individual whole-genome sequences. Today Nature has published another, Bayesian inference of ancient human demography from individual genome sequences.

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Out of Africa's end?

The BBC has a news report up gathering reactions to a new PLoS ONE paper, The Later Stone Age Calvaria from Iwo Eleru, Nigeria: Morphology and Chronology. This paper reports on remains found in Nigeria which date to ~13,000 years B.P. that exhibit a very archaic morphology. In other words, they may not be anatomically modern humans. A few years ago this would have been laughed out of the room, but science moves. Here is Chris Stringer in the BBC piece:

“[The skull] has got a much more primitive appearance, even though it is only 13,000 years old,” said Chris Stringer, from London’s Natural History Museum, who was part of the team of researchers.

“This suggests that human evolution in Africa was more complex… the transition to modern humans was not a straight transition and then a cut off.”

Prof Stringer thinks that ancient humans did not die away once they had given rise to modern humans.

They may have continued to live alongside their descendants in Africa, perhaps exchanging genes with them, until more recently than had been thought.

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