Evolution

Evolution is the way living things change over time in groups. These changes happen because of processes like natural selection and genetic drift. They act on small differences in genes. Over many generations, these changes can create new types of plants, animals, and other living things.

The idea of evolution was first explained by Charles Darwin and Alfred Russel Wallace in the 1800s. They saw that animals often have more babies than can survive. Each animal is slightly different, and some differences help them live better. These helpful differences can be passed to new babies.

Today, we know that the instructions for traits are stored in DNA. Changes in DNA, called mutations, can create new traits. When people or animals move between groups, this is called gene flow. All living things share a common ancestor from billions of years ago. Through evolution, we have many different species today.

Studying evolution helps us understand biology and other fields like computer science. Scientists look at fossils, DNA, and nature to learn how life changes over time.

Heredity

Further information: Introduction to genetics, Genetics, and Heredity

Evolution happens when the traits we get from our parents change over time. For example, in humans, eye colour is something we inherit. If one of your parents has brown eyes, you might have brown eyes too. These traits come from tiny parts called genes, which are found in every cell of our body. All the genes together make up our genotype.

We also have a phenotype, which is what we look like and how we behave. This is because of our genes and our environment. For example, getting a suntan depends on both our genes and how much sunlight we get. Some people, like those with albinism, don’t tan at all. These differences show how genes can affect what we see in ourselves and others.

Sources of variation

Main article: Genetic variation

Further information: Genetic diversity and Population genetics

Evolution can happen when there are differences in the genes of a group of living things. These differences come from changes in DNA called mutations, the mixing of genes during sexual reproduction, and the movement of genes between groups (gene flow). Even though new differences appear, most genes in a group stay very similar.

Mutations are changes in the DNA sequence and are the main source of genetic differences. These changes can affect how a gene works, stop it from working, or have no effect. Sometimes, mutations can make extra copies of genes, which can help create new genes with new functions. For example, the human eye uses several genes that all came from one original gene.

In asexual organisms, genes are passed on together, but in sexual organisms, offspring get a mix of genes from both parents. This mixing increases genetic differences and can make evolution happen faster. Gene flow happens when genes move between different groups of organisms, either through the movement of individuals or through processes like the transfer of pollen. This can bring new differences into a group.

Some changes that can be passed down are not changes in DNA sequences but are due to other factors, such as changes in how genes are turned on or off. These are called epigenetic changes and can also affect how organisms change over time.

Evolutionary forces

From a neo-Darwinian view, evolution happens when the types of genes in a group of living things change over time. This can happen in a few ways.

Natural selection is when traits that help a living thing survive and have babies become more common later. This is because those with helpful traits live longer and have more babies. For example, if a moth is a color that helps it hide, more baby moths will have that color too. Natural selection can work in different ways.

Genetic drift is when gene types change randomly from one group to the next. It can make some gene types more common or even gone just by chance, especially in small groups. This is different from natural selection.

Mutation bias means some types of changes in genes happen more often than others. These differences can change genes over time, but natural selection usually has a bigger effect on traits.

Natural outcomes

Evolution changes how living things look and act. It helps them find food, stay safe from predators, and find mates. Animals can also work together, usually to help family or through helpful symbiosis. Over time, evolution can create new species when groups of the same species can no longer breed with each other.

Evolution does not have goals. It does not always make things more complex. Even though complex species exist, simple life is still very common. Studying tiny organisms helps scientists watch evolution happen because they reproduce quickly.

Adaptation

Adaptation makes animals better fit to where they live. It can give new features or take away old ones. Sometimes parts of an animal’s body change but keep the same basic design. Other times, body parts lose their purpose and become smaller.

Coevolution

Animals and plants can affect each other. When two kinds of living things interact, like a pathogen and a host, they can change together over time.

Cooperation

Some changes between species help both. Animals of the same kind can also work together. A good example is eusociality in social insects like bees, termites, and ants.

Speciation

Speciation happens when one species splits into two or more new species. This needs barriers that stop the groups from breeding together. Scientists have seen this happen both in labs and in nature.

Extinction

Extinction is when a whole species disappears. This happens often as new species form and others vanish. The Cretaceous–Paleogene extinction event, when dinosaurs disappeared, is very famous. The Permian–Triassic extinction event was even bigger. The Holocene extinction is happening now because of human activity.

Applications

Evolutionary ideas help us in many ways. We can choose traits we like in plants and animals. This is called artificial selection. People have done this for thousands of years. Scientists now use this idea to create new medicines and useful proteins.

Understanding evolution helps doctors treat diseases. Germs like bacteria and viruses can change over time. Learning about evolution helps scientists create better treatments. The same idea is used in computers to solve tricky problems and design new technology.

Evolutionary history of life

See also: Timeline of the evolutionary history of life

The Earth is about 4.54 billion years old. The earliest signs of life on Earth go back to at least 3.5 billion years ago. Scientists have found tiny fossils and special materials in very old rocks that show life existed a very long time ago. Over time, life changed and evolved into the many different plants and animals we see today.

All living things on Earth share a common ancestor. This means every living thing comes from one original group of organisms that lived a very long time ago. As time passed, these organisms changed and formed new species. We can see evidence of this shared history in many ways, such as similarities in body shapes and the chemicals inside our cells. Even the tiny instructions inside our cells, called DNA, show how closely related different animals are.

History of evolutionary thought

Main article: History of evolutionary thought

Further information: History of speciation

The idea that one type of living thing could come from another goes back to early Greek thinkers like Anaximander and Empedocles. Later, during Roman times, the poet Lucretius wrote about these ideas in his work De rerum natura.

During the Middle Ages, many believed that all nature followed a divine plan, where every creature had a special role. However, some Arab scholars, like Ibn Khaldun, thought that humans might have evolved from earlier life forms.

In the 17th century, the Scientific Revolution began to question old ideas. Scientists started searching for natural explanations instead of divine ones. John Ray and later Carl Linnaeus helped sort living things into groups, though they still believed each group stayed the same.

Many scientists before Charles Darwin wondered if species could change over time. For example, Jean-Baptiste Lamarck thought animals could pass on traits they gained in life to their babies.

The big change came with Darwin and Alfred Wallace. They both suggested that species change through a process called natural selection. In nature, more animals are born than can survive. Those with helpful traits are more likely to live and have offspring. Over many generations, this can create new species. Darwin shared these ideas in his famous book, On the Origin of Species. His work changed how we see the natural world.

Main article: Modern synthesis (20th century)

In the 1920s and 1930s, scientists combined Darwin’s ideas with new findings about genes. This became known as the modern synthesis. It showed how natural selection works with genes to shape life over time.

Since then, scientists have kept discovering more. For example, we now know how DNA carries genetic information. There are also new ideas about how evolution works, like studying how changes during an animal’s growth can affect future generations.

Social and cultural responses

When Charles Darwin published his book On the Origin of Species in 1859, his idea that all living things change over time caused big debates. Many people thought about what this meant for religion and society. Today, most scientists agree with evolution, but some people still have questions about it.

Some religions have found ways to believe in both their teachings and evolution. Others feel that evolution does not match their religious stories and have concerns about it. One big debate happened in the United States, where some people wanted to teach creationism instead of evolution in schools. Courts decided that creationism and a later idea called intelligent design cannot be taught as science in public schools. These discussions have not been as big in places like China.