THE ORIGINS OF MAN -- HOMO SAPIENS
[Picture shows Species: Homo sapiens
Age: ~ 90,000 years
Date of Discovery: May 2, 1932
Location: Mount Carmel, Israel
Discovered by: T. McCown and H. Moivus, Jr.]
The species to which you and all other living human beings on this planet belong is Homo sapiens. Anatomically, modern humans can generally be characterized by the lighter build of their skeletons compared to earlier humans. Modern humans also have very large brains, which vary in size from population to population and between males and females, but the average is around 1300 cc.
Housing this enlarged brain has involved the reorganization of the skull into what is thought of as the "modern" appearance -- a high vaulted cranium with a flat and near vertical forehead.
The supraorbital torus is lost in most modern humans, and ridging above the orbits in general is very reduced. The widest part of the skull is high on the skull, as opposed to earlier Homo erectus and H.Ergaster. The back of the skull lacks the transverse torus of H. erectus and the occipital bun of H. neanderthalensis.
The origin of modern Homo sapiens is not yet resolved. Two extreme scenarios have been proposed. According to the first, the distribution of anatomical traits in modern human populations in different regions was inherited from local populations of Homo erectus and intermediate "archaic" forms. This "Multiregional Hypothesis" states that all modern humans evolved in parallel from earlier populations in Africa, Europe and Asia, with some genetic intermixing among these regions. Support for this comes from the similarity of certain minor anatomical structures in modern human populations and preceding populations of Homo erectus in the same regions.
A different model proposes that a small, relatively isolated population of early humans evolved into modern Homo sapiens, and that this population succeeded in spreading across Africa, Europe, and Asia -- displacing and eventually replacing all other early human populations as they spread. In this scenario the variation among modern populations is a recent phenomenon.
Part of the evidence to support this theory comes from molecular biology, especially studies of the diversity and mutation rate of nuclear DNA and mitochondrial DNA in living human cells.From these studies an approximate time of divergence from the common ancestor of all modern human populations can be calculated. This research has typically yielded dates around 200,000 years ago, too young for the "Multiregional Hypothesis." Molecular methods have also tended to point to an African origin for all modern humans, implying that the ancestral population of all living people migrated from Africa to other parts of the world -- thus the name of this interpretation: the "Out of Africa Hypothesis."
Whichever model (if either) is correct, the oldest fossil evidence for anatomically modern humans is about 130,000 years old in Africa, and there is evidence for modern humans in the Near East sometime before 90,000 years ago.
The remains of the male individual pictured, known as Skhul V, were recovered from the Skhul Cave near Mount Carmel, Israel, along with the skeletons of nine other adults and children. The anatomical features of this skull are reminiscent of earlier, "archaic" humans. One notable example is the bony torus over the orbits, or brow ridge. In the same photograph, though, note the high forehead, which rises nearly vertically from the face, and the expanded frontal portion of the braincase. These are features typical of modern human skulls. Also, at the back of the skull, note the lack of a projecting "bun", which occurs in many Neanderthal skulls.
The Skhul site was originally thought to be about 40,000 years old based on a comparison of animal remains and stone tools found at the site with those from other archeological sites in the region. The implications of this late date were important since it was assumed that the Neanderthal fossils found at the nearby fossil site of Tabun Cave must be older than the modern Homo sapiens population of Skhul. This assumption left open the possibility that the Tabun Neanderthals were the evolutionary ancestors of modern humans at Skhul.
However, with the application of more precise dating techniques, scientists found that the modern H. sapiens fossils at Skhul were about 90,000 years old, much older than was previously thought. This made the anatomically modern human population at Skhãl contemporaries of the Neanderthal population of Tabun. The implication is that the Tabun Neanderthals could not have been the ancestors of modern humans in the Near East.
|
HOMO ERECTUS: RELATED TO HOMO SAPIENS?
[Trinil 2, "Pithecanthropus I"
Species: Homo erectus
Age: 1.0-0.7 million years
Date of Discovery: October 1891
Location: Trinil, Java, Indonesia
Discovered by: Eugène Dubois]
To understand what we mean today by "Homo erectus", some history of paleoanthropological thought is needed. The first early human fossil found outside of Europe was the Trinil 2 fossil skullcap from the Solo River in Java (pictured). The fossil was placed in the species Pithecanthropus erectus by its discoverer Eugene Dubois. Almost 40 individuals have been recovered from Java to this day, roughly equivalent to the number of fossils found at the caves of Choukoutien in China. The Choukoutien fossils found were originally assigned the species name Sinanthropus pekinensis.
It was not until the 1950's that Ernst Mayr proposed that all of the specimens from these two roughly contemporaneous locales, along with others localities from Europe and Africa, represented a single species, Homo erectus. Since the 1950's, however, the early African populations of what Mayr termed Homo erectus have once again been split into a separate species Homo ergaster.
Homo erectus exhibits many features particular to the species, including a long skull shaped with thick cranial walls. The back of the skull is marked with a protruberance known as a transverse torus. Over the eyes is a large and prominent browridge, or supraorbital torus, which joins the rest of the frontal bone at a depression called the sulcus. Cranial capacities of Homo erectus average around 1000cc, which is far greater than earlier australopiths and even early Homo. The dentition of Homo erectus is nearly identical to modern humans, although the cheek teeth do remain larger, and the mandible is generally more robust.
