74,000 years ago, the Earth experienced the largest volcanic event of the last two million years when a supervolcano beneath Lake Toba in northern Sumatra erupted with a Volcanic Explosivity Index intensity of 8 (“Ultra-Plinean”), ejecting 2,800 km3 of magma, with around 800 km3 of this falling as ash. In comparison, Krakatoa, Tambora and Mount Pinatubo would have seemed like firecrackers. Much of the ash was blown north-west by the wind and the Indian subcontinent and part of the Malay Peninsula were blanketed in ash. Now known as Youngest Toba Tuff (YTT), these deposits ranged in depth from 15cm to as much as 6m at one site in Central India.
The effects of the explosion would have been to cause a “volcanic winter”, during which temperatures worldwide may have fallen by 3-5 degrees Celsius for several years. In 1998, Stanley H Ambrose suggested that the eruption caused a bottleneck in human populations (Ambrose, 1998). Geneticists Lynn Jorde and Henry Harpending believe the world population of anatomically modern humans fell to as few as 5,000-10,000 individuals.
Could this really have happened; could Homo sapiens really have teetered on the brink of extinction?
In the aftermath of the eruption, conditions for life would have become very harsh and the Indian subcontinent would certainly not have been the healthiest of places to be! But were any anatomically modern humans there? The first evidence of Homo sapiens outside of Africa are the 110-90,000 year old fossil remains found in the Levant. This migration seems to have petered out; the migrants either died without issue or (less likely) returned to Africa. The migration(s) believed to have given rise to the world’s present-day non-African population occurred much later. Estimates vary as to the timing, with some authorities claiming it was as long ago as 80,000 years ago but most opting for between 50-60,000 years ago, long after the Toba eruption.
Stephen Oppenheimer is among those who do believe that modern humans were already in India and Malaysia when Toba erupted. He believes the migrants left the Horn of Africa 80,000 years ago.
Oppenheimer claims the Toba eruption resulted in the extinction of human life in India, leaving a “genetic furrow” that is visible in Asia’s genetic record to this day. This arose as the subcontinent was repopulated by settlers from both East and West Asia. Although descended from the same root lines of the single exodus, Indian maternal branch genetic (mtDNA) lines are completely different from those of the Far East and mostly different from those in the West.
Oppenheimer also draws on archaeological evidence from Kota Tampan in the Lenggong Valley, Malaysia where stone tools were found in the 1960s. These were covered by volcanic ash, now known to be from the Toba eruption. The large pebble-tools, fashioned on one side only were thought to be the work of an earlier human species but in the absence of fossil remains the matter could not be settled one way or the other.
Work by Prof. Zuraina Majid, of the University of Science in Penang suggests that the local pebble-tool culture may have persisted continuously right up until only 7,000 years ago. If so, the possible implication is that the earlier pebble-tools were actually made by modern humans. Support for this view came in 1990 with the discovery of Perak Man, a 10,000 year old anatomically-modern human found in the same context as the pebble tools (Oppenheimer, 2003).
But not everybody accepts the bottleneck theory. Gathorne-Hardy & Harcourt-Smith (2003) point out that if Toba has caused a bottleneck in the human population, it would have also affected other species, especially other, more environmentally sensitive taxa with more specialised ecological requirements. These would have been expected to suffer at least a similar population crash leading to many becoming extinct. But there is no evidence for mammal extinction associated with Toba.
In 2007 dramatic evidence was presented that suggested that not only were modern humans in India at the time of the Toba eruption, but that they survived the catastrophe. A team led by Michael Petraglia of the University of Cambridge recovered stone artefacts from both above and below the 2.55m thick ash deposit near Jwalapuram, in the Jurreru River valley of southern India.
There appears to be a strong element of technological continuity between the two sets of artefacts and together with the presence of faceted unidirectional and bidirectional bladelike core technology, they suggest closer affinities to African Middle Stone Age traditions such as Howieson’s Poort than to those of the contemporaneous Eurasian Middle Paleolithic. The latter are typically based on discoidal and Levallois techniques. This, together with the behavioural flexibility needed to survive the catastrophe, suggests that modern humans were already in India at the time of the eruption (Petraglia et al, 2007).
