A new study published in the journal Science Advances in February 2020 reports that it has found the earliest interbreeding event between different human populations ever, where the “super-archaics” of Eurasia interbred with another group known as the Neanderthal-Denisovan population long ago.
Alan Rogers is interested in understanding how ancient human populations lived, examining the DNA obtained from what he, with other scientists, call hominins – early humans. What he is doing is looking for common genes, mutations, and other patterns that could help him work out how these groups are related genetically. The foundation of such work is statistical.
A 2017 study by Rogers showed that there were signs that Neanderthals and Denisovans went their separate ways as population groups earlier than scientists had thought before. The global population of Neanderthals then became tens of thousands, rather than the estimated thousand that was thought to exist so far. Rogers came up with a population size beyond which a bottleneck would form.
This explains why different Neanderthal fossils show remarkable diversity between themselves, depending on where they were found, but within groups, there is a lot of inbreeding. This accounts for the presence of harmful mutations.
Other anthropologists like Mafessoni and Prufer disagreed because their DNA analytic techniques showed differing results. The problem, said Rogers, is that both he and they are right – but neither method is good at explaining genetic data.
The current study shows that this is due to the earliest interbreeding event discovered so far in ancient human experience. This is unique in that the Neanderthal-Denisovan groups and the super-archaics are farther apart, genetically speaking than any other interbreeding populations discovered until now.
Based on this, the researchers theorize that the “Out of Africa” movement, in which humans were thought to have migrated from Africa into Eurasia, actually followed a different timeline than that currently accepted.
Rogers says, “We’ve never known about this episode of interbreeding, and we’ve never been able to estimate the size of the super-archaic population. We’re just shedding light on an interval that was previously completely dark.”
Moreover, the method he used to examine the DNA of ancient humans is a novel technique of exploring human genes from much more long ago than ever before. It uses shared mutations in modern Africans and Europeans, as well as Neanderthals and Denisovans.
The human genome has over 3 billion nucleotides or building blocks. When a change occurs in one of these at a gene site, it is called a mutation. If this is heritable, that is, passed on to the next generation, it can be one way to identify the individuals belonging to that family.
Using a small fraction of the genome, namely, a few million nucleotide sites, which had a common gene mutation, among two or three groups of humans, the 2017 researchers discovered 10 different patterns of nucleotides.
In the current study, the observed pattern of mutation sharing indicates that these populations interbred with others five times, with one of these episodes being unknown so far. The timing of the interbreeding in human history says a lot about how long it takes for a human population to achieve reproductive isolation.
They also used other methods to analyze the genome so that they could estimate the time when different human populations of long ago separated from each other, and how big these populations were. The super-archaic group, for instance, seems to have formed its distinct species group, and maybe the fossil group found in Eurasia.
The scientists think that humans may have migrated into Eurasia in three waves. Following the separation of the super-archaic group, the Neanderthal-Denisovan ancestors followed their paths and rapidly became integrated with the super-archaics. The last wave occurred with modern humans who also interbred with these two other populations.
Rogers described his feelings when he came up with this theory: “I’ve been working for the last couple of years on this different way of analyzing genetic data to find out about history. It’s just gratifying that you come up with a different way of looking at the data, and you end up discovering things that people haven’t been able to see with other methods.”
Earliest interbreeding event between ancient human populations discovered – https://unews.utah.edu/earliest-interbreeding-event/
Neanderthal-Denisovan ancestors interbred with a distantly related hominin Alan R. Rogers, Nathan S. Harris and Alan A. Achenbach, Science Advances 20 Feb 2020: Vol. 6, no. 8, eaay5483 DOI: 10.1126/sciadv.aay5483, https://advances.sciencemag.org/content/6/8/eaay5483
A Surprisingly Large Number Of “Stars” You See In The Sky Are Actually Spacecraft – Wonderful Engineering
Thousands of communication satellites are being designed and launched at a rapid pace. These satellites will have a negative impact on observational astronomy research and are likely to significantly disrupt recreational or traditional cultural stargazing.
