Facts About The Evolution Of Human | Science facts

The Story of Human Evolution
Few people seem to be interested in questioning the existence of the universe. Most people are too busy dealing with the responsibilities and distractions of daily life. They do not have the time or the inclination to contemplate the existence of the universe. They just want simple answers that are presented to them in an interesting way.

Other people say that there is no point asking why the universe exists, because without any evidence, we can only ever guess the answer. But questioning the existence of the universe is essential, because until we understand our relationship with the universe, then how can we ever really know who we are or what we are supposed to be doing, other than to blindly follow our instincts and attempt to satisfy our desires?
Unfortunately, debate about the existence of the universe is still being clouded by popular religious myths that were devised at a time when we knew very little about the universe. While some people close their minds in blind acceptance of these myths, others close their minds in blind reaction against them.
There are countless ideas and opinions that have been expressed over the last three thousand years of written history. The most influential of these ideas will be discussed later in this book. But after stripping away all of the myths and misconceptions, and distilling the answers down to their purest essence, there remains only two possibilities.
One possibility is that our universe exists for no reason and has no purpose, and so our lives have no meaning other than whatever meaning we invent for ourselves. The other possibility is that we were brought into existence by some kind of purposeful process beyond space and time. A process which designed the universe and planned the events that led to the natural evolution of intelligent life.
At this point in time, there is no conclusive evidence to prove either way, and there may never be any evidence. In order to gain the best possible understanding of our existence, we need to open our minds to both possibilities and thoroughly examine them both to their eventual conclusions. This book will attempt to undertake such an examination.
We will start our investigation by going back to the beginning, to the birth of the universe and the evolution of humankind. From there, we will follow the events of human history that led to the modern age, to the discovery of computer technology and genetic engineering. Along the way, we will look for clues that might reveal some kind of purpose to our existence.
The journey will not be easy. Most of what we think we know about our origins has only recently been reconstructed from scant pieces of evidence. And when we read about history, it is hard to separate fact from fiction. The truth always seems to become shrouded by thickening clouds of myth. History is forever being revised to support popular political or religious beliefs, and increasingly questionable interpretations of history continue to appear.
Sometimes even scientific beliefs can turn out to be myths. Science is about searching for the best explanation based upon the existing evidence, knowing that some day new evidence might be discovered and a better explanation might be found. In any case, the credibility of any scientific theory depends on its popularity among those who are in a position to impose their opinion.
The following account of human evolution has been kept simple in order for it to be more understandable. Most of the information presented here is widely accepted by the scientific community, but many of the details are still being argued over by evolutionary biologists. There are some things that we may never know for sure, and so when it comes to exploring our origins, we may need to accept that there will always be a degree of myth in our history.

The birth of the universe

At the beginning of time, the universe was born when space opened up and was filled with an enormous explosion of energy. As the energy from this explosion radiated out into space, it cooled down and began to condense into matter.
Within a fraction of a second, most of the initial energy had condensed into fundamental particles of matter. After hundreds of thousands of years, as the universe continued to expand and cool down, these particles began to condense into atoms.
Enormous clouds of atoms were drawn together by gravity. They spiraled inwards and were crushed together to form massive solid bodies of matter. The immense pressure and heat inside these bodies caused nuclear reactions, and they exploded with intense light and heat to become stars.
Great collections of these newly born stars were drawn together by gravity to form galaxies. Today’s universe contains hundreds of billions of galaxies, each containing hundreds of billions of stars. The universe has continued to expand now for over twelve billion years.

The formation of the earth

Stars release enormous amounts of energy by converting lighter elements like hydrogen into heavier elements like carbon and iron. All of the heavy elements in the universe were forged in the hearts of stars. Stars continue to burn brightly for billions of years, and then when they run out of nuclear fuel, they often explode, scattering their elements across space.
Our solar system was formed out of the rubble left behind by nearby stars that had exploded. This rubble was drawn together by gravity to form a huge spinning cloud of rocks and dust. At the center of this cloud, the cosmic material was crushed together and exploded into life as a medium sized star, our Sun.
As the remaining rubble continued to revolve around the Sun, it was drawn together by gravity. Huge pieces of rock collided and were fused together by heat to form the planets and their moons. Any material that was not absorbed by the planets was left to circle the sun as asteroids and comets.
Our Earth began as a mass of molten rock covered by a hard, crusty, outer layer. Movements and eruptions in the Earth’s surface produced mountains and valleys. As the surface of the Earth cooled down, clouds of steam condensed and water fell from the sky to form rivers, lakes, and oceans.

