See also Paleoanthropology in CogWeb's bibliography
"The terminology of our immediate biological family is currently in flux; for an overview, see a current hominoid taxonomy. The term ‘hominin’ refers to any genus in the human tribe (Hominini), of which Homo sapiens (modern man) is the only living specimen.
We don't have to go too far back into the past, however, to find relatives (cf. ‘We Were Not Alone’, SciAm Jan 2000). Discounting abominable snowmen, yeti, bigfoot, and other merely rumored possible members of our family, we know that only 28,000 years ago Neanderthals still thrived in Europe. More surprisingly, recent evidence (see below) suggests that a member of even longer standing, Homo erectus, who first appears in the fossil record nearly two million years ago, may have continued to inhabit the island of Java as recently as ten thousand years ago, or into historical times.
Looking further back, the various members of the genus Homo are the decendants of the australopithecines, who around three million years ago were represented by numerous species. These clearly belonged to the great apes: their brains were about the size of chimpanzees, we have found no record of their tool manufacture, and they were probably sexually promiscuous in the way chimpanzees are. There were also about the same size as chimps: Australopithecus afarensis weighed around 25 to 50 kilograms (60 to 120 lbs.) as an adult. The main difference between the two species is that the australopithecines walked upright - the first record of their footprints was discovered at Laetoli in East Africa and has been dated at 3.6 million years. Its recently discovered ancestor, Ardipithecus ramidus, retained more adaptations for climbing, as seen from the shape of the limbs. Its dates are very close to the split between the chimpanzees and the hominids; a find still closer is the recently discovered and still debated Orrorin tugenensis (below)."
"For a recent overview of all the different members of our family, see a discussion of hominoid taxonomy, Donald Johanson's Hominid Family Tree, and a simplified tree situating the new A. garhi (cf. below). While several of these extinct and living species are acknowledged to be our relations, the precise details of descent remain contentious. Note, for instance, that the discoverers of Orrorin (below) argue that Orrorin is our ancestor, while ardepithecus is the ancestor of Pan (the chimpanzees) and the Australopithecines went extinct (details in Orrorin tugenensis), while the discoverers of ...
Based on molecular evidence, the current consensus is that our closest living relatives, the two species of Pan (the chimpanzee and the bonobo), separated from the hominid lineage between five and six million years ago. While our line diverged into several species of australopithecines and then several species of homo, Pan separated into two species starting around a million years ago. Hominids, gorillas, chimpanzees, and bonobos - the four African species of Great Apes - have common ancestors somewhere between eight and ten million years ago (BBC report, external). For our living relatives, see the recent detailed tree showing humankind's relationship to the African apes. Looking even further back, see current speculations on the origins of the anthropoids. For primates in general, see Primate Info Net (external).
For detailed articles on the various members of the hominid family, see the external site Origins of Humankind. See also the quick overview at Talk Origins."
"The study of hominids have given a special place to our own ancestors, creating what appears to be a distorting factor in paleoanthropological interpretations. Since there is a relatively low number of relevant fossil finds, new finds often create an opportunity for reinterpreting the existing data, and this reinterpretation appears at times to favor placing one's own remains at the root of the human tree, rather than in the line of descent of the chimpanzees, our closest living relatives. Yet two recent finds from the period close to our split from the chimpanzees remain interesting whether they are our own ancestors or not."
"The Kenya Palaeontology Expedition (KPE) report in December 2000 the discovery of what is almost certainly a new species of hominid at Kapsomin in the Tugen hills in Kenya's Baringo district; see the BBC news story. The remains were found in volcanic sediments dated to between 5.6 and 6.2 million years old. They include a left femur, pieces of jaw with teeth, isolated upper and lower teeth, arm bones, and a finger bone; the excavations are ongoing. Preliminary analyses suggest the hominid, the size of a chimpanzee, was an agile climber and that it walked on two legs when on the ground. The tentative date of six million years indicate a date very close to the common ancestor of humans and chimpanzees, although this date may now need to be pushed back. The excavating team includes Martin Pickford from the KPE and Brigitte Senut from the Museum of Natural History in Paris.
"A related find from close to the same period (5.2 to 5.8 million years ago) is reported in Nature in July 2001; see report in Science 293. 5528 (13 Jul 2001): 187-189 (full text, external). It was discovered in 1997 by an Ethiopian-American team led by Yohannes Haile-Selassie and Tim White of the University of California, Berkeley. The specimen has been named Ardipithecus ramidus kaddaba, a species of the Ardipithecus ramidus first discovered in 1994. While Senut and Pickford (2001) propose that Ardipithecus is the ancestor of Pan, the chimpanzees (see details), Haile-Selassie and White (2001) argue it is more likely to be a human ancestor. They add that ongoing excavations may locate further remains to help determine the issue."
"Dean Falk and coworkers have recently examined australopithecine endocasts. In one of the four australopithecine species that were studied, certain parts of the cerebral cortex appeared advanced compared to the brains of living great apes. 'Endocasts from Australopithecus africanus reveal that its brain size was, on average, within the range of living chimpanzees. The underneath surfaces of its frontal lobes and the anterior tips of its temporal lobes, however, appear to have evolved to a point that was intermediary between the forms seen in great apes and humans'. This may be indicative that we descend from the gracile australopithecines.
"The most significant adaptation that distinguishes our first hominid ancestors from the chimpanzees is upright walking, or bipedalism. The adaptation strictly speaking predates the australopithecines. Various theories have attempted to explain the trait, the simplest being that upright walking freed the hands for carrying objects. Still, it is not clear why this capacity would matter enough to drive such a major adaptation.
In Human evolution: the water theory (1998, external), Elaine Morgan discusses an alternative theory, arguing that bipedalism may have arisen during an aquatic stage. The hypothesis is intriguing but hard to test.
Whatever its cause, bipedalism had the effect of opening up an evolutionary possibility space for future adaptations such as tool use and possibly enlarged brains (see below, What drove the transition to Homo?) and speech. Robert Provine, in his book Laughter (Little/Brown, spring 2000), argues that bipedalism was a necessary condition for language:
In quadrupeds, there is a one-to-one correlation between breathing pattern and stride because the lungs must be fully inflated to add rigidity to the thoracic complex (sternum, ribs and associated musculature) that absorbs forelimb impacts during running. Without such synchronization, the thorax is weak and unable to absorb the impact. When primates stood and walked on two legs, the thorax was freed of its support function during locomotion, breaking the link between breathing patterns and stride. This flexibility enabled humans to regulate breathing and ultimately, speak" (press release)."
