Creationism in Crisis
How the Human Genome Holds a Record of Our Evolutionary History
How the Human Genome Holds a Record of Our Evolutionary History
Reconstruction of an early Eurasian H. sapiens from remains found in Greece
The first anatomically modern Homo sapiens to migrate out of Africa were almost certainly hunter-gatherers. This much can be deduced from the fact that agriculturalists tend to be relatively sedentary and tied to the land. Our early ancestors, however, were migrants who spread relatively rapidly and one of the best habitats for hunter-gatherers is the coast where food in the form of shell-fish is abundant.
It is often assumed that these migrants travelled up the Nile or the Red Sea coast to the Middle East, and dispersed from there, but there is an alternative coastal route once they arrived at the Horn of Africa.
It is a short sea journey from there to what is now Yemen in Arabia and from there either up the Hijaz to the Middle East or along the south-east coat to what is now Oman. From Oman it is again a short sea-crossing at the Gulf of Hormuz, or even up the Arabian Gulf coast, into what is now Iran. From there, the whole of south and south-east Asia is accessible by coastal spread, as is Mesopotamia and then Central Asia either by going round the Black Sea coast, or the more difficult rout through the Caucasus mountains between the Black Se and the Caspian Sea.
Even Australia could be reached via land at a time when sea-levels were much lower than today at glacial maxima.
And now, a team of Australian researchers led by Raymond Tobler and Yassine Souilmi, of the Australian Centre for Ancient DNA, The University of Adelaide, Adelaide, South Australia, Australia, have found genetic evidence of a 30,000 year period of evolutionary adaptation to a colder environment, probably in Arabia of the immediate area, prior to a rapid dispersal across Eurasia as far as Australia. Functional targets in the genome include multiple interacting loci involved in fat storage, neural development, skin physiology, and cilia function, with associations with multiple modern Western diseases.
The team’s findings were published recently in PNAS, sadly behind a paywall, although the Abstract is published open access.
Three of the team have also written about their research and findings in an article in The Conversation. There article is reprinted here under a Creative Commons license, reformatted for stylistic consistency:
Ancient humans may have paused in Arabia for 30,000 years on their way out of Africa
Source: Shutterstock
Source: Shutterstock
Ray Tobler, Australian National University; Shane T Grey, Garvan Institute, and Yassine Souilmi, University of Adelaide
Most scientists agree modern humans developed in Africa, more than 200,000 years ago, and that a great human diaspora across much of the rest of the world occurred between perhaps 60,000 and 50,000 years ago.
In new research published in Proceedings of the National Academies of Sciences, we have uncovered dozens of distinctive historical changes in the human genome to reveal a new chapter in this story.
Our work suggests there may have been a previously unknown phase of humanity’s great migration: an “Arabian standstill” of up to 30,000 years in which humans settled in and around the Arabian Peninsula. These humans slowly adapted to life in the region’s colder climate before venturing to Eurasia and beyond.
The legacy of these adaptations still lingers. Under modern conditions, many genetic changes from this period are linked to diseases including obesity, diabetes, and cardiovascular disorders.
History in our genomes
Since the first human genome was published in 2000, the amount of human genomic data available has grown exponentially. These rapidly growing datasets contain traces of key events in human history. Researchers have been actively developing new techniques to find those traces.
When ancient humans left Africa and moved around the globe, they likely met new environments and challenges. New pressures would have led to adaptation and genetic changes. These changes would subsequently have been inherited by modern humans.
Previous research on genomic data shows ancient humans most likely left Africa and spread across the planet between 60,000 and 50,000 years ago.
However, we still don’t know much about genetic adaptations during this crucial time period.
Ancient adaptation events
Our team of evolutionary and medical researchers has shed new light on this period. By studying both ancient and modern genomes, we have shown genetic selection was probably an important facilitator of this ancient human diaspora.
Using ancient human genomes makes it possible to recover evidence of past events in which specific genetic variants were strongly favoured over others and swept through a population. These “hard sweep” events are surprisingly rare in modern human genomes, most likely because their traces have been erased or distorted by subsequent mixing between populations.
However, in earlier work we identified 57 regions in the human genome where an initially rare beneficial genetic variant effectively replaced an older variant in ancient Eurasian groups.
In our new study, we reconstructed the historical spread of these genetic variants. We also estimated the temporal and geographical origins of the underlying selection pressures.
Further, we identified the gene in each hard sweep region most likely to have been selected for. Knowing these genes helped us understand the ancient pressures that may have led to their selection.
Coping with cold
Our findings suggest early humans went through a period of extensive adaptation, lasting up to 30,000 years, before the big diaspora between 60,000 and 50,000 years ago. This period of adaptation was followed by rapid dispersal across Eurasia and as far as Australia.
We call this period the “Arabian standstill”. Genetic, archaeological and climatic evidence all suggest these ancient humans were most likely living in and around the Arabian Peninsula.
