Anthropology help

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In 1891, no fossils of Australopithecus had yet been found. In fact, the only human fossils that had been discovered were Neandertals, dismissed by many as pathological modern humans. Just 20 years earlier, Charles Darwin had published the Descent of Man, in which he formulated many of his ideas regarding human evolution. If Darwin was right, then there should be fossils of things that are not quite human and not quite ape discovered. Though Darwin hypothesized that this creature would be found in Africa, other scholars, like Ernst Haeckel, argued they would reside in Asia, given the close similarities between humans and orangutans. Haeckel hypothesized what this half-man, half-ape would look like, and even gave it a name: Pithecanthropus erectus. The writings of Darwin and Haeckel attracted the attention of a young Dutch anatomist named Eugene Dubois (pictured upper left). Dubois became obsessed with finding fossils of these early humans, and in 1887 he moved to Indonesia, which was at the time a Dutch colony (see map bottom left). Four years into his search, on the banks of the Solo River near a village called Trinil, Dubois found a tooth, partial skull, and a femur. The femur indicated that this creature walked on two legs, but the brain was only about 1,000 cc. It was too small to be a human brain and too large to be from an ape. It was exactly what he was hoping to find, and he named it, Pithecanthropus erectus. We now know these fossils as the very first of the species Homo erectus. Though as we’ve already learned, the earliest hominids are from Africa, not Asia, but these fossils were an important first step in our understanding of the evolution of our own genus: Homo.

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In this lecture, we will discuss the evolutionary changes that characterize the earliest members of our own genus. How do we know we’ve discovered a fossil from Homo and not from Australopithecus? Next, we will look at fossils from the very earliest members of our own genus. These are typically categorized into the species Homo habilis, though there is some evidence that there may have been two different species of early Homo co-existing. Soon after the evolution of our genus, we find a different kind of hominid: Homo erectus. Homo erectus is what Dubois found on Java, and we will look at this fascinating, global species in detail. In particular, we will look at the evolutionary trends that happen in the Homo erectus lineage and how anatomical and behavioral adaptations in this species set the stage for the evolution not only of our genus Homo, but our species Homo sapiens.

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Humans have exceptionally large brains and rely very heavily on material culture to survive. These two characteristics have turned out to be quite important in defining the genus Homo. Although we find stone tool technology in the smaller-brained Australopithecus genus, it is a combination of stone tool culture, larger brain size, and smaller tooth anatomy that can be used to identify our own genus. Of course, the evolution of our genus did not happen overnight, and so there are transitional fossils older than 2 million years old that bridge the gap between Australopithecus and Homo, and some researchers call these fossils Homo and some call them Australopithecus. But, isn’t that exactly what you would expect for an evolving lineage? Fossils that fit the criteria for inclusion within the genus Homo were discovered by Louis Leakey in Olduvai Gorge, Tanzania, in the 1960s. The brain was larger than that of an Australopithecus (~600 cc), the teeth were smaller, and the landscape was littered with Oldowan stone tools. In fact, these tools reflect a dietary change that would have selected for smaller, rather than larger, teeth. This dietary shift may have been critical in providing the energy necessary to grow a large brain as well. In other words, these features are probably linked to one another. Leakey and his colleagues named this new creature Homo habilis, which means “handy man.” Two of the fossils found by Leakey are shown here to the left; the skull OH 24 and a mandible OH 7. To the right is another Homo habilis skull discovered in Kenya. Additional finds of Homo habilis have revealed that this species probably had an Australopithecus-like body, with relatively long arms and short legs.

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Shown here is a skull discovered in Kenya in the 1970s and has recently been re-dated to a bit over 2 million years old. It has a larger cranial capacity than most specimens attributed to Homo habilis and the shape of the face and the tooth rows are a bit different than what is found in most Homo habilis fossils. There are many researchers who regard this as a different species and call it Homo rudolfensis. A recent discovery of additional fossils in Kenya support this idea that there were two different kinds of early Homo co-existing. Others regard these differences as normal variations one would find in a population of hominids. Figuring out which of these hypotheses is correct is not as easy at it sounds. There is tremendous variation within humans today, and that variation is not because there are different species of humans. But, at the same time, there are different species of mammals (like squirrels, or antelopes, or macaque monkeys) whose skeletons are not that different from one another. Perhaps we are underestimating the number of species in the fossil record? For the time being, let’s proceed as though these are all one species: Homo habilis, but keep in mind that the situation might be a tad more complex than that!

