What came first: the bipedal human ancestor or the grassland encroaching on the forest?
A new analysis of the past 12 million years' of vegetation change in the cradle of humanity is challenging long-held beliefs about the world in which our ancestors took shape – and, by extension, the impact it had on them.
The research combines sediment core studies of the waxy molecules from plant leaves with pollen analysis, yielding data of unprecedented scope and detail on what types of vegetation dominated the landscape surrounding the African Rift Valley (including present-day Kenya, Somalia and Ethiopia), where early hominin fossils trace the history of human evolution.
"It is the combination of evidence both molecular and pollen evidence that allows us to say just how long we've seen Serengeti-type open grasslands," said Sarah J. Feakins, assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences and lead author of the study, which was published online in Geology on Jan. 17.
Feakins worked with USC graduate student Hannah M. Liddy, USC undergraduate student Alexa Sieracki, Naomi E. Levin of Johns Hopkins University, Timothy I. Eglinton of the Eidgenössische Technische Hochschule and Raymonde Bonnefille of the Université d'Aix-Marseille.
The role that the environment played in the evolution of hominins—the tribe of human and ape ancestors whose family tree split from the ancestors of chimpanzees and bonobos about 6 million years ago—has been the subject of a century-long debate.
Among other things, one theory dating back to 1925 posits that early human ancestors developed bipedalism as a response to savannas encroaching on shrinking forests in northeast Africa. With fewer trees to swing from, human ancestors began walking to get around.
While the shift to bipedalism appears to have occurred somewhere between 6 and 4 million years ago, Feakins' study finds that thick rainforests had already disappeared by that point—replaced by grasslands and seasonally dry forests some time before 12 million years ago.
In addition, the tropical C4-type grasses and shrubs of the modern African savannah began to dominate the landscape earlier than thought, replacing C3-type grasses that were better suited to a wetter environment. (The classification of C4 versus C3 refers to the manner of photosynthesis each type of plant utilizes.)
While earlier studies on vegetation change through this period relied on the analysis of individual sites throughout the Rift Valley—offering narrow snapshots—Feakins took a look at the whole picture by using a sediment core taken in the Gulf of Aden, where winds funnel and deposit sediment from the entire region. She then cross-referenced her findings with Levin who compiled data from ancient soil samples collected throughout eastern Africa.
"The combination of marine and terrestrial data enable us to link the environmental record at specific fossil sites to regional ecological and climate change," Levin said.
In addition to informing scientists about the environment that our ancestors took shape in, Feakins' study provides insights into the landscape that herbivores (horses, hippos and antelopes) grazed, as well as how plants across the landscape reacted to periods of global and regional environmental change.
"The types of grasses appear to be sensitive to global carbon dioxide levels," said Liddy, who is currently working to refine the data pertaining to the Pliocene, to provide an even clearer picture of a period that experienced similar atmospheric carbon dioxide levels to present day. "There might be lessons in here for the future viability of our C4-grain crops," says Feakins.
University of Southern California: http://www.usc.edu
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
On a fall morning in 2009, a team of three young physicists huddled around a computer screen in a small office overlooking Broadway in New York. They were dressed for success—even the graduate student’s shirt had buttons—and a bottle of champagne was at the ready.
Light is the fastest thing around, but shaped beams travel slower than expected, even in a vacuum. No need to throw your physics textbooks out yet though
A new molten salt nuclear reactor design could make nuclear power safer and more economical.A new take on an old reactor design could make nuclear power cleaner and safer, and therefore more competitive with fossil fuels.
Forensic scientists can find crime-solving evidence in the tiniest details, such as the insects that arrive at the scene to feed on the decomposing corpse.
It may surprise you to learn that some processed foods made from GMOs — say, canola oil, for example — don't actually contain any genetically modified DNA or proteins.
Vanilla-flavored rocks hint at a planet scoured by intense acid rain during the Great Dying 252 million years ago
A plan to store the world’s nuclear waste deep inside the ice sheets of Greenland and Antarctica, the two Catholic priests behind it, and how their quest contributed to the search for extraterrestrial life.
By etching grooves into metal with a high-powered laser, physicists create a surface that repels water to the extent that droplets bounce away.
History shows us that social scientists are essential if we are to get the most out of our engineering and technological innovations
In the escalating battle of big data vs. human experts, score another win for numbers.