The species Homo erectus is thought to have diverged from Homo ergaster populations roughly 1.6 million years ago, and then spread into Asia. It was believed that Homo erectus disappeared as other populations of archaic Homo evolved roughly 400,000 years ago. Evidently, this is not the case. Recent studies into the complicated stratigraphy of the Java Homo erectus sites have revealed some surprising information. Researchers have dated the deposits thought to contain the fossils of H. erectus near the Solo River in Java to only 50,000 years ago. This would mean that at least one population of Homo erectus in Java was a contemporary of modern humans (Homo sapiens).
Convinced that the evolutionary history of man lay in East Asia, physician Eugène Dubois enlisted as an army surgeon in the Royal Dutch East Indies Army in Sumatra. He had little success in finding fossils in Sumatra.
In 1890, he moved to Java, where his excavations brought him to the Solo River. In 1891, Dubois discovered a heavily mineralized cranium belonging to an early human. Many of the features were worn flat, but the shape of the cranium was distinctively long and the forehead was flat. A heavy browridge was evident, along with a distinct sagittal keel, visible in frontal and three-quarters view as a bony ridge passing lengthwise along the skull.
It should be noted that this sagittal keel is distinct from the sagittal crest of the Paranthropus species (e.g. KNM WT 17000: Paranthropus aethiopicus, and OH 5: Paranthropus boisei). In three-quarters view, the temporal line, where the chewing muscles attach to the skull, is visible to the side of the skull, and distinct from the keel.
In 1893, Dubois named the specimen Pithecanthropus erectus. In the 1950's, Ernst Mayr proposed that the Javanese Pithecanthropus specimens and the Chinese Sinanthropus specimens were not only of the same species,but also members of our own genus: Homo. The species became Homo erectus and Trinil 2 is the type specimen of the species.
|
MORE REMAINS OF HOMO FLORESIENSIS FOUND IN INDONESIA
[BBC, October 11, 2005]
Scientists have discovered more remains of the strange, small people that once lived on Flores island, Indonesia.
The announcement last year detailing a single, partial skeleton caused a sensation when it was claimed to be a human species new to science. Homo floresiensis, as it was called, was little more than a metre tall and lived 18,000 years ago. Now, the same team tells Nature journal it has skeletal remains from at least nine of the "Hobbit-like" individuals.
The new discoveries include missing parts of the old skeleton -- designated LB1 after the caved dig site at Liang Bua - and a collection of other bones, such as jaw and cranial fragments, a vertebra, arm and leg bones, toes and fingers.
The team, led by Michael Morwood from the University of New England, Armidale, Australia, says the specimens have helped build a more rounded picture of LB1, with additional evidence of the little people's hunting and fire-making abilities.
The researchers say they are now more convinced than ever that Homo floresiensis represents a distinct species and not some diseased individual of modern human (Homo sapiens) as some sceptics have suggested.
"The finds further demonstrate that LB1 is not just an aberrant or pathological individual but is representative of a long-term population," they write in Nature.
A critical line in their argument is the length of time which the new collection of remains represents -- possibly 80,000 years -- making a disease explanation for the cause of the little people's stature and shape an unlikely one.
This sees isolated species, released from the pressures of predation but constrained by limited resources, evolving either smaller or larger forms than would otherwise be the case. In the case of H. floresiensis, it is said the creature could have come out of Homo erectus, a long-extinct early-human species that was known to populate Flores about 800,000 years ago.
The Hobbit was only 1m tall and possessed "primitive" features. Daniel Lieberman, of Harvard University in Massachusetts, US, said further discoveries on the island would help settle the issue.
"If the island-dwarfing hypothesis is correct, then the island's earliest inhabitants should be larger than the Liang Bua fossils; and if dwarfing occurred gradually, then it might even be possible to find fossils intermediate in size and shape between H. floresiensis and its ancestor," he wrote in a commentary in Nature. "More evidence on when Homo sapiens first arrived on Flores is also needed."
|
HOMO ERGASTER EMERGED IN AFRICA
By 1.9 million years ago, another lineage of the genus Homo emerged in Africa. This species was Homo ergaster. [Illustrated is the amazingly well preserved KNM ER 3733 cranium.] Traditionally, scientists have referred to this species as Homo erectus and linked this species name with a proliferation of populations across Africa, Europe, and Asia. Yet, since the first discoveries of Homo erectus, it had been noted that there were differences between the early populations of "Homo erectus" in Africa, and the later populations of Europe, Africa and Asia.
Many researchers now separate the two into distinct species Homo ergaster for early African "Homo erectus", and Homo erectus for later populations mainly in Asia. Since modern humans share the same differences as H. ergaster with the Asian H. erectus, scientist consider H. ergaster as the probable ancestor of later Homo populations.
H. ergaster had a rounded cranium and a prominent browridge. Its teeth were much reduced in size, especially when compared to Australopithecus. Several features that distinguish H. ergaster from H. erectus are thinner bones of the skull and the lack of an obvious sulcus, or depression, just behind the browridge.
By 1.6 million years ago, an advance in stone tool technology is identified with H. ergaster. Known as the Achulean stone tool industry, it consisted of large cutting tools, primarily hand axes and cleavers. Originally thought to be responsible for the spread of early humans beyond Africa, it is now known that the migration out of Africa predates this tool industry.
|
|
|
|
