Pliocene epoch
5.3 to 1.6 million years ago

5 MILLION YEARS AGO

Due to some as yet unexplained event leading to what is believed to be a long-term climate change throughout the world, the great African rainforests began to shrink in size, driving more and more of the early "human-like" primates from the rainforest tree tops and onto the drier and harsher savannah landscape.
Why the climate change? Nobody knows for sure. Some scientists speculate that perhaps many of the early "competing" primates had overpopulated the African rainforests and were now outstripping the food supply until the climate of Africa had to change (ie. fewer leaves in the trees to provide adequate humidity in the air and protect the fragile African soil and water supplies on the ground etc)? Or is there a natural explanation? (1)
Today, the only remnants of this great African rainforest may be found in difficult-to-reach places like the Congo along Africa's central west coast.
Before more sunlight reached the ground, primates (including the evolutionary branch that would lead to humans) were nocturnal creatures. But with fewer trees on the African continent, the primates slowly became specialists in gathering food during the day and sleeping at night.

4.9 MILLION YEARS AGO

While it may be true that life for our early ancestors may be getting a little easier at this time, it is believed we were still on the predator's menu thanks to the presence of sabretooths, giant carnivorous bears, lions, leopards, wild dogs and giant birds of prey.
Richard Coss, a psychologist at the University of California, argues that the transition from being hunted to the hunter stage has not been a particularly smooth one. He believes it is possible our ancestors had encountered numerous predators of which many were detrimental to humans in the early stages. But as time went by, humans developed better muscle coordination, started walking on two feet, used a communicative language for organising whole groups of hominids to achieve a common goal, built a technology and many other "human" characteristics and tools to help deal with the predators.
Hence Coss believes all our technology, socialisation, language, the aggressive behaviours displayed by males, our social values of trust and loyalty, our need to hoard as many tools as possible, and even many of our deepest fears and phobias are all part of our evolutionary hangovers from these ancient times when humans had to deal with the predators.
If this is true, such regular reinforcement of these difficult times including the presence of prehistoric drawings and some awesome stories handed down through the generations would be carried over in our genes and produce what we call instincts, which are essentially hardwired patterns stored in the brain. Richard Coss agrees. As Ken Grimes writes in his article Hunted!, published in the New Scientist magazine:
'[Richard] Coss is convinced that we still bear the marks of our time as a hunted creature. Inherited instincts and intuitions can remain hardwired into the brain for a very long time, he says, even once they have become obsolete. This might explain relic behaviours such as the Moro response - a reflex grasping action displayed by newborn babies when startled. It resembles the way in which an alarmed infant monkey clings to the furry belly of its mother. "This ancestral infant response, which disappears at about six months of age, is therefore at least six million years old," says Coss.' (2)

As further evidence, many people are still likely to be startled to this very day whenever movies from Hollywood producers depict predators on the big screen despite the safety of our modern society. And what about the general tendency for males to be aggressive when solving problems? Could we have learnt this now instinctual behaviour in the males species over millions of years?
Whether or not our minds and everything that we have developed and acquired today is the product of millions of years of experiencing what it is like being attacked and "eaten alive" by predators on a regular basis, further research is still being carried out on this controversial idea. (3)

4.1 MILLION YEARS AGO

Nearly 4 million years ago, hominids called Australopithecus walked the Earth. They had a skull structure slightly more human than ape to be considered a likely early ancestor.

Artist impression of a family belonging to the Australopithecus lineage. Source: Reader 1986, p.179.
These early hominids were small social creatures of 1.2 to 1.5 metres in height which lived in eastern and southern Africa. They walked on two feet (with slightly bent legs) with a brain no larger than a modern chimpanzee (or roughly one-third of a modern human). Although characteristically ape-like in appearance, primitive human-like features can be observed on the skull structure including a low forehead, a forward-jutting jaw, and small canines not projecting well above the other teeth. Probably their ancestral instinct to climb trees was still an integral part of their lives as observed in the curvature of the finger and toe (based on an analysis of the remains of a 40 per cent complete 3.18-million-year-old (4) skeleton nicknamed "Lucy" from Ethiopia, Africa).

