A genomic analysis in samples of Neanderthals and modern humans shows a decrease in ADHD-associated genetic variants
A genomic analysis in samples of Neanderthals and modern humans shows a decrease in ADHD-associated genetic variants
The frequency of genetic variants associated with attention-deficit/hyperactivity disorder (ADHD) has decreased progressively in the evolutionary human lineage from the Palaeolithic to nowadays, according to a study published in the journal Scientific Reports.
The new genomic analysis compares several ADHD-associated genetic variants described in current European populations to assess its evolution in samples of the human species (Homo sapiens), modern and ancient, and in samples of Neanderthals (Homo neanderthalensis). According to the conclusions, the low tendency observed in European populations could not be explained for the genetic mix with African populations or the introgression of Neanderthal genomic segments in our genome.
The new genomic study isled by Professor Bru Cormand, from the Faculty of Biology and the Institute of Biomedicine of the University of Barcelona (IBUB), the Research Institute Sant Joan de Déu (IRSJD) and the Rare Diseases Networking Biomedical Research Centre (CIBERER), and the researcher Oscar Lao, from the Centro Nacional de Análisis Genómico (CNAG), part of the Centre for Genomic Regulation (CRG). The study, whose first author is the CNAG-CRG researcher Paula Esteller -current doctoral student at the Institute of Evolutionary Biology (IBE, CSIC-UPF)- counts on the participation of research groups of the Aarhus University (Denmark) and the Upstate Medical University of New York (United States).
ADHD: an adaptive value in the evolutionary lineage of humans?
The attention deficit/hyperactivity disorder (ADHD) is an alteration of the neurodevelopment which can have a large impact on the life of the affected people. Featured by hyperactivity, impulsiveness and attention deficit, it is very common in modern populations -with a prevalence of 5% in children and adolescents- and can last up to adulthood.
From an evolutionary perspective, one would expect that anything detrimental would disappear among the population. In order to explain this phenomenon, several natural hypotheses have been presented -specially focused on the context of transition from the Palaeolithic to the Neolithic-, such as the known Mismatch Theory.
“According to this theory, cultural and technological changes that occurred over the last thousands of years would have allowed us to modify our environment in order to adopt it to our physiological needs in the short term. However, in the long term, these changes would have promoted an imbalance regarding the environment in which our hunter-gatherer ancestors evolved”, note the authors.
Therefore, several traits like hyperactivity and impulsiveness -typical in people with ADHD- could have been selectively favoured in ancestral environments dominated by a nomad lifestyle. However, the same features would have become non-adaptive in other environments related to more recent times (mostly sedentary).
Why is it one of the most common disorders in children and adolescents?
The new study, based on the study on 20,000 ADHD affected people and 35,000 controls, reveals the genetic variants and alleles associated with ADHD tend to be found in genes which are intolerant to mutations that cause loss of function, which shows the existence of a selective pressure on this phenotype.
According to the authors, the high prevalence of ADHD nowadays could be a result from a favourable selection that took place in the past. Although being an unfavourable phenotype in the new environmental context, the prevalence would still be high because much time has not passed for it to disappear. However, due to the absence of available genomic data for ADHD, none of the hypothesis has been empirically contrasted so far.
“Therefore, the analysis we conducted guarantee the presence of selective pressures that would have been acting for many years against the ADHD-associated variants. These results are compatible with the mismatch theory but they suggest negative selective pressures to have started before the transition between the Palaeolithic and the Neolithic, about 10,000 years ago”, say the authors.
Reference Article:
Esteller-Cucala, P.; Maceda, I.; Børglum, A.D.; Demontis, D.; Faraone, S.V.; Cormand, B.; Lao, O. “Genomic analysis of the natural history of attention-deficit/hyperactivity disorder using Neanderthal and ancient Homo sapiens samples”. Scientific Reports, May, 2020. Doi: 10.1038/s41598-020-65322-4
Bone circles made from the remains of mammoths reveal clues about Ice Age
Mysterious bone circles made from the remains of mammoths reveal clues about Ice Age
Mysterious bone circles made from the remains of dozens of mammoths have revealed clues about how ancient communities survived Europe's ice age.
About 70 of these structures are known to exist in Ukraine and the west Russian Plain.
New analysis shows the bones at one site are more than 20,000 years old, making it the oldest such circular structure built by humans discovered in the region. The bones were likely sourced from animal graveyards, and the circle was then hidden by sediment and is now a foot below current surface level.
The majority of the bones found at the site investigated, in the Russian Plains, are from mammoths. A total of 51 lower jaws and 64 individual mammoth skulls were used to construct the walls of the 30ft by 30ft structure and scattered across its interior. Small numbers of reindeer, horse, bear, wolf, red fox and arctic fox bones were also found.
