Evolution

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.

The places where animals have been killed or at least butchered by our ancestors represent obviously the best expression of the relation between man and his prey. Isaac (Isaac, 1976; Isaac & Cradeq, 1981), referring to African deposits of Lower Palaeolithic age, defines a simple kind of such sites as containing the skeleton of a single, large animal, associated with lithic artefacts (his type B sites): they represent a unique episode. However such accumulations seem to be very rare: in fact near the carcass of the huge beast almost always other generally much more fragmentary remains of other animals are found. These can represent "background" material without direct relation with hominid activity, but we cannot be sure of this. Evidently, Isaac's definition does not cover the effective variability of all Palaeolithic and Mesolithic kill and/or butchering sites. Therefore, I have tried, in my tesi di laurea, to develop a typolo gy of the possible kinds of bone concentrations reflecting man's animal procurement behaviour. For this aim, I drew information from various authors discussing the topic (Binford, 1984; Clark & Haynes, 1970; Crader, 1983; Meignen & Texieq, 1956) and read a selected number of papers dealing directly, or indirectly through discussions or summaries, with some 30 sites, my reading assignment depending to some extent on the accessibility of the papers included. I am aware that my sampling of sites is limited and perhaps biased and that the evidence as presented by the various authors is often equivocal, but I hope that my attempt will stimulate the development of a site typology which could be a useful tool for classification and research. 

2. Suggested site typology:

a. Butchering sifes: places with animal natural deaths, later utilised by mary such as sites FLK N Lev. 6 (fig.1) and FLK N Deinotherium at Olduvai (Crader, 1983; Leakey, 1971), and site HAS (fig.2) at Koobi Fora (Cradeq, 1983). 

b. Killing and butchering sites 1: a single animal carcass representing a unique hunting episode. This kind of accumulation is similar to Isaac's type B sites. An American example is Pleasant Lake (Fishea 1984; fig. 3). 

c. Killing and butchering sites 2: extensive disarticulation and dispersion of the bones of a few big animals at the most associated with a comparatively small number of stone artefacts. Examples are Windhoek (Clark & Haynes, 1970) and perhaps Mwanganda (Clark & Haynes,1970). 

d. Hunting losses: animals killed but not utilised by man; High Furlong (Hallam et al., 1973) would be an example. 

e. Hunting stations: dense distributions of osseous remains reflecting the reutilization of the locality for a lorig period, often on a seasonal base. Examples of such palimpsests of archaeological remains could be Mauran (Farizy & David, in press; Girard-Farizy & Leclerc, 1981), Stellmoor (Rus! 1937) and La Cotte de Saint-Brelade, lev. 3 and 6 (Scott, 1980; ftg. q. A subtype of hunting stations could be represented by American mass kills, as for example the Casper Site (Frison, 1974). In these sites, not examined here, animals are normally killed with game drive techniques. 

f. Hunting stops: they can be relatively simple or quite complex: sometimes the hunters seek shelter behind a high rock and light a small fire as suggested by Binford (Binford, 1981). An example could be Phase IVA of the Grotte de l'Hortus (de Lumley, 1971). 

g. Sighting sites: they would be characterised by modest bone accumulations in locations with a panoramic position and allowing to detect game and its movements easily. Examples are the Mesolithic sites described by Bagolini and Dalmeri (Bagolini & Dalmeri,

3.1. Lower Palaeolithic Scavenging: exploitation of the carcasses of big animals that died for natural causes; they are often found near lakes or swamps, as the elephant and maybe the Deinotherium at Olduvai (Leakey, 1971), the hippopotamus of Koobi Fora (Isaac, 7976) and the elephants of Kathu Pan (Klein, 1988), Namib IV (Kleirr, 1988) and Mwanganda's Village (Clark & Haynes, 1970). 

Hunting: scanty traces of hunters' action are encountered. At Olorgesailie, occasional killing of some baboons with a head blow seems to have occurred (Shipman, Bosler & Davis, 1981). At Torralba and Ambrona, people may have killed elephants using wooden spears (fragments of wooden artefacts are present) and big stones (Allain" 1952). At Lehringen (Movius, 1950), hominids killed an Elephas antiquus with a wooden spear discovered in the site (see also Weber, this volume). 

Planning: very limited or absent. The exploitation of animals would have been occasional and opportunistic with short and limited occupation of sites by small groups, as at Olduvai (Cradeq, 1983), Koobi Fora (Cradeq, 1983), etc. 

Food transport: Acheulean people are said to have carried away the most useful and meaty parts of animal carcasses at Torralba (Freemary 1975), Ambrona (Freem an, 1975), Elandsfontein (Klein, 1988), etc. In earlier times, people apparently consumed the meat on the find spot. Specialised activities: at the already cited sites of Torralba, Ambrona and at Mwanganda distinct associations between certain bones and tools would occur: they may represent specialised activity areas. 

