Human Evolution

[Jo Bowyer]

This is one of the largest Ice Age structures made of mammoth bones

Hunter-gatherers in what’s now Russia constructed the massive ring around 25,000 years ago

https://www.sciencenews.org/article/...orspicks032220

[Jo Bowyer]

The evolution of the vestibular apparatus in apes and humans

https://elifesciences.org/articles/5...20-elife-alert

Humans, gorillas, chimpanzees, orangutans and gibbons all belong to a group known as the hominoids. This ‘superfamily’ also includes the immediate ancestors and close relatives of these species, however in many instances the evolutionary relationships between these extinct ape species remain controversial.

While DNA can help evolutionary biologists to work out how living species are related to one another, fossils are typically the principle source of information for extinct species. Inferring evolutionary relationships from fossils must be done with caution, but the bony cavity that houses the inner ear – which is involved in balance and hearing and fairly common in the fossil record – has proven useful for tracing the evolution of certain groups of mammals. However, no one had previously looked to see if this structure could give insights into the evolutionary relatedness among living and extinct hominoids.

Urciuoli et al. have now used a 3D imaging technique to capture the complex shapes of the inner ear cavities of 27 species of monkeys and apes, including humans and two extinct apes (Oreopithecus and Australopithecus). The results confirmed that the shape of these structures most closely reflected the evolutionary relationships between the species and not, for example, how the animals moved.

Urciuoli et al. went on to identify features of these bony chambers that were shared within several hominoid groups, and to estimate what the inner ears of the ancestors of these groups might have looked like. The results for Australopithecus, for example, were consistent with it being most closely related to modern humans than other apes, while those for the enigmatic Oreopithecus supported the view that it was a much older species of ape that converged in some respects with other apes still alive today.

[Jo Bowyer]

The ancient hominid species that includes ‘Nutcracker Man’ may have made tools

https://www.sciencenews.org/article/...test_Headlines

P. boisei, a distant cousin to modern humans, lacked a thick, powerfully gripping thumb characteristic of its hominid contemporary, Homo erectus (SN: 3/24/15), a prolific maker of sophisticated stone tools. But the newly described hand bones suggest that P. boisei gripped well-enough to make and use simple stone and bone tools, just as other members of the human evolutionary family may have as early as 3.3 million years ago (SN: 5/20/15). That’s long before the emergence of the Homo genus, which appeared around 2.8 million years ago. But reports of tool-making before Homo originated are controversial.

“This is the first evidence that creatures that were almost certainly not our direct ancestors could have made tools,” says paleoanthropologist Bernard Wood of George Washington University in Washington, D.C. “So we can no longer assume — nor should we ever have assumed — that only Homo could make tools,” says Wood, who was not involved with the new research.

[Jo Bowyer]

The earliest known hominid interbreeding occurred 700,000 years ago

https://www.sciencenews.org/article/...orspicks022320

[Jo Bowyer]

Some West Africans may have genes from an ancient ‘ghost’ hominid

The passed-down DNA helps with functions including tumor suppression and hormone regulation

https://www.sciencenews.org/article/...test_Headlines

[Jo Bowyer]

Early humans in Africa may have interbred with a mysterious, extinct species – new research

https://theconversation.com/early-hu...new%20research

[Jo Bowyer]

A Siberian cave contains clues about two epic Neandertal treks

https://www.sciencenews.org/article/...test_Headlines

[Jo Bowyer]

Homo erectus arrived in Indonesia 300,000 years later than previously thought

https://www.sciencenews.org/article/...orspicks011220

[Jo Bowyer]

Why some scientists want to rewrite the history of how we learned to walk

https://theconversation.com/why-some...ed%20to%20walk

[Jo Bowyer]

Mammals' complex spines are linked to high metabolisms; we're learning how they evolved

https://www.sciencedaily.com/release...1107084036.htm

"The uniqueness of mammalian backbones is something that's been recognized for a long time, and our results show that there's a strong connection between the evolution of our backbones and the evolution of the soft tissues in our muscular and respiratory systems," says Angielczyk.