Organic molecules

Common elements like hydrogen, carbon, and oxygen are easily attracted to each other. They bond together to form chemical compounds like water and carbon dioxide. It is more natural for these elements to combine into chemical compounds than it is for them to be found in their pure form.
Under the right conditions, carbon has a tendency to bond with other common elements to form long and complex chains of atoms known as organic molecules. Organic molecules can then bond with other organic molecules, and there seems to be no limit to how long and complex these organic molecular chains can become.
Billions of years ago, the conditions on the surface of the earth were very favorable for the formation of organic molecules. These molecules were washed into the sea to form pools of organic matter on the sea floor. Over millions of years, they continued to bond together to form increasingly long and complex molecular chains.

The first spark of life

Life began when one of these complex organic molecules began reacting with the other molecules around it in an unusual way. It was able to attract all of the pieces that it needed to assemble an identical copy of itself. The copy then split away from the original and began to assemble its own new copy.
These self-replicating molecules may not have lasted long before they were broken down by other chemical reactions, but they were still able to spread through the pool of organic material fast enough to have a lasting chain reaction.
The process of self-replication was not always perfect. Quite often a piece was missing or the wrong piece was used, and the copy would be different from its parent. Very few of these mutated molecules were still capable of replicating, but occasionally, by pure chance, a new molecule was created that could survive longer or replicate faster than its parent.

Single cells

After millions of years and countless mutations, new and more complex molecules developed a protective layer. The chemicals needed for replication could still pass through this protective layer, but the molecule was now safe from harmful reactions. The protective layer slowly evolved into a cell wall, and safely contained within the cell, the chemical reactions of life were able to evolve to become much more complex.
It took hundreds of millions of years, but eventually a new process evolved for producing a copy of a cell. This new process used a number of molecules working together like an assembly line in a factory, using chemical attraction to assemble sophisticated molecules known as proteins, which then carried out all of the tasks associated with the survival and reproduction of the cell. The instructions for how to build these proteins were encoded in the main molecule, known as the DNA.
As the mutations continued over hundreds of millions of years, new strains evolved the ability to use sunlight to convert common chemicals into food. This ability, known as photosynthesis, has the side effect of producing oxygen.
Before photosynthesis, there was no oxygen in the earth's atmosphere. Then after millions of years of photosynthesis, the atmosphere became rich with oxygen. We know this because the oxygen reacted with dissolved iron in the seawater and deposited a layer of rust on the ocean floor. Oxygen also formed the ozone layer, which still protects the surface of the earth from the sun's deadly radiation.
There were occasions in the history of evolution, when a smaller cell became trapped inside the body of a larger cell, and the children of the smaller cell survived and reproduced inside the children of the larger cell. Sometimes these smaller cells provided benefits to the larger cell, and sometimes they continued to evolve inside the larger cell over millions of years to become permanent organs of the larger cell.
One of the most important steps in the evolution of life was the appearance inside some cells of an organ called the nucleus. The nucleus had evolved to become especially good at copying and repairing its own DNA, and so the DNA inside the nucleus was able to become thousands of times more complex. Cells with a nucleus soon evolved to become thousands of times larger and more sophisticated than cells without a nucleus.

