Human Evolution | Research & Encyclopedia Articles

Human Evolution

For well over a century, ever since Charles Darwin, Western scientific thought has stated that all of today's species, including man, have arisen by the modification of earlier, simpler forms of life. This means that the story of human evolution begins with a creature that most of us today would not consider human.

Today's human beings, or Homo sapiens sapiens , belong to the Hominid family tree. Hominid means "human types" and describes early creatures that split off from the apes and took to walking upright, or on their hind legs. In the overall history of life on Earth, the human species is a very recent product of evolution. There are no human-like fossils older than 4 million years, which makes them only one-thousandth the age of life on Earth. The oldest and first ancestor of all known hominids was probably Australopithecus afarensis, named for a region in Ethiopia. What distinguished it from the African pongids (gorillas and chimps), from which it split, was that it was clearly built for two-legged walking. It was only about 3.5-4 ft (about 1m) tall, and it had a brain the size of a chimpanzee. By about 2.5 million years ago, it appears to have evolved into the slightly taller Australopithecus africanus with a slightly larger brain. Altogether, there were probably four main species of australopithecines.

From Australopithecus came the oldest known hominid to be given the Latin genus designation Homo, or "Man." This was Homo habilis, called "nimble", "capable", or "handy" man. Taller than its predecessors, it also had a bigger brain and, for the first time, used tools made of stone. It is possible that it also was a hunter. By about 1.5 million years ago, the hominid brain had increased in size to about half what it is today, and this difference made for a new classification, Homo erectus, or "upright man." This was the first hominid to use fire and hand axes and to substantially travel about. Early or archaic Homo sapiens, called "wise" or "intelligent" man, appeared about 300,000 to 400,000 years ago, and although it wore clothing and buried its dead, it still did not have a modern-size brain. It was only about 40,000 years ago that Homo sapiens sapiens, or doubly "wise" man, appeared. This creature was anatomically indistinguishable from ourselves and had real language. Thus, in a relatively short period of time, modern humans turned from strictly hunting and gathering and took to domesticating animals and then plants. Soon settlements turned into real cities and a civilization based on agriculture came to be.

Although the course of human evolution may have followed this seemingly logical, progressive road, its discovery and understanding was by no means easy or quick, nor did the discovery story follow the same route. Since about the middle of the nineteenth century, scientists have had to struggle to try to put together the puzzle of human evolution using the equivalent of randomly found pieces. But well before Charles Darwin offered a unifying theory into which we could try to fit all of these pieces, the foundations of mankind's knowledge about human evolution had been laid.

The Greek philosopher Aristotle was one of the first to speculate on the possibility that organisms had evolved from one another. However, by medieval times, such ideas were overwhelmed by the power generated by a literal interpretation of the first chapter of Genesis in the Bible. This interpretation said that humankind came about from a single, unique act of creation. During the Renaissance, the Italian artist Leonardo da Vinci (1452-1519) performed comparative studies of men and beasts and wrote in his notes that "Man in fact differs from animals only in his specific [characteristics]," but his thoughts had little influence. Although the literal Biblical interpretation of human origins held sway even during the Scientific Revolution of the seventeenth century, it was during that time that a Frenchman, Isaac de la Peyrere (1594-1676), discovered what he believed were stone tools made by extremely ancient people. He published his findings in 1655, only to have his book burned. In 1700, the earliest recognition of a fossilized human part was given to a skull fragment found at Canstatt, near Stuttgart, Germany. Although it was described then as "ancient" in origin, this meant in the early eighteenth century that it was thought to be about 4,000 years old.

In the same century, however, the Swedish botanist Carolus Linnaeus published his Systema naturae, a methodical classification of all living things. It was here that he invented the system of binomial nomenclature that is still used today. Nomenclature is Latin for "list of names," and binomial means "two names" in Latin. With this system, the first name designates an organism's genus--a group of organisms that are closely related. Each genus is made up of smaller groups different from each other, called species. This is the second name. Linnaeus classified apes with humans by including them in the genus Homo, but gave only modern man the name Homo sapiens. His contemporary, the French naturalist Georges Buffon, endorsed an evolutionary concept of man and the earth itself, arguing that everything in nature develops and changes slowly and continuously.

It was not until the nineteenth century, however, that anyone said that modern human beings were the result of an extremely long and slow evolutionary process. In 1809, the French naturalist Jean Lamarck was the first biologist to state boldly that humans evolved from four-footed animals. Although he was wrong when he argued that changes came about because acquired characteristics were passed on to offspring, he was the first real evolutionist.

In 1859, the view of man's history and his place on earth was changed forever by the publication of On the Origin of Species by Means of Natural Selection, written by the English naturalist Charles Darwin. In this revolutionary book, which stated that all living things had achieved their present form by slowly occurring natural processes, Darwin barely mentioned human evolution. However, in his 1871 book, The Descent of Man, he argued that man had descended from subhuman forms of life.