"A new species of australopithecine was discovered in Ethiopia in 1999, dated to about 2.5 million years and in certain ways anatomically intermediate between A. afarensis and Homo habilis. What makes the find particularly interesting is that the archaeologists also found suggestive evidence that this type of early hominid used tools and ate meat. Its placement in the family tree is not settled; see diagram
Berhane Asfaw, Tim White, Owen Lovejoy, Bruce Latimer, Scott Simpson, and Gen Suwa. Australopithecus garhi: A New Species of Early Hominid from Ethiopia. Science 284 (April 23, 1999): 629-635.
Media reports (local copies):
Fox, Maggie. Meat-Eating Missing Link Fossil Found In Africa. Reuters, April 22, 1999.
"Little is known about the diets of hominids that predate the Homo genus, because these hominids did not leave archeological traces such as 'kitchen middens' and stone tools. Consequently, researchers have made inferences concerning hominid diet on the basis of craniodental morphology, gross dental wear, and dental microwear. The current consensus is that the 3-million-year-old Australopithecus africanus hominid subsisted on fruits and leaves, similar to the modern chimpanzee. Early hominid diets are of some theoretical significance, since one current view is that the emergence of the more intelligent Homo genus depended on the consumption of high-quality animal foods that made possible biological changes resulting in the evolution of a larger brain.
M. Sponheimer and J.A. Lee-Thorp (1999) now report a stable carbon isotope analysis of A. africanus fossils from Makapansgat Limeworks, South Africa. The authors sampled 4 of the 14 Australopithecus africanus individuals that have been unearthed at that location, and also analyzed the dental enamel of associated 3-million year old animals (65 individual animals from 19 mammalian taxa) in order to place A. africanus within a broader ecological context. The authors report their results demonstrate that A. africanus ate not only fruits and leaves, but they also ate large quantities of carbon-13 enriched foods such as grasses and sedges, or they ate animals that ate these plants, or both. The authors suggest their results indicate that early hominids such as A. africanus regularly exploited relatively open environments such as woodlands or grasslands for food, and that early hominids may have consumed high-quality animal foods before the development of stone tools and the origin of the genus Homo. (Science Week April 1999)
M. Sponheimer and J.A. Lee-Thorp (1999). Isotopic evidence for the diet of an early hominid, Australopithecus africanus. Science 283 (15 Jan): 368.
Contact: Matt Sponheimer, Rutgers University, New Brunswick 908-932-8789.
"The Australopithecines were a diverse set of species that thrived for several million years with little or no change in brain volume. What were the factors that led to the evolution of the much brainier Homo erectus? Some researchers emphasize a possible transition to hunting and meat-eating. Even though chimpanzees also hunt and there is now evidence that Australopithecines ate meat (see previous two sections), tool-based hunting may have created a novel set of adaptive pressures. Another possibility currently being raised by Richard Wrangham et al. is that late australopithecines began to cook tubers, which are and were plentiful on the East African savannah, and that this created a new dynamic that led to larger brains; see Pennisi's presentation.
O'Connell et al., in an article in the summer 1999 issue of the Journal of Human Evolution, muster evidence to support the tuber hypothesis. It is generally agreed that a 'grade shift' -- a conjunction of significant innovations -- in human evolution can be found in the fossil record of a little less than two million years ago. Here we see the first signs of hominins (human ancestors from the tribe Hominini) whose bodies, jaws and teeth begin to resemble those of modern humans, the type broadly labeled Homo erectus. O'Connell and colleagues challenge conventional wisdom by suggesting that the cascade of changes - involving anatomy, life history, culture and social structure - that resulted in the evolution of modern humans was set off not by hunting, but by systematic exploitation of subterranean food sources and recruitment of grandmothers to provide for their grandchildren.
Larger brains have plausibly been connected with the evolution of a distinct human sexual psychology, favoring pair-bonding over promiscuity. Among both species of chimpanzees, females have exclusive charge of infants. Because of promiscuous sexual practices, paternity is generally not trackable. Australopithecines have similar brains and bodies and we have as yet no reason to think they didn't follow similar practices. A selection for larger brains -- for whatever reason -- would run up against the problem of a baby's larger head needing to pass through the bones surrounding the birth canal. The solution in place today is that human babies are born very prematurely compared to the offspring of our closest relatives. The still soft head of a new-born infant is deformed into a tube as it is squeezed through the birth canal. The price humans pay for this is a requirement of increased maternal care; for instance, for many months the baby is completely incapable of any form of locomotion, or even of clinging to the mother. In addition, larger brains would have favored extending the period in which infants are primarily devoted to learning new skills. These factors are likely to have created a significant benefit for children who received care not only from their mothers but also from their fathers and possibly their grandmothers (in the latter case creating a selective pressure for menopause). In the case of fathers, natural selection would have favored males who were able to invest in their own rather than in others' offspring, thus creating selective pressures some way for males to track paternity. Pair-bonding is the likely solution -- one that necessitated novel psychological adaptations, possibly along with physiological ones such as continued sexual receptivity in females.
A large class of adaptations spring from this matrix of problems arising from larger brains. The dramatic increase in brain size from australopithecines to Homo erectus may represent the beginning of this process."
"In a recent article, Wood and Collard propose a revised definition for the genus Homo based on criteria considered verifiable. They suggest that a fossil species should be included in Homo only if the following can be demonstrated:
Wood and Collard argue that two species Homo habilis and Homo rudolfensis do not belong in the genus Homo but should be considered Australopithecines. The earliest taxon to satisfy the criteria is Homo ergaster, or early African Homo erectus, which currently appears in the fossil record at about 1.9 million years ago [see the May 2000 announcement of finds of hominids classified as Homo ergaster in the republic of Georgia, the oldest outside of Africa].
The adoption of the above criteria, the authors conclude, would mean the genus Homo would have both phylogenetic and adaptive significance. "Researchers can then explore whether this adaptive shift in hominin evolution corresponds with changes in climate, analogous evolutionary changes in other large mammal groups, particular innovations in the hominin cultural record, substantial expansions in geographic range, or changes in ecological tolerance as reflected in reconstructions of hominin habitats."
B. Wood and M. Collard: The human genus. Science 284 (2 Apr 99): 65.
Contact: Bernard Wood <firstname.lastname@example.org>"
"Excavations in 1997 in West Turkana in Kenya have uncovered evidence of stone flake production as early as 2.34 million years ago, several hundred thousand years earlier than previous finds. No hominid remains have been associated with the production sites. If the tool makers were Homo habilis, the dates for this species must be pushed back three hundred thousand years. It is also possible that the tool makers were australopithecines.