The process of evolution

Evolution begins when there is an error during reproduction and the new cell is different from its parent. Mutant cells usually die, and those that survive are likely to be disadvantaged by their mutation. Only very rarely will a mutant perform better than its parent. The descendents of the mutant cell may then successfully compete against the rest of the population and eventually replace them.
The more often an organism mutates, the faster it evolves, and so the faster it can adapt to changing conditions and the more successfully it can compete against other variations. The pressure to evolve faster has forced cell reproduction to maintain a consistently high rate of mutation. Only the need for enough healthy individuals to survive stops the mutation rate from being higher.
A larger population has a higher chance of producing a beneficial mutation. But then a considerable amount of time may need to pass before the mutant population grows large enough to have any chance of producing a second beneficial mutation.
This problem was overcome by the appearance of sexual reproduction. By combining the DNA from two parents, a child cell can inherit the beneficial mutations from two separate ancestries. Beneficial mutations can then spread back into an existing population, and this greatly magnifies the rate of evolution.
The rate of evolution is also increased by having only a limited period of time during which an organism can breed. After the breeding cycle is over, there is little evolutionary pressure to resist disease, cell degradation, and the other signs of aging which lead to a natural death. The lifespan of an organism becomes balanced between how much more the parent can contribute to its offspring and how heavily the parent must compete against its offspring for resources.

Multi-celled animals

After billions of years of evolution, the rivers, lakes, and oceans of the world were swarming with a rich variety of single celled organisms. Some cells, such as algae, got their energy directly from sunlight, and some cells survived by eating other cells.
The most advanced single celled organisms had tiny arms that could swim through the water. They responded to touch, had a sense of smell, and were sensitive to light. They could swim towards food, avoid obstacles and predators, and identify sexual partners.
Around a billion years ago, a mutation occurred during the reproduction of an algae cell that caused the newly divided cells to stick together. These cells formed sheets of algae that became the first primitive form of seaweed.
Other mutations led to changes inside the cells each time they divided. Different layers could now appear inside a growing organism. The instructions for how cells changed each time they divided were contained in the DNA. Any mutations to these instructions would change the size and shape of the growing organism.
Around 600 million years ago, the first multi-celled animals began to appear. The most successful of these were small, flat, worm-like creatures that absorbed algae through the outer layer of their bodies. Over time, they evolved the ability to wrap their bodies around large particles of food. Digestive juices were released onto the food to break it down before the nutrients were absorbed into the body.
Further mutations led to the development of an opening where food could be drawn in, digested, and then passed out. This opening slowly evolved into a tube running through the body. Food could be broken down more efficiently as it passed through the tube from the mouth to the rear.

Sensory perception

The success of an animal depended upon how much information it could collect from its surroundings. Worms had inherited a sense of smell from their single celled ancestors. They depended on this sense to detect the chemicals released by food. The cells around the mouth evolved so that when food was detected, signals would be passed through the body, triggering muscle cells to expand and contract, causing the worm to slowly wriggle towards the food.
The sensitive cells around the mouth and the cells that carried signals through the body evolved into a network of nerve cells. Any mutations to these nerve cells could change the way that the animal behaved. Evolution favored mutations that drove the animal to find more food, avoid danger, and breed more. The accumulation of advantageous mutations to nerve cells over millions of years led to the development of complex patterns of behavior.
However, it was not enough to always react in the same inherited way to each type of sensation. A particular smell might indicate food in some environments but danger in others. By remembering the association between a sensation and its outcome, mistakes did not have to be made a second time and successful outcomes could be pursued more vigorously.
Worms also inherited sensitivity to touch, temperature, and light from their single celled ancestors. A cluster of light sensitive cells has the potential to form a picture, and so there was strong evolutionary pressure for such clusters to evolve into early forms of eyes.
There was also strong evolutionary pressure for a large cluster of nerve cells to grow where the signal paths from the various senses intersected with the control paths for the muscles. This cluster of nerve cells evolved into the first primitive type of brain.

Predators and prey

Before worms could evolve to become larger, they first needed a system to pump oxygen and nutrients through their bodies. While most worms continued to feed on algae, the larger ones began feeding on the smaller ones. Those with tougher skin were harder to eat, and so over many millions of years, the skin of some animals evolved into a hard outer shell.
Animals with protective shells were best suited to crawling along the sea floor, but predators were able to move faster and find more food by swimming through the water. The most efficient way to swim was to wriggle from side to side. This style of motion was made more effective by having hard parts inside the body. These hard parts began as fluid-filled spaces which later accumulated minerals to take the form of bones.
Early animals were very successful at swimming around, looking for food, and finding sexual partners. As populations grew, so did the number of mutations. As long as life was easy, food was abundant, and partners were easy to find, then there would be nothing to stop new variations from flourishing. This stage of evolution was like a ‘trying out’ period for new animal designs. Within a short period of time, the oceans were filled with animals that came in a multitude of weird and wonderful shapes and sizes.
After millions more years of evolution, predators became larger, faster, and smarter. Only those smaller creatures that could swim faster, burrow into the sand, and those with protective shells were able to avoid being eaten. As smaller creatures became better at surviving in this hostile new environment, pressure grew on the predators to sharpen their hunting skills. The competition grew so fierce that most variations were wiped out. The only survivors were those whose body designs were so successful that many of their descendents are still alive today.

