and their length increased, and signs of battering on other artifacts increased. Some likely implications of these factors, among others, are that after this pivotal time hominins used tools more frequently, became better at making tools, and transported tools more often. Hunters or scavengers? Though substantial evidence of hunting and scavenging has been discovered at Olduvai Gorge, it is believed by archaeologists that hominins inhabiting the area between 1.9 and 1.7 million years ago spent the majority of their time gathering wild plant foods, such as berries, tubers and roots. The earliest hominins most likely did not rely on meat for the bulk of their nutrition. Speculation about the amount of meat in their diets is inferred from comparative studies with a close relative of early hominins: the modern chimpanzee. The chimpanzee's diet in the wild consists of only about five percent as meat. And the diets of modern hunter-gatherers do not include a large amount of meat. That is, most of the calories in both groups' diets came from plant sources. Thus, it can be assumed that early hominins had similar diet proportions, (see the middle-range theory or bridging arguments—bridging arguments are used by archaeologists to explain past behaviors, and they include an underlying assumption of uniformitarianism.) Much of the information about early hominins comes from tools and debris piles of lithic flakes from such sites as FLK-Zinjanthropus in Olduvai Gorge. Early hominins selected specific types of rocks that would break in a predictable manner when "worked", and carried these rocks from deposits several kilometres away. Archaeologists such as Fiona Marshall fitted rock fragments back together like a puzzle. She states in her article "Life in Olduvai Gorge" that early hominins, "knew the right angle to hit the cobble, or core, in order to successfully produce sharp-edged flakes ...". She noted that selected flakes then were used to cut meat from animal carcasses, and shaped cobbles (called choppers) were used to extract marrow and to chop tough plant material. Bone fragments of birds, fish, amphibians, and large mammals were found at the FLK-Zinj site, many of which were scarred with marks. These likely were made by hominins breaking open the bones for marrow, using tools to strip the meat, or by carnivores having gnawed the bones. Since several kinds of marks are present together, some archaeologists including Lewis Binford think that hominins scavenged the meat or marrow left over