Butchering tools: hand-axes and hachereaux are sometimes associated with big animals at Olorgesailie (Shipman, Bosler & Davis, 1981), Elandsfontein (Klein, 1988), Kathu Pan (Klein, 1988), Namib IV (Klein, 1988) etc., suggesting that they were used for butchering.

The Hata Member of the Bouri Formation is defined for Pliocene sedimentary outcrops in the Middle Awash Valley, Ethiopia. The Hata Member is dated to 2.5 million years ago and has produced a new species of Australopithecus and hominid postcranial remains not currently assigned to species. Spatially associated zooarchaeological remains show that hominids acquired meat and marrow by 2.5 million years ago and that they are the near contemporary of Oldowan artifacts at nearby Gona. The combined evidence suggests that behavioral changes associated with lithic technology and enhanced carnivory may have been coincident with the emergence of the Homo clade from Australopithecus afarensis in eastern Africa

We collected 400 vertebrate fossil specimens from the Hata Member (Table 1). Almost all of these come from within 3 m of the MOVT; most were found immediately above this unit. This assemblage largely reflects a mixture of grazers and water-dependent forms, which is broadly typical of later hominid-bearing Plio-Pleistocene occurrences and consistent with the sedimentological interpretation of the deposits as primarily lake marginal. Alcelaphine bovids are abundant and diverse. All indicators point to a broad featureless margin of a shallow freshwater lake. Minor changes in lake level, which were brought about by fluctuating water input, would probably have maintained broad grassy plains leading to the water’s edge. As discussed below, hominids were active on this landscape.

The bone modifications at these two excavated localities and at other localities from the same stratigraphic horizon across .2 km of outcrop demonstrate that stone tool–wielding hominids were active on the lake margin at 2.5 Ma. The bone modifications indicate that large mammals were disarticulated and defleshed and that their long bones were broken open, presumably to extract marrow, a new food in hominid evolution with important physiological, evolutionary, and behavioral effects. Similar patterns of marrow acquisition have been reported for younger sites such as Koobi Fora and Olduvai Gorge (12).

The situation on the Hata lake margin was even more difficult for early toolmakers. Here, raw materials were not readily available because of the absence of streams capable of carrying even pebbles. There were no nearby basalt outcrops. The absence of locally available raw material on the flat featureless Hata lake margin may explain the absence of lithic artifact concentrations. The bone modification evidence demonstrates that early hominids were transporting stone to the site of carcass manipulation. The paucity of evidence for lithic artifact abandonment at these sites suggests that these early hominids may have been curating their tools (cores and flakes) with foresight for subsequent use. Indications of tool curation by later hominids have been found at the more recent Pleistocene sites of Koobi Fora [Karari escarpment versus Ileret (13)] and Swartkrans [polished bone tools in a single repository (16)]. Additional research into the Hata beds may allow a determination of whether the butchery is related to hunting or scavenging. The Bouri discoveries show that the earliest Pliocene archaeological assemblages and their landscape patterning are strongly conditioned by the availability of raw material. They demonstrate that a major function of the earliest known tools was meat and marrow processing of large carcasses. Finally, they extend this pattern of butchery by hominids well into the Pliocene.

On a high grassy plateau in Algeria, just 100 kilometers from the Mediterranean Sea, early human ancestors butchered extinct horses, antelopes, and other animals with primitive stone tools 2 million to 2.4 million years ago. The dates, reported today, push back the age of the oldest tools in North Africa by as much as a half a million years and provide new insight into how these protohumans spread across the continent.

For decades, east Africa has been considered the birthplace of our genus Homo, and the epicenter of early toolmaking for almost 1 million years. The oldest known Homo fossils date back 2.8 million years in Ethiopia. Nearby, just 200,000 years later, scientists have found simple tools, such as thumb-size stone flakes, and fist-size cores from which such flakes were struck, in the nearby Rift Valley of Ethiopia.

After 25 years of excavations at the Ain Hanech complex—a dry ravine in Algeria—an international team reports the discovery of about 250 primitive tools and 296 bones of animals from a site called Ain Boucherit. About two dozen animal bones have cut marks that show they were skinned, defleshed, or pounded for marrow. Made of limestone and flint, the sharp-edged flakes and round cores—some the size of tennis balls—resemble those found in east Africa. Both represent the earliest known toolkit, the so-called Oldowan technology, named for the site where they were found 80 years ago at Olduvai in Tanzania.

Ain Hanech lacks volcanic minerals, which provide the gold standard for dating sites in eastern Africa. Instead, the researchers used three other dating methods, notably paleomagnetic dating, which detects known reversals in Earth’s magnetic field that are recorded in rock. The tools and cut-marked bones date as far back as 2.4 million years ago, the researchers report today in Science. They also used the identity of large, extinct animals, such as mastodons and ancient horses, to confirm the dates.