Plants

Around 500 million years ago, there were several hundred different types of marine animals including early forms of crabs and fish. Fresh water lakes had become fertile environments. Plants living in shallow water were able to gain more nutrients by anchoring themselves into the mud. Once anchored, they began branching towards the surface to collect more sunlight.
Plants and animals living near the water's edge were regularly exposed to the air by rising and falling tides, and lake water could become dangerously shallow during times of drought. Creatures living in these areas needed to survive for longer periods of time out of the water. Plants adapted by becoming weatherproof and growing strong enough to support their own weight. These changes allowed them to begin growing branches permanently above the water line.
Around 420 million years ago, the first plants appeared that could survive entirely on the land. Once they had taken their first step, nothing could stop them from spreading across the empty continents. They thrived in any region with regular rainfall and nutrient rich soil. They evolved rapidly as they adapted to new landscapes and climates. Within tens of millions of years, the land was covered by a dense forest of trees with branches and leaves.
Plants were soon followed onto the land by creatures with hard protective shells. Crabs, sea scorpions, and other shelled animals had been very successful in the sea. As they crawled onto the land they evolved into ants, beetles, spiders, and other insects. Within 50 million years, some variations had evolved wings and were able to fly.

Reptiles

Fish living in shallow water swamps and wetlands needed to propel themselves through the mud and vegetation. This favored stronger muscles around the fins, the bones in their fins became longer, and the tips of their fins became more claw-like. Their gills were less effective in the shallow muddy water, and so they developed lungs to draw more air from the surface. Those with thicker scales and more weatherproof skin were able to spend longer periods of time above the surface of the water.
By around 360 million years ago, animals that were half fish and half reptile were spending as much time crawling over the mud banks as they were swimming through the water. These creatures continued to evolve into reptiles, but they did not conquer the land for another 50 million years, not until their eggs had developed tough waterproof shells allowing them to be laid out of the water.

Mammals

The temperature of seawater does not vary much, and so animals living in the sea are able to keep a relatively constant body temperature. Moving onto the land meant surviving a much wider range of temperatures, with cold nights and cold winters. The chemical reactions inside cells are sensitive to temperature. As the temperature drops, these reactions become slower.
Reptiles depend on the warmth of the sun during the day. They become sluggish at night and in cold weather, and they can only live in regions that have mild winters. Their cells do not generate enough energy for them to actively hunt for food, and so they usually wait for prey to come near. Some early land reptiles evolved large fins on their backs to absorb more heat from the sun.
Reptiles walk on four legs that sprawl from the sides of their bodies, a configuration that helps them to move through the water. Around 300 million years ago, a new family of reptiles appeared with legs that were positioned beneath the body instead to give better support for walking on the land. These new animals were the earliest ancestors of mammals, and they rose to dominate a landscape rich with plant and insect life.
Early mammals also adapted to living on the land by evolving higher body temperatures. This allowed them to move faster over longer distances and more actively search for food. They could hunt any time of the day or night, in any season, and could survive further north or south in colder climates. They evolved hairs on their skin to retain body warmth in cold weather.

