Human evolution Guide, Meaning , Facts, Information and Description
Human evolution as a scientific field has a long and sometimes controversial history, however, since the mid-1990s, there has been a remarkable convergence of views about how humans have evolved. This convergence includes paleoanthropologists, geneticists, and molecular biologists and is the subject of books such as Steve Olson's Mapping Human History (2002). This modern synthesis is also remarkable for its specificity. For example, there is strong scientific evidence supporting these conclusions:
- around 2 to 2.5 million years ago, the genus Homo first appeared; (see, for example Cradle of Humankind)
- about 7,500 generations have passed since the appearance of modern humans;
- every person alive today is descended from a relatively small group of individuals living in Africa sometime between 100,000 and 200,000 years ago;
- mitochondrial Eve lived about 150,000 years ago;
- Y-chromosomal Adam lived between 35,000 and 90,000 years ago.
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2 Important fossils 3 Taxonomy 4 Additional notes 5 See also 6 External links 7 References |
The Homo genus
Anthropologists generally recognize three species of Homo:
- Homo habilis, from 2.4 to 1.5 million years ago (MYA)
- Homo erectus, from 1.8 to 0.3 MYA
- Homo sapiens, from 0.5 MYA to the present
A number of other species have been proposed, including:
- Homo cepranensis
- Homo rudolfensis
- Homo heidelbergensis (Heidelberg Man), also proposed as Homo sapiens heidelbergensis and Homo sapiens paleohungaricus.
- Homo neanderthalensis (Neanderthal Man), also proposed as Homo sapiens neanderthalensis, from 230 to 30 thousand years ago (TYA)
- Homo rhodesiensis (Rhodesian Man), also proposed as Homo sapiens rhodesiensis
- Homo ergaster, co-temporaneous with Homo erectus
- Homo georgicus, about 1.8 MYA
- Homo antecessor, about 0.8 MYA
- Homo floresiensis dubbed "Hobbit" for its small size, from about 12 TYA
- Homo sapiens idaltu, about 160 TYA
Neanderthal Man
There is ongoing debate over whether "Neanderthal Man" was a separate species, Homo neanderthalensis, or a subspecies of H. sapiens. While the debate remains unsettled, the preponderance of evidence, collected by examining mitochondrial DNA and Y-chromosomal DNA, currently indicates that there was no gene flow between H. neanderthalensis and H. sapiens, and therefore the two were separate species.
In 1997 Dr. Mark Stoneking, then an associate professor of anthropology at Penn State University, stated: "These results [based on mitochondrial DNA extracted from Neanderthal bone] indicate that Neanderthals did not contribute mitochondrial DNA to modern humans… Neanderthals are not our ancestors."² Subsequent investigation of a second source of Neanderthal DNA confirmed these findings.³
H. habilis, the first species of the genus Homo, evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5–2 MYA, when it diverged from the Australopithecines. H. habilis had smaller molars and larger brains than the Australopithecines, and made tools from stone and perhaps animal bones.
The conventional view of human evolution states that humans evolved in inland savanna environments. The marine biologist Sir Alister Hardy has proposed the Aquatic Ape Hypothesis, that humans developed in shore regions. But evidence supporting this is sparse and it is not widely accepted.
Human babies have far more fat reserves than other primates. It has been hypothesized that this is necessary to ensure brain development during times of food shortages (the brain consumes 60% of a baby's energy intake).
H. habilis
H. erectus
In the Early Pleistocene, 1.5–1 MYA, in Africa, Asia, and Europe, evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, Homo erectus.H. sapiens
Between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, the trend in cranial expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens. The direct evidence suggests that there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa and a subsequent migration from Africa which replaced the dispersed H. erectus. There is little evidence that this speciation occurred elsewhere, even though some fossil evidence for H. erectus has been found in China. However, the current evidence doesn't preclude multiregional speciation, either. This is a hotly debated area in paleoanthropology.Important fossils
Taxonomy
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Mammalia |
| Order | Primates |
| Suborder | Haplorhini |
| Catarrhini | |
| Superfamily | Hominoidea |
| Family | Hominidae |
| Subfamily | Homininae |
Additional notes
The origins of humanity is a subject of great political and religious controversy in the United States and certain other countries. See: creationism.
The classification of humans and their relatives has changed considerably over time. See the history of hominoid taxonomy.
Speculation about the future evolution of humans is often explored in science fiction. Sometimes evolution to a being of pure spirit is imagined, sometimes continued speciation as humans fill various ecological niches; see adaptive radiation.
Human evolution has possibly reached a peculiar point of development. Their rational understanding of the physical environment and their application of scientific knowledge has given them an unprecedented ability to adapt habitats to their wants and needs (i.e. agricultural development). Many believe this capacity reduces or prevents many theoretical mechanisms believed to be causing evolution. This is an oversimplified view however. It is true surviving well past maturation in industrialized nations is sociologically and technologically protected, thus reducing many of the selective pressures that existed in their former environments, but survival is not the only selective criterion for evolution and factors like reproductive success (i.e. sexual evolution) still vary for a myriad of potential reasons.
Other circumstances, like the scope and connectivity of the human population, will also tend to prevent mechanisms like cladogenesis, thus reducing biodiversity, but other mechanisms like genetic drift and the reduction in selective pressures could possibly cause anagenesis. Most of the natural changes will likely have the character of a negative adaptation (e.g. myopia becomes more and more common due to a lack of selective pressure for superior vision) however, but this is a human characterization of change that is dependent upon human goals and value systems.
As science and technology advances it is possible they will be able to not only consciously adapt their environment to their needs, but adapt their genetic information as well. This new form of evolution by design could more than compensate for the elimination of the natural mechanisms driving evolution. Beyond that it is possible they will abandon their biological machinery in favor of completely artificial systems.
This is an Article on Human evolution. Page Contains Information, Facts Details or Explanation Guide About Human evolution See also
External links
References