See H. Roche, A Delagnes, J.-P. Brugal, C. Feibel, M. Kibunjia, V. Mourre, and P.-J. Texier. Early hominid stone tool production and technical skill 2.34 Myr ago in West Turkana, Kenya. Nature 399 (1999): 57-60 (BBC report and abstract).
Paleoanthropologists once considered tool-making to be one of the defining characteristics of the genus Homo. Now, the very classification of Homo habilis as part of the genus Homo is questioned; the remains may more appropriately be grouped with the australopithecines. The diversity of tool-making and tool-using behaviors among chimpanzees has forced a complete revision of assumptions surrounding the concept of "man the toolmaker", including revision of ideas concerning the gender of the first tool users. Chimpanzees have diverse and regionally varied repertoires of tool-using, and other "cultural" behaviors. Tool use can no longer be used as a genus criterion. Nor is tool use clear evidence of a more abstract conceptual understanding. Cebus monkeys are considered prolific tool users but exhibit no apparent understanding of cause and effect, or of the difference between appropriate and inappropriate tools.
Nevertheless, complex innovations in composite tools remains a very recent phenomenon. With the appearance of near-modern brain size, anatomy, and perhaps of grammatical language approximately 300,000 years ago, the pace of the evolution of human technology quickened exponentially. A mere 12,000 years separate the first bow and arrow from the International Space Station. For a discussion, see S.H. Ambrose's comments in Science 2 Mar 01 291:1748."
"Eitan Tchernov, a palaeontologist at the Hebrew University of Jerusalem, reports in September '99 that excavations at the Erq-Lel-Ahmar site in Israel's Jordan Valley have revealed the remains of thousands of chopping tools, crude axes and stone knives thought to have been used by prehistoric human beings. They are dated to two million years -- 500,000 years before the first hominid (homo erectus) has been thought to leave Africa. The likely candidate behind the tools is homo habilis, not previously thought to have engaged in migrations. The results don't appear to have been published in scientific journals yet; see newspaper report."
"Homo ergaster and Homo erectus are the two immediate precursors of Homo sapiens. Homo ergaster is believed to have originated in Africa and to have given rise to H. erectus in Asia. As with other hominid fossil groups, precise evolutionary sequences and geographical loci continue to be debated. For recent finds in Georgia -- the earliest outside of Africa -- dating back 1.7 million years, see BBC news report (11 May 2000)."
"First discovered by Eugene Dubois in 1891 in Indonesia, this fossil group is currently viewed as the closest precursor to H. sapiens. It was initially given the names "Anthropithecus erectus" and "Pithecanthropus erectus" and seen to straddle the line between ape and human. Dubois' species and subsequent finds in China from 1927 ("Peking man") were in 1951 subsumed under the single category Homo erectus. It is now recognized as a widespread species exhibiting significant geographical variation.
"Most remains suggest a stocky build. However, the Turkana Boy (KNM-WT-15000) is estimated to be a youngster who would have grown to be about 6 ft tall; he is fairly slender. ER 1808 is another tall erectus, thought to be about 5'9" (175 cm), and possibly female. See Walker and Leakey (1993)."
"Stone tools dated to 1.36 million years ago provide the earliest evidence yet of human occupation of northeast Asia. Full news report (BBC 26 September 2001, external)."
"Morwood et al. (1998) examined stone tools from two fossil sites on the Wallacean island of Flores, between Southeast Asia and Australia, dating them to 800,000 to 900,000. (They used fission-track dating in zircon grains - a method of dating geological specimens by counting the radiation-damage tracks produced by spontaneous fission of uranium impurities.) Flores has been an island for a least a million years, so the toolmakers - Homo erectus - must have used watercraft to reach it. For a recent study that reaches similar conclusions, see O'Sullivan et al. Geology 29, 607 (2001)."
"There is some debate about where this human ancestor arose, some favoring Africa and others Asia; cf. the multiregionalism debate below. What is certain is that Homo erectus used fire and stone tools and appeared around 1.7 million years ago. The species disappeared from Africa around half a million years ago, but remained in Asia for another 250,000 years (and possibly much longer). Morwood et al. (1998) suggest this evidence, combined with the geographical radiation of Homo erectus in the Early Pleistocene (2 million to 10,000 BP; cf. Geological Time-scales) and other recent discoveries, indicates the cognitive capabilities of this species may be due for reappraisal. See Gibbons (1998).
For more material, see Mark Rose, First Mariners. Archaeology Magazine 51. 3 (May/June 1998) (external).
Contact: M.J. Morwood (email@example.com)."
"Japanese archaeologists report in the New Scientist (March 2000) that they have uncovered the remains of what is believed to be the world's oldest artificial structure, on a hillside at Chichibu, north of Tokyo. The site has been dated to half a million years ago, suggesting its architect was homo erectus. It consists of what appear to be ten post holes, forming two irregular pentagons which may be the remains of two huts. Thirty stone tools were also found scattered around the site. The shallow post holes were dug in a layer of volcanic ash, which can be reliably dated. The holes were clearly distinct from the volcanic layer, says Kazutaka Shimada, curator of the Meiji University Museum in Tokyo. 'They had well-defined edges'.
Before this discovery, the oldest remains of a structure were those at Terra Amata in France, from around 200,000 to 400,000 years ago; see artist's conception."
"Recent evidence suggests that homo erectus may have survived much longer than the current consensus suggests. Swisher et al. (1996) report that recent dating of erectus remains from Java place them between 27,000 years and 53,000 years ago. This is a million years after erectus is thought to have died out in Africa and raises the possibility erectus coexisted with modern homo sapiens in Southeast Asia. The erectus population on Java would have been cut off from the mainland for long periods of time by rising seas (though see below for the possibility of erectus watercraft). Isolated from the Eurasian gene flow, they would have been able to survive unchanged until modern humans arrived by boat around 40,000 years ago. See also Gibbons (1996).
For a discussion of the implications, see Dan Barnes on Recent Dates for Javanese Homo erectus followed by the AP report with interviews, and the multiregionalist Milfred Wolpert's response, all on the online Human Origin News (external). Note that Wolpert argues the remains are of homo sapiens, not erectus; this controversy is tied to the multiregional hypothesis (below)."