"We're interested in the big picture of how backbones evolve, and there are these long-standing ideas about it being related to the evolution of mammals' respiration, locomotion, and high acitvity levels," Angielczyk adds. "We're trying to test and refine those hypotheses, and to use them to better understand the broader question of how complexity increases through evolution."

And this big picture of how mammals' spines became complex could help to explain a lot about mammals alive today, including us. "Mammals kind of do their own thing," says Angielczyk. "If you look at mammals today, we have lots of weird features in our metabolism and our bodies and reproductive strategies. It would be really confusing to figure out how they evolved if you were only looking at modern mammals. But we have a really good fossil record of early mammal relatives, and that can help us understand the history of many of these very unusual traits."

[Jo Bowyer]

Neanderthal extinction linked to human diseases

https://www.sciencedaily.com/release...1107160610.htm

Archeological evidence suggests that the initial encounter between Eurasian Neanderthals and an upstart new human species that recently strayed out of Africa -- our ancestors -- occurred more than 130,000 years ago in the Eastern Mediterranean in a region known as the Levant.

Yet tens of thousands of years would pass before Neanderthals began disappearing and modern humans expanded beyond the Levant. Why did it take so long?

Employing mathematical models of disease transmission and gene flow, Greenbaum and an international team of collaborators demonstrated how the unique diseases harbored by Neanderthals and modern humans could have created an invisible disease barrier that discouraged forays into enemy territory. Within this narrow contact zone, which was centered in the Levant where first contact took place, Neanderthals and modern humans coexisted in an uneasy equilibrium that lasted tens of millennia.

Ironically, what may have broken the stalemate and ultimately allowed our ancestors to supplant Neanderthals was the coming together of our two species through interbreeding. The hybrid humans born of these unions may have carried immune-related genes from both species, which would have slowly spread through modern human and Neanderthal populations.

As these protective genes spread, the disease burden or consequences of infection within the two groups gradually lifted. Eventually, a tipping point was reached when modern humans acquired enough immunity that they could venture beyond the Levant and deeper into Neanderthal territory with few health consequences.

At this point, other advantages that modern humans may have had over Neanderthals -- such as deadlier weapons or more sophisticated social structures -- could have taken on greater importance. "Once a certain threshold is crossed, disease burden no longer plays a role, and other factors can kick in," Greenbaum said.

Why us?

To understand why modern humans replaced Neanderthals and not the other way around, the researchers modeled what would happen if the suite of tropical diseases our ancestors harbored were deadlier or more numerous than those carried by Neanderthals.

"The hypothesis is that the disease burden of the tropics was larger than the disease burden in temperate regions. An asymmetry of disease burden in the contact zone might have favored modern humans, who arrived there from the tropics," said study co-author Noah Rosenberg, the Stanford Professor of Population Genetics and Society in the School of Humanities and Sciences.

According to the models, even small differences in disease burden between the two groups at the outset would grow over time, eventually giving our ancestors the edge. "It could be that by the time modern humans were almost entirely released from the added burden of Neanderthal diseases, Neanderthals were still very much vulnerable to modern human diseases," Greenbaum said. "Moreover, as modern humans expanded deeper into Eurasia, they would have encountered Neanderthal populations that did not receive any protective immune genes via hybridization."

The researchers note that the scenario they are proposing is similar to what happened when Europeans arrived in the Americas in the 15th and 16th centuries and decimated indigenous populations with their more potent diseases.

[Jo Bowyer]

A toe bone hints that Neandertals used eagle talons as jewelry

https://www.sciencenews.org/article/...orspicks110319

[Jo Bowyer]

Human embryos have extra hand muscles found in lizards but not most adults

https://www.sciencenews.org/article/...test_Headlines

[Jo Bowyer]

Did a common childhood illness take down the Neanderthals?

A 21st century nuisance for parents may have proved deadly to early man

https://www.sciencedaily.com/release...0919080755.htm

[Jo Bowyer]

An island grave site hints at far-flung ties among ancient Americans

Great Lakes and southeastern hunter-gatherers may have had direct contact 4,000 years ago

https://www.sciencenews.org/article/...test_Headlines