In addition, there are recent genetic studies that do support the presence of modern humans in India 74,000 years ago (Kivisild et al, 2003; Metspalu et al, 2004).
Petraglia’s interpretations are also a problem for the Kota Tampan pebble tools being made by modern humans. If the Indian settlers were using a technology derived from the African MSA, why were their counterparts in Malaysia using far more primitive tools?
Human remains found in the context of ash from Toba are the one thing missing; the matter cannot be considered to be settled until such time as these come to light; but on the balance of probabilities it does seem likely that the effects of the Toba eruption were not as deleterious as some have supposed.
References:
Ambrose S H (1998): Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans, Journal of Human Evolution 34 (6): 623–651
Gathorne-Hardy F.J. & Harcourt-Smith W.E.H. (2003): The super-eruption of Toba, did it cause a human bottleneck? Journal of Human Evolution 45 (2003) 227–230
Kivisild T, Rootsi S, Metspalu M, Mastani S, Kaldma K, Parik J, Metspalu E, Adojaan M, Tolk H-V, Stepanov V, Golge M, Usanga E, Papiha S S, Cinnioglu C, King R, Cavalli-Sforza L, Underhill P A & Villems R (2003): The Genetic Heritage of the Earliest Settlers Persists Both in Indian Tribal and Caste Populations, Am. J. Hum. Genet. 72:313-332.
Metspalu M, Kivisild T, Metspalu E, Parik J, Hudjashov G, Kaldma K, Serk P, Karmin M, Behar D M, Gilbert M T P, Endicott P, Mastana S, Papiha S S, Skorecki K, Torrioni A & Villems R (2004): Most of the extant mtDNA boundaries in South and Southwest Asia were likely shaped during the initial settlement of Eurasia by anatomically modern humans, BMC Genet. 2004; 5:26
Oppenheimer S (2003): Out of Eden, Constable.
Michael Petraglia, Ravi Korisettar, Nicole Boivin, Christopher Clarkson, Peter Ditchfield, Sacha Jones, Jinu Koshy, Marta Mirazón Lahr, Clive Oppenheimer, David Pyle, Richard Roberts, Jean-Luc Schwenninger, Lee Arnold, Kevin White (2007): Middle Paleolithic Assemblages from the Indian Subcontinent Before and After the Toba Super-Eruption, Science 317, 114.
© Christopher Seddon 2009
Showing posts with label homo sapiens. Show all posts
Showing posts with label homo sapiens. Show all posts
Tuesday, 2 June 2009
Tuesday, 17 March 2009
Modern humans & Neanderthals in the Levant
The first evidence for modern humans leaving Africa comes from the Levant, where the caves of Mugharet es-Skhul and Jebel Qafzeh (Israel) have yielded the remains of over 20 individuals, many of whom appeared to have been intentionally buried. The remains have been dated to between 110,000-90,000 years ago on the basis of ESR and luminescence dating. Though possessing some archaic features such as robustness, they are essentially modern, anatomically lying within the range of Homo sapiens.
However Neanderthal burials are known from much later at Kebara, Amud and Tabun (Israel), dating to between 60,000-50,000 years ago; and Shanidar Cave (Iraq) and Dederiyeh Cave (Syria) dating to as late as 45,000 years ago: this suggests a later re-occupation of the region by Neanderthals.
Modern humans had returned to the region by 35,000 years ago, and possibly as early as 45,000 years ago.
The likeliest explanation is that the ranges of modern humans and Neanderthals fluctuated back and forth in accordance with climate change. Whenever the climate was warm, the region would be occupied by modern humans; when it was cool it would be occupied by Neanderthals. Faunal evidence shows that in cooler times Palearctic fauna spread down from Europe, but when the climate warmed Afrotropical fauna would move in and replace the Palearctic. The two human species were merely “going with the flow” like any other animal species.
