With the onset of the glacial maximum c. 20,000 years ago, and the ponding up of the Ob River, humans circulated less easily from one end of the steppe-tundra belt to the other. This barrier separated ancestral Europeans from ancestral East Asians.
Outside Africa, people seem to have the same amount of Neanderthal admixture, be they Europeans, East Asians, or Papua/New Guineans. How come?
Perhaps the admixture was a one-time event that occurred just as modern humans began to spread out of Africa and into the Middle East. Only there did they encounter an ‘almost-modern’ population that had long bordered and probably intermingled with the Neanderthals to the north. Our ancestors thus received Neanderthal admixture indirectly, via a partially hybridized population. As they spread beyond this transitional zone, they encountered archaic hominins that differed much more from them in appearance and behavior. Admixture accordingly decreased.
The above explanation is parsimonious but still leaves a few loose ends. According to an unpublished study by Sarah Joyce and Jeffrey Long, archaic admixture occurred in two stages: an early one in the Middle East, when modern humans first spread out of Africa, and a later one, when modern humans first spread from Asia to Oceania (Dalton, 2010).
This leads us to an alternate explanation: all of the archaic hominins throughout Eurasia, including the Neanderthals, were related to each other. The second admixture looks Neanderthal because it came from a related archaic population somewhere on the Asia/Oceania boundary.
Did archaic admixture also occur separately in Europe and East Asia? Not if we believe the Joyce and Long study. Moreover, there is growing evidence that ancestral Europeans and ancestral East Asians were one and the same people until 22,500 years ago, long after the Neanderthals had gone extinct (Laval et al., 2010). This might seem surprising. Modern humans were already in Eurasia by 40,000 BP, if not earlier. How could these early Eurasians have stayed together as a single breeding population for the next twenty thousand years?
They didn’t. The modern humans who initially settled the south and east of Asia were later pushed out and/or absorbed. Today, their descendants are limited to a few relic groups: the Veddas of Sri Lanka, the Andaman Islanders, the Semang of the Malayan Peninsula, and the Aetas of the Philippines.
Present-day Europeans and East Asians descend largely from a small nomadic population that once roamed Eurasia’s northern tier—a belt of steppe-tundra that stretched from southwestern France to Beringia during the last ice age. This population then split in two about 20,000 years ago at the glacial maximum: on the one hand, an immense ice sheet spread south and east from Scandinavia; on the other, large glacial lakes formed along the Ob (Rogers, 1986; Crawford et al, 1997). Chronologically, this barrier to east-west gene flow matches the dating by Laval et al. (2010) of the split between ancestral Europeans and ancestral East Asians.
Even before the ice age ended some 10,000 years ago, these two northern groups had been spreading south, initially into the Middle East on the west and into the Americas on the east. Later expansions encompassed not only the rest of Asia but also North Africa and Oceania. Today, a common northern origin is suggested by linguistic similarities. There seems to be a core Eurasiatic macrophylum, principally Indo-European, Uralic, and Altaic, that stretches across the northern tier of Eurasia. To the south are other related language families, principally Afro-Asiatic, Dravidian, and Amerindian, that have nonetheless undergone more change, due to linguistic ‘founder effects’ or to lexical and grammatical borrowing from pre-existing southern languages (Rogers, 1986; Wikipedia – Eurasiatic languages, Nostratic languages).
But how did these northerners replace humans who were not only ‘modern’ like themselves but also native to southern latitudes? After all, the southerners were playing on their own turf. They had been adapting to their own climate and ecosystem for much longer. What happened to the home team advantage?
Some answers are offered by Hoffecker (2002, p. 135). Among early modern humans, tools and weapons were more complex at arctic latitudes than at tropical latitudes. “Technological complexity in colder environments seems to reflect the need for greater foraging efficiency in settings where many resources are available only for limited periods of time.” Arctic humans coped with resource fluctuations and high mobility requirements by planning ahead and by developing untended devices (e.g., traps and snares) and means of food storage.
In addition, these increased cognitive demands fell on both men and women. Paternal and maternal investment were much more equal than in the tropical zone, where women could provide for their families year-round with less male assistance (Kelly, 1995, pp. 268-269; Martin, 1974, pp. 16-18). Indeed, because the arctic zone compelled men to shoulder most of the food provisioning, women were free to enter a new range of tasks: food processing (e.g., butchery and carcass transport); shelter building; garment making; leather working; transport of material goods; etc. (Waguespack, 2005). It was this technological revolution that ultimately led to what we now call ‘civilization’ (Frost, 2008).