Dinosaurs

Around 240 million years ago, another successful branch of reptiles evolved into the dinosaurs. These creatures also had legs that supported them on the land, and they also benefited from a higher body temperature. But the dinosaur's body weight was shifted back so they could stand on two legs. This allowed them to run faster and reach higher than the four legged mammals.
Maintaining a higher body temperature requires a considerable amount of energy. Warm blooded animals use up to ten times more energy than cold blooded ones do. They need to find more food and eat at more regular intervals. Warm blooded animals also grow faster, reproduce more, and evolve more rapidly. In the fierce competition for the position of top predator, the dinosaurs proved to be superior to the mammals, and by 200 million years ago, the dinosaurs had completely conquered the land.
Only the smallest mammals survived. These were forced to retreat into colder regions where they lived in burrows under the ground and only emerged at night to hunt for insects. Mammals adapted to the colder regions by giving birth to live young rather than laying eggs. The developing young were kept safe and warm inside the mother's body where they received oxygen and nutrients from the mother's blood. After being born, the infants continued to receive nutrients by drinking their mother's milk.

Learned behavior

Many animals are born with all of their survival skills. They do not need to learn anything from their parents and are able to fend for themselves as soon as they are born. But instinctual patterns of behavior can take thousands of generations to evolve, and there are limits to how complex this behavior can become. There are limits to how much information can be passed down to the next generation through body chemistry alone.
Some animals spend months or even years learning more complex patterns of behavior by imitating their parents and other family members. Mammals evolved an extra layer of brain tissue surrounding the instinctual part of their brain. This extra layer helped them to override their instinctual behavior with learned skills.
The more that mammals came to depend on learned behavior, the less able their young were to care for themselves, and the more time they needed to learn from their parents. The degree to which learned behavior was able to replace inherited behavior depended on how skillfully parents could care for and educate their increasingly helpless infants.
Most of an animal's brain is used to control its body, and so larger animals need larger brains. Animals that depend more on learning need an even larger brain in proportion to their body size. But brains can use up to ten times more energy than other organs in the body. And so the evolution of a larger brain was partly limited by the ability to find more food.
The evolution of a larger brain was also limited by how easily the head of a baby can pass through the mother's birth canal. Animals with larger brains need to be born at earlier stages of their development, when their heads are smaller. This makes newborn babies even more dependent on the care of their parents until their brains are fully developed.
As mammals evolved to depend more on learning, they also developed stronger emotional attachments. Strong instinctual feelings of affection were needed to drive parents to care for their children, drive children to imitate their parents, and keep family members together long enough for the young to learn how to survive.

Cooperation and competition

In the natural world, the number of animals that can survive in an area depends on the amount of food that the land can produce. Numbers may grow until there is no longer enough food to support every animal. Then competition between individuals to satisfy their hunger becomes fierce. Younger animals may not be able to compete against stronger and more experienced ones. The population will be limited by the number of young that can survive long enough to breed.
Some animals develop such strong instinctual affections that they continue to live together in family groups. Groups of animals must compete against nearby groups for food, but animals within each group can often do better by sharing their food with other group members and by cooperating in other ways that help the survival of the young.
Members of the same group still need to compete against each other. Stronger members will fight to breed with the most desirable partners. When food is scarce, they will muscle each other for the largest share of the meal. Weaker members will compete for the affections of those who can secure them more food and better protection.
For each type of animal, there will be a balance between how much they can cooperate and how much they need to compete against other group members. When conditions change, so will the best balance between competition and cooperation.

The extinction of the dinosaurs

Every day the earth is showered by rocks from outer space. Many of these explode in the atmosphere, appearing as bright streaks of light in the sky. Larger rocks can break through the atmosphere and smash into the earth, sometimes causing enormous damage. Approximately once every few thousand years, the earth is struck hard enough to destroy an area the size of a small city. One impact every few hundred million years can be so destructive that the whole world is shaken by earthquakes, tidal waves, and volcanic eruptions.
Around 65 million years ago, a massive rock slammed into the earth with devastating impact. The explosion was so powerful that it incinerated everything within a thousand mile radius. Forest fires and volcanic eruptions sent thick clouds of dust and smoke into the sky, blocking out the sun around the world for many months. As the sunlight faded, the temperature began to drop. Plants withered as they were starved of sunlight and food became scarce. All of the large land animals died, as did many of the smaller ones.
The only dinosaurs to survive were the birds, who were able to fly above the carnage to search for scraps of food. Among the survivors on the ground were the small furry mammals who were well adapted to cold conditions. Being the only remaining land animal with warm blood, no other animal could now compete against the mammals for dominance on the land. Mammals rapidly evolved into a wide variety of shapes and sizes to take advantage of all of the new opportunities left behind by the extinction of the dinosaurs.