The lithic technology employed by both human species was, up until 50,000 years ago, very similar, being fairly typical Middle Palaeolithic/MSA and it has been described as Levalloiso-Mousterian, dominated by the Levallois reduction technique.
Lieberman & Shea (1994) suggest that hunting strategies between the two species did in fact differ. Analysis of seasonally-deposited cementum in the teeth of mountain gazelle and other ungulates indicates that the Neanderthals hunted these animals over both dry and wet seasons, but modern humans only hunted them during the dry season. Analysis of the lithic hunting technology further suggests more extensive hunting by the Neanderthals. Far more points are found at Neanderthal sites; these show greater signs of wear; and raw materials were procured only a short distance away from each site.
Lieberman & Shea interpret this to mean that the Neanderthals practiced a locally-intensive “radiating mobility” strategy. Their activities were primarily organized from large general-purpose sites, with more specialized or seasonal activities being carried out at smaller sites on the periphery of the main one.
By contrast, the modern humans practiced a seasonal-based “circulating mobility” strategy, living at different sites at different times of the year to facilitate exploitation of seasonal resources.
Both strategies have their pros and cons. The “radiating mobility” strategy permits an increased capacity for storage and investment in material culture (site facilities and hard-to-transport items). The main problem is that resources around the central camp become depleted due to year-long exploitation and a law of diminishing returns begins to effect hunting and foraging activities.
The “circulating mobility” strategy avoids these problems by ability to relocate to sites near periodically-abundant resources, which will then have a year to recover after the group have moved on to the next site. The drawbacks are that the group has to do without items that cannot readily be moved from site to site.
These differing strategies may highlight behavioural differences between modern humans and Neanderthals, with the “circulating mobility” strategy arising from modern human behaviour (which it is inferred the Neanderthals were incapable of). Another possibility is that the heavily-built Neanderthals were not physically adapted for a highly-mobile lifestyle.
The final, conclusive re-occupation of the Levant by modern humans, followed by their expansion into Europe has been taken to support the “Big bang” theory of behavioural modernity arising only 50,000 years ago, after which modern humans were able to overcome the “climate barrier” and move into Europe. This theory is however predicated on a modern human migration out of Africa proceeding via the Levant rather than taking a southern route across the Red Sea, a possibility rejected by some authorities such as Stephen Oppenheimer (Oppenheimer, 2003).
References:
Daniel E. Lieberman and John J. Shea (1994): Behavioral Differences between Archaic and Modern Humans in the Levantine Mousterian, American Anthropological Association.
Oppenheimer S (2003): “Out of Eden”, Constable.
© Christopher Seddon 2009
However Neanderthal burials are known from much later at Kebara, Amud and Tabun (Israel), dating to between 60,000-50,000 years ago; and Shanidar Cave (Iraq) and Dederiyeh Cave (Syria) dating to as late as 45,000 years ago: this suggests a later re-occupation of the region by Neanderthals.
Modern humans had returned to the region by 35,000 years ago, and possibly as early as 45,000 years ago.
The likeliest explanation is that the ranges of modern humans and Neanderthals fluctuated back and forth in accordance with climate change. Whenever the climate was warm, the region would be occupied by modern humans; when it was cool it would be occupied by Neanderthals. Faunal evidence shows that in cooler times Palearctic fauna spread down from Europe, but when the climate warmed Afrotropical fauna would move in and replace the Palearctic. The two human species were merely “going with the flow” like any other animal species.
The lithic technology employed by both human species was, up until 50,000 years ago, very similar, being fairly typical Middle Palaeolithic/MSA and it has been described as Levalloiso-Mousterian, dominated by the Levallois reduction technique.
Lieberman & Shea (1994) suggest that hunting strategies between the two species did in fact differ. Analysis of seasonally-deposited cementum in the teeth of mountain gazelle and other ungulates indicates that the Neanderthals hunted these animals over both dry and wet seasons, but modern humans only hunted them during the dry season. Analysis of the lithic hunting technology further suggests more extensive hunting by the Neanderthals. Far more points are found at Neanderthal sites; these show greater signs of wear; and raw materials were procured only a short distance away from each site.
