Tag Archives: hominin

Oldest human skull out of Africa forces us to rethink migration timeline

A human skull dating from 210,000 years ago has been shown to be human. The skull was discovered in a Greek cave in the 1970s but was then classified as Neanderthal. A new analysis showed that it is indeed human — and its timeline is absolutely puzzling.

The Apidima 2 cranium (right) and its reconstruction (left). Apidima 2 does belong to a Neanderthal. Image credits: Katerina Harvati, Eberhard Karls University of Tübingen.

It’s easy to understand why the Apidima Cave in Greece was seen as a refuge for ancient humans. Located in southern Greece, it probably offered provided a more stable and warmer climate than most other places, with plenty of water and feeding opportunities around it. Undoubtedly, numerous humans took shelter in the area, though most of them passed without leaving behind a single (archaeological) trail. Two individuals, however, did.

Two fossilized human crania (Apidima 1 and Apidima 2) from Apidima Cave, were discovered in the late 1970s. However, the study of these fossils proved to be extremely challenging. Not only were the skulls broken and fragmented, but up until the 1990s, it was impossible to extract them from the surrounding rock matrix. Even after they were extracted, their analysis remained difficult.

Initially, scientists thought them to be Neanderthal.

Now, an international team of researchers used state-of-the-art computer modeling and uranium dating to re-examine the two skulls. They found that one of them, dating from 170,000 years ago is indeed Neanderthal. But the other one yielded a massive surprise: not only was it 40,000 years older than the other one, but it belonged to a Homo sapiens — not a Neanderthal.

This would make it the oldest out-of-Africa human skull ever discovered.

The Apidima 1 partial cranium (right) and its reconstruction from posterior view (middle) and side view (left). Image credits: Katerina Harvati, Eberhard Karls University of Tübingen.

This is more than just a quirk of history — it puts a new, unexpected constraint on the “Out of Africa” theory, the dominant model of early migration of anatomically modern humans (Homo sapiens).

“It shows that the early dispersal of Homo sapiens out of Africa not only occurred earlier, before 200,000 years ago, but also reached further geographically, all the way to Europe,” Katerina Harvati, a palaeoanthropologist at the Eberhard Karls University of Tuebingen, Germany, told AFP.

“This is something that we did not suspect before, and which has implications for the population movements of these ancient groups,” she added.

It’s generally believed that hominins, a subset of great apes that includes Homo sapiens and Neanderthals, emerged in Africa more than six million years ago. They gradually migrated away from the continent — not at once, but in several migration episodes starting two million years ago. Some 45,000 years ago, Homo sapiens emerged from out of Africa, establishing its dominance and gradually replacing Neanderthals (with episodes of mixing and interbreeding).

The Out Of Africa theory suggests that humans gradually replaced Neanderthals. Image via Wikipedia.

This old skull suggests that an earlier migration also happened way before this timeline, and the overall migration might have happened in multiple waves rather than one big gradual one.

“Rather than a single exit of hominins from Africa to populate Eurasia, there must have been several dispersals, some of which did not result in permanent occupations,” said Eric Delson, a professor of anthropology at City University of New York, who was not involved in the Nature study.

This is still a preliminary study, however — a snapshot in time. This may be an isolated individual or part of an isolated community of adventurers. It’s not clear whether they left anything behind, or interbred with Neanderthals or other hominins. It’s an enigmatic find, but it’s one for which we lack the context to properly understand. Without more evidence, it’s hard to say where this population came from, how far it ranged, and for how long it survived.

The study has been published in Nature.

The cave where the fossils which may belong to a new hominin species were found. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

Potential new species of human found in cave in Philippines

The cave where the fossils which may belong to a new hominin species were found. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

The cave where the fossils which may belong to a new hominin species were found. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

In a cave on a small island in the Philippines, scientists have found evidence of a new species of humans that lived at least 50,000 years ago. They called it Homo luzonensis, after the island of Luzon where the remains were found. These hominins were very short in stature, comparable to Homo floresiensis, nicknamed “hobbits”, which lived on the nearby Indonesian island called Flores. If the species is confirmed by DNA analysis, the findings will not only enrich the human family tree but also complicate the story of human migration and evolution in Asia.

Another one?