The evolution of mammals

Although there appears to be large differences between different species of mammal, all mammals are variations of the same basic design. For example, they all have the same set of bones. The bones of the human hand are arranged in a similar way to the bones of a bat's wing or a whale's flipper. The only significant difference is that the bones are different sizes.
Large differences can appear between ancestors and their descendents with only minor changes to those parts of the DNA that control the timing of childhood growth and the rate at which different body parts grow.
Species remain relatively unchanged for long periods of time. Significant mutations are rare, but when they do occur, a new group may break away from the original group and take over new environments for which they are better adapted. If the new group is successful enough, they may completely replace the original group.

Tree dwellers

While most mammals adapted to living on the ground, some adapted to living in the trees. Trees were safe from most predators and they provided a rich diet of fruit and insects. Some tree dwellers evolved fingers and thumbs for grasping onto branches. Long snouts are awkward when clinging to trees, and so their faces became flatter and their eyes moved to the front of their face, allowing better judgment of distances when leaping between trees.
Most animals that live on the ground need to be able to walk soon after they are born. But tree dwellers can cling to their mothers in the same way that their mothers can cling to trees. Being carried around and cared for by their mothers for a longer period of time allowed their brains to evolve to depend more on learned behavior and less on instinct.
Some tree dwellers became too large to walk across the tops of branches and began swinging beneath them instead. Their bodies became too heavy for their tails to act as a counterbalance, and so they lost their tails and developed a more upright posture to keep themselves balanced. Fewer branches could now support their weight. Instead of leaping between trees, they climbed down and walked between them.

The ancestors of humans

Around 7 million years ago, some of these ape-like creatures moved away from the forests and began living on the grass covered plains. As they spent less time in trees and more time traveling across open ground, evolutionary pressure favored those with longer legs, and they began walking upright.
Their hands were no longer needed for walking and could be used for a variety of other tasks such as gathering food or using sticks and stones as weapons. They could now hunt larger animals and carry the meat back to share with the rest of the group. Being able to provide better care for their increasingly helpless infants allowed them to continue to evolve larger brains that were more adapted towards learning. These animals were the early ancestors of humans.
They began breaking stones apart to create sharp edges which could be used to cut wood, meat, and bone. Around one million years ago, they learned how to keep fires burning and began cooking their meals. Cooked food required less chewing and so their jaws evolved to become smaller.
The competition between different groups of early humans was fierce. Those who could make better weapons, and those who were more skilled at using them had a distinct advantage. Increased competition, better parental care, better communication, and an increasingly complex lifestyle, all of these factors drove the evolution of a larger and more adaptable brain. Groups that evolved larger brains outcompeted and replaced groups that did not.

The power of speech

The shift towards learning was accompanied by an increased sense of curiosity. When one member of a group discovered a new way of doing something, the others would watch and imitate the idea. Older members of the group might be slow to change their habits, but the younger ones would grow up knowing only the new way. Group behavior usually adapts over time to make the most efficient use of the available resources. New discoveries are rare. New ideas usually come through contact with other groups.
Animals communicate by making sounds and using body gestures to express their emotions. As early humans became increasingly skillful, the sounds they made with their mouths became more controlled and meaningful. Grunting noises gradually changed into words. The need for improved voice control led to changes in throat design. These changes made it easier for them to choke while eating or drinking, but improved voice control outweighed this disadvantage.
The immediate advantage of improved communication led to stronger evolutionary pressure to learn more words and develop the creativity to string words together to form sentences. They were now able to learn more from each other and develop closer relationships by sharing personal experiences. And they could now cooperate much more effectively than ever before.
As cooperation between the sexes improved, the female body evolved more towards facilitating reproduction, while the male body evolved for more aggressive and physically demanding tasks such as hunting large animals and protecting the group. Women focused more on maintaining the camp, gathering and preparing food, and caring for family members.
Men and women were drawn together by shared interests and powerful sexual desires. The deeper emotional attachments that grow through familiarity then helped them stay together to share in the training of their children for adult life.

