Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
Biology for AP® Courses

Introduction

Biology for AP® CoursesIntroduction
Search for key terms or text.
The photo on the left shows large, stalk-like saguaro cacti with multiple arms, and the photo on the right shows a lizard on a rock.
Figure 18.1 All organisms are products of evolution adapted to their environment. (a) Saguaro (Carnegiea gigantea) can soak up 750 liters of water in a single rain storm, enabling these cacti to survive the dry conditions of the Sonora desert in Mexico and the Southwestern United States. (b) The Andean semiaquatic lizard (Potamites montanicola) discovered in Peru in 2010 lives between 1,570 to 2,100 meters in elevation, and, unlike most lizards, is nocturnal and swims. Scientists still do no know how these ectotherms, which rely on external sources of body heat, are able to move in the cold (10 to 15°C) temperatures of the Andean night. (credit a: modification of work by Gentry George, U.S. Fish and Wildlife Service; credit b: modification of work by Germán Chávez and Diego Vásquez, ZooKeys)

Chapter Outline

18.1 Understanding Evolution
18.2 Formation of New Species
18.3 Reconnection and Rates of Speciation

The field of biology is a diverse one that includes the study of organisms from the small and simple to the large and complex. From biological molecules to biomes, the one theme that remains consistent is evolution. All species of living organisms are descended from a common ancestor. Although it may seem that living things today stay much the same, this is not the case. Evolution is actually an ongoing process. Additionally, new species are discovered regularly. For example, scientists have used a method called fluorescent in situ hybridization, which uses fluorescent probes to locate specific genes on chromosomes, to discover a green sea slug that can perform photosynthesis just like a plant.1 The slug obtains genes related to photosynthesis from the algae it eats through a process called horizontal gene transfer. In this process, genes can be transferred directly from one cell to another. The algal genes code for products that repair and maintain chloroplasts eaten by the slug. You can read more about it at this website.

Teacher Support

The ongoing process of evolution includes the repeated formation of new species (speciation), changes within species (anagenesis), and death of species (extinction). Patterns in shared morphological and biochemical traits, including shared DNA sequences, can be used in constructing a diagram that illustrates the biodiversity, taxonomic links, and evolutionary history of extinct and extant living things. Such diagrams are commonly called “The Tree of Life.”

You may wish to share a tree of life diagram with students and use the diagram alongside facts about the rates of extinction (historically and currently) and species estimates versus species documentation to guide a discussion about evidence for evolution as an ongoing process. Ask students to discuss where in their daily lives they are aware of evidence of speciation, anagenesis, and extinction. Through discussion, elicit from students the importance of considering scale (both temporal and physical) when considering evidence of evolutionary change. Ideas and thoughts shared during this discussion may prove to be helpful reference points when students read about misconceptions of evolution later in the chapter.

Footnotes

  • 1Biol. Bull. 227: 300–312. (December 2014)
PreviousNext
Order a print copy
Citation/Attribution

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at https://openstax.org/books/biology-ap-courses/pages/1-introduction
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at https://openstax.org/books/biology-ap-courses/pages/1-introduction
Citation information

© Feb 10, 2025 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.