Chapter 13: How Populations Evolve

13.0 Biodiversity is the Product of Evolution

Life on Earth is characterized by a remarkable diversity of species, shaped over millions of years by the process of evolution. This diversity is evident in ecosystems such as the Sonoran Desert, which hosts a wide variety of plant and animal species adapted to its unique environment.

• Biodiversity refers to the variety of life forms within a given ecosystem, biome, or the entire planet.

• Evolution is the process by which different kinds of living organisms have developed and diversified from earlier forms during the history of the Earth.

• Scientists estimate that more than 8.1 million species have been identified, with many more yet to be discovered.

• Evolution explains both the unity (shared ancestry) and diversity (adaptation to different environments) of life.

Example: The Sonoran Desert's unique flora and fauna, such as cacti and lizards, illustrate how species adapt to specific environmental conditions through evolutionary processes.

Big Ideas of the Chapter

• Darwin’s Theory of Evolution (Sections 13.1–13.7): Explains the adaptation of organisms and the unity and diversity of life through natural selection.

• The Evolution of Populations (Sections 13.8–13.11): Describes how genetic variation makes evolution possible within a population.

• Mechanisms of Microevolution (Sections 13.12–13.18): Covers natural selection, genetic drift, and gene flow as processes that drive changes in populations over time.

Pretest: Key Concepts in Evolution

Before studying the details of evolution, it is helpful to review some foundational concepts:

1. Darwin’s Observations: Charles Darwin made critical observations about the diversity of life during his travels, especially in the Galápagos Islands, which contributed to his theory of evolution by natural selection.

2. Homologous Structures: Structures in different species that are similar due to shared ancestry (e.g., the forelimbs of humans and whales) are called homologous structures. These provide evidence for evolution.

3. Mechanisms of Evolution: Natural selection is the primary mechanism by which evolution occurs, but other mechanisms such as genetic drift and gene flow also play important roles.

Key Terms and Definitions

• Natural Selection: The process by which organisms better adapted to their environment tend to survive and produce more offspring. This is a key mechanism of evolution.

• Genetic Variation: Differences in DNA sequences among individuals within a population, which provide the raw material for evolution.

• Microevolution: Small-scale evolutionary changes within populations, typically described by changes in allele frequencies over time.

• Homologous Structures: Anatomical features that are similar in different species because of common ancestry.

Table: Mechanisms of Evolution

Summary

• Evolution is the unifying theme of biology, explaining both the similarities and differences among living organisms.

• Darwin’s theory of evolution by natural selection provides a scientific explanation for the adaptation and diversity of life.

• Understanding evolution is essential for studying all aspects of biology, from genetics to ecology.