The cut-marked bones represent “the oldest substantive evidence for butchery” anywhere, says paleoanthropologist Thomas Plummer of the City University of New York’s Queens College, who was not involved with the study. Although other sites of this age in east Africa have stone tools, the evidence for actual butchery of animals is not as strong, he says.

At Ain Hanech, the dates provide “convincing evidence for stone tools and cut-marked bones at about 2 million years or more,” says geochronologist Warren Sharp of the Berkeley Geochronology Center in California. But he finds the 2.4 million date “less compelling,” because of potential issues with the dating methods.

Whether the tools are 2 million or 2.4 million years old, they suggest toolmakers had spread farther and wider across Africa earlier than previously known. “There must have been a corridor through the Sahara with movement between east Africa and North Africa,” says paleoanthropologist Rick Potts of the Smithsonian Institution’s National Museum of Natural History in Washington, D.C. Alternatively, the new dates suggest hominins in at least two different parts of Africa, separated by 5000 kilometers, were sophisticated enough to independently invent rudimentary stone tools and habitually make them, Potts says.

Either way, the study suggests that by 2 million years ago or so, making stone tools and butchering meat with them was routine for human ancestors in distant corners of the African continent. And this technological revolution may have given them the tools they needed to travel farther and wider across Africa and beyond

Ancient humans used complex hunting techniques to ambush and kill antelopes, gazelles, wildebeest and other large animals at least two million years ago. The discovery – made by anthropologist Professor Henry Bunn of Wisconsin University – pushes back the definitive date for the beginning of systematic human hunting by hundreds of thousands of years.

Two million years ago, our human ancestors were small-brained apemen and in the past many scientists have assumed the meat they ate had been gathered from animals that had died from natural causes or had been left behind by lions, leopards and other carnivores.

But Bunn argues that our apemen ancestors, although primitive and fairly puny, were capable of ambushing herds of large animals after carefully selecting individuals for slaughter. The appearance of this skill so early in our evolutionary past has key implications for the development of human intellect.

"We know that humans ate meat two million years ago," said Bunn, who was speaking in Bordeaux at the annual meeting of the European Society for the study of Human Evolution (ESHE). "What was not clear was the source of that meat. However, we have compared the type of prey killed by lions and leopards today with the type of prey selected by humans in those days. This has shown that men and women could not have been taking kill from other animals or eating those that had died of natural causes. They were selecting and killing what they wanted."

That finding has major implications, he added. "Until now the oldest, unambiguous evidence of human hunting has come from a 400,000-year-old site in Germany where horses were clearly being speared and their flesh eaten. We have now pushed that date back to around two million years ago."

The hunting instinct of early humans is a controversial subject. In the first half of the 20th century, many scientists argued that our ancestors' urge to hunt and kill drove us to develop spears and axes and to evolve bigger and bigger brains in order to handle these increasingly complex weapons. Extreme violence is in our nature, it was argued by fossil experts such as Raymond Dart and writers like Robert Ardrey, whose book African Genesis on the subject was particularly influential. By the 80s, the idea had run out of favour, and scientists argued that our larger brains evolved mainly to help us co-operate with each other. We developed language and other skills that helped us maintain complex societies.

"I don't disagree with this scenario," said Bunn. "But it has led us to downplay the hunting abilities of our early ancestors. People have dismissed them as mere scavengers and I don't think that looks right any more."

In his study, Bunn and his colleagues looked at a huge butchery site in the Olduvai Gorge in Tanzania. The carcasses of wildebeest, antelopes and gazelles were brought there by ancient humans, most probably members of the species Homo habilis, more than 1.8 million years ago. The meat was then stripped from the animals' bones and eaten.

"We decided to look at the ages of the animals that had been dragged there," said Benn. "By studying the teeth in the skulls that were left, we could get a very precise indication of what type of meat these early humans were consuming. Were they bringing back creatures that were in their prime or were old or young? Then we compared our results with the kinds of animals killed by lions and leopards."

The results for several species of large antelope Bunn analysed showed that humans preferred only adult animals in their prime, for example. Lions and leopards killed old, young and adults indiscriminately. For small antelope species, the picture was slightly different. Humans preferred only older animals, while lions and leopards had a fancy only for adults in their prime.

"For all the animals we looked at, we found a completely different pattern of meat preference between ancient humans and other carnivores, indicating that we were not just scavenging from lions and leopards and taking their leftovers. We were picking what we wanted and were killing it ourselves."

Bunn believes these early humans probably sat in trees and waited until herds of antelopes or gazelles passed below, then speared them at point-blank range. This skill, developed far earlier than suspected, was to have profound implications. Once our species got a taste for meat, it was provided with a dense, protein-rich source of energy. We no longer needed to invest internal resources on huge digestive tracts that were previously required to process vegetation and fruit, which are more difficult to digest. Freed from that task by meat, the new, energy-rich resources were then diverted inside our bodies and used to fuel our growing brains.

As a result, over the next two million years our crania grew, producing species of humans with increasingly large brains – until this carnivorous predilection produced Homo sapiens.