Green corridors led humans out of Africa
Axel Timmermann, a climate scientist at the University of Hawaii at Manoa. In a new study
that charts the time frames when climate may have been changing and
influencing human migrations, Timmermann and his co-author, Tobias
Friedrich, also at the University of Hawaii, offer what may be the
clearest answer to this question yet: Humans were waiting for green,
resource-rich corridors to open up through the deserts of North Africa
and Arabia.
Scientists have long suspected that climate change played a crucial role in the timing and routes of migration out of Africa, but past climate models fell short of offering clear information about the early human diaspora. Timmermann and Friedrich created a model that coupled vegetation changes with climate variability — based on orbital variations, sea-level changes and atmospheric carbon dioxide levels — to investigate when and where people might have been moving starting about 125,000 years ago.
The new model shows that increased rainfall may have sprouted savanna-like corridors of vegetation between North Africa and the Arabian Peninsula between 115,000 and 75,000 years ago. This stretch was followed by a dry period from 71,000 to 60,000 years ago, and then another wet period between 60,000 and 47,000 years ago. Those windows align well with the clues provided by the human fossil, archaeologic and genetic records, Timmermann says.
Less than 2 percent of the genomes of non-African populations are composed of archaic DNA from a population that is now extinct. “This is consistent with the idea that there might have been an initial leakage [of population] out of Africa into Arabia about 120,000 years ago. This might represent a failed migration that mostly died out,” says de Menocal, who co-authored a commentary about Timmermann and Friedrich’s study in the same issue of Nature. Evidence for this initial foray — mostly from shards of rock produced during tool making — is sketchy, and the timing could overlap with the opening of green corridors that Timmermann and colleagues found starting about 115,000 years ago.
The genetics studies also found evidence for a population crash or bottleneck during the dry period between 70,000 and 60,000 years ago. “The genomics studies and the climate modeling study all complement each other nicely and show the advantages of using multiple lines of inquiry to address complicated questions,” de Menocal says.
The next step will be to seek out paleoclimate data
from the corridors where people may have been migrating to validate the timing of the wet and dry periods proposed by Timmermann’s model, de Menocal says. However, finding evidence of wetter times in the Sahara Desert has proved difficult. “This is such a dry place, any lakes [or other paleoclimate evidence] that might have been there during the wet phases have long since dried up and blown away.”
“This has been a big question for decades: What took us so long to expand out of Africa?” says Scientists have long suspected that climate change played a crucial role in the timing and routes of migration out of Africa, but past climate models fell short of offering clear information about the early human diaspora. Timmermann and Friedrich created a model that coupled vegetation changes with climate variability — based on orbital variations, sea-level changes and atmospheric carbon dioxide levels — to investigate when and where people might have been moving starting about 125,000 years ago.
The new model shows that increased rainfall may have sprouted savanna-like corridors of vegetation between North Africa and the Arabian Peninsula between 115,000 and 75,000 years ago. This stretch was followed by a dry period from 71,000 to 60,000 years ago, and then another wet period between 60,000 and 47,000 years ago. Those windows align well with the clues provided by the human fossil, archaeologic and genetic records, Timmermann says.
Less than 2 percent of the genomes of non-African populations are composed of archaic DNA from a population that is now extinct. “This is consistent with the idea that there might have been an initial leakage [of population] out of Africa into Arabia about 120,000 years ago. This might represent a failed migration that mostly died out,” says de Menocal, who co-authored a commentary about Timmermann and Friedrich’s study in the same issue of Nature. Evidence for this initial foray — mostly from shards of rock produced during tool making — is sketchy, and the timing could overlap with the opening of green corridors that Timmermann and colleagues found starting about 115,000 years ago.
The genetics studies also found evidence for a population crash or bottleneck during the dry period between 70,000 and 60,000 years ago. “The genomics studies and the climate modeling study all complement each other nicely and show the advantages of using multiple lines of inquiry to address complicated questions,” de Menocal says.
The next step will be to seek out paleoclimate data
from the corridors where people may have been migrating to validate the timing of the wet and dry periods proposed by Timmermann’s model, de Menocal says. However, finding evidence of wetter times in the Sahara Desert has proved difficult. “This is such a dry place, any lakes [or other paleoclimate evidence] that might have been there during the wet phases have long since dried up and blown away.”
Mary Caperton Morton
Morton
is a freelance writer and photographer (and EARTH roving correspondent)
who makes her home on the back roads of North America, living and
working out of a tiny solar-powered Teardrop camper. Follow her travels
at www.theblondecoyote.com.
Nenhum comentário:
Postar um comentário
Observação: somente um membro deste blog pode postar um comentário.