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Homo habilis fossils reflect a major change in how hominids were utilizing their landscape. Oldowan stone tools are quite common at Homo habilis fossil sites. The anatomy of the skull of Homo habilis shows a significant reduction in the size of the chewing muscles, in part, because the stone tools were doing much of the work that the anatomy previously was responsible for doing. Similarly, the jaws, face, and teeth of this species were smaller than what is found in Australopithecus. And their hand bones were well adapted for stone tool construction and use. They had larger brains, but their bodies remained small, with relatively long, Australopithecus-like arms. Driving many of these anatomical changes was an adaptive shift to surviving on a landscape that was becoming more and more grassland. The use of tools and the environments they inhabited may indicate that the earliest members of our genus were adopting a more varied, generalized diet of both plants and meat. This dietary flexibility would have helped them survive in difficult times, and would have helped fuel a growing brain.

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Around 1.8 million years ago, Homo habilis evolves into a new kind of hominid with a larger brain, even smaller back teeth, and long, human-like legs. This is Homo erectus. Homo erectus fossils are characterized by other features, like large browridges and long, low skulls. But, unlike every hominid up to this point in human evolution, this species is not found exclusively in Africa. Homo erectus expands both within and outside of Africa and quickly inhabits Europe and Asia, as illustrated on the map to the right. Homo erectus is therefore the first global human species. We, of course, already encountered Homo erectus outside of Africa in the Trinil skull (upper left) discovered by Eugene Dubois in 1891. But, the current holder of the title of the oldest hominid outside of Africa belongs to the skull on the bottom left from the site of Dmanisi, a 1.77 million-year-old fossil site in the former Soviet Republic of Georgia. Nevertheless, let’s start in Africa and look at the evolution of Homo erectus on that continent.

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The image here shows just how different Homo erectus is from an Australopithecus. Keep in mind that this robust Australopithecine lived at the very same time as Homo erectus; these two species, both upright walking hominids, would have met one another on the grasslands of East Africa. But, they were quite different. Australopithecus possessed large chewing muscles anchored to the sagittal crest atop the skull. The premolars and molars were enormous, helping this species eat a diet of hard nuts and seeds. In contrast, the skull of Homo erectus, shown on the right, lacks a sagittal crest, has a much larger brain, and much smaller teeth. These adaptations reflect a more diverse diet, including a diet of meat. Homo erectus also had a larger body size and longer legs than Australopithecus and Homo habilis. Much of what we know about this species derives from a remarkably preserved skeleton of a juvenile boy discovered in the 1980s at a site in Kenya called Nariokotome.

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On the left is the Nariokotome Homo erectus skeleton. It is 1.6 million years old and strikingly complete. Unlike Australopithecus and Homo habilis, this skeleton has human-like limb proportions. In other words, the legs are quite long and the arms are quite short. This anatomical change indicates that Homo erectus walked just like modern humans do, and that they no longer were climbing trees. This skeleton is from a young boy, perhaps only 11 years old or so at the time of his death. But, he had already reached 5 foot 6, and would have grown more, perhaps reaching 6 feet tall. Thus, unlike previous hominids, Homo erectus was quite large. Additional finds reveal diversity in body size, however, so not all Homo erectus individuals were this big. The skull of the Nariokotome boy is shown on the right. He has a large brain, about 900 cc. This is larger than the typical Homo habilis (~600 cc), but smaller than a modern human (~1,400 cc). In fact, the cranial capacity of the Nariokotome boy is exactly between the average chimpanzee and the average human.

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Not only can we use the skeletal anatomy of Homo erectus fossils to infer how they walked, but they also left us fossilized footprints. At a 1.5 million-year-old site in Kenya called Ileret, scientists have recently unearthed a large collection of footprints made by Homo erectus. These prints are indistinguishable from prints that a modern human would make, indicating that this species moved just like we do. The feet are arched and the big toe is in-line with the other toes as is found in human feet. So, although the brain was still outside the range found in modern humans, the mode of locomotion was essentially identical. There is also a skull from Ileret (shown from top; bottom left) that is smaller and has a smaller browridge than many other fossils attributed to Homo erectus. This is skull KNM-ER 42700. That means that this is the 42,700th fossil discovered at this locality in Kenya! Researchers have recently exceeded 60,000 fossils! Of course, not all of these are hominids, but it indicates just how numerous fossils can be in some of these localities. The anatomy of the Ileret skull indicates that Homo erectus was quite variable, and may have maintained a high level of sexual dimorphism.

Image of Ileret cast courtesy of Jeremy DeSilva.