The fossils from the island of Luzon were excavated during three expeditions in 2007, 2011, and 2015. Inside the island’s Callao cave, researchers found seven teeth (five from the same individual), two finger bones, two toe bones, and an upper leg bone. All were dated as being at least 50,000 years old by radiocarbon decay analysis. These fossils were found alongside those of butchered animals, suggesting that the cave’s inhabitants were at least sophisticated enough to devise cutting tools and rafts to reach the island from the mainland.

Individually, the bones are very similar to other Homo species in terms of shape and size. However, taken together, they reveal a combination of features that no other hominin shared. Homo luzonensis‘ molars were very small, even smaller than the hobbits. The premolars were relatively large, however, and had up to three roots rather than one — a feature shared by Homo erectus. The finger and toe bones were curved, suggesting tree-climbing ability that is more reminiscent of hominids living two million years ago in Africa.

Five fossil teeth from the same individual have unusual features that helped researchers determine that they might be dealing with a new species of human. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

Five fossil teeth from the same individual have unusual features that helped researchers determine that they might be dealing with a new species of human. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

These findings suggest that the landscape occupied by our species was once quite crowded. We now know that Homo sapiens were contemporaries not only with their famous cousins, the Neanderthals, but also with Homo floresiensisthe Denisovans (a species that lived around a cave in the Altai Mountains of western Siberia), and now this fifth species, Homo luzonensis. This dramatically complicates the story of human migration into Asia suggesting that several human lineages had already occupied East Asia by the time the first modern humans reached China as early as 80,000 years ago.

A Homo luzonensis toe bone, showing the longitudinal curve. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

A Homo luzonensis toe bone, showing the longitudinal curve. Credit: CALLAO CAVE ARCHAEOLOGY PROJECT.

Homo luzonensis was typically around 30 to 50 kilograms, stood 1 to 1.5 meters tall, and had brains around one-third the size of our own. Just like the hobbits on Flores, Homo luzonensis may be descendants of Homo erectus populations that crossed the sea from mainland Asia to Luzon. The small body and unusual skeletal traits may have been adaptations pressured by island dwarfing —  a process whereby some creatures confined to isolated habitats such as islands are known to have become smaller over time due to limited resources and ecology.

Digital reconstruction of homo floresiensis, nicknamed 'the hobbit'. Credit: Wikimedia Commons.

Digital reconstruction of homo floresiensis, nicknamed ‘the hobbit’. Credit: Wikimedia Commons.

It’s not clear yet if we’re dealing with a new species at all. The team of researchers, led by Florent Détroit of the Musée de l’Homme in Paris, was unable to extract DNA from the fossils. Until a proper DNA analysis confirms the distinct lineage, Homo luzonensis’ inclusion in the human family tree remains questionable. For instance, the fossils might belong to hybrids — the products of interbreeding between two or more earlier Homo species. Or perhaps Homo erectus populations that arrived at Luzon simply acquired some traits that made them more adapted to their environment, rather than speciating.

The findings are still incredibly exciting, nevertheless. It’s amazing to hear that our species lived at the same time as four other human lineages and perhaps interacted with them. What a sight that must have been to behold.

Credit: David Raichlen, University of Arizona.

Some of our ancestors walked on two legs millions of years before Homo sapiens evolved

Credit: David Raichlen, University of Arizona.

Credit: David Raichlen, University of Arizona.

After carefully investigating 3.6 million-year-old hominin footprints discovered in Laetoli, Tanzania, scientists determined that human-like bipedalism evolved far earlier than previously thought.

“Fossil footprints are truly the only direct evidence of walking in the past,” said David Raichlen, associate professor at the University of Arizona. “By 3.6 million years ago, our data suggest that if you can account for differences in size, hominins were walking in a way that is very similar to living humans. While there may have been some nuanced differences, in general, these hominins probably looked like us when they walked.”

Our ancestors used to walk with a similar upright gait 3.6 million years ago. Credit: David Raichlen, University of Arizona.

Our ancestors used to walk with a similar upright gait 3.6 million years ago. Credit: David Raichlen, University of Arizona.

Ever since Darwin’s theory of natural selection showed that humans must have descended from a primate ancestor, scientists have been scrambling to pinpoint the origin of bipedal locomotion. Our species, Homo Sapiens, emerged no more than 300,000 years ago, but our ancestors had been walking on two legs long before this time — very likely well before the genus Homo emerged some 2 to 2.5 million years ago.

Previous evidence suggests that hominins — a broader set of ancestors — started walking on two legs around 7 million years ago. However, these early ancestors also retained a crouched, bent-legged posture reminiscent of today’s chimps.

