The assumption is: about 20-40,000 years ago, Australia and Papua were connected by land and this, for some reason, caused a migration of natives into Northern Australia from Papua, and this was of a size to be equivalent to a bottleneck.
Is this clear enough, or are you now getting ready for further odd exchanges?
Where is the evidence, data, or what have you, for this land bridge and migration, and when did it then disappear?
Itâs not an assumption, itâs a reliable conclusion based on evidence.
You can start with the DNA evidence. Then you can look at the physical evidence for the land bridge.
I think if we need to make many unwarranted assumptions about a model then it is on shaky ground. I also agree that admitting how certain assumptions can affect the outcome of your model is standard stuff in science. I donât know the geographic isolation study you are mentioning so I canât comment on that. The first study that you mention revealed that Australian Aborigines and Papuans are more closely related to each other than to any other population (figure 2). The inference that they share ancestry is based on the genetic data. As is the inference of gene flow. Iâm not sure how that is an assumption. Whether the gene flow was from a land bridge or by boat travel doesnât matter much to me. As for bottlenecks, the one proposed around 50 kya is not just an assumption, its based again on the genetic data they obtained. You can see this in the supplementary materials S07 & S08. They also admit there is room for improvement for their model here as well as some simplifying assumptions made. But the signal for the genetic bottleneck is nonetheless there. Anyway, Iâm not much bothered with the genetic data as I hold to a literal Adam and Eve but not as the sole progenitors of all humans. I tend toward Swamidass on this issue. Also, if you have time check out the third study lead by Reich and colleagues. Lots of good stuff there too.
From your Wikipedia source:
âWhen sea levels fell during the Pleistocene ice age, including the last glacial maximum about 18,000 years ago, the Sahul Shelf was exposed as dry land. Evidence of the shoreline of this time has been identified in locations which now lie 100 to 140 metres below sea level. A useful interactive timeline of sea level changes has been developed by Monash University. The Arafura Shelf formed a land bridge between Australia, New Guinea, and the Aru Islands, and these lands share many marsupial mammals, land birds, and freshwater fish as a result. Lydekkerâs Line, a biogeographical line, runs along the edge of Sahul Shelf where it drops off into the deep waters of the Wallacea biogeographical area. Wallacea sits in a gap between the Sahul Shelf and the Sunda Shelf, part of the continental shelf of Southeast Asia.â
If we have data for various fish and marsupial mammals, we should have skeletons, artifacts, and other evidence that would identify natives from New Guinea, and their migration. In fact, the discussion that I heard did not mention anything like this - something so central to the model.
My remark to another participant (into which you inserted yourself) was to echo the remarks of the scientist presenting his finding, in that he anticipated controversy, because the subject is just that. Also, this period is an ice age, and intuition would indicate migrations towards warmer climate, not the reverse. Again, please do not use my remarks for further arguments - the comment I made is reasonable and is shared by other scientists - models come with assumptions and some may cause controversy and differences in opinionâŚ
So what youâre doing is making assumptions about what we should find, while ignoring what we have found. This is not science.
I do not disagree with your comments, nor am I overly bothered by models that deal with genetic diversity - these are matters for scientists who practice in this area. My models are very different, but I am acutely aware of the valid criticisms made in peer reviews of mine, and other models - so I make general comments that reflects my experience. I will add that the modelling I have carried out, with all of its limitations and assumptions, has proved very useful - but it is a useful tool.
I Hold to a Biblical view of Adam and Eve (perhaps I should say an Orthodox Christian view) as the first truly human beings created in Godâs image. I cannot see how any genetic modelling could, or would, impact on this. I have read a handful of papers on population modelling and this has convinced me these models, generally speaking. are more or less similar to mine as far as assumptions and limitations go.
Ahh okay thank you for the clarity. Iâm new to the forum so I wasnât familiar with your views. I think the evidence can be more or less convincing as well based on starting points. And I also think it is somewhat opaque unless you spend a lot of time trying to understand population genetics. You say your view canât be changed by genetic evidence and that is quite alright with me. To be sure, though, this data does give problems to the YEC study cited to start this thread.
The discussions on genetic diversity, most recent common ancestors, pop modelling, and Adam and Eve has, imo, undergone such twists and turns over the years on this site, that I find it difficult to develop any coherent view of the protagonists. One extreme view seems to focus on Adam and Eve as the initial couple, and all humans are descended fro them over the past 6,000, while the other extreme insists there was no Adam and Eve, that all humans and primates have a common ancestor, and any differences are relatively minor, or a matter of degrees. There seem to be âin-betweenâ views, such as non-historic symbolic A&E, some type of archetype or representative A&E, and other views that, for the life of me, I cannot make any sense.
