terça-feira, 17 de março de 2015

Homo erectus

Homo erectus 
Early African Homo erectus fossils (sometimes called Homo ergaster) are the oldest known early humans to have possessed modern human-like body proportions with relatively elongated legs and shorter arms compared to the size of the torso. These features are considered adaptations to a life lived on the ground, indicating the loss of earlier tree-climbing adaptations, with the ability to walk and possibly run long distances. Compared with earlier fossil humans, note the expanded braincase relative to the size of the face. The most complete fossil individual of this species is known as the ‘Turkana Boy’ – a well-preserved skeleton (though minus almost all the hand and foot bones), dated around 1.6 million years old.  Microscopic study of the teeth indicates that he grew up at a growth rate similar to that of a great ape. There is fossil evidence that this species cared for old and weak individuals. The appearance of Homo erectus in the fossil record is often associated with the earliest handaxes, the first major innovation in stone tool technology.
Early fossil discoveries from Java (beginning in the 1890s) and China (‘Peking Man’, beginning in the 1920s) comprise the classic examples of this species. Generally considered to have been the first species to have expanded beyond Africa, Homo erectus is considered a highly variable species, spread over two continents (it's not certain whether it reached Europe), and possibly the longest lived early human species - about nine times as long as our own species, Homo sapiens, has been around!
Image of reconstruction based on ER 3733 by John Gurche
Where Lived: 
Northern, Eastern, and Southern Africa; Western Asia (Dmanisi, Republic of Georgia); East Asia (China and Indonesia)
When Lived: 
Between about 1.89 million and 143,000 years ago
Homo erectus lived between about 1.89 million and 143,000 years ago.
Year of Discovery: 1891
History of Discovery: 
Eugène Dubois, a Dutch surgeon, found the first Homo erectus individual (Trinil 2) in Indonesia in 1891. In 1894, Dubois named the species Pithecanthropus erectus, or ‘erect ape-man.’ At that time, Pithecanthropus (later changed to Homo) erectus was the most primitive and smallest-brained of all known early human species; no early human fossils had even been discovered in Africa yet.
Ranges from 4 ft 9 in - 6 ft 1 in (145 - 185 cm)
Ranges from 88 - 150 lbs (40 - 68 kg)
Height & Weight Supplemental Information: 
There was a large amount of variation in the size of Homo erectus individuals. Many fossils cannot be attributed to male or female, so we present the entire size range here. The fossils from Africa indicate a larger body size than those from China, Indonesia, and the Republic of Georgia.
We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas, using groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.
Below are some of the still unanswered questions about Homo erectus that may be answered with future discoveries:
  1. Was Homo erectus the direct ancestor of Homo sapiens, our own species?
  2. Data suggest that increasing body size, greater reliance on animal food resources, and increased range size were part of a web of factors that facilitated the initial early dispersal of H. erectus from Africa. Was one of these factors more important than the others?
  3. Are the fossils from earlier time periods in East Africa, and from Georgia, all part of a single species (Homo erectus), regionally variable in size and shape? Or are there actually several species of early human represented by what we are now calling Homo erectus?
  4. How well did Homo erectus master the control of fire and how widespread was fire used? What does this say about possible dietary shifts in this species?
  5. Did Homo erectus grow up in a more human-like pattern and rate, or a more ape-like one?  Was Homo erectus the first early human species to experience an adolescent growth spurt?
First paper:
Dubois, E.,. 1894. Pithecanthropus erectus: eine menschenaehnlich Uebergangsform aus Java. Batavia: Landsdrukerei.

Other recommended readings:
Antón, S.C., 2003. Natural history of Homo erectus. Yearbook of Physical Anthropology 46, 126–170.
Le Gros Clark W.E., 1964. The fossil evidence for human evolution, 2nd ed. Chicago: University of Chicago Press.
Leonard, W.R., Robertson, M.L., 1997. Comparative primate energetics and hominid evolution. American Journal of Physical Anthropology 102, 265–281.
Mayr, E., 1950. Taxonomic categories of fossil hominids. Cold Spring Harbor Symp Quant Biol 25, 109–118.

How They Survived: 
The tall bodies and large brains of Homo erectus individuals required a lot of energy on a regular basis to function. Eating meat and other types of protein that could be quickly digested made it possible to absorb nutrients with a shorter digestive tract, making more energy available faster. There is also speculation that honey and underground tubers may have been significant food sources for Homo erectus.
Soon after we see evidence in the fossil record of the earliest Homo erectus fossils (by about 1.9 million years ago), we see evidence in the archeological record for the first major innovation in stone tool technology (by about 1.76 million years ago). Known as the Acheulean stone tool industry, it consisted of the creation of large cutting tools like handaxes and cleavers. Increased reliance on a broader set of tools may have helped Homo erectus survive during changing climates.

The earliest evidence of hearths (campfires) occur during the time range of Homo erectus. While we have evidence that hearths were used for cooking (and probably sharing) food, they are likely to have been places for social interaction, and also used for warmth and to keep away large predators.

Evolutionary Tree Information: 
Some scientists distinguish between the African (Homo ergaster) and Asian (Homo erectus sensu stricto) fossils of this taxon, while others lump them together as Homo erectus sensu lato.  In either case, there is general agreement that it descended from an earlier species of Homo (e.g., Homo habilis) and represents one of the widest dispersals of early humans in our evolutionary history.  It is likely that distinct populations of Homo erectus sensu lato led to the emergence of later hominin species, such as Homo heidelbergensis, and ultimately to our own species, Homo sapiens.

At the beginning of its time range, around 1.9 Mya, H. erectus coexisted in East Africa with several other early human species including Homo rudolfensis, Homo habilis, and Paranthropus boisei. Sometimes they were even found at the same fossil sites. At the end of its time range, around 143,000 years ago, it coexisted with Homo sapiens and possibly Homo floresiensis in Indonesia.
Image of skull; D3444 Dmanisi, Republic of Georgia, 3/4 view
This elderly male belonged to a population of Homo erectus that spread from Africa to the Caucasus Mountains in western Asia. Most of his teeth fell out long before he died, and his jaw deteriorated as a result. Members of his social group must have taken care of him.
Image of Homo erectus; KNMER-1808 femoral cross section
An outer layer of abnormal bone on this female’s thigh shows evidence of bleeding just before death. After consulting doctors and accounts of wilderness explorers, researchers concluded that an overdose of vitamin A—perhaps from eating a carnivore’s liver, which concentrates vitamin A—caused the bleeding and her death.
Image of skeleton, front view, WT 15000
This Homo erectus youth lived in a hot, dry part of East Africa near an ancient marsh. His teeth indicate that he grew up quickly, at a rate similar to that of a living great ape. His is one of the most complete early human skeletons ever found.
Image of Homo erectus, Trinil 1
When this skull cap was discovered in 1891, it was the first early human fossil recognized outside Europe. It is sometimes called "Java Man" because it was found on the island of Java, Indonesia.

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