interpreting Evidence of Human Evolution

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In the fossil human record, the most famous fossil discoveries have been those that provided evidence to either support a current theory, reject a previ­ously supported theory, or that have created new theories about human history. The information that new discoveries provide comes more from the analysis and interpretation of the evidence than from its display in a museum and observation by the public. Although interpretations can vary based on the knowledge and opinions of an indi­vidual, they provide meaning for the object. The evidence holds the facts, and it is the interpreta­tion of the evidence that exposes the facts. Over time, as new discoveries continue to fill in the fos­sil record of human existence, it is not the fossil skeletons and artifacts themselves but the inter­pretation of the evidence that allows for solution of the puzzle. A fossil, in and of itself, is nothing more than the preserved remains of an organism, but analyzing it and drawing a conclusion from this analysis reveal its true historical footprint. A large portion of our current knowledge is the result of this process of observation, then analysis, followed by interpretation, and finally assump­tion, deduction, hypothesis, and theory.

Generally, the more complete the specimen, the more information it reveals, but even small partial fossil remains can give an overwhelming amount of data about human history. A simple leg bone can help researchers date the characteristic ability of hominids to stand erect and walk upright on two legs. Even a fractured, partial skull bone can help prove if bipeDalí walking or the enlargement of the brain arose first in hominids. The morphol­ogy is what tells the story. But as interpretations are based on the perceptions and opinions of the individual investigator, they are not infallible. As a result, the theories created from these interpreta­tions are always subject to change over time. As new evidence becomes available, the current theo­ries are either rejected or confirmed; they evolve. It is not uncommon for several interpretations to exist that conflict with each other. Although the interpretation of evidence is not flawless, it is fun­damental for the understanding of human evolu­tion. As our only source of information about , every new piece of evidence is valuable and influential. This is especially true because only a small number of all the hominids that have ever lived on Earth became fossilized, and of those that were, only a fraction have been discovered. But as more evidence is found each year, we develop a better understanding of, and appreciation for, our .

Early Interpretations: Germany and Java

Even before the first fossil humans were discov­ered, many naturalists in the 19th century had already begun to recognize that the earth was much older than described in the Bible. Therefore, the length of existence of humans on Earth became open to interpretation, and the field of was born. The first discovered human fossils were those of a Neanderthal in August 1856. Found in a limestone quarry in the Neander Valley, the bones were brought to Johann Fuhlrott, who recognized them as both human and ancient. He gave the bones—consisting of a skull­cap, two femora (thighbones), fragments of an upper and lower left arm, a partial pelvis, and sev­eral other small bones—to Hermann Schaaffhausen, an anatomy professor.Schaaffhausen’s report described the anatomical features with great detail, and he concluded that they belonged to a strong, muscular individual. What most intrigued Schaaffhausen were the pronounced ridges above the eyes and the low, narrow forehead, which he said resembled the skulls of the large apes. From this, he concluded that “man coexisted with the animals found in the diluvium; and many a barba­rous race may, before all historical time, have disappeared, together with animals of the ancient world, whilst the races whose organization is improved have continued the genus.” His inter­pretation fit into the common idea of the time. Before Charles Darwin’s publication of On the Origin of Species (1859), the dominant theory was one that proposed a variety of species had existed. This was a more fundamental approach, in which the thought was that all the species that exist today existed in the past, but some species have become extinct. So Neanderthals, Schaaffhausen concluded, were a “barbarous race” of humans that had coexisted with the ancient relatives of modern humans but had gone extinct sometime in the past. The human fossil record at that time was not seen as evidence for the idea of human evolution, only as evidence of human antiquity and diversity.