Since the EC view seems to oscillate about some type of Adam and Eve as a historic couple, and no couple but someone representative of modern humans, I have tried to understand this point of view based on various models on human population distribution. The interesting models use data that is: (a) historic - recorded for many centuries, and I suppose estimated from ancient times, using a stochastic model that accounts for a recent common ancestry based on a couple, and the current population and distribution forming over 6-10,000 years; and (b) data derived from genetics from a relatively large sample of modern human beings, and the genetic diversity is rationalised using a model that assumes a bottle neck of a relatively small population, and this spread from Africa, for over a lengthy period (I recall perhaps 1.6 million years, but I can be corrected on this). I have tried to point out the assumptions inherent in these approaches and caution against making biblical conclusions from them.
There are other reports, such as the one I referred to for Australians, and these require 20-40,000 years to account for genetic diversity, bottleneck and migration from New Guinea. Btw, artifacts, caves and paintings in Australia have been reported to be 40,000 years old, and these require a viable population to produce them.
My involvement in this tortuous discussion exchange over perhaps a year, has been to point out the assumptions built into any model, and to show that none of these replace or negate the Biblical story of Adam and Eve, as understood by Orthodox Christianity.
As an aside, I recall looking pictures of Adam and Eve and the picture of Godâs figure imparting life to Adam (Michelangelo) and racked my brain to see if I could think of anything like these images in the Orthodox Churches I have attended. I could be wrong, but I cannot recall one icon or painting of this sort - I think this is one way of showing the different emphasis Orthodoxy may place on this subject matter.
In any event, I trust this detailed response (ramble) may be helpful to someone on this site.
There may be some confusion here about the difference between assumptions and conclusions. If a study of genetic data finds evidence for a genetic bottleneck in the population, the bottleneck is a conclusion of the study, not an assumption. Typically, the conclusion is reached by comparing data to the predictions of models with and without a bottleneck. An assumption might be the specific form of the bottleneck, or features that are shared between the models, e.g. the mutation rate.
The relevant question is how robust the conclusions are to changes the assumptions. The presence of a bottleneck is usually quite robust, while the timing of the bottleneck is not.
I have lost track of what exactly is being disputed in the last dozen or so posts⌠but it may well be that the âWallace Lineâ is relevant to your future postings:
âThe Wallace Line or Wallaceâs Line is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace that separates the ecozones of Asia and Wallacea, a transitional zone between Asia and Australia. West of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origin is present. Wallace noticed this clear division during his travels through the East Indies in the 19th century.â
âDuring ice age glacial advances, when the ocean levels were up to 120 metres (390 ft) lower, both Asia and Australia were united with what are now islands on their respective continental shelves as continuous land masses, but the deep water between those two large continental shelf areas was, for over 50 million years, a barrier that kept the flora and fauna of Australia separated from those of Asia.â
âWallacea consists of islands that were not recently connected by dry land to either of the continental land masses, and thus were populated by organisms capable of crossing the straits between islands. âWeberâs Lineâ runs through this transitional area (to the east of centre), at the tipping point between dominance by species of Asian against those of Australian origin.â
âIt can reasonably be concluded it was an ocean barrier preventing species migration because the physical aspects of the separated islands are very similar.[7] Species found only on the Asian side include leaf monkeys and ponderous-beaked hornbills while Australian wallabies, spiny anteaters, tree kangaroos and gliding possums are not.â
A model may provide an outcome of a number of individuals to account for the genetic diversity - this is a result from the model. Data (or the preferred term amongst some, evidence) is required to confirm or negate the conclusion, and such data may take the form of remains of a community consistent with the bottleneck - until this is provided, it can only be understood as a result of the model.
The example of Australia provides data that is consistent with a stable population (with a period twice that predicted by the genetics model) but not of anything that would be equated with a specific bottleneck. The other model (if memory serves) fails to provide any data for any population meeting the requirements of a bottleneck 1.6 m years ago. Therefore we must assume the results of the model (as well as other factors in the model) are valid, and we cannot assume or state these results are confirmed.
This seems to represent a fundamental misunderstanding. The genetic diversity for a population is a dataset, otherwise known as evidence. That evidence may support either a model with a bottleneck or a model without a bottleneck. Any conclusion drawn from that data about a bottleneck will be based on evidence. Itâs nice if you can find confirmatory evidence of a different kind â consilience is an important feature of science, after all â but thereâs no requirement that you do so to conclude that yes, a bottleneck occurred. As with any scientific study, there may be more or less confidence in the result, and more or less competence by the researchers. But there is nothing about the process here that means we have to withhold provisional assent until some other kind of data arrives.
This is entirely analogous to what high energy physicists do. They collect data from particle decays. To search for a particular decay mode, they model what their data should look like with and without the decay mode present, and see which one fits better. If the model with the decay mode is sufficiently better than the model without, then they publish a paper saying that they have detected the decay X->yz. No other data sources are required.
If you see weaknesses in a particular study, or contradictions between studies, we can certainly discuss them. What study of Australia are you talking about here?
Yes, this is correct, and the reason I have tried to keep my comments general, and bring the discussion back to the reason we are exchanging opinions (biblical doctrine), is not to indulge in an attack on this type of modelling, but to ask, âAre the results and assumptions sufficient to warrant a rethink of doctrines such as the so called original sin, and historic Adam and Eve?â Imo I cannot see anything so clear cut and detailed from genetic modelling that would cause me to rethink such doctrine.