Walking on two feet probably became an important step in the evolution of this group of hominids for the following reasons:
To gain a better view of the surrounding countryside as required to find a number of potential food sites and observe possible threats to one's survival such as a predator or uncontrolled fire;

Africa at this time is losing its great forests and has now become a patchwork of forest and savanna. Hence for Australopicines to migrate safely from one forest to the next, they learned to walk upright. As an incentive, the large wetlands in some parts of Africa may have forced the Australopicines to walk upright to avoid drowning themselves in the water;

To show leadership or aggression in a group, it is important to increase one's physical height by standing tall on two feet (and yet still be able to crouch down and keep a small size when hiding from predators). It is a bit like the way two male antelopes will come together in a fight. The antelopes would temporarily get up on two feet and come down on each other as a sign of greater aggression, strength and size;

To reduce surface area of skin exposed to sunlight and so lower the rate of water loss that would otherwise reduce the primates ability to endure the heat of the day as they chased prey over long distances or wandered around from one tree to the next searching for food; and

To allow primates to free two limbs - one to hold and the other to manipulate - so they may build and use tools needed to make the task of acquiring food and fending off predators and other primate groups easier to perform.

The success of these creatures can also be better understood thanks to the following statement by Professor Tim White from the University of California at Berkeley, USA:
'Australopithecus became a superior omnivore, able to eat tubers and roots with more fibre and grit, adapting it better to times of scarcity during periods of extended drought.
'They may have been small-brained, but they stuck around a long time, fully half of our zoological family's six-million-year existence on the planet.' (The Canberra Times: Latest fossil finds in Ethiopia will provide the missing link: scientists. 15 April 2006, p.13.)

Fruit and nuts remained a staple for these hominds.
## SPECIAL UPDATE ##
15 April 2006
There is a general belief among the scientists that the more human-like Australopithecenes evolved from some species of Ardipithecus (a more ape-like creature) sometime between 7 and 4.4 million years ago. But the further we go back, the harder it becomes to determine which ape-like species is a member of the human family tree.

3.7 MILLION YEARS AGO

Scientists discover embedded in 3.7 million year old volcanic ash footprints in Tanzania during the mid-1970s. What makes these footprints special is how they were produced by human-like creatures walking on two feet (possibly our own ancestors). This has to be clear evidence that a number of hominid creatures (and certainly those leading to modern humans) were already walking upright by this time.

2.8 MILLION YEARS AGO

Professor Gunther Korschinek and his scientific colleagues at the Technical University of Munich, Germany, have found stardust deep beneath the Pacific Ocean dated to this time.
The discovery suggests the Earth was showered by this stardust material and higher levels of cosmic rays for up to a period of 300,000 years (5). The consequence of this is that any increase in cosmic rays reaching the surface of the Earth can affect the genetic material of early humans more readily. So the scientists have suggested the possibility that such rays could have assisted in the evolution of humans during this time.
Or it could have been detrimental to the evolution of humans. In which case, those humans that were born with deformaties were probably quickly wiped out. But if humans were born the unusually good characteristics necessary to improve their own survival and allow them to breed with other humans, the modified genes could easily be transferred to future generations of humans.
Either way, the importance of radiation from various sources in modifying our genes cannot be discounted.
Did humans gain new characteristics soon after being exposed to the cosmic rays from an ancient supernova?

1 TO 3 MILLION YEARS AGO

A scientific study of the fossilised bones of 324 baboons and 140 australopithecines uncovered during this period have confirmed that many did bear the marks of encounters with predators. The marks look typical of tooth and claw damage, especially of the big cats and predatory hyenas variety. (6) It would appear our ancestors were more prey than predator during this time.
The group structure of Australopithecus is most interesting. Apparently, Australopithecus males would often stick in one group for all their lives. Females, on the other hand, were more likely to move to different groups. This ensures inbreeding within the species is minimised.
Australopithecus were scavengers of dead animals to help supplement their standard plant diet of leaves, roots and fruit. An increase in meat consumption would go hand-in-hand with an increase in brain size because of the extra nutrients (eg. protein and fats) in the meat needed for the brain to develop and grow.
It would be another 2 million years before humans would learn to speak in a highly sophisticated and rational way and hence develop the necessary level of social organisation and technology capable of defending itself against virtually all great predators.

2.5 MILLION YEARS AGO

Africa was experiencing a 10,000-year drought during the Pliocene epoch at around this time. According to some scientists, it was enough to devastate the gorilla population in southern Zaire and so allow a new breed of chimps to carve an existence.
Some scientists believe it could also have affected early humans causing our bodies to adapt and find ways to get through periods of famine until the next period of abundance.
The drought is thought to be a natural cataclysmic event.