The genetic adaptations involved parts of the genome related to fat storage, nerve development, skin physiology, and tiny hair-like fibres in our airways called cilia. These adaptations share striking functional similarities with those found in humans and other mammals living in the Arctic today.
We also detected similar functional similarities with previously identified human adaptive genes derived from historical mixing events with Neanderthals and Denisovans. These distant relatives of humans are also thought to have adapted to cold Eurasian climates.
Overall, these changes seem likely to have been driven by adaptation to the cool and dry climates in and around prehistoric Arabia between 80,000 and 50,000 years ago. The changes would also have prepared the ancient humans for the cold Eurasian climates they would eventually encounter.
Old adaptations, modern diseases
Many of these adaptive genes have links to modern diseases, including obesity, diabetes, and cardiovascular disorders. The adaptations around the human expansion from Africa may have established genetic variations that, under modern conditions, are associated with common diseases.
As we have suggested in another study, genes that were adaptive in the past might contribute to modern human susceptibility to various diseases. Identifying the genetic targets of historical adaptation events could help the development of therapeutic approaches and preventive measures for contemporary populations.
Our findings contribute to a new but growing literature highlighting the importance of adaptation in shaping human history. They also show the growing potential of evolutionary genetics for medical research.
Ray Tobler, Postdoctoral fellow, Australian National University; Shane T Grey, Chair professor, Garvan Institute, and Yassine Souilmi, Group Leader, Genomics and Bioinformatics, Australian Centre for Ancient DNA, University of Adelaide
This article is republished from The Conversation under a Creative Commons license. Read the original article.
SignificanceInterestingly, the team state that the period of genetic adaptation lasted until the introgression of Neanderthal genes, which was followed by the rapid dispersal across Eurasia. The possibility is thus that it was this introgression of Neanderthal DNA which enabled these H. sapiens to disperse into the colder northern parts of Eurasia rather than adaptation to cold weather in Arabia.
We analyze the functional and spatiotemporal properties of 57 hard sweeps inferred in ancient human genomes to reconstruct human evolution during the poorly understood Out of Africa migration. Our analyses reveal a previously unsuspected extended period of genetic adaptation lasting ~30,000 y, potentially in Arabia or surrounding regions, prior to a rapid dispersal across the rest of Eurasia as far as Australia. Functional targets include multiple interacting loci involved in fat storage, neural development, skin physiology, and cilia function, with associations with multiple modern Western diseases. Similar adaptive signatures are also evident in introgressed archaic hominin loci and modern Arctic human groups, indicating that cold environments were a prominent historical selection pressure that potentially facilitated the successful peopling of Eurasia.
Abstract
The evolutionarily recent dispersal of anatomically modern humans (AMH) out of Africa (OoA) and across Eurasia provides a unique opportunity to examine the impacts of genetic selection as humans adapted to multiple new environments. Analysis of ancient Eurasian genomic datasets (~1,000 to 45,000 y old) reveals signatures of strong selection, including at least 57 hard sweeps after the initial AMH movement OoA, which have been obscured in modern populations by extensive admixture during the Holocene. The spatiotemporal patterns of these hard sweeps provide a means to reconstruct early AMH population dispersals OoA. We identify a previously unsuspected extended period of genetic adaptation lasting ~30,000 y, potentially in the Arabian Peninsula area, prior to a major Neandertal genetic introgression and subsequent rapid dispersal across Eurasia as far as Australia. Consistent functional targets of selection initiated during this period, which we term the Arabian Standstill, include loci involved in the regulation of fat storage, neural development, skin physiology, and cilia function. Similar adaptive signatures are also evident in introgressed archaic hominin loci and modern Arctic human groups, and we suggest that this signal represents selection for cold adaptation. Surprisingly, many of the candidate selected loci across these groups appear to directly interact and coordinately regulate biological processes, with a number associated with major modern diseases including the ciliopathies, metabolic syndrome, and neurodegenerative disorders. This expands the potential for ancestral human adaptation to directly impact modern diseases, providing a platform for evolutionary medicine.
Tobler, Raymond; Souilmi, Yassine; Huber, Christian D.; Bean, Nigel; Turney, Chris S. M.; Grey, Shane T.; Cooper, Alan
The role of genetic selection and climatic factors in the dispersal of anatomically modern humans out of Africa
Proceedings of the National Academy of Sciences; 120(22), e2213061120. DOI: 10.1073/pnas.2213061120
Copyright: © 2023 The authors.
Published by PNAS. Open access only.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
So, which creationist is going to point to the part where the scientists admit that this wasn't evolution at work, but the result of supernatural magic, because that provides a better scientific explanation of the facts?
Hint: it isn't there. There is no doubt in serious evolutionary science that the TOE is fundamental to understanding what can be observed and is the only scientific theory capable of so doing.
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