Archaeologists from the University of Exeter have also found for the first time the remains of charred wood and other soft non-woody plant remains within the circular structure, situated just outside the modern village of Kostenki, about 500km south of Moscow. This shows people were burning wood as well as bones for fuel, and the communities who lived there had learned where to forage for edible plants during the Ice Age. The plants could also have been used for poisons, medicines, string or fabric. More than 50 small charred seeds were also found - the remains of plants growing locally or possibly food remains from cooking and eating.Dr Alexander Pryor, who led the study, said: "Kostenki 11 represents a rare example of Palaeolithic hunter-gatherers living on in this harsh environment. What might have brought ancient hunter gatherers to this site? One possibility is that the mammoths and humans could have come to the area on masse because it had a natural spring that would have provided unfrozen liquid water throughout the winter - rare in this period of extreme cold.
"These finds shed new light on the purpose of these mysterious sites. Archaeology is showing us more about how our ancestors survived in this desperately cold and hostile environment at the climax of the last ice age. Most other places at similar latitudes in Europe had been abandoned by this time, but these groups had managed to adapt to find food, shelter and water."
The last ice age, which swept northern Europe between 75-18,000 years ago, reached its coldest and most severe stage at around 23-18,000 years ago, just as the site at Kostenki 11 was being built. Climate reconstructions indicate at the time summers were short and cool and winters were long and cold, with temperatures around -20 degrees Celsius or colder. Most communities left the region, likely because of lack of prey to hunt and plant resources they depended upon for survival. Eventually the bone circles were also abandoned as the climate continued to get colder and more inhospitable.
Previously archaeologists have assumed that the circular mammoth bone structures were used as dwellings, occupied for many months at a time. The new study suggests this may not always have been the case as the intensity of activity at Kostenki 11 appears less than would be expected from a long term base camp site.
Other finds include more than 300 tiny stone and flint chips just a few millimetres in size, debris left behind the site's inhabitants as they knapped stone nodules into sharp tools with distinctive shapes used for tasks such as butchering animals and scraping hides.
The research, conducted by academics from the University of Exeter, University of Cambridge, Kostenki State Museum Preserve, University of Colorado Boulder and the University of Southampton, is published in the journal Antiquity.
Press release "Mysterious bone circles made from the remains of mammoths reveal clues about Ice Age" from the University of Exeter.
Archaeologists identify first prehistoric figurative cave art in Balkans
Archaeologists identify first prehistoric figurative cave art in Balkans
An international team, led by an archaeologist from the University of Southampton and the University of Bordeaux, has revealed the first example of Palaeolithic figurative cave art found in the Balkan Peninsula.
Dr Aitor Ruiz-Redondo worked with researchers from the universities of Cantabria (Spain), Newfoundland (Canada), Zagreb (Croatia) and the Archaeological Museum of Istria (Croatia) to study the paintings, which could be up to 34,000 years old.
The cave art was first discovered in 2010 in Romualdova Pećina ('Romuald's cave') at Istria in Croatia, when Darko Komšo, Director of the Archaeological Museum of Istria, noticed the existence of the remains of a red colour in a deep part of the cave.
Following his discovery, the team led by Dr Ruiz-Redondo and funded by the French State and the Archaeological Museum of Istria, with the support of Natura Histrica, undertook a detailed analysis of the paintings and their archaeological context.
This led to the identification of several figurative paintings, including a bison, an ibex and two possible anthropomorphic figures, confirming the Palaeolithic age of the artworks. Furthermore, an excavation made in the ground below these paintings led to the discovery of a number of Palaeolithic age remains; a flint tool, an ochre crayon and several fragments of charcoal.
Radiocarbon dating of these objects show an estimated age of around 17,000 years and other indirect data suggest the paintings date to an even earlier period - at around 34,000-31,000 years ago. Further research will be conducted in order to establish the precise age of the rock art.
Findings are published in the journal Antiquity.
This discovery expands the so far sparse register of Palaeolithic art in south east Europe. It makes Romualdova Pećina the first site where figurative Palaeolithic rock art has been discovered in this area. Together with Badanj in Bosnia and Herzegovina, the two are the only examples of rock art from the Palaeolithic period in the Balkans.
Dr Aitor Ruiz-Redondo, a British Academy-funded Newton International Fellow at the University of Southampton and postdoctoral researcher at the University of Bordeaux, said: "The importance of this finding is remarkable and sheds a new light on the understanding of Palaeolithic art in the territory of Croatia and the Balkan Peninsula, as well as its relationship with simultaneous phenomena throughout Europe."
A new project started by Dr Ruiz-Redondo and his team, funded by the British Academy, will develop further research at these two sites during the next few years.