It took several years for the full scope of Darwin’s idea of evolution as “descent with modi­fication” to be realized. The leap to the thought that “species are the modified descendants of other species,” as Darwin described, was a difficult one. Many did not want to accept an idea that pro­posed humans had descended from the same ancestors as the apes. Darwin’s publication of On the Origin of Species laid the foundation for this change, but it was another decade until it emerged. In 1868 and 1871, Ernst Haeckel and Charles Darwin, respectively, published books that sup­ported the idea that both apes and humans share a common ancestry. The first fossil evidence to sup­port their ideas was not discovered until 1891 in East Java, Indonesia, by Eugene Dubois. The fossil remains, known as Java man, consisted of a skull­cap, a femur, and several teeth. The femur was similar to that of a modern human femur, which meant that the animal had been bipeDalí. However, the skull showed apelike characteristics, most notably the pronounced ridges above the eyes. The size of the brain, 900 milliliters (ml) in volume, although considerably smaller than the brain of modern humans (which is around 1400 ml in vol­ume), is much larger than those of the modern apes, around 400 ml. Therefore, because the brain was larger than that of modern apes, Dubois asserted that these remains were that of an ape-like man and not of a man-like ape. He named it Pithecanthropus erectus, meaning “upright ape­man.” Dubois claimed that it could be classified neither as human nor ape but was an intermediate between modern humans and the common ances­tor of humans and apes. His evidence demon­strated that bipeDalíity arose prior to the enlarged brain size; Darwin had proposed that a large brain preceded bipeDalíity. Today this ancestor is classi­fied as , and most anthropologists believe that the earlier ancestor of modern humans is the Homo erectus found in Africa, not in Asia.

Early Interpretations: South Africa and

Another major discovery was that of the Taung skull in 1924. Found in a quarry in South Africa, the fossil consists of an almost complete face, a mandible with teeth, and an endocranial cast of the braincase. An endocranial cast is a cast of the cranial cavity showing the approximate shape and size of the brain. The fossil, among others, was given to Raymond Dart, an anatomist and anthro­pologist, who recognized it as the skull of a child of an unknown hominid species, intermediate between humans and apes. Dart named it africanus, meaning “southern ape of Africa.” The brain was larger than that of an immature ape but not as large as that of a mod­ern human child. This trend was also seen in the teeth, which were smaller and more human-like than those of the chimpanzee, which Dart’s critics believed he had found. The skull also showed human-like characteristics such as a less robust mandible and a rounded forehead that lacked the pronounced eyebrow ridge. Dart was criticized at the time because most of the traits he described as human-like could be attributed to the fact that it was a juvenile and had not fully developed its facial features and secondary sexual characteris­tics. There was one feature, however, that his crit­ics could not attribute to immaturity. What convinced Dart he had discovered a bipeDalí man­like ape was the position of the foramen magnum, the hole in the skull where the spinal cord attaches to the brain. It was positioned at the base of the skull, the same as in humans, not at the back of the skull, as in apes. This meant it had walked upright, on two legs. His interpretation was also criticized because, at the time, it was believed that the ancestors of humans would be found in Asia and not in Africa because of the discoveries of Java man and later Peking man in Asia. Also, because the earth was considered to be only around 65 million years old at the time, the Taung child would have appeared too late to be a human ancestor. Dart’s interpretation of the Taung child as representing an extinct race of hominids that can be categorized between living apes and mod­ern humans is important because it was the first major fossil human evidence from Africa. It con­firmed Darwin’s theory that human origins would be traced back to Africa and not Asia or Europe. As a result, more people began to search in Africa for human fossils. Today, hundreds of human fossils from Africa support Dart’s original interpretation.

