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.
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"¹, suggest new lines of inquiry and raise hopes about progress in understanding the origins of speech and language.
The Homo genus
- Homo habilis, from about 2.4 to 1.5 million years ago (MYA)
- Homo erectus, from about 1.8 (including ergaster) or from about 1.25 (excluding ergaster) to 0.07 MYA
- Homo sapiens, from about 200 thousand years ago (TYA) to the present
A number of other species have been proposed, including:
- Homo cepranensis
- Homo rudolfensis
- Homo rhodesiensis (Rhodesian Man) from about 2.5 to about 1.75 MYA. Also proposed as Homo sapiens rhodesiensis
- Homo ergaster from about 1.8 to about 1.25 MYA. Also proposed as Homo erectus ergaster
- Homo georgicus, about 1.8 MYA
- Homo antecessor from about 0.8 MYA
- Homo heidelbergensis (Heidelberg Man) from about 500 TYA to about 300 TYA. Also proposed as Homo sapiens heidelbergensis and Homo sapiens paleohungaricus.
- Homo neanderthalensis (Neanderthal Man) from about 250 to 30 TYA. Also proposed as Homo sapiens neanderthalensis.
- Homo sapiens idaltu from about 160 TYA (proposed subspecies).
- Homo floresiensis from about 12 TYA (announced 2004). Nicknamed hobbit for its small size.
There is not yet consensus as to which of these groups should count as separate species and which as subspecies of another species. In some cases this is due to the paucity of fossils, in others due to the very slight differences used to distinguish species in the Homo genus.
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.
In the Early Pleistocene, 1.5–1 MYA, in Africa, Asia, and Europe, presumably H. habilis 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. A famous example of Homo Erectus is Peking Man; others were found in Indonesia, and sites in Africa and Europe.
There is ongoing debate over whether the "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
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. (There is little evidence that this speciation occurred elsewhere.) Then a subsequent migration within and out of Africa eventually replaced the earlier dispersed H. erectus. However, the current evidence doesn't preclude multiregional speciation, either. This is a hotly debated area in paleoanthropology.
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, at least for a while, 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).
- Petralona , Greece, about 300k years old. Contained many features of H. erectus.
- Arago , France, about 300k years old. Oldest skull clearly of H. sapiens origin.
- Archaeological Site of Atapuerca , Spain. The earliest and most abundant evidence of humankind in Europe. It is a World Heritage Site.
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.
- Theories of the origin of humans
- Single origin hypothesis
- Multi-regional origin
- Homo neanderthalensis
- Skull 1470
- Physical anthropology
- Darwinian happiness
- Darwinian medicine
- DNA Shows Neandertals Were Not Our Ancestors
- The Tree of Life
- FOXP2 and the Evolution of Language
- Relations of the Homo sapiens
- Neanderthals on Trial Nova Online - Provided by PBS.
- Becoming Human - Provided by PBS.
- Wolfgang Enard et al. "Molecular evolution of FOXP2, a gene involved in speech and language." Nature, Vol 418 (22 August 2002) p. 870.
- DNA Shows Neandertals Were Not Our Ancestors
- Ovchinnikov, et al. "Molecular analysis of Neanderthal DNA from the Northern Caucasus." Nature 404, 490 (2000).