Evolution of Homo sapiens
Since the mid-1990s, there has been a remarkable convergence of views about the evolution of Homo sapiens amongst paleoanthropologists, geneticists, and molecular biologists. This convergence 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.
The role of language in the story of human evolution remains largely a matter of speculation, but recent discoveries about the FOXP2 gene, "the first gene known to be involved in the development of speech and language"ÃÂù, have suggested new lines of inquiry and raised hopes about progress in understanding the origins of speech and language.
| Table of contents |
|
2 Important fossils 3 Taxonomy 4 Additional notes 5 See also 6 External links 7 References |
The Homo genus
Although other species have been proposed and written about, anthropologists generally recognize three species of Homo:
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 Neandertals did not contribute mitochondrial DNA to modern humans... Neandertals are not our ancestors."ÃÂò
Subsequent investigation of a second source of
Neanderthal DNA confirmed these findings.ÃÂó
H. habilis, the first species of the genus Homo, evolved in South and East Africa in the late Pliocene or early Pleistocene (2 - 2.5 million years before present) when it diverged from the Australopithecines (Australopithecines and Hominenes are collectively referred to as Hominids). Both genera were bipedal. H. habilis had smaller molars and larger brains than the Australopithecines, and made tools from stone and perhaps animal bones.
In the Early Pleistocene, from 1.5 to 1 million years ago, hominines 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.
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).
The conventional view of human evolution states that humans evolved in inland savanna environments. Stephan Cunnane of the University of Toronto has proposed the aquatic ape hypothesis, where humans developed in shore regions, but evidence supporting this is sparse and it is not widely accepted.
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 out of Africa of H. erectus, 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.
The origins of humanity is a subject of great political and religious controversy in the United States and certain other countries. See: creationism.
Older classifications had the superfamily Hominoidea which included three families: Hominidae (humans), Pongidae (the great apes), and Hylobatidae (gibbons and siamangs). Many taxonomists put Pongidae and Hominidae together as one super-family. The chimpanzee (Pan troglodytes) and bonobo (Pan paniscus) are often grouped in the genus homo by evolutionarists. It is an interesting fact that Linnaeus, who first grouped the chimpanzee (only one species was known at the time) in a different genus than Man, later regretted this (in his view) artificial division.
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.
It is believed by some that human evolution has ended, because humanity as a species no longer has to adapt to its environment: rather, humans are capable of changing their environment to suit their own needs.
Neanderthal Man
H. habilis
H. erectus
H. sapiens
Important fossils
Taxonomy
Additional notes
See also
External links
References