Change Over Time Concept Map
Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced conditions that were different from those on the mainland. Perhaps, Darwin hypothesized, the species gradually changed over many generations and became better adapted to the new conditions.
The gradual change in a species over time is called evolution.
Darwin concluded that the living things that came to the Galapagos Islands from the mainland had changed over time. The living things changed so that they could live better in the island environment.
Darwin s ideas are often called the Theory of Evolution. A scientific theory is a well tested idea.
Darwin proposed that, over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear.
Darwin suggested that evolution happens because of natural selection. In natural selection, individuals that are better adapted to their environment are more likely to survive and reproduce.
Factors that affect natural selection are overproduction, competition, and variation.
Most species produce far more offspring than can possibly survive. Overproduction makes it more likely that some offspring will survive.
Food and other resources are limited. Members of a species must compete with each other for these resources. Some members of a species may not find enough to eat, so they do not survive.
Any difference between individuals of the same species is called a variation.
Some variations make individuals better adapted to their environment. Individuals that are better adapted are more likely to survive and produce more offspring. Their offspring may inherit these helpful variations. After many generations, more members of the species will have the helpful variations.
Variations in characteristics are caused by mutations and the shuffling of alleles are meiosis.
Fossils, patterns of early development, and similar body structures all provide evidence that organisms have changed over time.
Fossils show that living things from the past were very different from the living things of today.
Scientists study what organisms look like when they are just beginning to develop. For example, the early stages of all animals (embryos) of all animals with backbones all look similar. Patterns of early development can show that animals are related. These animals share common ancestor that evolved over time into different species.
How bones arranged in the body also gives clues to evolution. Many animals with backbones have body structures that do different thinks, but the bones are arranged in the same way. This shows that the animals evolved form a common ancestor.
DNA and proteins also give clues to how different species are related. The more alike DNA and protein structures are, the more closely related the species are.
After studying DNA and protein structures, along with fossils, early development, and body structures, scientists have a good idea about how species are related. To show these relationships, scientists draw branching tree diagrams.
A new species can form when a group of individuals remains isolated form the rest of its species long enough to evolve different traits. Rivers, canyons, and mountains can separate a small group of individuals from the rest of it species.
The millions of fossils that scientists have found are called the fossil record. Types of fossils are molds, casts, and petrified.
Almost all of the species found as fossils are now extinct. A species is extinct if no members of that species are still alive. Most living things died without leaving fossils behind so the fossil record is not complete. Because of these missing fossils, scientists still have questions about what really happened in Earth s history.
By studying the fossil record, scientists have created a calendar of Earth into units of time called eras (longer periods of time) and periods (shorter periods of time). The calendar of Earth s history is called the Geologic Time Scale.