Now, using a combination of experimental data and morphological analysis, Raichlen and colleagues showed that the Laetoli footprints were made by fully upright, bipedal individuals. These people were members of the genus Australopithecus — the same genus which “Lucy” — the famous 3.2 million-year-old human ancestor whose fossilized bones were discovered in Ethiopia in 1974.

The researchers compared the depth and shape of the Laetoli fossilized footprints with the impressions left by eight volunteers who walked either in an upright or stooped posture. The analysis of the toe to heel ratio — a characteristic which reflects how the center of pressure moves along the foot with each step — revealed that the Laeoli footprints were more similar to those made by modern humans walking upright. In light of this discovery, picturing an Australopithecus marching in the distance on two-legs sounds like a breathtaking sight.

Australopithecus Africanus. Credit: Wikimedia Commons.

Australopithecus Africanus. Credit: Wikimedia Commons.

Hominins began to walk this way to adapt to a new lifestyle that involved spending less time in the trees and more time foraging over longer and longer distances. As the forests gradually dried out as a result of climate change, our ancestors were pressured to look for new shelter and food sources. Walking upright uses less energy than bipedal motion in an ape-like, crouched posture so, eventually, natural selection favored this sort of gait.

The findings suggest that hominins were walking upright as early as 3.6 million years ago. However, the exact timeline and stages when human-like locomotion diverged from the ape-like gait of our ancestors remain unknown, the authors said. To solve this mystery, scientists will have to study far older footprints.

“The data suggest that by this time in our evolutionary history, selection for reduced energy expenditures during walking was strong,” said Raichlen. “This work suggests that, by 3.6 million years ago, climate and habitat changes likely led to the need for ancestral hominins to walk longer distances during their daily foraging bouts. Selection may have acted at this time to improve energy economy during locomotion, generating the human-like mechanics we employ today.”

Human-like walking evolved before the genus Homo, more than 3.6 million years ago

Hominins may have started walking like us much more earlier than believed, new research shows.

Walk-cycle-poses.

Image credits Ajay Karat.

It may not be obvious, but we draw a lot of meaning from the way we walk — from the way we walk and other animals don’t, to be more precise.

At the start of each playthrough in the latest installment of Civilization, a narrator eases you into the game with the words “from man’s first upright steps”. We laugh when pets rise on their hind feet and share videos of it with our friends, chuckling all around at the animal that ‘thinks it’s human!’. That ubiquitous picture showing the evolution of man starts with an ape walking on all fours in the left and ends with a man walking on just two. And, well, to understand somebody, your best bet seems to be to walk a mile in his or her shoes.

In subtle ways, we see our bipedal walk as something that sets us apart from the rest of the animals on Earth. Something that’s intrinsic to what it means to be human.

UpRight

As such, ever since we’ve realized that people had to evolve from apes, our collective imagination has given quite a lot of thought to the moment when our ancestors rose from ape-like postures to the upright gait we use today. Scientists have also been interested in finding out when it happened, as that would give us precious insight into the way our ancestors lived, hunted, and evolved.

Fossilized footprints discovered in Laetoli, Tanzania, suggests that the hallmark human-like, extended leg bipedalism evolved substantially earlier than previously believed.

“Fossil footprints are truly the only direct evidence of walking in the past,” said David Raichlen, PhD, associate professor at the University of Arizona, one of two authors of the paper describing these findings.

“By 3.6 million years ago, our data suggest that if you can account for differences in size, hominins were walking in a way that is very similar to living humans. While there may have been some nuanced differences, in general, these hominins probably looked like us when they walked.”

Our species, Homo sapiens sapiens, is believed to have emerged some 200,000 to 300,000 years ago. Homo, our genus (extended family) as a whole, likely emerged some 2-2.5 million years ago. These are ‘humans’.

We refer to the wider set of ancestors that came before Homo as ‘hominins‘, although there is still a lot of debate on what species should be included in that group and what the relationships between them are. This is partly due to the fact that species evolve gradually, in small increments, making it hard to distinguish clearly, partly due to a lackluster fossil record, and partly because evolutionary anthropologists seem decided not to agree on anything, ever.

Common wisdom up to now held that hominids took to two feet around 7 million years ago. Based on observations of how other primate species evolved, however, it was also largely held that these hominids likely walked in a crouched posture with legs bent for quite some time.