It was during the same decade in which Darwin's epochal first book was published that the physical evidence to back up his theory began to accumulate. The following, which describes these discoveries in the order in which they were made, can be better understood if read in light of the brief story of man's evolution outlined earlier, since it arranges these discoveries using today's knowledge and benefits from hindsight. Furthermore, today's physical anthropologists have at their disposal not only an extensive fossil record and an excellent knowledge of comparative anatomy, but they benefit from other disciplines and scientific areas such as geology and plate tectonics, molecular anthropology, radioactive isotope dating methods, and observations made of primate behavior. One amazing bit of new information gained from recent molecular DNA studies is that man and the chimpanzee share more than 99 percent of their genetic material.

Back in 1856, when human fossils were found in the Neander Valley near Dusseldorf, Germany, science had no methods for judging their age and could only say that they were very ancient individuals. This particular "ancient" skeleton was the first extinct human form ever recognized and is today classified as Homo sapiens neanderthalensis. It was regarded then as being halfway between apes and humans, and it is now known to have lived between 100,000 and 70,000 years ago. It is still debated whether Neanderthals evolved into fully modern people or were driven to extinction by an invasion of modern types from elsewhere.

In 1868, five skeletons were found in Cro-magnon caves in southwest France that were unquestionably modern, or Homo sapiens sapiens , and were given the name Cro-magnon man. The geological evidence at the site seemed to indicate that they were around 40,000 years old. In 1894, a Dutch paleontologist, Marie-Eugene Dubois (1858-1940), discovered the first-known fossil of Homo erectus, which came to be called Java man.

After the turn of the century, there was much discussion that a "missing link"--or half-man, half-ape--probably existed in the distant past. In 1912, a British lawyer, Charles Dawson (1864-1916), announced the discovery near Piltdown Common, near Lewes, England, of skull pieces that showed its owner had a large, modern brain and human teeth set in the jaw of an ape. Although this turned out to be a hoax, many scientists embraced so-called Piltdown man as the missing link. This deliberate fraud confused the human evolution picture for a full 40 years until it was finally exposed.

In 1923, another variety of Dubois's Homo erectus was found in China by the Austrian paleontologist Otto Zdansky and was called Peking man (the complete skull of which was discovered in 1929 by Weng Chung Pei). The year 1924 became significant when Raymond A. Dart (1893-1988), an Australian anthropologist, discovered the first Australopithecus fossil in South Africa. The Scottish paleontologist Robert Broom (1866-1951) supported Dart's theory that it was a primitive precursor of modern man, and he found a similar skeleton on his own in South Africa in 1936.

It was not until 1959 that the priority of African hominids over Asian hominids assumed a strong position. In that year, Mary Douglas Leakey (1913-), the wife of British anthropologist Louis S. B. Leakey (1903-1972), found skull fragments at Olduvai Gorge in Tanzania that proved to be a species of Australopithecus, called Zinjanthropus, that was 1,750,000 years old. It was also Louis Leakey who discovered in 1961 what he called Homo habilis. The skull of this creature held a larger brain than Australopithecus and was between 1.8 and 2 million years old.

In 1974, the American archeologist Donald C. Johanson (1943-) discovered a 4-million-year-old fossil whose scientific name is Australopithecus afarensis, but whose popular name became Lucy. Although her brain was only about one-third as large as today's human, the interesting thing about her was that she was completely bipedal. Many think that the sudden brain development that later occurred in hominids was the result of having their hands freed from walking and becoming available to use tools.

In recent years, new fossil discoveries and genetic evidence have fueled a debate concerning when and where Homo sapiens sapiens emerged. In 1988, researchers found numerous fossil fragments in a cave in Israel that suggest that anatomically modern humans lived there about 92,000 years ago. These results suggest that modern humans may have existed much longer than supposed, and they also support the theory that modern humans evolved first in Africa and then spread throughout the world. This notion, called the out-of-Africa model, says that Neanderthals found in Europe and elsewhere were a distinct and parallel human species that came to a dead end. This model is opposed by the multi-regional model, which argues that modern humans arose virtually simultaneously and independently in several different places in Africa, Europe, and Asia.

In 1997, Svante Pääbo of the University of Munich and his colleagues looked at a small stretch of DNA from a Neanderthal bone. They compared it with the DNA from more than 1,600 modern humans of various racial groups. The scientists saw no evidence of a relation. This suggests that Neanderthals were indeed a distinct species, which supports the out-of-Africa model. By Pääbo's calculations, Neanderthals and modern humans must have evolved separately for more than a half million years to have become so different. However, research is still needed to confirm this finding.

As we approach the end of the twentieth century, only one thing is certain: The mystery of human origins is a difficult and perhaps even more complicated problem than ever imagined.

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