Literature on Homo Erectus:
Brown, F., Harris, J., Leakey, R. & Walker, A. (1985). Early Homo erectus skeleton from west Lake Turkana, Kenya. Nature 316: 788-792.
Gibbons, Ann (1996). Human origins - Homo erectus in Java - a 250,000-year anachronism. Editorial. Science 274, 5294 (Dec 13): 1841-1842.
Gibbons, Ann (1998). Paleoanthropology - Ancient island tools suggest Homo erectus was a seafarer. Editorial. Science 279, 5357 (March 13): 1635-1637.
Morwood, MJ, PB O'Sullivan, F. Aziz, A. Raza (1998). Fission-track ages of stone tools and fossils on the east Indonesian island of Flores. Nature 392, 6672 (March 12): 173-176.
Swisher III, CC, WJ Rink, SC Antón, HP Schwarcz, GH Curtis, A Suprijo, and Widiasmoro (1996). Latest Homo erectus of Java: Potential contemporaneity with Homo sapiens in Southeast Asia. Science. 274 (5294): 1870-4.
Walker, A.and Leakey, R.(1993). The Nariokotome Homo erectus Skeleton. Springer-Verlag.
From Archaic to Modern Homo Sapies
"Ongoing excavations at Boxgrove (external) near Chichester in Southern England have revealed human remains dating back 500,000 years. Stone axes and other lithic tools lie next to a butchered rhinoceros, deer, bison and horse. The remains are classified as Homo heidelbergensis, a possible precursor to the Neanderthals. Recent discoveries at Atapuerca in Spain of hominids tentatively dated to 800 ka bp may be remains of the same species.
Ongoing excavations at Blombos Cave (external) in South Africa have uncovered remains from around 90,000 years ago. The bones are anatomically modern. The findings demonstrate a rich cultural life and early technological innovations. For a journalistic take, see Stone Age man wasn't so dumb (Feb. 2000).
Paviland Cave Research Project (1996-1998). Paviland Cave (external), on the south coast of the Gower peninsula, South Wales, United Kingdom, is an Early Upper Palaeolithic (Early Stone Age) archaeological site, dating to roughly 30,000 - 20,000 years ago. It is the richest site of its kind in Britain, with four and a half thousand finds, including worked bone and stone (lithic) tools."
"Human populations have undergone dramatic expansions in size, but other than the growth associated with agriculture, the dates and magnitudes of those expansions have never been resolved. Genetic approaches to the study of human population expansions have focused on variation at a single genetic locus, the 'control region' of mitochondrial DNA. But in the study of demographic history, single-locus investigations suffer from pronounced statistical and biological limitations. The statistical problem is that the conclusions rely on only one particular realization of a gene genealogy, the 'tree' determining the ancestral relationships among a set of alleles. The biological problem is that there are a large number of functional genes in the mitochondrion, and due to a complete linkage, a selective sweep for any one of the genes may lead to a spurious signal of expansion."
Reich and Goldstein (University of Oxford, UK) present two new statistical tests for population expansion, using variation at a number of unlinked genetic markers to study the demographic histories of natural populations. The authors report that analysis of genetic variation in various aboriginal populations throughout the world reveals highly significant evidence for a major human population expansion in Africa, but no evidence of expansion outside of Africa. The inferred African expansion is estimated to have occurred between 49,000 and 640,000 years ago, certainly before the Neolithic expansions, and probably before the splitting of African and non-African populations. The authors suggest that in showing a significant difference between African and non-African populations, their analysis supports the unique role of Africa in human evolutionary history. The authors also suggest that the missing signal in non-African populations may be the result of a population bottleneck associated with the emergence of these populations from Africa, as postulated in the 'Out of Africa' model of modern human origins (see below). (Procedings of the National Academy of Sciences, US 95 (7 Jul 98): 8119.)"
Contact: David B. Goldstein.
"Woodruff and Gagneaux translated the variation in the DNA sequences within humans, chimpanzees, and gorillas into a measure of genetic diversity. Chimps and gorillas, they found, have roughly equal level of diversity. Humans, however, although we are spread out over a vastly larger geographic area, have a significantly lower level of genetic diversity. Woodruff sums it up succinctly: "There's more diversity in one social group of 55 chimps than in the entire human population."
This lack of genetic diversity suggests the human lineage has gone through a population bottleneck at some point in its past history. When this happened or for what reason has not been determined. A plausible earliest date can be set by considering the large differences found between Neanderthal DNA and modern genes (Krings 1997, 1999, and Goodwin 2000). Unless these differences result from a Neanderthal bottleneck, the common ancestor of Neanderthals and modern humans -- Homo erectus -- was genetically far more diverse than current human populations. Since the human-Neanderthal split, according to the genetic analyses so far undertaken, took place around 500,000 and 800,000 years ago, the bottleneck on the human population must have occurred since this split."
"See Brooks, Martin (1999). Apocalypse then. Our genes show that early humans teetered on the brink of extinction. New Scientist 163. 2199 (14 August): 32.
For a colorful overview of the possible effects of climatic and catastrophic events on human evolution, see The Signposts Perspectives: 59,999,999 BC- 51,000 BC. (external).
Stanley Ambrose suggests in a recent article in the Journal of Human Evolution that the eruption of Mount Toba in Sumatra around 71,000 years ago may have caused a worldwide bottleneck in human populations. See abstract.
In response to Martin Brooks' 'Apocalypse then', Mike Weale at the Centre for Genetic Anthropology, University College London, argues in a recent letter (external) to the New Scientist (4 September 1999) that 'there are plenty of other ways to explain why the diversity of human mitochondrial DNA is low compared to that of chimps and gorillas':
A recent selective sweep is one answer, in which a new DNA molecule with some selective advantage replaced all others in the population. Another is simply chance. Studies on other parts of the genome, such as the Y chromosome, will help to resolve this issue. Even if a common population bottleneck is indicated for all genes, this need not mean these were the only humans alive at the time. All it means is that any other humans were replaced without contributing to the gene pool when our ancestors, possessing perhaps some cultural innovation, multiplied. Genocide? Possibly, although competitive exclusion is an alternative explanation. Either way, the low diversity of our mitochondrial DNA may indicate too much success rather than near failure.
Peter Frost notes that a recent study by Cargill et al. (1999) shows that genetic variability is inversely related to the gene's selective value. Variability is highest at 'degenerate' sites, lower in non-coding regions, and lowest in coding regions. So the lower the selective value of a gene, the more it will accumulate 'junk' variability. The higher its selective value, the more this 'junk' variability will be eliminated. Somewhat counterintuitively, a low degree of variation in the human population could be the result of several regional mutations that confer a selective advantage, spreading through the whole population in a manner Brace calls mosaic evolution. Instead of tidy lineages and population replacements, we get a situation where gene flow in effect creates a single (if still varied) but widely dispersed population.