Walk a mile in this mud

Raichlen’s and his colleagues’ work focuses on reconstructing walking mechanics starting from fossilized footprints and skeletons of early human ancestors. Together with co-author Adam Gordon (University at Albany), he used a combination of morphological studies and experimental data to show that the Laetoli footprints point to a fully upright, human-like bipedal style of walking.

In one experiment, the duo asked eight volunteers to walk in either an upright or stooped posture, with bent knees and hips, on a mud surface — then compared the depth and shape of their footprints to the Laetoli ones. When they analyzed the impression made by the toe versus the heel, which reflects how the center of pressure moves along your foot as you take a step, they found the footprints at Laeoli were much more similar to the footprints made by modern humans walking upright than stooped.

Our ancestors used to walk with a similar upright gait 3.6 million years ago. Credit: David Raichlen, University of Arizona.

Our ancestors used to walk with a similar upright gait 3.6 million years ago. Credit: David Raichlen, University of Arizona.

Raichlen believes this can be explained by simple economics. When walking upright, having your legs fully extended uses less energy than adopting a stooped, more ape-like position. This suggests that the switch to a more human-like gait likely had something to do with how our ancestors found food, and how far they had to travel to find it.

“The data suggest that by this time in our evolutionary history, selection for reduced energy expenditures during walking was strong,” said Raichlen.

“This work suggests that, by 3.6 million years ago, climate and habitat changes likely led to the need for ancestral hominins to walk longer distances during their daily foraging bouts. Selection may have acted at this time to improve energy economy during locomotion, generating the human-like mechanics we employ today.”

Raichlen, however, cautions that we still don’t know when hominins started adopting different gaits than other primates — we just know that they were walking upright 3.6 million years ago. Until we find the right footprints, that question will remain unanswered.

The paper “Using experimental biomechanics to reconstruct the evolution of hominin locomotor postures” has been presented at the American Association of Anatomists‘ annual meeting during the 2018 Experimental Biology meeting.

Scientists find 1.85 million year old human-like bone

Anthropologists have discovered the oldest known fossil of a bone resembling that of humans; the 1.85 million year old bone is the oldest evidence of a ‘modern’ hand and suggests that ancient humans may have been much larger than previously thought.

The hand is one of the critical features distinguishing humans, and even a 3.6 cm(1.5-inch), two-million-year-old fragment provides valuable clues. Image credits: M. Domínguez-Rodrigo.

A key feature that distinguishes humans from other species is the ability to create and use tools. But in order to be able to create and use the tools, you need not only a big brain, but also very able hands. It’s not just the opposable thumbs – the entire structure of the hand is remarkable.

“The hand is one of the most important anatomical features that defines humans,” said study lead author Manuel Domínguez-Rodrigo, a paleoanthropologist at Complutense University of Madrid. “Our hand evolved to allow us a variety of grips and enough gripping power to allow us the widest range of manipulation observed in any primate. It is this manipulation capability that interacted with our brains to develop our intelligence.”

Many mammals and other animals have grasping appendages similar in form to a hand such as paws, claws, and talons, but these are not scientifically considered to be grasping hands. The only true grasping appears in primates, and apes are sometimes considered to have 4 hands, because they can also grasp with their ‘feet’.

If the bone is proportional in size to human bones, then the possessor of this bone would have been 5 feet 9 inches (1.75 meters) – a remarkable size when you compare it to Homo habilis, a hominin that measured only 3 feet high. The fact that human ancestors were so large comes as a surprise, but then again, there’s also a chance that the finger/body ratio wasn’t the same for them as it is for us.

Tiny but significant. Credit: Jason Heaton

Some scientists have often proposed that our hands evolved in conjunction with our use of tools, but recent discoveries suggest that the history of human hands is much more complicated. Modern humans are the only living higher primates to have straight finger bones, while hominin fingers were more curved, because they spent a great portion of time in the trees.

In a study published Tuesday in Nature Communications, researchers report the finding of an old fossil which also indicates straight fingers, and this just makes things more complicated. The straightness and other features of this new bone suggest adaptations for life on the ground rather than in the trees. This fills an important gap, but also raises more questions.

“Our discovery fills a gap — we found out that such a modern-looking hand is at least 1.85 million years old,” Domínguez-Rodrigo said.

Unfortunately, before we find more fossils, those questions will likely remained unanswered.