Of course, none of this could have been foreseen at the time. Northern Eurasians were simply pre-adapted for what came later. They were especially able to exploit the shift to agriculture and the ensuing need for seasonal planting, harvesting, and food storage, as well as more complex forms of social organization. This was their competitive edge over humans farther south.
References
Cavalli-Sforza, L.L., A. Piazza, P. Menozzi, and J. Mountain. (1988). Reconstruction of human evolution: Bringing together genetic, archaeological, and linguistic data, Proceedings of the National Academy of Science USA, 85, 6002-6006.
Crawford, M.H., J.T. Williams, and R. Duggirala. (1997). Genetic structure of the indigenous populations of Siberia. American Journal of Physical Anthropology, 104, 177-192.
Dalton, R. (2010). Neanderthals may have interbred with humans. Genetic data points to ancient liaisons between species. Naturenews, April 20.
http://www.nature.com/news/2010/100420/full/news.2010.194.html
Frost, P. (2008). The path to civilization? Evo and Proud, March 10, 2008.
http://evoandproud.blogspot.com/2008/03/path-to-civilization.html
Green, R.E., J. Krause, A.W. Briggs, T. Maricic, U. Stenzel, M. Kircher, et al. (2010). A draft sequence of the Neandertal genome, Science, 328, 710-722.
http://www.sciencemag.org/cgi/reprint/328/5979/710.pdf
Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.
Kelly, R.L. (1955). The Foraging Spectrum. Diversity in Hunter-Gatherer Lifeways. Washington: Smithsonian Institution Press.
Laval, G., E. Patin, L.B. Barreiro, and L-Quintana-Murci. (2010). Formulating a historical and demographic model of recent human evolution based on resequencing data from noncoding regions, PloS ONE 5(4) : e10284
Martin, M.K. (1974). The Foraging Adaptation — Uniformity or Diversity? Addison‑Wesley Module in Anthropology 56.
Rogers, R.A. (1986). Language, human subspeciation, and Ice Age barriers in Northern Siberia. Canadian Journal of Anthropology, 5, 11‑22.
Waguespack, N.M. (2005). The organization of male and female labor in foraging societies: Implications for early Paleoindian archaeology. American Anthropologist, 107, 666-676.
Wikipedia. (2010). Eurasiatic languages,
http://en.wikipedia.org/wiki/Eurasiatic_languages
Wikipedia. (2010). Nostratic languages,
http://en.wikipedia.org/wiki/Nostratic_languages
Outside Africa, people seem to have the same amount of Neanderthal admixture, be they Europeans, East Asians, or Papua/New Guineans. How come?
Perhaps the admixture was a one-time event that occurred just as modern humans began to spread out of Africa and into the Middle East. Only there did they encounter an ‘almost-modern’ population that had long bordered and probably intermingled with the Neanderthals to the north. Our ancestors thus received Neanderthal admixture indirectly, via a partially hybridized population. As they spread beyond this transitional zone, they encountered archaic hominins that differed much more from them in appearance and behavior. Admixture accordingly decreased.
The above explanation is parsimonious but still leaves a few loose ends. According to an unpublished study by Sarah Joyce and Jeffrey Long, archaic admixture occurred in two stages: an early one in the Middle East, when modern humans first spread out of Africa, and a later one, when modern humans first spread from Asia to Oceania (Dalton, 2010).
This leads us to an alternate explanation: all of the archaic hominins throughout Eurasia, including the Neanderthals, were related to each other. The second admixture looks Neanderthal because it came from a related archaic population somewhere on the Asia/Oceania boundary.
Did archaic admixture also occur separately in Europe and East Asia? Not if we believe the Joyce and Long study. Moreover, there is growing evidence that ancestral Europeans and ancestral East Asians were one and the same people until 22,500 years ago, long after the Neanderthals had gone extinct (Laval et al., 2010). This might seem surprising. Modern humans were already in Eurasia by 40,000 BP, if not earlier. How could these early Eurasians have stayed together as a single breeding population for the next twenty thousand years?
They didn’t. The modern humans who initially settled the south and east of Asia were later pushed out and/or absorbed. Today, their descendants are limited to a few relic groups: the Veddas of Sri Lanka, the Andaman Islanders, the Semang of the Malayan Peninsula, and the Aetas of the Philippines.
Present-day Europeans and East Asians descend largely from a small nomadic population that once roamed Eurasia’s northern tier—a belt of steppe-tundra that stretched from southwestern France to Beringia during the last ice age. This population then split in two about 20,000 years ago at the glacial maximum: on the one hand, an immense ice sheet spread south and east from Scandinavia; on the other, large glacial lakes formed along the Ob (Rogers, 1986; Crawford et al, 1997). Chronologically, this barrier to east-west gene flow matches the dating by Laval et al. (2010) of the split between ancestral Europeans and ancestral East Asians.
