Tag: Staff Picks

Inbreeding, Small Populations, and Demographic Fluctuations Alone Could Have Led to Neanderthal Extinction

Credit: Petr Kratochvil (CC0)
Neanderthal man

Neanderthal extinction could have occurred without environmental pressure or competition with modern humans

Small populations, inbreeding, and random demographic fluctuations could have been enough to cause Neanderthal extinction, according to a study published November 27, 2019 in the open-access journal PLOS ONE by Krist Vaesen from Eindhoven University of Technology, the Netherlands, and colleagues.

Paleoanthropologists agree that Neanderthals disappeared around 40,000 years ago—about the same time that anatomically modern humans began migrating into the Near East and Europe. However, the role modern humans played in Neanderthal extinction is disputed. In this study, the authors used population modelling to explore whether Neanderthal populations could have vanished without external factors such as competition from modern humans.

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Using data from extant hunter-gatherer populations as parameters, the authors developed population models for simulated Neanderthal populations of various initial sizes (50, 100, 500, 1,000, or 5,000 individuals). They then simulated for their model populations the effects of inbreeding, Allee effects (where reduced population size negatively impacts individuals’ fitness), and annual random demographic fluctuations in births, deaths, and the sex ratio, to see if these factors could bring about an extinction event over a 10,000-year period.

The population models show that inbreeding alone was unlikely to have led to extinction (this only occurred in the smallest model population). However, reproduction-related Allee effects where 25 percent or fewer Neanderthal females gave birth within a given year (as is common in extant hunter-gatherers) could have caused extinction in populations of up to 1,000 individuals. In conjunction with demographic fluctuations, Allee effects plus inbreeding could have caused extinction across all population sizes modelled within the 10,000 years allotted.

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The population models are limited by their parameters, which are based on modern human hunter-gatherers and exclude the impact of the Allee effect on survival rates. It’s also possible that modern humans could have impacted Neanderthal populations in ways which reinforced inbreeding and Allee effects, but are not reflected in the models. 

However, by showing demographic issues alone could have led to Neanderthal extinction, the authors note these models may serve as a “null hypothesis” for future competing theories—including the impact of modern humans on Neanderthals. 

The authors add: “Did Neanderthals disappear because of us? No, this study suggests. The species’ demise might have been due merely to a stroke of bad, demographic luck.” 

Black Hole Eats Star

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Join Melissa Hoffman of the National Radio Astronomy Observatory for a tour of one of the most disruptive events in Universe.

What happens when a black hole has a star for dinner?

In this new video, Melissa Hoffman of the National Radio Astronomy Observatory takes us on a tour of one of the most disruptive events in Universe: a black hole ripping apart a nearby star.

Astronomers call these stellar deaths tidal disruption events, and only a few of them have been observed.

Using radio and infrared telescopes, including the National Science Foundation’s Very Long Baseline Array (VLBA), in 2018 an international team of astronomers witnessed this event in a pair of colliding galaxies called Arp 299.

Paleontologists discover complete Saurornitholestes langstoni specimen

Illustration by Jan Sovak

Discovery provides valuable insight into evolution of theropod dinosaurs around the world

A small, feathered theropod dinosaur, Saurornitholestes langstoni was long thought to be so closely related to Velociraptor mongoliensis that some researchers called it Velociraptor langstoni — until now.

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The discovery of a nearly complete dromaeosaurid Saurornitholestes langstoni specimen is providing critical information for the evolution of theropod dinosaurs, according to new research by a University of Alberta paleontologist.

The 76-million-year-old species was long thought to be so closely related to Velociraptor from Mongolia that some researchers even called it Velociraptor langstoni–until now.

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The landmark discovery was made by world-renowned paleontologists Philip Currie and Clive Coy from the University of Alberta and David Evans, James and Louise Temerty Endowed Chair of Vertebrate Palaeontology at the Royal Ontario Museum. The research illustrates how Saurornitholestes differs from Velociraptor. Importantly, the research also identifies a unique tooth evolved for preening feathers and provides new evidence that the dromaeosaurid lineage from North America that includes Saurornitholestes is distinct from an Asian lineage that includes the famous Velociraptor.

