One of the most hotly debated issues in paleoanthropology (the study of human origins) focuses on the origins of modern humans, Homo sapiens.
Roughly 100,000 years ago, the Old World was occupied by a morphologically diverse group of hominids. In Africa and the Middle East there was Homo sapiens; in Asia, Homo erectus; and in Europe, Homo neanderthalensis.
However, by 30,000 years ago this taxonomic diversity vanished and humans everywhere had evolved into the anatomically and behaviorally modern form. The nature of this transformation is the focus of great deliberation between two schools of thought: one that stresses multiregional continuity and the other that suggests a single origin for modern humans.
The Multiregional Continuity Modelcontends that after Homo erectus left Africa and dispersed into other portions of the Old World, regional populations slowly evolved into modern humans.
This model contains the following components:
- some level of gene flow between geographically separated populations prevented speciation, after the dispersal
- all living humans derive from the species Homo erectus that left Africa nearly two million-years-ago
- natural selection in regional populations, ever since their original dispersal, is responsible for the regional variants (sometimes called the races) we see today.
- the emergence of Homo sapiens was not restricted to any one area, but was a phenomenon that occurred throughout the entire geographic range where humans lived
In contrast, the Out of Africa Modelasserts that modern humans evolved relatively recently in Africa, migrated into Eurasia and replaced all populations which had descended from Homo erectus. Critical to this model are the following tenets:
- after Homo erectus migrated out of Africa the different populations became reproductively isolated, evolving independently, and in some cases like the Neanderthals, into separate species
- Homo sapiens arose in one place, probably Africa (geographically this includes the Middle East)
- Homo sapiens ultimately migrated out of Africa and replaced all other human populations, without interbreeding
- modern human variation is a relatively recent phenomenon
The multiregional view posits that genes from all human populations of the Old World flowed between different regions and by mixing together, contributed to what we see today as fully modern humans.
The replacement hypothesis suggests that the genes in fully modern humans all came out of Africa. As these peoples migrated they replaced all other human populations with little or no interbreeding.
To understand this controversy, the anatomical, archaeological, and genetic evidence needs to be evaluated.
Anatomical evidence…
Sometime prior to 1 million years ago early hominids, sometimes referred to as Homo ergaster, exited Africa and dispersed into other parts of the Old World.
Living in disparate geographical areas their morphology became diversified through the processes of genetic drift and natural selection.
- In Asia these hominids evolved into Peking Man and Java Man, collectively referred to as Homo erectus.
- In Europe and western Asia they evolved into the Neanderthals.
Neanderthals lived in quasi isolation in Europe during a long, relatively cool period that even included glaciations.
Neanderthals are distinguished by a unique set of anatomical features, including:
- a large, long, low cranial vault with a well-developed double-arched browridge
- a massive facial skeleton with a very projecting mid-face, backward sloping cheeks, and large nasal aperture, with large nasal sinuses
- an oddly shaped occipital region of the skull with a bulge or bun
- molars with enlarged pulp chambers, and large, often very heavily worn incisors
- a mandible lacking a chin and possessing a large gap behind the last molar
- a massive thorax, and relatively short forearms and lower legs
- although short in stature they possessed robustly built skeletons with thick walled limb bones
- long clavicles and very wide scapulas.
By 130,000 years ago, following a prolonged period of independent evolution in Europe, Neanderthals were so anatomically distinct that they are best classified as a separate species, Homo neanderthalensis.
This is a classic example of geographic isolation leading to a speciation event.
In contrast, at roughly the same time, in Africa, a body plan essentially like our own had appeared. While these early Homo sapiens were anatomically modern they were not behaviorally modern. It is significant that modern anatomy evolved prior to modern behavior. These early sapiens were characterized by:
- a cranial vault with a vertical forehead, rounded occipital and reduced brow ridge
- a reduced facial skeleton lacking a projecting mid-face
- a lower jaw sporting a chin
- a more modern, less robustly built skeleton.
Hence, the anatomical and paleogeographic evidence suggests that Neanderthals and early modern humans had been isolated from one another and were evolving separately into two distinct species. (Source,)…
(http://www.actionbioscience.org/evolution/johanson.html)
(Donald C. Johanson)
No matter what people look like or where their families have lived for generations, acclaimed fossil hunter Donald C. Johanson says, the qualities that make them human can be traced to a (single location).
“Each and every one of us in this room, regardless of the color of our skin, is an African,” Johanson told a standing-room-only crowd at the University of Delaware for the annual Dr. Arnold M. Clark Memorial Lecture. “Whenever we grasp a branch of the human tree, its roots go back to Africa.”