Dart’s theory about human origins in Africa was meeting stiff opposition because some natural­ists gave priority to the theory of Asian ancestry. This theory became even more dominant with the discovery known as Peking man. Since the discov­ery of Pithecanthropus erectus by Dubois in Java had become popular, the fossils of Peking man were more readily accepted. The first evidence was that of two fossil human teeth from Zhoukoudian near Beijing. In 1926, they were given to Davidson Black, an anatomy professor, who began excavat­ing the same site the next year. Following the dis­covery of another tooth there, he created a new genus and species, Sinanthropus pekinensis, the “Chinese man of Peking.” Many anthropologists did not accept his conclusion based solely on three teeth. It was not until 1929 that a braincase of Sinanthropus was found. Although it possessed a slightly larger brain and steeper forehead than the Java man, analysis showed that it was an early human very similar to that individual. From this, Black concluded that Sinanthropus was an inter­mediate form between Pithecanthropus and the Neanderthals. Today, it is classified as Homo erec­tus. While proving that Pithecanthropus was an early human form and not an ape form, it also gave some insight on the advancements made by Sinanthropus. Among the stone tools found at the site were animal bones that showed signs that they had been burned. Black interpreted this as evidence that Sinanthropus used fire; this contention is still debated. By 1937, 14 fragmented skulls, more than 100 teeth, and various other bone fragments had been found at the site. In 1941, unfortunately, the original fossils were lost, stolen, or destroyed while in transit to the United States for safekeeping during World War II, but not before casts of the fossils were made. The casts still exist today.

Later Interpretations: South Africa and Tanzania

Although the discovery of Peking man fostered the claim that Asia was the origin of human existence, Dart’s discovery of the Taung child had already begun the shift in focus toward an African origin for human beings. One such supporter of Dart’s interpretation of human evolution in Africa was Robert Broom. Convinced that Dart’s theory of Australopithecus as an ape-human intermedi­ate was correct, the Scottish physician stopped practicing medicine to take a position as an assis­tant in at the Transvaal Museum in Pretoria in 1934. During excavations at a lime­stone mine in Sterkfontein in 1936, Broom found an incomplete Australopithecus skull. He immedi­ately presented the evidence as proof of the validity of Dart’s interpretation. Broom’s next discovery came at Kromdraai, across the valley from Sterkfontein, in 1938, when a young boy named Gert Terblanche found hominid fossils. The fossils were of a mandible and maxilla, with teeth. The thickness of the bones and the large molar teeth led Broom to classify the remains as Paranthropus robustus. At another nearby site, Swartkrans, additional fossils were found that further revealed the facial structure of these hominids. After observing the similarities between the fossils found at Kromdraai and Swartkrans and those of known Australopithecus africanus (both are bipeDalí with brain capacities intermediate between modern humans and apes), Broom’s Paranthropus robus- tus became referred to as Australopithecus robus- tus. It is now considered a facially robust species of australopithecine that went extinct about 1 mil­lion years ago. One of Brooms’s most important discoveries was made in 1949 with the help of his assistant John Robinson at Swartkrans. The hom­inid fossils were much more human-like and even­tually became classified in the genus Homo. The significance of this find at Swartkrans was that it demonstrated for the first time the apparent coex­istence of two types of hominids. This coexistence of more than one lineage of hominid from the divergence of early australopithecines was later seen in East Africa as well.

The pioneering discoveries of the Leakey family in , Tanzania, in East Africa, have become the cornerstone of our knowledge of the human lineage. Louis Leakey assumed that held the secrets to human evolu­tionary history. Throughout the 1950s, he searched for hominid fossil remains with little success, find­ing only a few hominid teeth and the remains of large mammals. The fossil remains he believed had been killed and eaten by humans because of the various stone tools found in the same sites. As Louis Leakey maintained at the time that tool­making was the distinguishing characteristic between humans and ape-like forms, he claimed that these sites were used by the earliest members of the genus Homo. But in 1959, Mary Leakey found, in a site known as FLK 1, the skull of a robust Australopithecus. Very similar to the skulls found by Broom in Swartkrans and Kromdraai, the skull, named Olduvai Hominid (OH) 5, had massive chewing molars, undersized canines and incisors, a small brain size (about 530 ml), and a large sagittal crest (the ridge of bone that runs along the midline of the skull as the attachment site for jaw muscles). This indicated great jaw strength. Although Louis Leakey had argued that modern humans did not have an australopithecine ancestry, the evidence contradicted his theory that toolmaking was a uniquely human (Homo) abil­ity. To resolve this conflict, he classified the skull as an australopithecine but of a new genus and species, Zinjanthropus boisei. Nicknaming it the “Zinj skull,” Leakey described it as a distinct form from the South African specimens found by Broom and Robinson. Not long afterward, Robinson challenged Leakey’s evidence as insuffi­cient for classifying his australopithecine in a new genus. Eventually renamed Australopithecus boi- sei, just as Robin-son’s Paranthropus robustus was renamed Australopithecus robustus, both are now sometimes reclassified again as further evi­dence has been found to justify Paranthropus as a genus distinct from Australopithecus. There con­tinues to be debate to this day whether this dis­tinction should be made.

