Saturday, June 24, 2017

Scientists Have Found the Oldest Known Human Fossils


This is interesting.  We have cultural information that humanity was augmented around 200,000 years ago.  Now we have a good look at the pre inflexion skull and it suggests a radically different brain architecture just a 100,000 years earlier with modern volumes.  Changing around the architecture to what we know to be unique to start with could only be done with major DNA augmentation.  

The answer to that will be DNA if we can find it here.

What this does inform is that an emergent homo sapiens existed but lacked significant brain assets.  Changing this short circuited millions of years of doubtful brain development.

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Scientists Have Found the Oldest Known Human Fossils 

The 300,000-year-old bones and stone tools were discovered in a surprising place—and could revise the history of our species. 

A view looking south of the Jebel Irhoud site in Morocco. Shannon McPherron, MPI EVA Leipzig 

https://www.theatlantic.com/science/archive/2017/06/the-oldest-known-human-fossils-have-been-found-in-an-unusual-place/529452/ 

Hundreds of thousands of years ago, around 62 miles west of what would eventually become Marrakesh, a group of people lived in a cave overlooking a lush Moroccan landscape. They rested there, building fires to keep themselves warm. They hunted there, sharpening stone tools to bring down animals. And they died there, leaving their bones behind in the dirt. At the time, there would have been nothing particularly notable about these cave-dwellers. They were yet more Homo sapiens, members of a nascent ape species that had spread across Africa. But in their death, they have become singularly important.
That cave is now called Jebel Irhoud, and bones of its former occupants have been recently unearthed by an international team of scientists. They mark the earliest fossilized remains of Homo sapiens ever found. Until now, that honor belonged to two Ethiopian fossils that are 160,000 and 195,000 years old respectively. But the Jebel Irhoud bones, and the stone tools that were uncovered with them, are far older—around 315,000 years old, with a possible range of 280,000 to 350,000 years.
It’s not just when these people died that matters, but where. Their presence in north Africa complicates what was once a tidy picture of humanity arising in the east of the continent. “What people, including myself, used to think was that there was a cradle of humankind in East Africa about 200,000 years ago, and all modern humans descend from that population,” says Philipp Gunz from the Max Planck Institute for Evolutionary Anthropology, who was involved in the new excavation. “The new finds indicate that Homo sapiens is much older and had already spread across all of Africa by 300,000 years ago. They really show that the African story of our species was more complex than what we used to think.”“Humans had already migrated across the African landscape, and were evolving at a continental scale.”
Jebel Irhoud rose to prominence in 1961, when miners turned the site into a quarry. They were looking for barite minerals, but to their surprise, they found a fossilized skull. Soon, they disinterred more bones: another skull, a child’s jaw, and fragments of arm bones and hips. From the start, these specimens were controversial. Their exact location was never recorded, which makes it very hard to work out their age. Scientists initially thought that they were the 40,000-year-old remains of Neanderthals—and were wrong on both counts. They’re much older, and they’re more likely to be Homo sapiens. 
After those discoveries, Jebel Irhoud was neglected. But in 2004, Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology led a team back to the site, clearing away decades’ worth of accumulated debris in a search for more fossils. And after a few seasons of digging, they found some—a partial skull, fragments of facial bones, a nearly complete adult jawbone, and other bits and pieces from at least five individuals.
These people had very similar faces to today’s humans, albeit with slightly more prominent brows. But the backs of their heads were very different. Our skulls are rounded globes, but theirs were lower on the top and longer at the back. If you saw them face on, they could pass for a modern human. But they turned around, you’d be looking at a skull that’s closer to extinct hominids like Homo erectus. “Today, you wouldn’t be able to find anyone with a braincase that shape,” says Gunz.  Comparison of the skulls of a Jebel Irhoud human (lleft) and a modern human (right) (NHM London)
Their brains, though already as large as ours, must also have been shaped differently. It seems that the size of the human brain had already been finalized 300,000 years ago, but its structure—and perhaps its abilities—were fine-tuned over the subsequent millennia of evolution.
At Jebel Irhoud, the team also found several stone tools—small pieces of flint with sharp edges. Several of these had clearly been heated in the distant past, but not because their makers were deliberately burning the implements. More likely, “you can imagine that people were dropping stones on the ground, and later starting fires on top,” explains Shannon McPherron, an expert on stone tools who was involved in the new study.
The team exploited this incidental heating to date the tools. Over time, flint gradually builds up a small charge as it reacts to natural sources of radiation around it. That charge dissipates whenever it’s heated, before growing again. By testing the stones back in their lab, McPherron’s team could work out how much charge they had accumulated since they were last heated—which must have been when they were dropped in the caves. This technique, known as thermoluminescence, told them that the tools were roughly 280,000 and 350,000 years old.  Some of the Middle Stone Age stone tools from Jebel Irhoud (Mohammed Kamal / MPI EVA Leipzig)
The team checked those dates by estimating the ages of the fossils. They first did that a decade ago, using the fossils collected in the 1960s, and they arrived at an age of 160,000 years. But that was based on imperfect guesses about the sediments in which the bones had been buried. This time, after taking careful readings from the site itself, the team could more accurately re-do their calculations. They got a much older date of 286,000 years, which matches well to the estimated age of the tools. “I think it’s a pretty tight picture,” says McPherron.
The new dates radically change the position of the Jehul Irhoud residents in the family tree of our species. Based on the earlier age estimates, scientists had always viewed these people as a primitive group of humans who were clinging on in North Africa while their more modern cousins were sweeping out of the East. “People thought that North Africa had nothing to do with modern human evolution, and that this was a relict population,” says Gunz. “Now we know that they’re close to the root of the Homo sapiens lineage.”
The new specimens cast fossils from other parts of Africa in a new light. For example, the so-called Florisbad skull, which was discovered in South Africa in 1932, is around 260,000 years old. Based on that old age, “people had a hard time accepting this as a member of Homo sapiens, but I think our work brings the Florisbad skull back into the discussion,” says Gunz. If the skull really did belong to a member of our species, it means that around 300,000 years ago, humans had already “migrated across the African landscape, and were evolving at a continental scale,” says Gunz.
The team have done a good job, says Erella Hovers from the Hebrew University of Jerusalem, but “whether this is a breakthrough in our understanding of human evolution, I’m not sure.” Others had already suggested that the origin of our species was tied to the dawn of the Middle Stone Age—a period between 250,000 and 300,000 years ago, when people went from making large stone hand-axes to smaller, lighter tools like awls and spear tips. Those lighter tools had already been found in other parts of Africa, so the Jebel Irhoud finds “support a hypothesis that has been around for a while,” Hovers says.
That’s true, says McPherron, but until now, the bones and stones were telling different tales. The stones were all over Africa by 300,000 years ago, and the fossils were apparently no older than 195,000. Were the tools even made by Homo sapiens or some other hominid? “We had a disjuncture,” he says. “We had a major transition in behavior but no biological transition to go with it. Jebel Irhoud fills that gap nicely.”
It’s possible that people spread all over Africa, aided by their new stone technology, which allowed them to kill large animals from a distance. Certainly the Sahara would have permitted their passage: At the time, it was a lush, green savannah and not the impassable desert of today. Alternatively, humans may have already spread throughout the continent, and regional innovators developed Middle Stone Age tools independently.
Regardless, the new finds are “a very important discovery,” says Zeray Alemseged from the University of Chicago. “They’re placed at a critical time period when the earliest members of our species could have evolved, and they’re critical for better understanding the patterns of physical and behavioral evolution [among humans] across the African continent. They confirm the pan-African nature of human ancestry.”

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