2 MILLION YEARS AGO

Africa is still getting drier and becoming more like a grassland. And now some scientists believe they may know why. Apparently the tilt of the Earth is different at this time compared to today and is such that the polar ice caps could not melt properly in the summer time. The result is a locking up of more water as polar ice caps reduced the humidity in the air and with it the general rainfall in continents like Africa.
Despite the drier conditions, at least half a dozen different species of hominids appeared at this time. The large variety of hominids would coincide with a great diversity of animal life especially on the African continent, both of the familiar and unfamiliar types.
Of all the hominids present at this time, the oldest known artificially-made tools were probably fashioned by Homo Habilis. From an abundant supply of stones and wood in certain parts of the European and African continent at this time, these hominids used their hands to create simple knifes and spear implements to improve hunting techniques and to fend off invaders and predators from a prescribed territory.
Studies of skull and bone fragments suggested Homo Habilis were slightly taller and had a fractionally larger brain capacity than their predecessors, Australopithecus.
Did Homo Habilis develop the tools for gathering food first before using them as a defence against predators and eventually, with further refinement, for hunting? Some scientists believe it may have started in the latter situation. As Louise Barrett, a primatologist from Liverpool University, said:
'It is surely more reasonable to imagine that early humans discovered weapons as a means of driving away predators, then adopted them for scavenging [or gathering] and then hunting, than that we spontaneously "invented" hunting tools.' (7)

But this could end up being another chicken-and-the-egg situation. For example, a chimpanzee can quickly learn to cusp its hands into the shape of a bowl for temporarily holding food or water. Or why not a piece of bark for the same purpose? Some chimpanzees are even smart enough to select and even mould with its hands a piece of bark to gather food or water more efficiently. Since eating and drinking has to be performed more regularly and early in life compared to defending against predators, one could argue the tools were probably developed for gathering food first.
Whatever the truth, certainly by the time humans did start making tools, they would have eventually seen the value of using the tools both as a means of defending themselves against the predators and as a means of hunting and gathering of food.
As these changes were taking place among the hominids, the original and thick gondwanic rainforests covering much if not all of Australia for literally many millions of years according to pollen records obtained from a number of sites around Australia, became only a minor part of Australia's vegetation by around 2 million years ago. More open and drier temperate forests would form the dominant feature of this continent.
The trend towards a diminishing rainforest size seems to be common in other parts of the world. For example, in Africa, the great rainforests covering much of the continent had already began to shrink in size (or disperse) nearly 5 million years ago as a result of a climate change caused by some natural event. Perhaps the Himalayas is having an effect on climate west of these great mountains?
But why would Australia by affected by the climate change? It is certainly not in the rainshadow of the Himalayan mountains.
Or perhaps Australia is such a geologically inactive continent that what people call the mountains along the eastern seaboard had now being weathered away sufficiently to hills by the wind and rain. Once the continent had a reduced mountain range, the likelihood of cloud formation occuring over the range would probably be reduced with rain becoming less and less frequent and predictable. Only a large inland sea at the centre of Australia could maintain any resemblance of reasonably high rainfall over the mountain range called the Blue Mountains given the high humidity expected in the air which would see a large amount of water run down to fill the great rivers in the west and eventually refill the inland sea.
But should this inland sea ever disappear altogether, Australia would turn into the driest continent in the world and one of the most difficult places for humans to grow food and carve an existence on this increasingly inhospitable land.
Turning back to the hominids that would eventually lead to the existence of humans, there existed another hominid species from East Africa nearly 2 million years ago known as Homo Augasta. These hominids had a more familiar human appearance compared to Homo Habilis, had a larger brain, were better adapted to a changing environment, produced the Rolls Royce of stone tools (eg. axes), had greater social skills, developed the beginnings of a rudimentary verbal language for communicating with each other as needed for better survival, and had the sophisticated tools and knowledge to reduce competition from other hominids and various predators.
We owe our large brains directly from Homo Augasta. In fact, the moment these prehistoric humans learned to develop relationships with other people through language and getting together on a social level and hence a chance to organise the group to perform specific tasks, the brains of Homo Augusta had to expand because of the range of extra patterns needed to be learnt through language and other skills as required to survive not only in the harsh environment, but also within the group itself.