Cargill, M. et al. 1999. 'Characterization of single-nucleotide polymorphisms in coding regions of human genes'. Nature Genetics 22: 231-238."
"Archaeologists in Zambia have uncovered evidence that early humans used paint for aesthetic purposes far earlier than previously thought (see BBC report, 2 May 2000). The team found pigments and paint grinding equipment dated to 350 - 400 kya; the previously oldest pigments are 120,000 years old. Over 300 fragments of pigment have now been uncovered in a cave at Twin Rivers, near Lusaka, Zambia, originally gathered from the surrounding area. One of the team who made the discovery, Dr Lawrence Barham from the University of Bristol, said: "We're dealing here with people who were perhaps using symbols far earlier than we expected." He speculates "It also implies the use of language, so it's an important discovery, full of implications for the development of new behaviours." Composite tools of more than one type of material -- for instance wood and stone -- also date from this period; cf. Mithen's (1996) notion of cognitive fluidity."
"About 10 kilometers east of Dusseldorf in Germany, in the valley of the Dussel, there is a little town called Neander. One hundred and forty-three years ago, in the summer of 1856, some workmen broke into a cave to get at the limestone inside and discovered a set of ancient bones. Most of the bones were smashed to bits by the workmen, but some of the bones, including part of the skull, survived, and the skeleton was soon recognized by anthropologists as belonging to an ancient race of men who came to be known as the Neanderthals. A Neanderthal fossil had actually been discovered some years earlier in Gibraltar, but not recognized as such. Neanderthal-like fossils have also been found in France, Spain, Italy, Yugoslavia, Iraq, and Israel.
For more than a century, one of the central questions in paleoanthropology has been whether modern man evolved from this hominid -- or was the Neanderthal a separate branch that became extinct?
In general, 'Neanderthals' is the informal designation of a morphologically distinctive group of large-brained hominids who inhabited Europe and western Asia between approximately 200,000 and less than 30,000 years ago. They are sharply distinguished from modern humans by a wide range of cranial and postcranial characteristics, although they do share a number of derived bony features with other members of the European/western Asian hominid clade that diversified in this part of the world after approximately 500,000 years ago. Subsequent to approximately 150,000 years ago, the Neanderthals appear to have been the sole surviving species of this clade. Some researchers describe them as a robust species of homo occupying cold climates in Europe and Western Asia from around 200 to 30 ka bp. Their brain volume was slightly larger than the contemporary average - cf. Neanderthal skulls.
The Neanderthals were apparently highly successful over a large region for a substantial period of time, but this situation changed dramatically with the arrival in Europe of the first modern humans, Homo sapiens. The evidence is that these "Cro-Magnons" had begun to arrive both in eastern Europe and in the far northeast of the Iberian Peninsula by approximately 40,000 years ago, and within little more than 10,000 years, the Neanderthals were gone (for recent finds in central Europe dating to 28,000 kya, see 'The Latest Neanderthal' (SciAm, external)). The mechanism of their eviction has long been debated, but there are four main possibilities. The first and second of these possibilities, that the Neanderthals were eliminated by the moderns in direct conflict (cf. a proposed scenario and map in Der Spiegel, March 2000; external, and Valerius Geist's response) or by indirect economic competition, both imply the separate species status of the Neanderthals, as does any combination of these two possibilities. The alternative possibilities, that the Neanderthals had simply evolved rapidly into moderns, or that the genes of the invading moderns simply "swamped" those of the Neanderthals, both imply some form of species continuity (cf. Loring Brace, below).
See Ian Tattersall and J.H. Schwartz: Hominids and hybrids: The place of Neanderthals in human evolution. Proc. Natl. Acad. Sci. US 22 Jun 99 96: 7117.
Web sites: Neanderthals: A Cyber Perspective (external)"
"A topic of much debate is the date for the evolution of language. In part, there is a definitional problem: while vervets use vocal cries that share many of the characteristics of words, and bonobos (more so than chimpanzees) can be trained to communicate with signs. The female bonobo Kanzi, for instance, one of the primary subjects in E. Sue Savage-Rumbaugh's research, has demonstrated impressive symbolic abilities. In her SRCD Monograph, Savage-Rumbaugh has documented that Kanzi could comprehend more than 440 novel sentences of request and performed equal to or somewhat better than did a 2-1/2 yr old girl tested in the same manner and with the same sentences. Kanzi's language production was assessed by Patricia Greenfield of UCLA at the level of a 1-1/2 yr old child. (Contact: Sue Savage-Rumbaugh and Duane Rumbaugh <LRCDMR@langate.gsu.edu>.)
This of course still leaves a considerable distance between the linguistic capabilities and performance of human beings and that of our closest relatives. However, it is not in principle difficult to imagine forms of speech intermediate to ours in complexity; for instance, speech with a reduced set of phonemes, grammatical categories, and sentence forms. The difficulty is determining what kinds of evidence are relevant to this question, and how to evaluate the scarce clues available to us."
"It is no doubt the case that achaeological remains of culture can tell us something about the cognitive abilities of the people in question. However, in order to interpret the cultural remains, we need a theory of how various cognitive abilities enable (and are required to account for) certain cultural activities. At present, there is no clear consensus on such a theory. In the context of language, we specifically need a model of how the biological and cultural innovations of language - and they must of necessity go hand in hand - impact our cognitive skills. Is it for instance the case, as Merlin Donald (1991) argues, that human beings today can function very well without language, retaining their abilities to interpret events, interact socially, plan their days, and communicate through a range of mimetic means? Or, on the contrary, are human minds generated by language in a radical way, so that deprived of language, we descend to the cognitive skills of chimpanzees? This view might be suggested by the apparently severely reduced cognitive capacities of children raised by animals. It is also a view that resonates with the idea that human beings are caught in the "prison-house of language" (Nietzsche), depending for their basic cognitive skills on the culturally constructed nature of language.
In my view, it is fruitful to examine the cognitive abilities associated with the imagination as more fundamental to advances in human cognition than language per se. Such advances are required for the emergence of certain forms of language, notably those that do not refer directly to what is present. Thus, evidence of imagination can be taken as a minimal requirement for language as internal thought. However, the converse does not necessarily hold: internal thought does not appear to require language."
