Monday, May 11, 2020

Dispute Over Our Ancestors

From Phys.org:
An important advancement in studies has been achieved after scientists retrieved the oldest human genetic data set from an 800,000-year-old tooth belonging to the hominin species Homo antecessor. The findings by scientists from the University of Copenhagen (Denmark), in collaboration with colleagues from the CENIEH (National Research Center on Human Evolution) in Burgos, Spain, and other institutions, are published April 1st in Nature.

"Ancient protein analysis provides evidence for a close relationship between Homo antecessor, us (Homo sapiens), Neanderthals, and Denisovans. Our results support the idea that Homo antecessor was a sister group to the group containing Homo sapiens, Neanderthals, and Denisovans," says Frido Welker, Postdoctoral Research Fellow at the Globe Institute, University of Copenhagen, and first author on the paper. (Read more.)

From National Geographic:
The remains went unnoticed and undisturbed until 2013, when spelunkers in South Africa’s Rising Star cave system came across hundreds of bone fragments and teeth from a newfound cousin to modern humans, a relative now called Homo naledi. Now, researchers poring over the cave’s fossils have pieced together the child’s partial skeleton—the first such juvenile H. naledi skeleton ever assembled.

Recovered from the cave system’s Dinaledi chamber, the individual—named DH7 (Dinaledi Hominin 7)—is thought to have died between eight and 15 years old. The newly described bones, unveiled today in the journal PLOS ONE, consist of a lower right jawbone and 16 fragments from the rest of the body. Such complete skeletons from young hominins other than modern humans and Neanderthals are exceedingly rare because the smaller, softer bones are less likely to fossilize. (Read more.)

From Ars Technica:
For most of the last few million years, our ancestors shared their world with several other hominin species. In some ways, most of those species looked and acted like their neighbors, but there were undoubtedly some striking differences, too. Every hominin species in the fossil record has its own unique mix of familiar human traits and more ape-like ones, shaped by their environments and lifestyles.
In some cases, we're not even entirely sure which of those species were our direct ancestors and which were more like cousins. That complexity makes it difficult to figure out exactly when (and why) hominins stopped hanging out in trees and started walking upright.
The size and shape of different parts of a bone can reveal plenty about how an animal—or a person—lived. Some things, like the general shape of our femurs, are the product of generations of evolution, which selected the traits that were most useful for bipeds. Others are the product of a lifetime of activity, because bone remodels itself constantly in response to the stress we put on it, so denser bone tends to form where the bone is under the most pressure. But you can't see those patterns just by looking at the outside of the bone.
University of Kent paleoanthropologist Leoni Georgiou and colleagues used CT scanning to look at those patterns of bone density inside the femurs (thigh bones) of two early hominins. In particular, they looked at the femoral head—the ball of bone at the top of the femur, which fits into the socket of the pelvis to form the hip-joint. That's where a lot of the weight of the body gets distributed downward through the rest of the leg and the feet, so it's an important clue about whether extinct hominins walked or climbed. (Read more.)

Also from Phys.org:
In this study, Bolter and colleagues examined fossils from the Dinaledi Chamber of the Rising Star Cave System in South Africa. This site is famous for providing abundant remains of the Homo naledi, including individuals ranging from infants to adult. These fossils date to the late Middle Pleistocene, between 335,000 and 226,000 years ago, possibly overlapping in time with the earliest members of our own species. The team identified a collection of arm and leg bones and a partial jaw as the remains of a single young individual designated DH7.

The bones and teeth of DH7 were not fully developed and display a mixture of maturity patterns seen in modern humans and earlier hominins. DH7 is estimated to be similar in its to immature specimens of other fossil hominins between 8-11 years old at death. The authors note, however, that if Homo naledi had a slower growth rate like , DH7 might have been as old as 15. Further study is needed to assess how Homo naledi grew and where it fits into the evolution of human growth and development. (Read more.)
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