THE LIVING WORLD

Unit Five. Evolution of Animal Life

21. How Humans Evolved

21.6. Out of Africa Homo erectus

Our picture of what early Homo was like lacks detail because it is based only on a few specimens. Some scientists still dispute H. habilis’s qualifications as a true human because it had not moved far from its australopithecine roots. There is no such doubt about the species that replaced it, Homo erectus. Many specimens have been found, and H. erectus was without any doubt a true human.

Java Man

After the publication of Darwin’s book On the Origin of Species in 1859, there was much public discussion about “the missing link,” the fossil ancestor common to both humans and apes. Darwin was convinced our origin lay in Africa. Puzzling over the question, a Dutch doctor and anatomist named Eugene Dubois was swayed by Alfred Russel Wallace’s conviction that our origins lay instead in southeast Asia. Dubois was particularly intrigued by the orangutans, the “old men of the forest” from Java and Borneo. Many of the orangutan’s anatomical features seemed to fit the picture of a “missing link.” So Dubois closed his medical practice to seek fossil evidence of the missing link in the home country of the orangutan, Java.

Dubois enrolled as an army surgeon in the Royal Dutch East Indies Army and set up practice, first in Sumatra, then in a small village on the Solo River in eastern Java. In 1891, while digging into a hill by the river (figure 21.8) that villagers claimed had “dragon bones,” he unearthed a skull cap and, upstream, a thighbone. He was very excited by his find, informally called Java man, for three reasons:

1. The structure of the thighbone clearly indicated that the individual had long, straight legs and was an excellent walker.

2. The size of the skull cap suggested a very large brain, about 1,000 cubic centimeters.

3. Most surprising, the bones seemed as much as 500,000 years old, judged by other fossils Dubois unearthed with them.

The fossil hominid that Dubois had found was far older than any fossil hominid discovered up to that time, and few scientists were willing at the time to accept that it was an ancient species of human. In the years since Dubois died, about 40 individuals similar in character and age to his fossil have been found in Java, including in 1969 the nearly complete skull of an adult male.

Figure 21.8. Where Homo erectus was first discovered.

Digging into a hill on the bank of the Solo River in 1891, Eugene Dubois discovered the first fossil evidence that man's origins go back more than a million years.

Peking Man

Another generation passed before scientists were forced to admit that Dubois had been right all along. In the 1920s a skull was discovered in a cave on “Dragon Bone Hill” some 40 kilometers south of Peking (now Beijing), China, that closely resembled Java man. Continued excavation at the site eventually revealed 14 skulls, many excellently preserved, together with lower jaws and other bones. Crude tools were also found, and most important of all, the ashes of campfires.

Casts of these fossils were distributed for study to laboratories around the world. The originals were loaded onto a truck and evacuated from Peking in December, 1941, at the beginning of Japan’s invasion in World War II, only to disappear into the confusion of history. No one knows what happened to the truck or its priceless cargo.

A Very Successful Species

Java man and Peking man are now recognized as belonging to the same species, H. erectus. H. erectus was a lot larger than H. habilis—about 1.5 meters tall. It walked erect, as did H. habilis, but had a larger brain, about 1,000 cubic centimeters. The cranial capacity of H. erectus was about halfway between that of Australopithecus and Homo sapiens. Its skull had prominent brow ridges and, like modern humans, a rounded jaw. Most interesting of all, the shape of the skull interior suggests that H. erectus was able to talk.

Where did H. erectus come from? It should come as no surprise to you that it came out of Africa. In 1976 a complete H. erectus skull was discovered in East Africa. It was 1.5 million years old, a million years older than the Java and Peking finds. Far more successful than H. habilis, H. erectus quickly became widespread and abundant in Africa and within 1 million years had migrated into Asia and Europe. A social species, H. erectus lived in tribes of 20 to 50 people, often dwelling in caves. They successfully hunted large animals, butchered them using flint and bone tools, and cooked them over fires—the site in China contains the remains of horses, bears, elephants, deer, and rhinoceroses.

H. erectus survived for over a million years, longer than any other species of human. These very adaptable humans disappeared in Africa only about 500,000 years ago, as modern humans were emerging. Interestingly, they survived even longer in Asia.

Key Learning Outcome 21.6. Homo erectus evolved in Africa and migrated from there to Europe and Asia.