"Earlier claims of a Neanderthal flower burial in Shanidar is now contested; see Gargett, R.H. (1989) Grave shortcomings: The evidence for Neanderthal burials. Current Anthropology. 30. 157-90. The precise implications of such a find also need to be argued and spelled out in detail."
"Evidence that Neanderthals had a morphologically near-modern vocal apparatus is presented in Arensburg, B., Tillier, A.M., Vandermeersch, B., Duday, H., Schepartz, L.A. and Rak, Y. (1989). A middle palaeolithic human hyoid bone. Nature 338: 758-760. It is depicted to scale in Donald C. Johanson and B. Edgar's From Lucy to Language (Simon and Schuster, 1996), p. 107. For a discussion, see Arensburg, B., Schepartz, L.A., Tillier, A.-M., Vandermeersch, B., Duday, H. & Rak, Y. (1990) A reappraisal of the anatomical basis for speech in Middle Palaeolithic hominids. American Journal of Physical Anthropology. 83. 137-46. See also Arensburg, B. & Tillier, A.-M. (1991) Speech and the Neanderthals. Endeavour. 15 (1). 26-8.. For background, see Aiello and Dean's An Introduction to Human Evolutionary Anatomy, p. 243.2"
"Kay, Cartmill, and Balow at Duke have recently measured the relative size of the hypoglossal canal in primates. This canal, a hole at the base of the skull in the area where the spinal cord enters the head, is the conduit for the nerve fibers from the brain to the muscles of the tongue, and an interesting index of complex speech. See the Duke University press release (external) and John Wilford's presentation of the results in The New York Times, April 28, 1998. In brief, the findings indicate that the enlargement of the hypoglossal canal to modern proportions happened already in early forms of archaic homo sapiens around 400,000 years ago. Neanderthals show the same-sized canal and according to this line of evidence would have possessed complex speech. Because of their shorter neck, their range of vowels may have been narrower. More recently, this line of reasoning has been challenged; cross-species comparisons suggest the hypoglossal canal may not be a meaningful indicator of adaptations for speech. See Kay et al. (1998).
Contact: Matt Cartmill, Biological Anthropology and Anatomy, Duke University, NC.
For evidence that the Neanderthal were poor at cultural innovation, yet capable of acquiring novel technology from their Homo sapiens sapiens neighbors, see Paul Mellars, The Neanderthal legacy: an archaeological perspective from western Europe (Princeton, NJ: Princeton University Press, 1996)."
For a recent review, see Strait, DS; Grine, FE; Moniz, MA. (1997). A reappraisal of early hominid phylogeny. Journal of Human Evolution. 32 (1): 17-82.
deCastro, JMB; Arsuaga, JL; Carbonell, E; Rosas, A; and others (1997). A hominid from the lower Pleistocene of Atapuerca, Spain: Possible ancestor to Neanderthals and modern humans. Science 276 (5317):1392-1395.
Gabunia, L. & Vekua, A. (1995) A Plio-Pleistocene hominid from Dmanisi, East Georgia, Caucasus. Nature. 373: 509-12.
Grün, R., Brink, J.S., Spooner, N.A., Taylor, L., Stringer, C.B., Fransiscus, R.G. & Murray, A.S. (1996) Direct dating of Florisbad hominid. Nature. 382 (6591): 500-1.
McDermott, F., Stringer, C.B., Grün, R., Williams, C.T., Din, V.K. & Hawkesworth, C.J. (1996). New Late-Pleistocene Uranium-Thorium and ESR dates for the Singa hominid (Sudan). Journal of Human Evolution 31 (6): 507-516.
Mellars, Paul. Origins of Anatomically Modern Humans. Journal of Field Archaeology 24, 3 (Fall, 1997):377 (4 pages - book reviews).
Rightmire, G.P. (1996) The human cranium from Bodo, Ethiopia: Evidence for speciation in the Middle Pleistocene. Journal of Human Evolution. 31: 21-39.
Tautavel Man. A web presentation by the French Ministry of Culture of an archaic homo found in Southern France in 1971 and dated to 450,000 years. Full text and illustrations (external).
Turner, A. (1992) Large carnivores and earliest European hominds: Changing determinants of resource availability during the Lower and Middle Pleistocene. Journal of Human Evolution. 22 (2): 109-26.
"Archaeological finds from Java to Kenya demonstrates with certainty that Homo erectus inhabited a vast territory extending through Eurasia and Africa. Appearing in the lower pleistocene, around two million years ago (cf. Geological Time-scales), the remains are initially confined to the tropics, but Homo erectus soon spread into temperate zones. Its toolkit was simple but adequate for this first of hominids to join the league of major predators.
Somewhere around 250 000 years ago, we begin to see changes in skull sizes in Africa. Over the next 100,000 years, there are numerous finds of so-called Archaic Homo sapiens (see literature above). The first Levallois flint tools appear in southern Africa around 120,000 years ago. In the Levant, various populations with a broad range of modern and archaic features coexist in the period between 120,000 and 60,000. Recent evidence indicates Homo sapiens reached Australia more than 60,000 years ago; archaeological and genetic data suggests that fully modern peoples did not move into Europe until some 10,000 years later (Mellars 1992), possibly because it was already inhabited by Neanderthals.
Where did these populations come from? Did Homo sapiens emerge in a single speciation event in Africa some time around a quarter of a million years ago, expanding into the territory of Homo erectus and replacing it? Or did local populations of Homo erectus, spread through the breadth of the vast Eurasian and African continents, evolve together into Homo sapiens, mixing genes and also retaining local characteristics? Archaeologists working in the field for a long time leaned towards the latter scenario, suggesting that human evolution shows regional continuity (the so-called Multiregional model). Europe and Western Asia posed a special case, as it was populated by Neanderthals, a form of archaic Homo that may or may not be the an ancestor of the subsequent modern human population (see above for background and below for discussion).
During the late 1980s, initial studies of global DNA diversity at a stroke changed this picture. The much greater amount of genetic variation in Africa pointed clearly to that continent as the locus of the first fully modern human populations. In a landmark paper, Cahn, Stoneking, and Wilson presented an analysis of a sampling of human mitochondrial DNA — inherited only through the maternal line — from around the globe. They argued that the roots from the "most parsimonious tree" that described the phylogenetic relationship of human mitochondria had deep roots in Africa, the next deepest roots were in Asia, followed by European and New World lineages. Using a mitochondrial clock, they computed the time at which all these mitchondria coalesced into a common ancestor — the Mitochondrial Eve. She lived, they argued, some 180,000-270,000 years ago in North Africa.