(Lucy – conjectural re-creation)
Johanson, a professor and founding director of the Institute of Human Origins at ArizonaStateUniversity, is best known for his groundbreaking 1974 discovery in Ethiopia of a 3.2 million-year-old skeleton that is viewed as a transitional fossil between ape and human. Dubbed “Lucy” after a Beatles song Johanson had recently heard, the fossil led to major revisions in scientific thought about human ancestry.
In his lecture at UD, Johanson noted that Lucy has become “an icon of paleoanthropology” and a benchmark against which later discoveries have been compared as scientists seek to understand where various fossils fit into the evolutionary process. Evidence shows, for example, that Lucy was an adult female, about 3-and-a-half feet tall and 60-65 pounds, with short legs and long arms. She had a softball-size brain, comparable to modern apes, but stood and walked upright as humans do.
Johanson described the day he happened to notice a tiny bone on the ground in the Ethiopian portion of East Africa’s Rift Valley, where the geology has left a treasure trove of fossils and, he said, “has opened a window to the past.” He recognized the bone as a human elbow, and he and his team eventually uncovered Lucy’s fairly complete skeleton in that location.
(Lucy’s – re-constructed skeleton)
“This was a major breakthrough at the time,” he said, because previous discoveries from the same time period consisted only of small fragments. But Lucy was just the start, Johanson said, describing how paleoanthropologists have since found more than 500 fragments of her same species from various sites in Africa.
He noted that other information has also come to light, the result of scientific research that has mapped the human genome. Based on that genetic information, it’s clear that humans originated in southern Africa and moved from there into other parts of the world, he said, describing an evolutionary “tree” in which species developed, adapted and, often, died out.
“We are all united by the past,” Johanson said, calling for humanity to take responsibility for protecting the natural world for future generations. “Today, we are globally a common species. We are the ones that survived.”
(Fossil Skeleton From Africa Predates Lucy)
Ardi, short for Ardipithecus ramidus, is the newest fossil skeleton out of Africa to take its place in the gallery of human origins. At an age of 4.4 million years, it lived well before and was much more primitive than the famous 3.2-million-year-old Lucy, of the species Australopithecus afarensis.
(Ardipithecus Ramidus)
Since finding fragments of the older hominid in 1992, an international team of scientists has been searching for more specimens and on Thursday presented a fairly complete skeleton and their first full analysis.
By replacing Lucy as the earliest known skeleton from the human branch of the primate family tree,…
(Discovering Ardi)
(Ardi – conceptual re-construction)
..the scientists said, Ardi opened a window to “the early evolutionary steps that our ancestors took after we diverged from our common ancestor with chimpanzees.”
The older hominid was already so different from chimps that it suggested “no modern ape is a realistic proxy for characterizing early hominid evolution,” they wrote.
The Ardipithecus specimen, an adult female, probably stood four feet tall and weighed about 120 pounds, almost a foot taller and twice the weight of Lucy. Its brain was no larger than a modern chimp’s. It retained an agility for tree-climbing but already walked upright on two legs, a transforming innovation in hominids, though not as efficiently as Lucy’s kin.
Ardi’s feet had yet to develop the arch-like structure that came later with Lucy and on to humans. The hands were more like those of extinct apes. And its very long arms and short legs resembled the proportions of extinct apes, or even monkeys. (Source, archaeologyinfo.com).
Ardipithecus Ramidus had a more primitive walking ability than later hominids, and could not walk or run for long distances.
The teeth suggest omnivory, and are more generalised than those of modern apes.
Ardipithecus Kadabba…
Ardipithecus kadabba fossils…
Ardipithecus kadabba is “known only from teeth and bits and pieces of skeletal bones,” and is dated to approximately 5.6 million years ago.
It has been described as a “probable chronospecies” (i.e. ancestor) of Ardipithecus ramidus. Although originally considered a subspecies of Ardipithecus Ramidus, in 2004 anthropologists Yohannes Haile-Selassie, Gen Suwa, and Tim D. White published an article elevating Ardipithecus Kadabba to species level on the basis of newly-discovered teeth from Ethiopia.
These teeth show “primitive morphology and wear pattern” which demonstrate that Ardipithecus Kadabba is a distinct species from A. ramidus. The specific name comes from the (Afar) word for “basal family ancestor”.(Source Wikipedia).
Well boys and girls, ..that’s enough about Lucy and Ardi and the anthropological science concerning how Homo sapiens developed from (hedonistic) ..beasts of the forest, ..into “hedonistic” politicians, ..that unambiguously believe what is yours, ..is theirs, ..and what is theirs, ..is theirs.
(I’ll drink to that).
According to Webster: “he”don·is“tic,” The doctrine holding that behavior is motivated by the desire for pleasure and the avoidance of pain.
Question: “Does Barack Obama feel America’s pain?
Think about it, I’ll be back tomorrow
Crusader Rabbit…
pearlsofprofundity 