Even before the ice age ended some 10,000 years ago, these two northern groups had been spreading south, initially into the Middle East on the west and into the Americas on the east. Later expansions encompassed not only the rest of Asia but also North Africa and Oceania. Today, a common northern origin is suggested by linguistic similarities. There seems to be a core Eurasiatic macrophylum, principally Indo-European, Uralic, and Altaic, that stretches across the northern tier of Eurasia. To the south are other related language families, principally Afro-Asiatic, Dravidian, and Amerindian, that have nonetheless undergone more change, due to linguistic ‘founder effects’ or to lexical and grammatical borrowing from pre-existing southern languages (Rogers, 1986; Wikipedia – Eurasiatic languages, Nostratic languages).
But how did these northerners replace humans who were not only ‘modern’ like themselves but also native to southern latitudes? After all, the southerners were playing on their own turf. They had been adapting to their own climate and ecosystem for much longer. What happened to the home team advantage?
Some answers are offered by Hoffecker (2002, p. 135). Among early modern humans, tools and weapons were more complex at arctic latitudes than at tropical latitudes. “Technological complexity in colder environments seems to reflect the need for greater foraging efficiency in settings where many resources are available only for limited periods of time.” Arctic humans coped with resource fluctuations and high mobility requirements by planning ahead and by developing untended devices (e.g., traps and snares) and means of food storage.
In addition, these increased cognitive demands fell on both men and women. Paternal and maternal investment were much more equal than in the tropical zone, where women could provide for their families year-round with less male assistance (Kelly, 1995, pp. 268-269; Martin, 1974, pp. 16-18). Indeed, because the arctic zone compelled men to shoulder most of the food provisioning, women were free to enter a new range of tasks: food processing (e.g., butchery and carcass transport); shelter building; garment making; leather working; transport of material goods; etc. (Waguespack, 2005). It was this technological revolution that ultimately led to what we now call ‘civilization’ (Frost, 2008).
Of course, none of this could have been foreseen at the time. Northern Eurasians were simply pre-adapted for what came later. They were especially able to exploit the shift to agriculture and the ensuing need for seasonal planting, harvesting, and food storage, as well as more complex forms of social organization. This was their competitive edge over humans farther south.
References
Cavalli-Sforza, L.L., A. Piazza, P. Menozzi, and J. Mountain. (1988). Reconstruction of human evolution: Bringing together genetic, archaeological, and linguistic data, Proceedings of the National Academy of Science USA, 85, 6002-6006.
Crawford, M.H., J.T. Williams, and R. Duggirala. (1997). Genetic structure of the indigenous populations of Siberia. American Journal of Physical Anthropology, 104, 177-192.
Dalton, R. (2010). Neanderthals may have interbred with humans. Genetic data points to ancient liaisons between species. Naturenews, April 20.
http://www.nature.com/news/2010/100420/full/news.2010.194.html
Frost, P. (2008). The path to civilization? Evo and Proud, March 10, 2008.
http://evoandproud.blogspot.com/2008/03/path-to-civilization.html
Green, R.E., J. Krause, A.W. Briggs, T. Maricic, U. Stenzel, M. Kircher, et al. (2010). A draft sequence of the Neandertal genome, Science, 328, 710-722.
http://www.sciencemag.org/cgi/reprint/328/5979/710.pdf
Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.
Kelly, R.L. (1955). The Foraging Spectrum. Diversity in Hunter-Gatherer Lifeways. Washington: Smithsonian Institution Press.
Laval, G., E. Patin, L.B. Barreiro, and L-Quintana-Murci. (2010). Formulating a historical and demographic model of recent human evolution based on resequencing data from noncoding regions, PloS ONE 5(4) : e10284
Martin, M.K. (1974). The Foraging Adaptation — Uniformity or Diversity? Addison‑Wesley Module in Anthropology 56.
Rogers, R.A. (1986). Language, human subspeciation, and Ice Age barriers in Northern Siberia. Canadian Journal of Anthropology, 5, 11‑22.
Waguespack, N.M. (2005). The organization of male and female labor in foraging societies: Implications for early Paleoindian archaeology. American Anthropologist, 107, 666-676.
