Evolution of Modern Humans

[sayak83]

A fourth Homo species contemporary to modern humans found in South Africa.

Homo naledi.. found in South Africa... lived merely 300,000-200,000 years ago... making it contemporary to Homo Sapiens (us, East Africa) along with Neanderthals(Europe) , Denisovians(East Asia) and late Erectus(South East Asia). 6 independent labs using double blind studies directly on the bones and teeth converged on the age range. What is surprising is that this upright walking human cousin was equally adept in swinging through the trees and a brain size less than 600 cc. Yet they had fully modern hands, made tools and deliberately buried their dead. Now two highly inaccessible and deep cave chambers have been found with rich collection of naledi skeletons that were deliberately put there by others of the species. In their traits Homo naledi look like descendants of Australopithecus sediba that lived in the region 1.8 million years ago with similar types of adaptations, but this is speculative. The interesting question is whether brain size is decoupled with intelligence and more tied with arboreality. It's hard to carry a heavy brain while swinging through the trees, and whether the more tree-dwelling line of humans found a way to make brains more intelligent without increasing its size... while the terrestrial line did not have to make such a constraint. The reason this is important is that naledi has the characteristic dome shaped head of Modern humans implying an expanded neocortex like humans, while all at a miniature scale. Clearly much research awaits. One can compare with Homo fluorensis for a similar case.

News - Young Homo naledi surprises - Wits University

Meet ‘Neo’, the most complete skeleton of Homo naledi ever found | New Scientist

Homo naledi’s Hands and Feet | The Scientist Magazine®

 

[It Aint Necessarily So]

What do you think of Pangea and early humans. I suspect continental drift played a role

You are correct if what you mean is the breakup of Pangaea and the subsequent repositioning and recombination of its fragments:

"Geology strikes again

"Something very interesting happened over geological time that is considered key in the history of the evolution of man. We have already considered how the asteroidal impact that divided the Mesozoic and Cenozoic eras opened up niches for the small, surviving mammals and how the increases in atmospheric oxygen and temperature powered the radiation of primates in the Eocene epoch of the Cenozoic era. Now let’s see look at the geological change that forced man’s ancestors down from the trees.

"There had been a gap between the continents of North and South America through which the waters of the Atlantic and Pacific Oceans flowed freely. Drifting tectonic plates, volcanic island building activity due to the Pacific plate subducting below the Caribbean plate, and accumulating sediments began creating the Isthmus of Panama beginning about 12 million years ago and ending about 3-4 mya.

"The formation of the Isthmus of Panama had an enormous impact on Earth’s climate and terrestrial environments, an effect that had a fateful impact on man’s arboreal ancestors. By shutting down the flow of water between what is now the Pacific ocean and the Caribbean sea in the Atlantic, currents in both oceans were rerouted, creating among other things, what we call the Atlantic Gulf Stream, a swift warm current ranging from the Gulf of Mexico around the tip of Florida, up the eastern North American coast to Newfoundland, and across the Atlantic to the Old World. These oceanic changes had global atmospheric consequences as well. Western Europe became warmer, and parts of Africa that had been jungle (rain forest) slowly became the relatively treeless savannas we see there today.

"Some species that were highly specialized for life in the trees went extinct, but some that were able to adapt survived, including our ape ancestors. The transition was rapid in geologic terms, but not in the terms of lifetimes of successive generations of our forebears. Continents just don’t move that fast. Exposing apes to increasingly more treeless environments powered the environmental changes that led to the evolution of man, who is very different from his ape cousins of both then and today. Changes in environment accelerate evolution.

"Over uncounted generations, ape-men came down from the trees, stood up, grew taller, became more gracile, grew bigger brains, developed more articulate hands, lost most of their body hair, learned to hunt and eat meat, tamed fire, made tools, acquired language, migrated across continents, formed complex societies and eventually developed complex cultures capable of sailing, agriculture, and domesticating animals. These are many of the features that distinguish man from his arboreal, brachiating cousins and ancestors.

"Just how this transition occurred is still being worked out. Many species of hominan fossils have been found, some with familiar names like Australopithecus afarensis, Homo erectus, and the Homo sapiens neanderthalis.