Another issue that existed was Louis Leakey’s doubt that his A. boisei was the actual maker of the stone tools found in the similar strata. The size of its brain was quite small, and as a result of this evi­dence, he did not believe that it would have pos­sessed the cognitive ability needed to create tools. The fashioning of stone tools required several com­plex levels of thought. It required knowledge of rocks to know which type is ideal. It required a capacity to understand physics, to know at what angle and with how much strength to strike the stones together. It also required an advanced ability to recall previous events, such as hunts, to know how to make the tools effective and efficient. These are all advanced, higher levels of cognitive thinking that Louis Leakey did not think an australopithecine brain was capable of accomplishing. His unwaver­ing theory proved to be correct when in 1964 he, along with his own team members as well as Phillip Tobias and John Napier, described a specimen they thought was the creator of the stone tools. First discovered by Jonathan Leakey in 1960, the fossil remains consisted of an incomplete mandible with several teeth, various hand and wrist bones, and two parietal bones. From an examination of the mandible and teeth, the team determined that the hominid had possessed a less robust jaw, smaller and more rounded molars, and a facial structure much more similar to modern humans than any australopithecine. The parietal bones gave perhaps the most significant and most debated evidence. Tobias estimated that the bones from the juvenile skull would have given a brain capacity at maturity of 675 ml, much larger than any australopithecine. Between 1960 and 1964, additional similar hom­inid fossils were found, and by 1964 enough evi­dence existed, Leakey claimed, to classify the hominid remains as or “handy man.” Its increased brain capacity and reduced molar size convinced Leakey that Homo habilis was the tool­maker. The ability to use tools allowed for a more general . This is reflected in the reduced molar size, which had been specialized for plant consump­tion in the australopithecines. Many believe that H. habilis was a scavenger rather than strictly a plant eater. This may explain why H. habilis, which coexisted with Australopithecus for over a million years, was able to survive longer within the same environment. Its decreased specialization allowed this species to more easily adapt to global climate changes in the past.

Later Interpretations: Ethiopia and Tanzania

The next major fossil hominid discovery occurred in northeast Africa in 1974. Donald Johanson of the International Afar Research Expedition found almost 40% of the skeleton of “Lucy,” perhaps the most famous fossil hominid. Discovered in Hadar, Ethiopia, Lucy was a young female adult hominid. As most fossil hominid discoveries until that point consisted of fragmented bones, indi­vidual teeth, or scattered, almost random remains and only occasionally a complete skull, the fact that Lucy was an almost complete skeleton, of a single individual, made her a celebrity overnight. The Lucy skeleton contains fragments of arm bones, ribs, vertebrae, a partial pelvis, one femur, partial lower leg bones, a fragmented skull, and a mandible complete with teeth. When no duplicate bones were found, Johanson concluded they were from a single individual, making Lucy an incredi­ble discovery. After analyzing the remains, he recognized that Lucy had been bipeDalí and that, although her brain was relatively small, her whole body was proportionally small. She would have stood about 3 feet tall and had a brain size around only 400 ml. This brain size was well within the ape range. This was significant because Lucy was found to be about 3.2 million years old, over half a million years older than A. africanus and A. boisei. Lucy had a smaller, more ape-like brain than A. africanus and A. boisei, but she had a hominid-like postcranial skeleton that walked upright and bore many similarities to modern humans. As a result, she proved that bipeDalíity had existed in human precursors far earlier than had been thought and, more importantly, that bipeDalíity arose before an enlarged brain size. This officially disproved Darwin’s theory that an enlarged brain size had predated bipeDalíity.

