Evolution of life

The story of our evolution from star dust

In the beginning, space opened up and was filled with an enormous burst of energy. As the energy radiated out, it cooled and began condensing into matter. Within a fraction of a second, most of it had condensed into subatomic particles. After hundreds of thousands of years, those particles condensed into atoms.

Galaxies formed as vast clouds of atoms were attracted by gravity and crushed together. The crushed atoms fused and ignited into nuclear fireballs to become stars. Today's universe contains hundreds of billions of galaxies, each containing billions of stars. The universe has been expanding now for almost 14 billion years.

Stars release enormous amounts of energy by converting lighter elements like hydrogen into heavier elements like carbon and iron. Most 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 sometimes explode, scattering their elements across space.

Our solar system was formed out of a cloud of gas mixed with dust and rubble from nearby stars that had exploded. As it was pulled in and crushed by gravity, it ignited into life as a medium-sized star, our Sun. Most of the remaining rocks collided and were fused together by heat to form the planets and their moons.

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 cooled down, clouds of steam condensed and rain poured down to form rivers, lakes, and oceans.

The spark of life

Common elements like hydrogen, carbon, and oxygen are 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 than it is for them to be found in their pure form.

Carbon atoms easily bond with other atoms to form long complex chains of atoms known as organic molecules. These molecules can continue bonding to form even longer and more complex chains, with no clear limit to how long and complex they can become.

Billions of years ago, conditions on earth were favorable for the formation of organic molecules. These molecules washed into the sea to form pools of organic matter on the sea floor, where they kept joining and growing for millions of years.

Life began when one of these complex organic molecules reacted with the surrounding material in an unusual way. It attracted all of the parts it needed to assemble an identical copy of itself. The copy then split away from the original and began assembling its own new copy.

These self-replicating molecules may not have lasted long before they were broken down by chemical reactions, but they were still able to spread through the pool of organic material fast enough to keep the reaction going.

The copies they made were 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 flawed copies were still able to replicate, but occasionally, by pure chance, a new molecule was created that could survive longer or replicate faster than its parent. The evolution of life on earth had begun.

Over millions of years and countless mutations, some molecules evolved a protective barrier. The material needed for replication could still pass through this barrier, but the replicating molecule was now safer from harmful reactions, allowing the machinery of life to become much more complex.

After hundreds of millions more years of evolution, they became cells containing an assembly line of molecules, all working together to give the whole cell everything it needed to thrive and multiply.

The process of evolution

Evolution happens 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 descendants 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 adapts to changing conditions, and the better it competes with rival forms of life. The rate of mutation also balances the survival of enough healthy offspring against the energy required to make perfect copies.

Larger populations have a higher chance of producing a beneficial mutation. But then a considerable length of time may need to pass before the mutant population grows large enough to have a good chance of producing another beneficial mutation.

This problem was overcome by the appearance of sexual reproduction. By combining the mutations from two separate ancestries, beneficial mutations can spread back into an existing population, exponentially increasing the rate of evolution.

After an organism's 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 a parent can contribute to its offspring versus how heavily the parent must compete against its offspring for resources.

Multi-celled organisms

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, like algae, could convert sunlight into chemical energy. Other cells got their energy from consuming nearby cells as food.

Some cells evolved tiny arms that could propel them 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, some algae cells joined together to form sheets which became the first primitive form of seaweed.

A few hundred million years later the first multi-celled animals appeared. The most successful of these were small, flat, worm-like creatures that absorbed algae directly through their skin.

Some of these evolved the ability to wrap themselves around food, and release digestive juices onto the food to break it down before absorbing the nutrients. This evolved into an opening where food could be drawn in, digested more efficiently, and then passed out.

An animal's survival depended on its ability to sense its surroundings, and these worm-like creatures had inherited senses from their single-celled ancestors. A complex network of sensory cells around the mouth could detect chemicals released by food. Signals were sent along nerve cells, triggering muscle cells to expand and contract, wriggling the animal towards the food.

Evolution strongly favored any mutation to this network of cells that might drive the animal to find more food, avoid danger, or breed more. This led to the rapid development of complex behavior.

Yet it was not enough to always react 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.