In this "out-of-Africa" scenario, modern humans arose in Africa around 200,000 years ago and then spread elsewhere, replacing Neandertals and Homo erectus -- and any other hominid relatives in our evolutionary past. A Japanese team estimated that all non-Africans are descendants of a small band of humans that left Africa around 100,000 years ago. In May 2001, R. Spencer Wells et al. report that their examination of the Y-chromosome shows no trace of any non-African material: "This really puts the nail in the coffin of multiregionalism" (BBC report, external). Decades of anthropological debate over modern human origins based on interpretations of measurements of limb proportions and a host of bumps and grooves on ancient fossils teetered on the verge of irrelevance."
"There are, however, difficulties with the model. Alan Templeton took the data from Cahn, Stoneking and Wilson's paper and showed that the number of trees that could be constructed from their data was astronomical. Their 'most parsimonious tree' was not unique; in fact, Templeton found even more parsimonious trees with strikingly different topologies. These suggested the possibility of a continuous and distributed origin of modern homo sapiens, fueled by a continuous exchange of genes.
This lead to the construction of the Multi-regional hypothesis for the origins of modern homo. In this view, the evolution and diversification of modern homo sapiens took place across a large geographic region that encompassed Africa, Asia, and Europe. Exchange of genes through migration took place during the 200,000+ years of modern homonid evolution. There is no single cradle of origin but a 'thousand points of light'. The hypothesis appeared to find the strongest support in South-East Asia.
Paleoanthropologist Loring Brace (1995) points out that the out-of-Africa hypothesis is not supported by much of the archaeological evidence. Most strikingly, there is no detectable break in cultural development in South-east Asia that suggests the replacement of Homo erectus by migrating Homo sapiens. The mtDNA analysis relies on a steady trickle of mutations -- the so-called genetic clock; this assumption may be flawed. Further genetic data could also turn the tide: recent examinations of genetic variation in New Guinea -- for a preview, see Redd & Stoneking (1998) -- finds that it is comparable to that of Sub-Saharan Africa; this would seem to indicate a longer history than that presumed by the out-of-Africa hypothesis, and could be explained by a continuity with local Homo erectus populations. In addition, data obtained by Mike Hammer and colleagues on Y-chromosome variation ties New Guinea and Australia to Indonesia and eastern Asia with a date that goes far enough back into the Pleistocene that Homo erectus becomes the predicted progenitor (cf. Hammer 1996 and Karafet 1997; as of July 1999, not all the relevant data has been published). Brace's extensive craniofacial data support this view; according to him, there are similarities in skull features between Asian Homo erectus populations and modern Asians.
The discovery (May 1999) that the gracile Australian Mungo Man is as old as 62,000 years has added to the complexity of this debate; this population may have merged with the more robust peoples arriving later (see Peter Brown's Australian paleoanthropology index (external). Thorne's DNA analysis of Mungo Man (January 2001) supports this scenario. The results indicate that the gracile population that first settled Australia 60,000 or earlier are not descendants of a recent wave out of Africa. They also indicate that significant genetic variation continued to exist in the region; around 20,000 years ago, Australia may have seen the arrival of a robust-looking population of homo, which subsequently mixed and merged with the local gracile-looking population.
Adcock, G.J. et al. (2001). Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins. Proc. Natl. Acad. Sci. US 16 Jan 01 98: 537. E-mail W. James Peacock.
Relethford, John H. (2001). Ancient DNA and the origin of modern humans. Proc. Natl. Acad. Sci. US 16 Jan 01 98: 390. E-mail John H. Relethford
According to Milford Wolpoff (1997), the fundamental claim of multiregional evolution is that excepting extinctions, ancient populations have multiple descendants and modern populations have multiple ancestors. In Brace's view, novel adaptations can spread efficiently across the Old World without the need for much population movement. Given even the tiniest trickle of a gene flow, natural selection will ensure that novel genes that have an adaptive advantage spread through the population. This process would leave the rest of the phenotype unchanged, thus preserving a large number of regional characteristics -- what Brace calls mosaic evolution. Instead of replacement, we get evolutionary continuity in each region, leading to different races. These races do not differ in significant functional adaptations, but show variation in matters that have little significance for survival, such as the specific proportions of the face, the texture of the hair, or the color of the skin. For the application of genetics to the question of race, see K. Owens and M-C. King (1999), Genomic views of human history.
If evolution is continuous and there is no replacement, why are modern human crania distinct from their generally more robust archaic predecessors? Brace argues that steady reductions in the size of canines over the past 100,000 years may be due to mutations in the parts of the genes that produce the relevant growth enzymes; small changes here would make the enzyme less efficient and lead to smaller teeth. As long as the larger teeth are not selected for by evolutionary pressures, there will be a slow drift towards smaller teeth. Thus, it is cooking innovations that are responsible for the reduction of tooth size. Around ten thousand years ago, the selective forces on teeth drops dramatically with the invention of pottery and the possibility of surviving on liquid food; before this period, there are no instances of toothless individuals, but they become common subsequent to this date. One of Brace's former students, Margaret J. Schoeninger, wrote her dissertation on changing amounts of strontium in Archaic and Modern Homo Sapiens as an index of meat eating: while an archaic diet consisted of 40-60% meat, this fell dramatically around 18,000 years ago in the Middle East. Primitive sickles from the period confirm an increased reliance upon grains, although this is eight to ten thousand years before agriculture (Schoeninger 1980).
For an update on the multiregional debate, see Wong's report, Is Out Of Africa Going Out The Door? Scientific American, July 1999 (external). On the other hand, the genetic analyses reported in R. Thomson et al. (2000) suggest that the spread of Y chromosomes out of Africa is much more recent than previously believed -- on the order of 50,000 years. For a journalistic presentation, see the BBC report (external) on work by Wells et al. backing up this result.. Ke et al. (2001) reach a similar conclusion:
'To test the hypotheses of modern human origin in East Asia, we sampled 12,127 male individuals from 163 populations and typed for three Y chromosome biallelic markers (YAP, M89, and M130). All the individuals carried a mutation at one of the three sites. These three mutations (YAP+, M89T, and M130T) coalesce to another mutation (M168T), which originated in Africa about 35,000 to 89,000 years ago. Therefore, the data do not support even a minimal in situ hominid contribution in the origin of anatomically modern humans in East Asia.' (Science 292, 1151 (2001).