The next task for Johanson was to classify Lucy. Together with Tim White, the two began to study and analyze fossils from Hadar and Laetoli that coincided with the same period in history, from about 3 million years ago and older. The Hadar fossils included Lucy and several other fossil hom­inids, such as the “First Family” found at a differ­ent site the year after Lucy. There, the remains of 13 individuals were discovered, including men, women, and juveniles. From the Laetoli site in Tanzania came the famous “Laetoli footprints,” discovered by Mary Leakey, and also numerous hominid fossils that dated back to roughly the same time as those found at Hadar. With the Lucy skeleton providing the evidence that bipeDalíity was possible over 3 million years ago in Hadar, Ethiopia, and the Laetoli footprints demonstrating that it definitely occurred in Tanzania 3.7 million years ago, the two pieces of the puzzle needed only to be brought together. White’s casts of the Laetoli fossils were compared with Johanson’s fossils from Hadar, and the two men created many influential and, as always, controversial theories. Their inter­pretation of the fossil evidence led them to con­clude that the Hadar hominids represented neither apes nor any known hominid species. These hom­inids, along with the Laetoli specimens of the same age, represented a single hominid species that was yet unidentified. The unique characteristics of the species included full bipeDalíity, arms longer (pro­portionally to their legs) than in modern humans, a small brain, sexual dimorphism, and dental anatomy somewhat intermediate between apes and humans (with some exclusive characteristics). Because no stone tools were recovered at any of the sites and their brain size was very small, Johanson and White recognized that these early hominids did not use stone tools. They classified these hominids as Australopithecus afarensis, the last common ancestor between humans and chim­panzees that existed from 3.9 million years ago until about 3 million years ago. One problem that this exposed was why, if stone tools were not used for another million years, did bipeDalíity exist if the adaptation of bipeDalíity was to free the hands for tool use?

Recent Interpretations

By the 1980s, Africa had become generally accepted as the birthplace of human origins because of the overwhelming amount of fossil hominid evidence that had been found there. The only dilemma was that, although the previous decades had brought forth an unprecedented amount of fossil evidence for the divergence between apes and early hom­inids, no link had been found in Africa between the primitive Homo species, such as H. habilis, and the later, more modern Homo species such as H. neanderthalensis and H. sapiens. The only evi­dence of this link that existed at that time was that of Homo erectus. Many held that Dubois’ H. erec­tus from East Java, Indonesia, in Asia, was the missing link, but no specimen from that period, about 1.8 to 1 million years ago, had been found in Africa. That was until 1984, when a team led by Richard Leakey discovered a hominid skeleton even more complete than that of the Lucy skeleton. Discovered near the western shore of Lake Turkana in Kenya, it became known as the “Turkana boy.” The skeleton was of a young male that Leakey and White determined had been about 12 years old when it died, although some speculate it could have been as young as 9 years old. The overall height of the individual was 5 feet 4 inches, which many estimate would have been about 6 feet at adulthood. The Turkana boy was the first evidence of an essentially fully human anatomy. Only slight skeletal variations exist between Homo erectus and Homo sapiens. These variations include a nar­rower pelvis in H. erectus, increasing its ability to run, longer arms than in modern humans, and an upwardly narrowing chest, similar to but not to the extent of Lucy. This shape of the chest put the shoulders of H. erectus in a position adapted more for tree-dwelling than balanced, bipeDalí walking. Its running ability suggested that it was a hunter, not a scavenger as many believed H. habilis had been. The brain capacity of the Turkana boy was about 880 ml and estimated to have been about 910 ml as an adult. Although the brain was only slightly smaller than in modern humans, the skull structure showed many ape-like characteristics, such as pronounced eyebrow ridges, the lack of a prominent chin, and a low forehead. Richard Leakey quickly classified the fossil hominid as Homo erectus, an African example of the species originally found in Asia by Dubois. He was con­vinced that the increased brain capacity, similar to a modern infant, was evidence of an ability to make tools, which were found in similar strata. The brain and vertebrae were, however, not large enough to convince Leakey that communication would have been possible to the extent that it is in modern humans today. Various discoveries in the following years led to a debate about whether the African H. erectus species should be classified as separate from the Asian species and renamed H. ergaster. This is still debated today, although most classify the African species with the Asian species, all as H. erectus. The overall significance of the Turkana boy was that it showed an early Homo species had indeed become fully human, anatomi­cally, in Africa.