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Shown here are three more skulls of African Homo erectus. The top image to the left is of the top of a skull from ~1.2 million-year-old deposits at Olduvai Gorge, called OH 9. Notice the enormous browridge, and a large area for muscle attachments on the back of the skull. This specimen also has very thick bone comprising the skull. To the right of OH 9 is the Daka skull, a ~1 million-year-old fossil discovered by Tim White’s team in Ethiopia. The importance of this skull is that it looks in many ways like Homo erectus fossils discovered in Asia, which we’ll learn more about in just a moment. There were some researchers who were beginning to think that the African Homo erectus fossils were different enough from the Asian Homo erectus fossils to call them a different species. They even had a name for this species: Homo ergaster. By finding a specimen (Daka) that bridges the gap between these fossils, there is more support for the idea that Homo erectus is just one species. The bottom image is a later Homo erectus fossil also from Ethiopia, called Bodo. It is 600,000 years old and has a brain size that is within the range of what is found in humans today. It is a million years younger than some of the first Homo erectus fossils we started with, like the Nariokotome boy from Kenya, and shows that brains were getting bigger this whole time. One neat thing about this skull was the discovery of deliberate cut marks on it, which indicate that Bodo was defleshed after his death, either ritually or due to cannibal activity by Homo erectus.

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As we have already discussed in regards to Eugene Dubois’ 1891 discovery of the Trinil Homo erectus skull on the Indonesian island of Java, this species expanded its territory beyond the borders of the African continent. Interestingly, almost immediately after Homo erectus, presumably in Africa, it spreads (see map on bottom right) east into Asia. Half a million years later, Homo erectus expands into Europe. This expansion indicates that Homo erectus was adaptable, and had evolved the intelligence to use resources in its environment to make the tools necessary to survive. Some of the oldest fossils of early Homo erectus found outside of Africa are from the 1.8 million-year-old site of Dmanisi, which is in the former Soviet Republic of Georgia. Dmanisi has turned out to be one of the most productive early Homo fossil sites ever found, with several skeletons and five skulls discovered, including the one shown here. The skulls have cranial capacities in the 600 cc and 700 cc range, which helps bridge the size in most Homo habilis and most Homo erectus. Like Homo erectus, the Dmanisi individuals also had long legs compared to their arms.

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Since Dubois’ work in the late 1800s, many other paleontologists have worked on the island of Java and found many more fossils of Homo erectus, including over a dozen partial skulls. The most complete fossil skull is shown here: Sangiran 17. Notice the long, low skull with a thick browridge and flat surface for neck muscles in the back. Also, notice the relatively large face, with enormous cheek bones. It has a large brain of 1,000 cc, which is not quite within the range of most humans today, but certainly larger than any ape or Australopithecus. There is also a thick sagittal keel across the top of the skull. A sagittal keel is a thickening of the cranium down the midline of the skull. Do not mistake this for the sagittal crest- it is very different since the temporalis muscle does not anchor to it. Instead, it may just resist the bending forces on the skull during chewing with the front teeth. In many ways, this skull looks like the skulls of similarly aged Homo erectus back in Africa, indicating that there was gene flow connecting these populations and maintaining a single species.

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There are also wonderful fossils of Homo erectus from several sites in China. The three important sites are shown on the map. There are not any hominids yet from Majuangou, though stone tools and animal bones with cutmarks on them indicate that hominids were active in this area 1.7 million years ago. Gongwangling preserves a 1.2 million year old Homo erectus skull with a brain size of 800 cc. But, the most productive Homo erectus site is Zhoukoudian, a cave not far from Beijing, preserving what many call the fossils of “Peking Man.” In the 1920s and 1930s remains of up to 40 individuals, including several nearly complete skulls were discovered. These date to about 750,000 years. Fortunately, the great paleoanthropologists Franz Weidenreich made detailed copies of these fossils (casts) that he distributed all over the world, and published his detailed anatomical descriptions of these fossils. This is fortunate because during World War II, the entire fossil collection was lost. Many recent efforts have been made to rediscover where these fossils may have ended up, but none have been successful.

Before we leave Asia and look at the European fossil record, there is one more important discovery that was made in those Zhoukoudian caves: evidence for controlled fire. Fire is critically important because it allowed Homo erectus to stay warm, and to inhabit cooler climates that otherwise would have been inhospitable. Additionally, it allowed these hominids to cook their food. Cooking softens food and makes it more digestible that eating raw food. Cooking thus was a critical human adaptation that allows us to access more nutrients and calories from our food in a more rapid and physically easier manner. There is now evidence from a South African cave that Homo erectus had controlled fire by 1 million years ago.