Wikipedia. (2010). Eurasiatic languages,
http://en.wikipedia.org/wiki/Eurasiatic_languages
Wikipedia. (2010). Nostratic languages,
http://en.wikipedia.org/wiki/Nostratic_languages
8 comments:
If the first agriculturists who entered Europe were partly descended from west steppe-tundra populations would that explain why there is confusion about whether the genetic evidence comcerning Y-chromosome haplogroups in western Europe is for cultural or demic diffusion of agriculture?
On moving south of the steppe tundra Europeans would be moving in on the land of others. The pattern seems to be that the successful invaders elbow out the male line of the natives. The first agriculturists to enter Europe could have had a disproportionate amount of a West European Y-chromosome haplogroup which was 'coming home'.
Tod,
Personally, I think the diffusion of agriculture was more cultural than demic. This is a question we'll be seeing a lot more data on very soon.
The present decade has brought and will bring answers to three major questions on the evolution of early modern Europeans:
1. How much Neanderthal admixture exists in modern Europeans? (current answer: 1 to 4%).
2. Are present-day Europeans the descendants of early modern Europeans (i.e. Upper Paleolithic) or were these replaced by immigrant farming peoples from the Middle East? (current answer: much debate and no real consensus)
3. When did Europeans begin to look European? Was this a slow incremental process that began with the arrival of modern humans in Europe 35,000 years ago? Or was it a relatively fast process that began long after the arrival of modern humans in Europe? (current answer: most of the data points to a relatively narrow time frame and late date)
Peter,
When you ask "when did Europeans begin to look European?" to which phenotype or phenotypes are you referring, considering the phenotypic diversity within Europe and the fact that the phenotypes found in southern Europe can be found outside of Europe in the Middle East and Caucasus region?
Anon,
I was especially referring to European-specific color traits, i.e.:
a)diversification of hair and eye color into a broad palette of hues, in contrast to the species norm of black hair and brown eyes;
b) whitening of skin color up to the physiological limit of human depigmentation.
These color traits seem to be a relatively late evolutionary development and probably arose after the glacial maximum (20,000-15,000 BP) that separated ancestral Europeans from ancestral East Asians. These traits also occur sporadically in the Middle East, where they probably reflect gene flow from Europe during historic and prehistoric times.
There are also morphological changes that seem to be older and less specific to European populations, i.e., lengthening of head hair and remodeling of face shape. These changes probably arose before the glacial maximum, this being the reason why they occur over a larger geographic area.
Inuit women chew hides to make them easier to work I wonder if there is a way of detecting that in the teeth of Upper Paleolithic women, ( or the lack of it in Neanderthal females). Anyway chewing hides would have meant a tremendous amount of stress on facial structures for women, according to some people the fine facial features and high rates of malocclusion of Europeans are all down to a lack of chewing stress. Although they slow cooked their meat the lack of chewing stress from food would be more than compensated by chewing hides. The first known impacted wisdom tooth is in a woman and 13,000- to 15,000 years old
Sexual Dimorphism in Chin Shape: Implications for Adaptive Hypotheses.
Thanks for the link on the chin Todd.
The authors conclude:
'These findings provide the first quantitative, morphologically based evidence in support of adaptive hypotheses that predict dimorphism in chin shape, including the sexual selection hypothesis'
I was more interested in how the chin evolved from hominids that didn't have it.
P. Frost : "These traits also occur sporadically in the Middle East, where they probably reflect gene flow from Europe during historic and prehistoric times."
You can also add south Asia, central Asia, Siberia (even Mongolia and north-western China) even if it's rare. It's still probably reflecting some input from some ancient migrations from the west (I'm thinking mostly of (apparently) chalcolithic/bronze age Indo-european migrations).
Here are a lot such pictures of Asians here :
http://pastmist.wordpress.com/
A few here too, specially concerning central Asia and Mongolia :
http://pastmist.wordpress.com/critiques-reponses/
"Some answers are offered by Hoffecker (2002, p. 135). Among early modern humans, tools and weapons were more complex at arctic latitudes than at tropical latitudes. “Technological complexity in colder environments seems to reflect the need for greater foraging efficiency in settings where many resources are available only for limited periods of time.” Arctic humans coped with resource fluctuations and high mobility requirements by planning ahead and by developing untended devices (e.g., traps and snares) and means of food storage.
In addition, these increased cognitive demands fell on both men and women."
In a previous post on neanderthal admixture, you argued against the idea of neanderthals contributing to eurasian intelligence or whatever by pointing out neanderthal too complexity was on the low end of hunter-gatherer complexity. Here, you seem to be arguing something of the opposite, especially with mention of "increased cognitive" demands. Where do you stand exactly?
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