Since the 1980s, hominid fossils have been found in Africa, Asia, Europe, and America. With each new discovery, we learn more about our human history and our evolution. Every new piece of evidence holds the ability to alter what is thought to be true. Therefore every theory about human evolution can, and does, evolve. And theo­ries will continue to evolve, just as humans and every other species on Earth continue to evolve. For example, a hominid discovery in Chad in 2001 of a Sahelanthropus tchadensis was dated to be about 7 million years old. Yet this hominid form had been bipeDalí, demonstrating an even greater antiquity for bipeDalíity in hominids. Another dis­covery, reported in 2006, of Homo erectus, found in Dmanisi on the European continent, gave many new insights. These fossils from Dmanisi had brain capacities similar to H. habilis but were deter­mined to be H. erectus, based on their cranial morphology. If this was a H. erectus, it meant that humans may have left Africa for Europe and Asia far earlier than many had theorized.

What is even more important than the idea that the theories of human evolution can evolve is the need to understand that these theories exist only because of the interpretations drawn from the evi­dence. The Lucy skeleton was an amazing discovery; to be able to show and display an almost complete skeleton of a human from millions of years ago is a great scientific achievement. But more importantly, the information gained from investigators’ analysis of the remains has provided an immense amount of information about human history on Earth.

It is now considered a fact that the enlargement of the human brain developed after the ability to walk upright on two legs. This theory is universally accepted because fossil evidence exists where the leg morphology is similar to modern humans but the cranial capacity of the individual is vastly reduced. In Africa, two different hominid species were found at separate sites, several years apart, but because they were found in strata dated to the same era, it is known that more than one hominid species existed at the same time in the past. The amount of knowledge that now exists about human evolution simply through the analysis of some fos­silized bones found in the ground is astonishing. Through interpretation of these fossilized bones and stone artifacts, a story emerges of struggle, defiance, adaptation, and triumph. In short, it is the story of human evolution over millions of years.

Michael F. Gengo

See also ; Darwin, Charles; Dating Techniques; Evolution, Organic; Fossil Record; Fossils, Interpretations of; Fossils and Artifacts; Haeckel, Ernst; Huxley, Thomas Henry; Laetoli Footprints; Olduvai Gorge

Further Readings

Aczel, A. (2007). The Jesuit and the skull: Teilhard de Chardin, evolution, and the search for Peking man. New York: Penguin.

Clark, W. E. L. (1955). The fossil evidence for human evolution. Chicago: University of Chicago Press. Ember, C., Ember, M., & Peregrine P. (2007). Physical anthropology and archaeology. Englewood Cliffs, NJ: Prentice Hall.

Johanson, D., & Shreeve J. (1989). Lucy’s child: The discovery of a human ancestor. New York: Early Man Publishing.

Poirier, F., & McKee J. (1999). Understanding human evolution (4th ed.). Englewood Cliffs, NJ: Prentice Hall.

Stringer, C., & Andrews P. (2005). The complete world of human evolution. New York: Thames & Hudson.

Tattersall, I. (1995). The fossil trail: How we know what we think we know about human evolution. New York: Oxford University Press.

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