Human migration

Early humans lived in family tribes that moved around the countryside following herds of wild animals and gathering different fruits as they came into season. They slept in caves or made simple shelters under trees. Clothes were made from animal skins. Hand axes were the all purpose tools. Warm clothes and effective weapons allowed them to slowly migrate to colder climates and less fertile environments.
They spread across Africa, Europe, and Asia in waves of migration that continued for hundreds of thousands of years. Each new wave either wiped out the previous inhabitants or interbred with them. Interbreeding had the advantage that any successful qualities of the new arrivals were combined with native adaptations that suited the local geography and climate. The results can be seen today. Modern humans all share similar abilities to our last common ancestor, but we come in a variety of shapes and colors.

The development of culture

As speech gradually improved over the last hundred thousand years, people began to entertain each other with stories about things they had seen or heard. Casual conversations became an important force in shaping human behavior. People were forced to restrain themselves and show more respect for others. Wrongdoers would be shamed by the rest of the group. Over time, each tribe developed its own set of rules to reduce conflict in areas such as leadership, ownership, and sexual relationships.
Human consciousness was slowly awakening, but people had nothing more than their imaginations to help them understand their place in the world. They sensed powerful forces at work around them in the mountains, forests, rivers, seas, and in the sky. Some of these forces were kind and generous, others were unpredictable and destructive. They imagined these forces to have feelings and perceived them to be spirits or gods. Believing their lives to be at the mercy of these spirits, they prayed and offered sacrifices to gain their favor and avoid their anger.
Stories about the spirits helped to explain the various mysteries of nature. Often these stories were cleverly devised to promote good communal values and strengthen existing tribal laws. As the most popular myths and legends were passed down from generation to generation, they gained a kind of sacred authority. Many of them became the subjects of ritual songs and dances. People learned common values and gained a common understanding of the world through their shared mythology.
The development of language, laws, and customs marked a turning point in evolution. Evolution would now be more about evolving human cultures rather than evolving human brains. As cooperation improved between groups sharing similar cultures, hostility increased between groups with different cultures. People whose language, laws, and customs allowed them to organize into larger groups, better educate their young, and defend more territory, were more successful at preserving and spreading their culture.

Farming villages

Over the last 2 million years, the earth has been frozen a number of times in what is commonly known as the ice ages. During these periods, many parts of the world became uninhabitable and much of the rest was only marginally productive. The last ice age began around 80 thousand years ago and receded only 12 thousand years ago. As the ice melted away, vast areas of land were revealed. Rivers of fresh water began flowing across fertile plains.
Around 10 thousand years ago, in some parts of the world, people began planting seeds and covering the countryside with food producing plants. The earliest and most successful crops were grasses with large seeds such as barley, wheat, and rice. These grasses were easy to grow, the seeds were high in protein, and they did not need to be eaten immediately. Grass seeds could be kept in storage for months or even years.
Early farming communities also began gathering herds of wild animals. Very few animals were suitable for farming. Most were too aggressive or too nervous to be kept on a farm. Farm animals needed to be easy to feed and have temperaments that were easy for humans to tame. The earliest farm animals were sheep and goats.
The change in lifestyle from hunting and gathering to farming was only made possible in those parts of the world where some wild grasses had large edible seeds, and where some wild animals were suitable for domestication. The river valleys to the east of the Mediterranean were among the first locations in the world to meet these requirements.
People living in the river valleys no longer needed to go searching for food. They had settled on land which could produce abundant quantities of food year after year. Land being farmed could produce hundreds of times more food than land being used to hunt and gather. Plentiful food supplies allowed populations to grow, and permanent farming villages began to appear.
As populations grew to become unsustainable, the farmers spread out and established settlements in nearby lands. With more food, larger populations, better organization, and superior technology, they quickly replaced any earlier inhabitants. Through the taking of slaves and by other means, the new arrivals would often absorb the native people and adopt aspects of their culture and language.
Farming villages were attractive targets for bandits who preferred to use force to take what they needed rather than produce it themselves. Communities could join together to establish a common defense, but they could not hold back larger invasions. Farms would eventually fall under the control of the most powerful bandit army. Successful bandit leaders rose to become regional warlords and kings. Kings maintained their power by fighting off rivals, marrying for alliances, and passing their kingdoms down to their sons.
Innovations such as plowing and irrigation allowed farmers to produce more food with less effort. Surplus food could be traded for clothes, tools, pottery, weapons, and other useful items. Farming villages became towns populated by specialists such as carpenters, merchants, and tailors. People would travel from miles around to trade their goods and services.

