Evolution

Living things change over a very long time. These changes happen through traits. Traits are things like eye color. Parents pass these traits to their babies.

Inside every living thing is a tiny code. This code tells the body how to grow. Sometimes the code changes in a small way. These small changes can help a living thing. It might help them live better in their home. This is how all life on Earth grows and changes.

All life on Earth changes over a long time. This is called evolution.

It happens when traits change in a group of living things. Traits are features like eye color. These traits come from DNA. DNA is a molecule that carries instructions for life.

One way evolution happens is through natural selection. This idea was studied by Charles Darwin and Alfred Russel Wallace. It works because traits vary between individuals. Some traits help a living thing survive and have babies. These helpful traits are passed to the next generation. Over time, these traits become more common.

Other changes can happen through mutation. A mutation is a change in the DNA code. Some mutations do nothing at all. Others can be helpful or harmful. Evolution also happens through gene flow. This is when genes move between different groups. For example, mice might move from the coast to the land. This brings new traits to the new group.

All life shares a very old ancestor from long ago. This ancestor lived about 3.5 billion years ago.

Evolution is the way living things change over many generations. It explains why there is so much variety in life on Earth.

This change happens when certain traits become more or less common in a group. These traits are passed from parents to their offspring. Evolution can lead to new species forming or even the loss of species through extinction. This long process has shaped every living thing we see today.

How does this change actually work? It starts with genetic variation, which means individuals in a group are slightly different.

One way this happens is through mutation. A mutation is a change in the DNA sequence. These changes can be helpful, harmful, or have no effect at all. Another way is through gene flow, where individuals move between different groups. For example, mice might move from the coast to the inland.

In the mid-19th century, two scientists helped us understand this. Charles Darwin and Alfred Russel Wallace both thought of natural selection.

Darwin wrote about his ideas in a famous book called On the Origin of Species. Natural selection happens because more offspring are often born than can survive. Because traits vary, some individuals have features that help them survive better. These survivors then pass those helpful traits to the next generation.

We can see the history of life in the fossil record.

It shows a path from tiny microbes to huge, complex animals. All life on Earth shares a last universal common ancestor, often called LUCA. This ancestor lived about 3.5 to 3.8 billion years ago.

Scientists use DNA to see how closely different species are related. They can also look at physical shapes to build a tree of life.

Evolution is not just about old fossils; it is happening now. It helps us understand how bacteria can become resistant to medicine. It also helps people working in agriculture and computer science. You can see evolution in your own family through inherited traits.

Just like you might inherit eye color, living things inherit DNA instructions. These instructions guide how every creature grows and lives in its home.

Evolution is the process of change in the heritable characteristics of biological populations over many generations. It explains how the immense biodiversity of life on Earth developed. This change occurs when evolutionary processes act upon genetic variation within a group. As these processes work, certain traits become more or less common in the population. This shift in traits can lead to the formation of new species, known as speciation. It can also result in changes within a species, called anagenesis, or the total loss of a species through extinction.

To understand how evolution works, we must look at how traits are passed down. These traits are controlled by genes, which are portions of a DNA molecule. DNA is a long biopolymer that encodes genetic information through a specific sequence of bases. The complete set of an organism's genes is called its genotype. The observable physical traits and behaviors resulting from this genotype are called the phenotype. While some phenotypes result from environmental interactions, like a suntan, heritable traits are passed through DNA. Within a cell, these DNA strands are organized into structures called chromosomes.

Natural selection is a primary mechanism driving these changes. This theory was conceived independently by two British naturalists, Charles Darwin and Alfred Russel Wallace, in the mid-19th century. Darwin detailed his ideas in the book *On the Origin of Species*. Natural selection relies on several observable facts. First, organisms often produce more offspring than can survive. Second, individuals in a population vary in their morphology, physiology, and behavior. Third, different traits provide different rates of survival and reproduction, which is called differential fitness. Finally, these traits are heritable, meaning they can be passed to the next generation.

Genetic variation is the essential raw material for evolution. This variation comes from several sources, including mutation, gene flow, and sexual recombination. A mutation is a change in the DNA sequence of a cell's genome. Mutations are the ultimate source of all new genetic variation. They can be beneficial, neutral, or deleterious, which means they are harmful. Sometimes, a large section of a chromosome is duplicated. This duplication provides extra copies of genes that can eventually evolve new functions. For example, the human eye uses four different genes for light sensing that all descended from one ancestral gene.

Another source of variation is gene flow, which is the exchange of genes between different populations. This can happen when individuals move from one area to another, such as mice moving between coastal and inland habitats. In some cases, genetic material moves between different species through horizontal gene transfer. This is very common among bacteria and can lead to the rapid spread of traits like antibiotic resistance. In sexual organisms, variation is also increased through recombination. During this process, organisms exchange DNA between matching chromosomes. This creates offspring with new combinations of alleles, which are different forms of a specific gene sequence.

All life on Earth is connected through a shared history. Scientists believe all living things share a last universal common ancestor, or LUCA. This ancestor lived approximately 3.5 to 3.8 billion years ago. We can trace this history through the fossil record, which shows a progression from early biogenic graphite to multicellular organisms.

While scientists once used physical shapes to reconstruct phylogenetic trees, they now more commonly compare direct genetic sequences. This allows them to see how closely related different species are based on their DNA.

Evolutionary biology is a dynamic field that uses mathematical models and laboratory data to test hypotheses. These discoveries have a massive impact beyond just studying nature. The principles of evolution influence agriculture, medicine, and even computer science. By studying how populations change, researchers can better understand how diseases spread or how to improve crop yields. Evolution is not just a study of the past; it is a framework for understanding the living world today.