If you look up in the sky, you might notice a sequence of bright star-like objects moving in a straight line. Those aren’t stars. They’re Starlink satellites, and they’ll soon be even more noticeable in the dark sky.
Samantha Lawler, assistant professor of astronomy at the University of Regina, recently wrote a piece in The Conversation warning that “one out of every 15 points” of light in the sky could someday be a satellite rather than a star. Moreover, she said he also thinks that satellite companies like Elon Musk’s SpaceX’s Starlink will immensely impact space research.
“This will be devastating to research astronomy and will completely change the night sky worldwide,” she wrote.
Lawler’s forthcoming study will be published in The Astronomical Journal, which will show evidence for the adverse stargazing effects of satellite megaconstellations like SpaceX’s.
Given that firms like SpaceX offer internet to locations around the world that might otherwise be without it, Lawler believes that regulatory agencies should limit the number of visible satellites in orbit.
“Our perspective of the stars will soon be changed forever,” she added if that doesn’t happen.
“We can’t accept the global loss of access to the night sky, which we’ve been able to see and connect with for as long as we’ve been human,” she wrote.
Our orbit is clogged with space debris. Starlink’s satellites have to avoid space junk as well. Will legislators intervene to put a stop to it? If prior responses to existential concerns like climate change are any indication, it will be considered later rather than sooner.
Dinosaur tail found in Chile stuns scientists – Phys.Org
Chilean paleontologists on Wednesday presented their findings on a dinosaur discovered three years ago in Patagonia which they said had a highly unusual tail that has stumped researchers
The remains of the Stegouros elengassen were discovered during excavations in 2018 at Cerro Guido, a site known to harbor numerous fossils, by a team who believed they were dealing with an already known species of dinosaur until they examined its tail.
“That was the main surprise,” said Alexander Vargas, one of the paleontologists. “This structure is absolutely amazing.”
“The tail was covered with seven pairs of osteoderms … producing a weapon absolutely different from anything we know in any dinosaur,” added the researcher during a presentation of the discovery at the University of Chile.
The osteoderms—structures of bony plaques located in the dermal layers of the skin – were aligned on either side of the tail, making it resemble a large fern.
Paleontologists have discovered 80 percent of the dinosaur’s skeleton and estimate that the animal lived in the area 71 to 74.9 million years ago. It was about two meters (almost seven feet) long, weighed 150 kilograms (330 pounds) and was a herbivore.
According to the scientists, who published their research in the journal Nature, the animal could represent a hitherto unknown lineage of armored dinosaur never seen in the southern hemisphere but already identified in the northern part of the continent.
“We don’t know why (the tail) evolved. We do know that within armored dinosaur groups there seems to be a tendency to independently develop different osteoderm-based defense mechanisms,” said Sergio Soto, another member of the team.
The Cerro Guido area, in the Las Chinas valley 3,000 km (1,800 miles) south of Santiago, stretches for 15 kilometers. Various rock outcrops contain numerous fossils.
The finds there allowed the scientists to surmise that present-day America and Antarctica were close to each other millions of years ago.
“There is strong evidence that there is a biogeographic link with other parts of the planet, in this case Antarctica and Australia, because we have two armored dinosaurs there closely related” to the Stegouros, said Soto.
Alexander Vargas, Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile, Nature (2021). DOI: 10.1038/s41586-021-04147-1. www.nature.com/articles/s41586-021-04147-1
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Total solar eclipse brings darkness to Antarctic summer – CBC.ca
Video released by NASA shows a total solar eclipse as seen from Western Antarctica on Saturday.
The Earth’s southernmost continent experiences continual daylight from mid-October until early April, but the eclipse brought a few minutes of total darkness.
NASA said the period of totality began at 2:44 a.m. ET.
A solar eclipse occurs when the moon moves between the sun and Earth, casting a shadow on Earth, fully or partially blocking the sun’s light in some areas.
For a total eclipse to take place the sun, moon, and Earth must be in a direct line. The only place that this total eclipse could be seen was Antarctica.
The eclipse was also expected to be visible partially from South Africa, Chile, New Zealand and Australia on Saturday.
North America gets its next glimpse of a full solar eclipse on April 8, 2024.
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