If it is important I will try and locate the Australian study - my recollection is that it was publicised as an important result, and the person in question also admitted to (anticipating) some controversy - I suspect this comment caused me to listen, rather than another report on bottlenecks and so on.
As far as a general approach to modelling, my experience has dealt with complex chemical reaction mechanisms and reaction routes, and I have at all times based my conclusions on either (a) the results are validated based on experimental data, or (b) the results cannot be validated and are thus reported as speculative. If other modellers, within a different context, (for whatever reason) take a different approach, it is for them to come to their conclusions and discuss them in the appropriate literature. However, biblical doctrine is to me a different matter and requires more than a scientistâs preference and inclination, before I would question it.
Here is the talk. Iâll have to watch it later, but thanks to @Eddie for his glowing review and, of course, to @glipsnort for the talk itself. Sounds fantastic!
Thatâs me â thanks for your kind words. I did put a good deal of thought into that talk, and tried to pick kinds of evidence that could be explained without too many technical digressions.
There are generally complications and anomalies in the real world. In particular, in a process with billions or trillions of events, more than a few one in a million events will occur. The overall picture is very clear, though. What I would wish to hear from critics would be some kind of coherent explanation for genetic data that doesnât include large-scale common descent.
Historically, a number of physicists have moved into genetics. More recently, a lot of people have moved into biology from fields with strong computational and mathematical components: physics, math and statistics, computer science and even electrical engineering. Traditional training for biologists did not equip most of them to handle large data sets and large-scale computing. These days, there is less of a need as there are more programs in computational biology/bioinformatics.
As for how I made the transition, I read some textbooks and applied for a job as a software engineer at a genome center, with the understanding that I wanted to do science. Then I learned on the job.
No, before becoming a physicist I was training to be a literary critic (although Iâd already majored in physics by that time).
I have just found this book that provides some interesting discussions, and one chapter deals with mathematical models of population ecology. I find this quote interesting:
The Undeniable Effectiveness of Mathematics in the Special Sciences, Mark Colyvan.
âI have argued that mathematics can play a number of useful roles in ecological theory. Mathematics can represent biological facts and it is often able to do this is such a way as to make certain biological explanations more accessible. Mathematics is well suited to drawing attention to similarities between apparently different systems (and often provide the appropriate level of abstract representation for investigating the similarities). This, allows each of these areas to learn from one another, and reduces duplication of research. Finally, I argued that there are explanations in ecology where the mathematics carries the bulk of the explanatory burden, and these explanations are appropriately seen as mathematical explanations of biological phenomena.â
A couple of remarks, late to the party.
First on Eddieâs exchange with Joshua etc on MRCA, which was a subject that I looked at even prior to the Hump of the Camel coming online in 2011. Eddie wonders about the refutation of Paulâs teaching that Adam and Eve were the ancestors of all humans whatoseoever.
Iâm not sure Paul puts it that clearly, but in our scientific terms the concept is meaningless, because we have no definition of âhumanâ, rather inconsistently thinking either of H sapiens, or of the genus Homo, or of a variable bunch of the higher species or hybrids of that genusâŚ
Yet Paulâs concept of âmanâ corresponded to none of those biologically-based categories, but defined as human (his) present humanity, and those descended from Adam and Eve. If A&E were MRCAs in the sense of Rohdeâs thesis, all that Paul says of Adam would be true, his definition of âmanâ covering all those linked by blood both to the covenant-relationship of God to Adam, and to the stain of original sin.
Whatever he might have assumed about the history of mankind, what he wrote under the Holy Spirit is what matters.
Talking of original sin, my second point is about the supposed conflict between east and west on this. I wrote on it here back in 2012.
Usually this is described in terms of an opposition between Irenaeus (East) and Augustine (West), but in fact (a) they are considering different theological issues, (b) they both regard the effects of sin in the world as being the direct result of Adamâs first sin, (c) although the Orthodox âancestral sinâ has a different flavour from Augustineâs it is still considered the cause of human death and originating in Adam, and (d) Augustine is a saint in Orthodoxy as in Catholicism: his views on original sin are held by many within Orthodoxy, to the extent that 20th Century Russian theologians seeking to refute it sold the idea in terms of Orthodoxyâs bondage to âforeignâ western ideas.
The net result is that to divorce the question of sin and death from an historical Adam, you have to overturn not only western, but eastern tradition.
History should have taught us by now that western and eastern tradition are insufficiently reliable to be trusted over reality and the Bible itself. But I note yet again the complete lack of any attention paid to Second Temple Judaism and early Christianity. Itâs like you people think Christianity started in the fourth century. Itâs a huge blind spot, and thatâs why youâre suffering.
âLet your conversation be always full of grace, seasoned with salt, so that you may know how to answer everyone.â -Colossians 4:6
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