Climate Change and The Dawn of Man

Australopithecus and a closely related genus Paranthropus. The members of these two early genera weighed about the same as chimpanzees (although males weighed much more). When on the ground they walked upright but they were active in trees.

Experts recognize two species of Australopithecus. A. africanus that occupied southern Africa and A. afarensis which occupied northeastern Africa. These groups of animals did not evolve directly from the apes but they were intermediate in form between apes and humans.

Australopithecus resembled apes in having front teeth that were large in relation to the size of their molars. The animal fed largely on coarse food, probably fruits an seed pods.

The most famous example of this genus called "Lucy" came from Ethiopia (found in 1973). "Lucy" was an Australopithecus afarensis

Rivers cut through the terrain of east Africa such as the Olduvai gorge pictured here. These have been extremely fruitful localities for recovering early hominid remains. Ashes produced by the associated volcanism in east Africa have provided radiometric dates which tell scientists about the timing of the the early hominid appearances.

The oldest fossil of the genus Homo is dated at about 2.5 million years.

Scientists do not know which of the two species of Australopithecus was the predecessor of Homo

It appears that by about 2.0 million years ago there were two species of Homo. However, these are simply grouped together under "early Homo"

Early Homo appears to have a much larger brain than did the Australopithecus. Some early Homo fossils have been found with "stone tools" which resulted in the name Homo habilis or "handy man"

The link to climate change

Brain size, climbing and the shrinkage of forests

Homo has much larger brain sizes than did the Australopithecus. The size of the Homo brain can be attributed to the style of infant development. The brains of all newborn primates (including monkeys, apes, and humans) account for 10% of the total body weight. Most of the growth of the brain in monkeys and apes occurs before birth with little additional growth after.

In humans growth of the brain continues to grow rapidly after birth for about the first year. Within one year a baby human has about twice the brain capacity as a chimpanzee.

This pattern of brain growth in humans is a reflection of the delayed maturation cycle in humans. Humans mature much slower than do other primates. Remember our baby teeth are not replaced with permanent teeth until we are much older.

This delayed maturation is more than offset by the increased intelligence associated with a larger brain capacity. The human intelligence is able to deal with a variety of environmental problems because the greater intelligence. Humans are neither strong or fast but have come to dominate the Earth.

It may not be hard to understand why it took over 1.5 million years for Humans to evolve after the appearance of the Australopithecus. Remember the Australopithecus spent a great deal of time in the trees. A mother Australopithecus could not climb and care for a helpless infant while climbing trees. The rapid maturation of the Australipithecus infant was important therefore to the survival of the mother and child. A mother Australipithecus could leave her infant much sooner (presumably in the trees) in order to find food. This would not be possible for Homo mothers since their infant is not able to fend for itself until much later in life.


At 2.5 million years ago there was a dramatic change in climate and remember that this was a time of drying and cooler climatic conditions. This was particularly true in Africa which was also being affected by the uplift of the mountains in eastern Africa. Much of the forest were eliminated and replaced by grass lands. This meant that the Australopithecus group lost much of its source of food, the trees with fruit and berries.

The climate change at 2.5 million years ago also greatly affected many other groups of mammals. Many of the groups adapted to forests were eliminated along with the forests. Other mammals expanded which were well adapted to the grassland environment.

At about 1.6 million years ago Homo erectus evolved. This was the first Homo to walk completely upright. This was also the first Homo to migrate outside of Africa. This species has been found in China, and in Europe. It has also been found in Java which gave rise to the name "Peking Man"

Homo erectus

This is fossil of a 1.6 million year old boy who was 11 to 14 years old.

Some scientist believe the next phase of Human evolution was the appearance of a form called Neanderthal. This fossil group has characteristics that link it to Homo sapiens but is also different enough that some scientist place it into a separate species, H. neanderthalensis. This group had more massive bodies than modern man and the brains were larger (this does not mean they were smarter). They seem to have stronger muscle attachments on the bones which suggest they were stronger than modern man.

The Neanderthals have been found in caves which suggest they took shelter in these dwellings.They have been found from Spain to Asia. They were first found in Germany in the Neander Valley which is why they are called Neanderthals.

The Neanderthals lived until about 35,000 years ago. This means they lived during the same time that the Homo sapiens were appearing. The two groups, Homo sapiens and H. neanderthalensis groups were probably reproductively isolated from one anther.

The Neanderthals disappeared from eastern Europe during the last ice advance in Europe 40,000 years ago. They survived in western Europe and the middle East for another 5000 years.

At this same time humans that were anatomically identical to modern man expanded throughout Europe. The fact that H. sapiens suddenly replaced Neanderthals in Europe further suggest the two did not (could not) interbreed.

Africa now appears to be the most likely source region for the first Homo sapiens.

Some scientists believe that Homo erectus may have given rise to both Homo sapiens and to Homo neanderthalensis.

Although H. neanderthalensis appears to have been more primitive than H. sapiens, they did use tools made from stones. Interestingly, they also appear to have had religion.

A burial site has been found in Iraq which has a Neanderthal laid to rest along with stone tools and cooked meat thought to prepare the person for the after life.

Human Expansion and the Extinction of large Mammals