Animals were evolving into something that might be described as 'opportunity-seeking biological machines': driven to satisfy their needs, stimulate their senses, find the things that bring them pleasure, and avoid the things that give them pain.

Predators and prey

While most early animals grazed on algae, some of the larger ones began feeding on the smaller ones. Some adapted by evolving protective shells. While these armored animals crawled along the sea floor, others gained an advantage by swimming through open water, propelling themselves with a side-to-side motion made more efficient by the evolution of a backbone.

Early animals were very successful at swimming around, looking for food, and finding partners to mate with. Populations grew and they spread throughout the oceans and rivers, continuing to evolve and adapt to take advantage of new environments.

As long as food was abundant and partners were easy to find, there was little to stop new variations from flourishing. This era was like a 'trying out' period for new animal designs. Within a relatively short time, the earth's waters were filled with a vast array of exotic animals of diverse shapes and sizes.

After millions more years of evolution, predators became larger, faster, and smarter. Only the smaller creatures that could swim faster, burrow into the sand, or hide inside 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. This 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 descendants are still alive today.

Plants and animals

Shallow water provided a fertile environment. Plants living on the water's edge were able to gain more nutrients by anchoring themselves into the mud and branching towards the surface to collect more sunlight.

Shallow water plants and animals were regularly exposed by rising and falling tides. Rivers and lakes became dangerously shallow in times of drought. Anything living in the shallows needed to survive longer out of the water by becoming weatherproof and supporting their own weight.

Plants that could survive entirely on the land appeared around 500 million years ago. Once they had taken their first step, little could stop them from spreading across the empty continents, thriving in regions with regular rainfall and nutrient-rich soil.

They evolved rapidly, adapting to new landscapes and climates. Within a few hundred million years, the land was covered by a dense forest of trees with branches and leaves.

Plants were soon followed onto the land by animals with protective shells. As they crawled onto the land they evolved into insects and spiders. Within a hundred million years, some evolved wings and could fly.

Fish living in shallow water swamps and wetlands needed to propel themselves through the mud and vegetation. This favored fins with stronger muscles and longer bones. The tips of their fins became more claw-like. Gills were less effective in shallow muddy water so they evolved lungs to draw more air from the surface.

By around 375 million years ago, some animals evolved to spend as much time crawling over mud as they did swimming through water. However, these animals did not conquer the land until their eggs had evolved tough waterproof shells allowing them to be laid out of the water.

Warm-blooded animals

The temperature of seawater does not vary much. Animals living in the sea keep a relatively constant body temperature. Moving onto the land meant surviving a wide range of temperatures, with cold nights and cold winters. The chemical reactions inside cells are sensitive to temperature. As the temperature drops, reactions become slower.

Reptiles depend on the warmth of the sun. They become sluggish at night and in cold weather. They only live in regions with mild winters. Their cells do not generate enough energy to actively hunt for food. They usually wait for prey to come near. Their four legs sprawl from the sides of their bodies to help move them through the wetlands they thrived in.

Around 260 million years ago, a new family of animals adapted to the land by evolving warm blood and legs positioned beneath their body, allowing 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 survive in colder climates. These were the ancestors of mammals, and they came to dominate a landscape rich with plant and insect life.

Maintaining a high body temperature requires a lot of energy. Warm-blooded animals use up to ten times more energy than cold-blooded ones do. They need to find food and eat at more regular intervals. They also grow faster, reproduce more, and evolve more rapidly. By burning energy faster, they also gained the advantage of quicker thinking.

Dinosaurs and mammals

The earth is a molten rock orbiting a nuclear fireball. The thin rocky crust on which we live often shifts and shakes. Asteroids and comets collide with such impact that everything within a thousand miles is incinerated. Forest fires and volcanic eruptions can fill the air with toxic smoke and dust, blanketing the sky for months or even years. Plants either freeze or they wither as they are starved of sunlight. Food becomes scarce and almost everything dies.

Our survival has always depended on staying lucky enough for the atmosphere to be breathable and for temperatures not to freeze or fry us.

Life on earth has almost been wiped out several times, but in the calm between mass extinctions, dinosaurs appeared. These monsters also benefited from warm blood, but their body weight was shifted back so they could stand on two legs, allowing them to run faster and reach higher than four-legged mammals. In the fierce competition for the position of top predator, dinosaurs proved superior to mammals and soon came to dominate the land.

