The importance of evolution to the study of biology was stated best by Theodosius Dobszhansky, who said, "Nothing in biology makes any sense except in the light of evolution." While most of biology attempts to describe what the natural world is like, evolution explains how and why it became that way. The forces that drive changes in species are vital to an understanding of life itself.

Evolution, it is often grinningly said, is an evolving science. Ideas about evolution have changed dramatically throughout history. Many cultures have ancient creation myths that explain the origin of the earth and the forms of life found on it. Many of these stories include explanations of how plants of animals gained the forms they have today. In Western cultures, ideas about evolution were originally based on the Bible. The book of Genesis relates how God created all life on earth about 6000 years ago in a mass creation event. Proponents of creationism support the Genesis account and state that species were created in the forms they hold today. This oldest formal conception of the origin of life is still supported by some today.

However, about 200 years ago, evidence began to surface that cast doubt on creationism. As we will discuss in Evidence of evolution, fossilized remains of plants and animals, observation of natural population, and other lines of evidence suggested that species have not always held the forms they do today. The evidence lead to an increased interest in the idea of evolution. That species might change over time was first suggested by Count George-Louis Leclerc de Buffon. It was later popularized by his student, Jean-Baptiste Lamarck, who added a possible mechanism by which this change might take place. However, it was not until 1859, when Charles Darwin wrote his book, On the Origin of Species, that the modern study of evolution began to take shape.

Charles Darwin is considered the father of modern evolution. In On the Origin of Species, he outlined his view that species not only changed over time, but had been doing so for a very long time. Darwin proposed these changes occurred through time according to a mechanism called "survival of the fittest" or natural selection. Unfortunately, Darwin could not explain how natural selection caused the change in species he observed because the field of genetics had not yet been discovered, much less studied. In the early 1900's, however, genetics became widely studied, and Darwin's theory found support in the evidence uncovered in this and other fields. In the 1940's, scientists from the fields of experimental genetics, population genetics, natural history, and paleontology pooled the evidence from their fields to create a modern theory of evolution that included a genetic explanation for Darwin's mechanism of natural selection. This theory, called the modern synthesis, is the most widely accepted theory of evolution today.

In the Sparknotes on evolution, we will first look at the history of ideas about evolution. We will examine thinkers before Darwin and take a closer look at Darwin's work. Next, we will explore the lines of evidence for evolution used by evolutionary biologists today and how that evidence was combined with Darwin's theory to create the modern synthesis.

After that we will take a look at what the modern study of evolution has taught us so far. We will examine the different forms natural selection can take and how it can result in the formation of new species. Next we will investigate populations. We will see how populations can experience reproductive isolation and we will learn a mathematical model for studying population genetics.

Finally, we will take a look at larger patterns in evolutionary history. We will see the types of evolution that can occur and how those types have shaped the history of life on earth.