Cf. the subsequent discussion. Some reservations regarding these results is warranted, as the analysis of the geographical distributions of the human genome is far from complete and the statistical analyses is relatively likely to contain flawed assumptions.
Alan Templeton (2002), returning to the debate he may be said to have initiated (see above), notes that new information on the human genome is now available, and a reassessment of the multiregionalism debate is possible. He presents a 'formal statistical analysis of human haplotype trees for mitochondrial DNA, Y- chromosomal DNA, two X-linked regions and six autosomal regions', concluding that ...
A coherent picture of recent human evolution emerges with two major themes. First is the dominant role that Africa has played in shaping the modern human gene pool through at least two—not one—major expansions after the original range extension of Homo erectus out of Africa. Second is the ubiquity of genetic interchange between human populations, both in terms of recurrent gene flow constrained by geographical distance and of major population expansion events resulting in interbreeding, not replacement. (page 45; cf. excerpt).
I had written in late 2001, 'The final nail in the coffin of multiregionalism is not yet in. Evidence of ancient genetic continuities from local populations may still surface, even though several studies now point univocally towards a recent African origin of all contemporary human beings'. Templeton's evidence for repeated migrations out of Africa, in a general context of ubiquitous interbreeding, presents an elegant and convincing synthesis of the opposing positions in the debate. His analysis suggests replacement did not take place, yet crucial new mutations took place in Africa and flowed out of Africa in at least two major expansions."
"The replacement hypothesis has also been applied to Europe, where people from the Middle East are cast as newcomers into Neanderthal territory, displacing them completely over a period of some five thousand years (a view held by the noted Cambridge archaeologist Paul Mellars). If we look at the European mtDNA gene pool, we find that no lineages go back any further than 50,000 years (Richards et al 1996); this time depth corresponds roughly to the entry of the Aurignacian culture into Europe from the Middle East (Mellars 1992). Recent comparative analyses of contemporary human and fossil Neanderthal DNA indicates that Neanderthals split from our ancestors as early as 700,000 years ago, and that there was no subsequent interbreeding (Krings 1997 and 1999). Again, the analysis was done on a small part of mDNA, and relies on a genetic clock argument. Brace argues instead that Neanderthals simply evolved into modern northern Europeans. His skull measurements show that Neanderthals cluster with one and only one modern population: that of Britain and Scandinavia. Robust features of the skeleton, such as brow ridges, simply vanish when the selective force of evolution is no longer active. That the process of that reduction in robustness by which modern appearance arose, he argues, is why virtually all early Upper Paleolithic groups present a kind of 'mixed' appearance.
This story can be told with great precision using data from teeth. Brace writes, 'As soon as earth oven cookery became a standard part of Neanderthal food-preparation practices coincident with the onset of the last glaciation, tooth size began to reduce at the rate of one percent every two-thousand years. There was a reduction of about 30% of total tooth size between the early Neanderthals of around 130,000 years ago and the "classic" Neanderthals of 50 to 70,000 years ago. Then between 50 and 35,000 years, there was another 10% drop to the point where there is virtually no difference in size between the last people being called Neanderthals (and really more because of stone tool typology than what they actually looked like) and the oldest Upper Paleolithic specimens. And if one looks at the shoulder reinforcements of those same specimens, they are perfectly intermediate between earlier full Neanderthal form and that of living Europeans. Tooth size continued to drop and the difference in tooth size in living Europeans and the early Upper Paleolithic is greater than the difference between the latter and the classic Neanderthals. The assumptions of two distinct populations living in different areas is a product of mind set and not of the data'.
These dramatically different models -- and the genetic evidence still favors the Out of Africa hypothesis -- both require further data before the debate is over. A more extensive analysis of Neanderthal genes beyond mitochondrial DNA would go some way to clear up the question. Further fossil finds may also throw light on the debate.
In April 1999, Portugese archeologists reported the discovery of a hybrid Neanderthal-Cro Magnon child dating from 4,000 years after the commonly agreed date of the disappearance of full Neanderthals (see media report (local) and Discover article (external)). The view that the skeleton represents a hybrid is contested, however; Brace suggests it is simply another example of the gradual reduction in robustness that was taking place across European Neanderthal populations, which in his view did not disappear but change into modern Europeans.
For an update on this discussion, see Bower, Bruce (1999). DNA's Evolutionary Dilemma: Genetic studies collide with the mystery of human evolution. Science News February 6, 1999. pp. 88-90. See also an update on the African Eve hypothesis (8 September '99).
References on the Multiregionalism debate:
Brace, C. Loring (1995). Biocultural interaction and the mechanism of mosaic evolution in the emergence of "modern" morphology. American Anthropologist 97 (4): 711-23.
Hammer, Michael F. and Stephen L. Zegura (1996). Role of the Y chromosome in human evolutionary studies. Evolutionary Anthropology 5. 4: 116-134.
Karafet, Tatiana, et al. (1997). Y chromosome markers and trans-Bering Strait dispersals. American Journal of Physical Anthropology 102.3: 301-314.
Krings, M. et al. (1999). Proc. Nat. Acad. Sci. USA 96: 5581-5585.
Krings, M; Stone, A; Schmitz, R W; Krainitzki, H; Stoneking, M; Paabo, S. Neandertal DNA sequences and the origin of modern humans Cell 90 (1997): 19-30. Abstract.
Mellars, P.A. (1992). Phil. Trans. Royal Society Lond. B. 337: 225-234.
Redd, Alan J. and Mark Stoneking (1998). Evolutionary affinities of aboriginal Australian and Papua New Guinea populations: A comparison of mitochondrial, HLA, and Y chromosome genetic data. American Journal of Physical Anthropology Supplement 26: 185.
Richards, M. et al. (1996). Am. J. Hum. Genet. 59: 185-203.
Schoeninger, Margaret J. (1980). Changes in Human Subsistence Activities From the Middle Paleolithic to Neolithic Period in the Middle East. U. of Mich. Ph. D. thesis.
(1982). Diet and the evolution of modern human form in the Middle East. American Journal of Physical Anthropology 58. 1 (May): 37-52.
(1996). Stable isotope studies in human evolution. Evolutionary Anthropology 4 (3): 83-98.
Templeton, Alan (2002). Out of Africa again and again. Nature 416 (2002): 45 - 51. Full text (external); excerpt (local).
Wolpoff, M.H. and R. Caspari (1997). Race and Human Evolution. Simon and Schuster, New York."
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