"Today we have multiple species of hominan (sic) fossils, and the task before the scientists is to determine in what order these changes occurred in our ancestors, which fossils are ancestral, and which represent failed branches from our family tree that went extinct. Kenyanthropus and Paranthropus, for example, probably represent the latter, whereas it is thought that Australopithicus afarensis, Homo habilis, Homo erectus, and Homo heidelbergensis were ancestral forms, although this has been extremely difficult to establish."

 

[sayak83]

New fossils show the gradual evolution of Modern humans from ancient groups in Africa over a 400,000 year period

For decades, researchers seeking the origin of our species have scoured the Great Rift Valley of East Africa. Now, their quest has taken an unexpected detour west to Morocco: Researchers have redated a long-overlooked skull from a cave called Jebel Irhoud to a startling 300,000 years ago, and unearthed new fossils and stone tools. The result is the oldest well-dated evidence of Homo sapiens, pushing back the appearance of our kind by 100,000 years.


The Discoveries suggest that our species came into the world face-first, evolving modern facial traits while the back of the skull remained elongated like those of archaic humans. The findings also suggest that the earliest chapters of our species’s story may have played out across the African continent. The team now has new partial skulls, jaws, teeth, and leg and arm bones from at least five individuals, including a child and an adolescent, mostly from a single layer that also contained stone tools. In their detailed statistical analysis of the fossils, Hublin and paleoanthropologist Philipp Gunz, also of the Max Planck in Leipzig, find that a new partial skull has thin brow ridges. And its face tucks under the skull rather than projecting forward, similar to the complete Irhoud skull as well as to people today. But the Jebel Irhoud fossils also had an elongated brain case and “very large” teeth, like more archaic species of Homo, the authors write.


This scenario hinges on the revised date for the skull, which was obtained from burnt flint tools. (The tools also confirm that the Jebel Irhoud people controlled fire.) Archaeologist Daniel Richter of the Max Planck in Leipzig used a thermoluminescence technique to measure how much time had elapsed since crystalline minerals in the flint were heated by fire. He got 14 dates that yielded an average age of 314,000 years, with a margin of error from 280,000 to 350,000 years. This fits with another new date of 286,000 years (with a range of 254,000 to 318,000 years), from improved radiometric dating of a tooth.


They suggest that these ancient humans were part of a large, interbreeding population that spread across Africa when the Sahara was green about 300,000 to 330,000 years ago; they later evolved as a group toward modern humans. “H. sapiens evolution happened on a continental scale,” Gunz says.

 

[Jayhawker Soule]

All primate species have their roots in Asia.

^ yet another belligerent alternative fact.

 

[Jayhawker Soule]

The modern humans slowly evolve from descendents of H. ergaster is East Africa from 200,000 years ago onwards.
Evolution of Modern Humans: Early Modern Homo sapiens

See Dating expert ages oldest modern human ...

A Griffith University geochronologist's state-of-the-art dating methods push back the origins of our species by an unprecedented 100,000 years, uncovering the oldest modern human and our deep biological history in Africa.

Professor Rainer Grün, director of the leading Australian Research Centre for Human Evolution (ARCHE), was among an international research team that dated fossils discovered at the archaeological site of Jebel Irhoud, Morocco.

The finds - reported on the front cover of Nature - are dated to about 300,000 years ago and represent the oldest securely aged fossil evidence of our own species.​

 

[sayak83]

See Dating expert ages oldest modern human ...

A Griffith University geochronologist's state-of-the-art dating methods push back the origins of our species by an unprecedented 100,000 years, uncovering the oldest modern human and our deep biological history in Africa.

Professor Rainer Grün, director of the leading Australian Research Centre for Human Evolution (ARCHE), was among an international research team that dated fossils discovered at the archaeological site of Jebel Irhoud, Morocco.

The finds - reported on the front cover of Nature - are dated to about 300,000 years ago and represent the oldest securely aged fossil evidence of our own species.​

You should probably look at post 23 above.
The 300,000 year fossils however are not fully modern, with skull shape still retaining the features of Heidelbergensis. So the fossils are to humans between moderns and Heidelberg man.

 

[metis]

Man did not originate in Africa. We have two separate origins. There is no hominid "common ancestor". Europeans and Asians originated in Eurasia near the Caucasus and Urals mountains.

All primate species have their roots in Asia.

Not true as the earliest have been found in Africa with these species.