Lieberman & Shea interpret this to mean that the Neanderthals practiced a locally-intensive “radiating mobility” strategy. Their activities were primarily organized from large general-purpose sites, with more specialized or seasonal activities being carried out at smaller sites on the periphery of the main one.
By contrast, the modern humans practiced a seasonal-based “circulating mobility” strategy, living at different sites at different times of the year to facilitate exploitation of seasonal resources.
Both strategies have their pros and cons. The “radiating mobility” strategy permits an increased capacity for storage and investment in material culture (site facilities and hard-to-transport items). The main problem is that resources around the central camp become depleted due to year-long exploitation and a law of diminishing returns begins to effect hunting and foraging activities.
The “circulating mobility” strategy avoids these problems by ability to relocate to sites near periodically-abundant resources, which will then have a year to recover after the group have moved on to the next site. The drawbacks are that the group has to do without items that cannot readily be moved from site to site.
These differing strategies may highlight behavioural differences between modern humans and Neanderthals, with the “circulating mobility” strategy arising from modern human behaviour (which it is inferred the Neanderthals were incapable of). Another possibility is that the heavily-built Neanderthals were not physically adapted for a highly-mobile lifestyle.
The final, conclusive re-occupation of the Levant by modern humans, followed by their expansion into Europe has been taken to support the “Big bang” theory of behavioural modernity arising only 50,000 years ago, after which modern humans were able to overcome the “climate barrier” and move into Europe. This theory is however predicated on a modern human migration out of Africa proceeding via the Levant rather than taking a southern route across the Red Sea, a possibility rejected by some authorities such as Stephen Oppenheimer (Oppenheimer, 2003).
References:
Daniel E. Lieberman and John J. Shea (1994): Behavioral Differences between Archaic and Modern Humans in the Levantine Mousterian, American Anthropological Association.
Oppenheimer S (2003): “Out of Eden”, Constable.
© Christopher Seddon 2009
Sunday, 28 December 2008
Omo remains (Homo sapiens)
The Omo I (Kibish) and Omo II (Kibish) remains are currently the oldest-known fossils of anatomically-modern humans (Homo sapiens). They were recovered by Richard Leakey in 1967 from the base of Member I of the Kibish Formation near the Omo River in south-western Ethiopia. Both Omo I and Omo II comprise a braincase and some postcranial material. Omo I fully modern in appearance; Omo II is slightly more primitive with a long, low cranium. However both are believed to be about the same age.
Originally believed to be around 130,000 years old, the Omo remains have recently been assigned a date of 195,000 +/- 5,000 years old, based on argon-40/argon-39 dating of volcanic tuffs (ash) found within Member I at levels. This makes them substantially older than the Herto remains discovered in 1997, previously thought to be the earliest-known fossil remains of modern humans. What is curious is that the 156,000 year old Herto remains, despite being around 40,000 years more recent than the Omo remains, retain more primitive features and were originally assigned their own subspecies, Homo sapiens idaltu.
Reference:
McDougall I, Brown FH & Fleagle JG (2005): Stratigraphic placement and
age of modern humans from Kibish, Ethiopia, Nature 734 Vol 433 17 Feb 2005.
© Christopher Seddon 2008
Originally believed to be around 130,000 years old, the Omo remains have recently been assigned a date of 195,000 +/- 5,000 years old, based on argon-40/argon-39 dating of volcanic tuffs (ash) found within Member I at levels. This makes them substantially older than the Herto remains discovered in 1997, previously thought to be the earliest-known fossil remains of modern humans. What is curious is that the 156,000 year old Herto remains, despite being around 40,000 years more recent than the Omo remains, retain more primitive features and were originally assigned their own subspecies, Homo sapiens idaltu.
Reference:
McDougall I, Brown FH & Fleagle JG (2005): Stratigraphic placement and
age of modern humans from Kibish, Ethiopia, Nature 734 Vol 433 17 Feb 2005.
© Christopher Seddon 2008
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