1.77 MILLION YEARS AGO

Scientists discover a paleomagnetic reversal, an occurrence where the Earth's magnetic poles reverse positions, according to geophysical surveys of the magnetic patterns recorded in rocks on the sea floor. Between 1.77 and 1.5 million years ago, the north pole was actually over Antarctica and the south pole near the arctic region.
When a reversal of the Earth's magnetic poles occurs, there is an increase in radiation and cosmic rays from space on the Earth's surface (even over the equatorial regions), resulting in the quicker death or extinction of some animal species and the sudden genetic mutation of other species. Could early humans have benefited from a change in their genetic material due to an increase in radiation levels during a brief period of magnetic pole reversal? (8)

NOTES

Some scientists speculate that the "drying up of Africa" would actually coincide with a supernova explosion nearly 2.8 million years ago causing the Earth to heat up slightly and evaporate enough of the moisture to turn the continent into a dry savanna landscape as we see today.
If this is true, then why did the Earth retain so much rainfall over the continent during the Jurassic period despite being much warmer than it was 3 million years ago or even today? What is maintaining the dry conditions on the continent to this very day?
Mountain-building? Volcanoes? More supernovas? Or the arrival of a new species called humans?
Perhaps the clues can be found by the way animals and humans graze for food and firewood near the fringes of the Saraha desert today. Or are we living in a period of increasing dryness and high temperatures because of a continued natural event occurring to this day?
Perhaps we need to ask these scientists, where's the supernova explosion maintaining these current dry and hot conditions on the planet Earth?
As Korschinek and his colleagues wrote following the discovery of stardust beneath the Pacific Ocean dated to 2.8 million years ago:
'It has not yet been established that such an increase of the cosmic ray intensity [from an ancient supernova] could have had a significant influence on the Earth's climate.' (The Canberra Times: Stardust under the Pacific suggests birth of human life. 30 October 2004, p.20.)

Grimes 2002, p.35.

Ian Tattersall, curator of the American Natural History Museum in New York, is playing it safe by not entirely supporting this theory from Coss. He said:
'Though such ingredients make for a dramatic story, they are inherently untestable. How could we place a probability on them, or show them to be wrong?' (Grimes 2002, p.37.)

The age has been placed to within plus or minus 10,000 years using recent advances in the potassium-argon dating technique, which allowed scientists to date the layers of volcanic ash where Lucy's body was found.

Evidence for the existence of this stardust on the Earth and the timing for when it was deposited on the Earth's surface was determined after scientists understood the major composition of stardust is the radioactive element known as iron-60 and has a natural decay rate, or half-life, calculated by the scientists of approximately 1.5 million years.
You see, all ancient stars undergoing a supernova explosion will always contain high amounts of heavy metals in their chemical composition of which the highest quantity is iron.
Iron is what made the Earth. And life cannot exist without some iron in its own chemical composition. So we should expect stardust to contain iron in reasonable quantities.
Iron is a by-product of the intense nuclear fusion reactions that occur at the core of stars.
So when scientists managed to find a preserved layer of unusually high quantities of the radioactive element iron-60 underneath the Pacific ocean but not in the magma part of the Earth, scientists had no choice but to accept this as evidence for stardust. And because iron-60 has a decay rate, or half-life, of 1.5 million years, scientists have pinpointed the timing for this supernova explosion at around 2.8 million years ago.

Grimes 2002, p.35. Scientists studying the skull of a 2 million year old toddler known as Taung Child have found evidence of puncture marks in the base of the eye socket. After looking at the way modern eagles eat their prey (including small primates) and the damage left behind in the eye sockets, Dr Lee Berger of the University of the Witwatersrand in Johannesburg, South Africa, will conclude in a report expected to be published in the American Journal of Physical Anthropology that the child had died after being picked up by an ancient predatory bird (possibly an eagle or a flightless creature with a beak), taken to a nest, its eyes were ripped out, and eventually eating alive.
All the hallmarks of a bird eating the child can be found from the damage done to the eye sockets. As Dr Berger said:
'I looked into the eyes of the skull. I saw the marks — they were perfect examples of eagle damage.' (The Sydney Morning Herald: Stone Age whodunit is solved. 14-15 January 2006, p.3.)

Grimes 2002, p.37.

Tattersall 1995, p.122.
Second image is a reconstruction of a fairer-skinned couple version of Australopithecus based on fossils found in Africa. Source: Tattersall 1995, p.39.