 

[Valjean]

You should probably look at post 23 above.
The 300,000 year fossils however are not fully modern, with skull shape still retaining the features of Heidelbergensis. So the fossils are to humans between moderns and Heidelberg man.

No-one's saying they're fully modern. They're just saying they're sapiens.

 

[sayak83]

No-one's saying they're fully modern. They're just saying they're sapiens.

Yes I understand that. It's often easy to forget that evolution is a continuous process over time and drawing the boundary between one species from the next over a temporal series is more of a utilitarian enterprise.

 

[sayak83]

How scientists extract data from fossilized bones

a) Morphometrics

Morphometrics is the quantitative analysis and comparison of key structural features of skeletons. Consider the skull of hominids. The skull contain important structural regions where bones meet meet other bones or where important muscles are attached. For example the muscle attachment of jaw (important for chewing), location of the connection of the spinal cord entry in the skull relative to the skull (bipedalism), location of the ear hole, length on shape of the brain case etc. These values can be measured for various skulls and multivariate analysis can show how near or far in the morphological space the various skulls are with respect to each other. Today in geometric Morphometrics, the entire skull is scanned and digitized and a grid of points is "wrapped" around the digitized version using Morphometrics software, anchored at important structural nodes. Similar thing can be done for all other skulls. Then various skull grids can be compared and overlaid on each other showing significant differences and similar. The skull can even be transformed in 3D from one to another to quantitatively determine the level of transformation needed. This establishes not only which skeletons belong within the variability of the same species but if different species are closely related or distantly related as the skulls need slight or radical transformations. Also distortions caused by fossilization can be corrected.


Morphometrics is augmented through CT scans that reveal the inner structures of the bones. It was CT scan that showed that Neanderthal ear bones were very different from ear bones of Modern humans suggesting some unique developments in their hearing faculty. CT scan and geometric Morphometrics now help paleontologists to create growing computer databases of mathematical information about the structure and topology of skeletons of various extinct species. The detailed connectivity information can be deployed to identify bones and to provide quantitative best fits for parts of connected skeletal bones that have not fossilized.

Then stereo lithography and 3D printing can be used to construct the entire skeleton based on information that has been recovered through Morphometrics.

Geometric morphometrics in anthropology - Wikipedia

Geometric morphometrics | Virtual Anthropology

 

[sayak83]

Growth Rates of Ancient Humans and Atomic Physics

The modification of growth rates from birth to adulthood is an important distinction between apes like chimpanzees and humans. The brain growth of apes are fast before birth and slows down afterwards, while brain growth in human babies continues to be rapid after birth. At birth, human babies have brain that are 33% larger than ape babies (normalized by body mass), but by adulthood the brain size of humans is 3 times as large as apes. This additional growth means humans go through a much extended period of immaturity compared to apes.

Apes have an infancy of five years followed by an adolescence of seven years and then adulthood.
Humans however have two extra phases. Humans have an infancy of three years, childhood from three to seven years, a juvenile phase between seven and ten years and then an adolescence of seven years.
Thus apes are adult at twelve years while humans become adult at seventeen. This extended pre-adult phase allows human brains both to grow (till 8th birthday) and connect up (that continues till age 20) to absorb and adapt to more complex social life of a human group.

An important question in evolution therefore is how this change in the rates and phases of growth proceeded along the hominid lineage?


One way to estimate it is to compare the age of eruption of molars. In chimpanzee, molar teeth erupts at 3,6 and 10 years. In humans in contrast, the same set erupts at 6,12 and 18 years. Studies have shown that by the time of Homo ergaster, the childhood of hominids have already started to extend. Their molars were erupting probably at 5,9 and 15 years.

But teeth also preserve a finer level of detail. Teeth have the equivalent of tree rings. These very thin lines of teeth enamel are deposited every day. These incremental lines are called cross striations and they can be used to date the teeth since it's eruption.
Biorhythms (Part One): Why Teeth are like Tree Rings and Ticking Clocks

The problem with this is that the teeth would have to be cut open to reveal these cross striations. And this where one of the most powerful X ray facility in the world comes in.

Teeth, the hardest bones in the world are really tough to X-ray. But European Synchrotron Research Facility in France, housing the world's most powerful X-ray beam is upto the task.