The Bronze Age

Naturally occurring lumps of copper could be found in many parts of the world. This reddish brown metal was reasonably soft and could be beaten and shaped into tools, weapons, and ornaments. By around 3000 BC, it was discovered that melting copper and tin together formed a hard metal alloy called bronze. The durability of bronze and its ability to keep a sharp edge led to the development of more sophisticated tools and weapons.
The populations of some of the more fertile parts of the world began to climb into the hundreds of thousands. Towns grew into cities with marketplaces, courts, and temples. They were governed by royal families who ruled from stone palaces and were protected by armies of trained soldiers carrying bronze weapons.
Before the domestication of large animals, the only way for people to travel was on foot, and the only way to carry goods was on their backs. Now animals such as horses, donkeys, and camels were carrying large quantities over long distances in shorter periods of time. The invention of the wheel revolutionized transport. As horse drawn chariots became popular, towns began building stone roads and bridges.

The rise of empires

Trade between kingdoms became essential. Most regions enjoyed at least one advantage in agriculture, mining, forestry, or the production of some other resource. Although greed for resources often led to conquest, nations that traded grew wealthy without the cost of war. New ideas were spread by traders who journeyed to foreign lands.
As the volume of trade grew, merchants needed to keep track of the amount of goods that were being traded. They began keeping records by making impressions in pieces of clay. Clay could be found almost anywhere and was already being used to make pottery. Markings on clay tablets could be easily erased or made permanent by baking them in brick ovens.
As the centuries passed, the markings on clay tablets became more complex and meaningful. New symbols with more abstract meanings allowed writing to be used for more than just trade and commerce. Professional scribes began to record laws, myths, and historic events.
Great wars and invasions were fought by expanding empires seeking to increase their wealth and power. The treasures of neighboring cities were seen as a particularly tempting prize for conquest. But the size of empires was limited by the speed of communication and travel.

Ancient temples

Desperate to give meaning to their confused and often miserable lives, people listened to those who claimed to have special knowledge of the gods. Ancient priests became skilled in the art of crafting idols for the people to worship. Beyond calming people's fears and anxieties about the unknown, religions helped to bind early civilizations together under a common set of beliefs.
Priests worked with kings to prohibit unacceptable acts and promote family and community values. They performed sacred rituals such as crowning kings, sanctifying marriages, and burying the dead. Temples offered ambitious men an alternative path to power. Priests often helped to soften the cruelty of kings by forcing the palace to compete against the temple for the loyalty of the people.

The Iron Age

Iron is one of the most common elements on earth, but it is rarely ever found in its pure metallic form. In ancient times, metallic iron could only be found in meteorites, making it much more valuable than gold or any other precious metal. Only royalty could afford to own weapons made of iron.
Around 1200 BC, people learned how to extract large quantities of iron by smelting iron ore in furnaces. Knowledge of iron spread rapidly through conquest with iron weapons. By 1000 BC, iron had become the chosen metal for tools and weapons throughout the ancient empires. Iron was stronger than bronze and its ore was much easier to find than copper or tin.

The art of writing

In some parts of the world, the symbols used for writing changed to represent sounds instead of whole words. The invention of the alphabet allowed the written word to better reflect the power of speech. Animal skins and papyrus scrolls started to replace clay tablets. The first significant works of literature soon began to appear.
In the centuries that followed, the growing collection of writings continued to inspire new ideas and developments, while at the same time leaving behind a faint sketch of how history unfolded. As the growing populations struggled through wars, famines, and plagues, the battle for survival and the emergence of new ideas now came to depend increasingly on the discovery of new technologies.