Chapter 2: “Reproduction and Survival” Lesson 3: “Change Over Time” Life Science Chapter 2: “Reproduction and Survival” Lesson 3: “Change Over Time”

What is natural selection? Dramatic changes have occurred on Earth over time. Climates have changed. Forests have become deserts. Seas have dried up. These changes affect the organisms in these environments. Organisms must change in order to survive. A population is all the members of a single species living in the same geographic area. Variations result from changes in an organism’s genetic material.

What is natural selection? (Continued) Natural selection is a scientific theory presented by Charles Darwin which states that… An organism with favorable variations is well suited to its environment. An organism with favorable variations is more likely to survive and reproduce than other organisms. These favorable variations will be passed on to the next generation. Over time, offspring with favorable variations make up a greater percent of a population. Because the organisms with the most favorable traits survive, Darwin’s theory is sometimes called “survival of the fittest.”

What is natural selection? (Continued)

What is natural selection? (Continued) Throughout Earth’s history, many organisms have emerged and many have also become extinct. An extinct species no longer exists anywhere on Earth. Species become extinct because they can no longer adapt.

What is evidence of change over time? Any remains, traces, or imprints of organisms that lived long ago are called fossils. Fossils provide clues that tell us how environments have changed. It is believed that Mississippi was once covered by water. We know this because of the fossil remains of the Basilosaurus.

What is evidence of change over time? Scientists also use fossils to determine the past climate of an area. Fossils also provide clues about what organisms were like in the past and how they have changes. Earth’s history is marked by geologic and climatic change. Fossil evidence indicates that species change over time to survive.