About Us


The ESRF - The European Synchrotron Radiation Facility - is the most intense source of synchrotron-generated light, producing X-rays 100 billion times brighter than the X-rays used in hospitals. These X-rays, endowed with exceptional properties, are produced at the ESRF by the high energy electrons that race around the storage ring, a circular tunnel measuring 844 metres in circumference.Thanks to the brilliance and quality of its X-rays, the ESRF functions like a "super-microscope" which "films" the position and motion of atoms in condensed and living matter, and reveals the structure of matter in all its beauty and complexity.

The ESRF produces X-rays of high energy, called “hard” X-rays, which have wavelengths of 0.10 to 0.01 nm or energies in the range 10 to 120 keV. (In synchrotron science, it is more usual to speak of energies.) Because of their higher energies, hard X-rays penetrate deeper into matter than soft X-rays, those with energies below 10 keV. The synchrotron X-ray beam can have other valuable properties, including time structure (a flashing beam), coherence (a parallel beam) and polarisation.

In addition to being absorbed by a material, X-rays can also interact with the atoms, giving rise to diffraction or scattering of the X-rays. X-ray absorption can also be followed by re-emission of the energy absorbed, for example as fluorescence. These interactions with matter are used to gain information about the composition of a sample, including the type and location of individual atoms within it.

In 2012 a large sample of Neanderthal and human teeth were put under this X ray beam to image the daily lines of the teeth and hence to determine the ages and rate of growth of Modern humans compacted to Neanderthals.


http://www.sciencemag.org/news/2010/11/neandertal-children-developed-fast-track

Fortunately, Smith and Hublin found a powerful new tool that would let them "see" inside fossil teeth without damaging them—the 52 kilo-electron-volt synchrotron x-ray beam at the European Synchrotron Radiation Facility (ESRF). Working with paleontologist Paul Tafforeau of ESRF, the multinational team used the beam to x-ray teeth from dozens of Neandertals, including 11 juveniles, and several fossil H. sapiens. By counting daily growth lines laid down in the enamel and comparing the number of days that passed between birth and key developmental events, such as the eruption of the first, second, and third molars, the researchers could calculate the age at death as well as the rate of dental growth.

State-of-the-art synchrotron imaging of the tiny upper jaw (maxilla) of the Engis 2 Neanderthal allows scientists to virtually isolate the permanent teeth inside the bone (center image), count tiny growth lines inside the first molar teeth (lower image), and determine that it died at age 3. Fossil courtesy of the Université de Liège. Photo credits Graham Chedd (PBS), Paul Tafforeau (ESRF), and Tanya Smith (Harvard University and MPI-EVA).

They found that it took the Neandertals 2.5 years to form their first molar crowns, compared with 3 years on average in modern humans. Second molars appeared by age 8 in Neandertals, and 10 to 12 years on average in modern humans. This suggests that Neandertals reached adulthood a few years earlier than modern humans, they report online today in the Proceedings of the National Academy of Sciences.

Key findings of the associated papers were as follows:-
"Data from many fossils were quantified and analyzed, and nine Neanderthals at different stages of maturity were synchrotroned. These were then compared with similar analyses on five early moderns and a large sample of recent people from different regions. The results seem to finally establish that early moderns such as those from Skhul and Qafzeh were maturing dentally at the slow rate of recent humans, while the Neanderthals were growing somewhat faster, particularly in the case of the later erupting teeth. Thus, for example, the Neanderthal children from Engis, Scladina, and Le Moustier should have been about four, eleven, and sixteen years old respectively from modern development patterns, but the synchrotron showed that they were actually about three, eight, and twelve. Not only were the Neanderthals maturing faster, but the more rapid growth of their molars meant that these teeth had thinner enamel than ours."
-Chris Stringer in " Lone Survivors"
Thus Neanderthals were still maturing faster than modern humans by about four years even though they had comparable brain size. This suggests a faster more energy demanding childhood and lesser time for the brain to retain flexibility and adapt to the society through rewiring. These considerations have large implications on how fast Neanderthals can innovate new things or adapt to changes and also how many children a single mother can simultaneously raise to maturity.


In this way scientists were able to extract vital information of the life history differences between Neanderthals and modern humans using combined knowledge of archaeology, biology and the tools of 21st century atomic physics.