As some dinosaurs evolved to become enormous, mammals evolved into tiny creatures scurrying beneath their feet, living in underground burrows, often in colder regions, only emerging at night to hunt for insects. They adapted by growing fur and 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 receiving nutrients from their mother's milk.

Around 66 million years ago, a huge asteroid slammed into the earth, wiping out all the large land animals and many of the smaller ones. The only dinosaurs to survive were small ground-dwelling birds, scratching the scorched earth for seeds and grubs.

Also among the survivors were small furry mammals, kept safe in their burrows, well adapted to the cold and dark. No longer dominated by dinosaurs, mammals could now rapidly evolve into a vast array of shapes and sizes to take advantage of all of the opportunities left behind by the extinction of dinosaurs.

Although there appear 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 basic 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 with only minor changes to those parts of the genetic code 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.

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 family members. Mammals evolved an extra layer of brain tissue surrounding the instinctual part of their brain, which helped them override their instinctual behavior with learned skills.

The more that animals 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 family. 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 learning evolved, animals also evolved stronger emotional attachments. Strong instinctual feelings of affection drove parents to care for their children, and children to imitate their parents. This kept family members together long enough for the young to learn how to survive.

Humans

While most mammals adapted to living on the ground, some adapted to living in trees. Trees were safe from most predators and provided a rich diet of fruit and insects. Some tree dwellers evolved fingers and thumbs for grasping onto branches. Long snouts were awkward in trees, so their faces became flatter and their eyes moved to the front of their face, allowing better judgment of distance when leaping between trees.

Animals that live on the ground often need to be able to walk soon after they are born. But tree dwellers can cling to their mothers the same way their mothers clung to trees. Being carried around and cared for by their mothers for longer allowed their brains to evolve to depend more on learned behavior and less on instinct.

Some tree dwellers grew too large to walk across the tops of branches and began swinging beneath them instead. Their bodies grew too heavy for their tails to counterbalance, so they lost their tails and developed a more upright posture to keep themselves balanced. Fewer branches could support their weight, so instead of leaping between trees, they climbed down and walked between them.

Around 7 million years ago, some of these ape-like creatures moved out of the deep forest into woodlands and grasslands. As they spent less time in trees, evolutionary pressure favored walking on two legs. With their hands no longer needed for walking, they could hunt and gather food more effectively, using sticks and stones as weapons.

They could now hunt larger animals and carry the meat home to share with the rest of the tribe. Providing better care for their increasingly helpless infants allowed them to continue evolving larger brains more adapted towards learning. They broke stones apart to create sharp edges for cutting wood, meat, and bone. Around a million years ago, they learned how to keep fires burning and began cooking their meals.

Competition between 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 replaced groups that did not.

The shift towards learning was accompanied by an increased sense of curiosity. When a group member discovered a new way of doing something, others would watch and imitate the idea. Older members of the group might be slow to change their habits, but 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 using sounds and body gestures to express their feelings. As the sounds made by early humans became more controlled and meaningful, grunting evolved into words and sentences. They could now cooperate much more effectively, learn more from each other, and develop closer relationships by sharing experiences.

Early human tribes roamed the countryside, following herds of wild animals and gathering different fruits as they came into season. They slept in caves and made simple shelters under trees. They wore clothes made from animal skins. Hand axes were the all-purpose tool. Warm clothes and effective weapons allowed them to 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 replaced 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.

Culture

As speech improved, and people spoke about what they had seen or heard, casual conversations became an important force in shaping human behavior. People were forced to restrain themselves and show respect for others. Wrongdoers would be shamed. Each tribe developed rules to reduce conflict in areas such as leadership, ownership, and sexual relationships.

Early humans had little more than their imaginations to help them understand their place in the universe. 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 favor and avoid angering the spirits.

Stories about spirits were often devised to give life lessons or strengthen tribal laws. As they were passed down from generation to generation, they gained sacred authority, and became the subject of ritual songs and dances. People learned common values and gained a common understanding of the world through their shared mythology.

Language, laws, and shared stories marked a turning point. From now on, evolution would be less about evolving brains and be more about evolving human cultures.

© Cosmic Nexus