“Palaeontology in general is a gigantic puzzle where most of the pieces are missing. The discovery and description of this specimen represents the recovery of many pieces of the puzzle,” said Currie, professor in the Department of Biological Sciences and Canada Research Chair in Dinosaur Paleobiology. “This ranks in the top discoveries of my career. It is pretty amazing.”

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Another piece of the puzzle

Saurornitholestes is a small, feathered carnivorous dinosaur within the dromaeosaurid family (also known as “raptors”) that was previously known from fragmentary remains. Discovered by Coy in Dinosaur Provincial Park in 2014, the new skeleton is remarkably complete and exquisitely preserved, with all the bones (except for the tail) preserved in life position. The new research, which focuses on the skull, shows that the North American form has a shorter and deeper skull than the Velociraptor. At the front of the skull’s mouth, the researchers also discovered a flat tooth with long ridges, which was likely used for preening feathers. The same tooth has since been identified in Velociraptor and other dromaeosaurids.

“Because of their small size and delicate bones, small meat-eating dinosaur skeletons are exceptionally rare in the fossil record. The new skeleton is by far the most complete and best-preserved raptor skeleton ever found in North America. It’s a scientific goldmine,” said Evans.

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The study also establishes a distinction between dromaeosaurids in North America and Asia. “The new anatomical information we have clearly shows that the North American dromaeosaurids are a separate lineage from the Asian dromaeosaurids, although they do have a common ancestor,” said Currie. “This changes our understanding of intercontinental movements of these animals and ultimately will help us understand their evolution.”

Future research will investigate the remainder of the skeleton as well as additional analyses on the relationships between dromaeosaurids.

The paper, “Cranial Anatomy of New Specimens of Saurornitholestes langstoni (Dinosauria, Theropoda, Dromaeosauridae) from the Dinosaur Park Formation (Campanian) of Alberta,” was published in The Anatomical Record (doi: 10.1002/ar.24241).

Ancient Egyptians

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In ancient Egypt, Sacred Ibises were collected from their natural habitats to be ritually sacrificed, according to a study released November 13, 2019 in the open-access journal PLOS ONE by Sally Wasef of Griffith University, Australia and colleagues.

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Egyptian catacombs are famously filled with the mummified bodies of Sacred Ibises. Between around 664BC and 250AD, it was common practice for the birds to be sacrificed, or much more rarely worshipped in ritual service to the god Thoth, and subsequently mummified. In ancient sites across Egypt, these mummified birds are stacked floor to ceiling along kilometers of catacombs, totaling many millions of birds. But how the Egyptians got access to so many birds has been a mystery; some ancient texts indicate that long-term farming and domestication may have been employed.

In this study, Wasef and colleagues collected DNA from 40 mummified Sacred Ibis specimens from six Egyptian catacombs dating to around 2500 years ago and 26 modern specimens from across Africa. 14 of the mummies and all of the modern specimens yielded complete mitochondrial genome sequences. These data allowed the researchers to compare genetic diversity between wild populations and the sacrificed collections.

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If the birds were being domesticated and farmed, the expected result would be low genetic diversity due to interbreeding of restricted populations, but in contrast, this study found that the genetic diversity of mummified Ibises within and between catacombs was similar to that of modern wild populations. This suggests that the birds were not the result of centralized farming, but instead short-term taming. The authors suggest the birds were likely tended in their natural habitats or perhaps farmed only in the times of year they were needed for sacrifice.

The authors add: “We report the first complete ancient genomes of the Egyptian Sacred Ibis mummies, showing that priests sustained short-term taming of the wild Sacred Ibis in local lakes or wetlands contrary to centralised industrial scale farming of sacrificial birds.”

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Citation: Wasef S, Subramanian S, O’Rorke R, Huynen L, El-Marghani S, Curtis C, et al. (2019) Mitogenomic diversity in Sacred Ibis Mummies sheds light on early Egyptian practices. PLoS ONE 14(11): e0223964. https://doi.org/10.1371/journal.pone.0223964

Funding: Human Frontier Science is acknowledged for financial support in the form of a grant to DL, SI, BH, and EW(RGP0036/2011). SW thanks Griffith University for a PhD scholarship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.