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The fossil record seems to indicate that early Homo erectus spreading and migrating out of Africa generally took a right and headed east into Asia. However, there is now evidence from cave sites in Spain that by 1.2 million years ago, these hominids started to look left, and headed west into Europe. One of the oldest sites that has yielded hominid fossils in Europe is called Gran Dolina, which is about 900,000 years old. Shown here are excavations happening at Gran Dolina (upper left) and a map of where this locality is (lower left). The image to the upper right is the face of one of the many hominids found at Gran Dolina. This is the face of a child, though there are plenty of adult bones recovered from Gran Dolina as well. In many ways, these fossils are like those of Homo erectus found elsewhere. However, there are differences too. The nose is wider, and there is increased robusticity. There are other fossils from Italy, Germany, and England that are Homo erectus-like in many ways, but are different in others. Interestingly, these European fossils begin to resemble, in many ways, fossils found in younger sediments in Europe: the Neandertals. It appears as though Homo erectus migrated into Europe and became somewhat isolated from the rest of the Homo erectus population. This isolation led to anatomical differences in these hominids, and eventually led to the group we call Neandertals. But, does that mean they evolved into different species? Some think so, and regard these fossils from Gran Dolina as a new kind of hominid: Homo antecessor. Others think probably not, and regard these as just a regional variant of Homo erectus.

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Let’s review. By the time we reach Homo erectus, especially later Homo erectus living about half a million years ago in Asia, Africa, and Europe, these hominids begin to very closely resemble you and me. They have brains that are within, or very close to, the low range of human brain size today. They have small teeth and rely very heavily on material culture to survive. They have controlled fire and cook their food. And they have long legs, with a striding bipedal gait indistinguishable from yours and mine. Many of the biological features we find in humans today evolved not with our own species, Homo sapiens, but with the immediate ancestor of H. sapiens, Homo erectus. As is illustrated here, compared to Homo habilis, Homo erectus evolved smaller teeth and smaller jaws. The brain increased in size, though was housed within a very robust skull with thick bones and a prominent browridge. And Homo erectus evolved larger, human-like, body size with an increase in leg length. Why did this happen?

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Most likely what drove all of these changes were changes in diet and how these hominids accessed resources from their environment. Homo erectus was a hunting hominid, and ate more meat than earlier hominids. Though meat eating started long before Homo erectus, these earlier hominids were mostly scavenging, since the stone tool cut-marks are often found on top of bite marks made by carnivores. Homo erectus is found most often with different, more sophisticated tools than the Oldowan tools found with later Australopithecus and with Homo habilis. These tools are called Acheulean. The handaxe is the most common Acheulean tool type; it is shown in the upper right image next to a site in Kenya called Olorgesailie where handaxes litter the landscape by the hundreds. The handaxe can be used to cut and scrape the meat from an animal carcass as is cartooned in the bottom image. These tools are often found in association with the fossil skeletons of very large, butchered animals, like hippopotamus and elephants. Now, keep in mind that Homo erectus was not a carnivore, and relied very heavily on food gathering of tubers, nuts, berries, and many other foods to survive as well. Most likely, Homo erectus lived in groups and shared with one another the foods they had gathered and hunted. This increase in food quality and available energy fueled the growth of an energetically expensive brain. Even though brains are only about 2% of the body mass, they eat up 20% of the body’s energy! Having a large brain if nutrients are scarce could be detrimental to an individual and could lead to selection against large brains. Large brains can only evolve if there is ample nutrition to support such an energetically expensive tissue. This happened with Homo erectus. And it created a feedback loop whereby the larger-brained individuals were more intelligent and could make more effective material culture to access resources from their environments and support the enlarged brain. This is one of the best examples of how culture and biology interact in human evolution.

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Let’s wrap up this chapter with a final review of Homo erectus. We begin to find fossils of this species at sites dated around 1.8 million years old in Africa and Asia. Homo erectus spreads throughout the Old World and populates areas from South Africa to Spain to Indonesia and everywhere in between. Their success is dependent on their ability to use material culture to survive in these diverse ecosystems. They use more sophisticated tools, called Acheulean, and by a million years ago are controlling fire for cooking. These cultural innovations impact the biology of Homo erectus as this species evolves larger brains, smaller teeth, and smaller jaws and chewing muscles. They evolve larger body size and limb portions that are identical to humans today. One thing to note is that the earliest Homo erectus fossils from Africa and Dmanisi look very different from the later Homo erectus fossils from Bodo and Zhoukoudian. Some researchers feel these differences warrant the naming of different species. But other researchers argue that all we are seeing is evolution within a species over time. Brains get gradually bigger; teeth get gradually smaller; skulls get gradually thicker and then thinner later. These changes mirror the technological advances being made by Homo erectus and illustrate the intertwined relationship of culture and biology on these hominids. Many of these changes we see in Homo erectus foreshadow the evolution of our own species, Homo sapiens, which will be the subject of the next lecture.

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