New species arise in the process of speciation. Allopatric speciation occurs when some members of a species become geographically separated. Sympatric speciation occurs without geographic separation. Coevolution occurs when species evolve together. Darwin thought that evolution occurs gradually. This model of evolution is called gradualism. The fossil record better supports the model of punctuated equilibrium.
- CA.9–12.IE.1.g; CA.9–12.LS.8.d
- NSES.9–12.C.3.5; NSES.9–12.C.6.3
- AAAS.9–12.1.A.3; AAAS.9–12.11.B.3; AAAS.9–12.11.C.6
- Describe two ways that new species may originate.
- Define coevolution, and give an example.
- Distinguish between gradualism and punctuated equilibrium.
allopatric speciation: evolution of a new species that occurs when some members of an original species become geographically separated from the rest of the species
coevolution: process in which two interacting species evolve together, with each species influencing the other’s evolution
gradualism: model of the timing of evolution in which evolutionary change occurs at a slow and steady pace
punctuated equilibrium: model of the timing of evolution in which long periods of little evolutionary change are interrupted by bursts of rapid evolutionary change
speciation: process by which a new species evolves
sympatric speciation: evolution of a new species that occurs when without geographic separation first occurring between members of an original species
Introducing the Lesson
Impress students with the incredible diversity of species. Tell them that there are tens of millions of species alive on Earth today, most of which have yet to be identified, and they represent only 1 percent of all the species that ever lived on Earth.
- Ask: How did all these species evolve? (Encourage multiple responses.)
- Tell students they will learn how new species evolve when they read this lesson.
With the class, do the quick speciation activity at the URL below. It is an effective way to show students how new species could evolve through genetic drift.
All your students and especially visual learners will have a better understanding of speciation if they do the tutorial at the URL below. It provides a clear, well-illustrated explanation of the species concept and ways that speciation can occur. It covers all the lesson topics.
Interested students can read about the diversity of evidence for macroevolution at the URL below. Ask them to summarize the evidence for the class.
Assign the case study “Something Fishy in Paxton Lake” at the URL below. In the activity, students will design an experiment to test the hypothesis that speciation has occurred in stickleback fish in the lake.
A widely believed misconception is that “missing links” disprove evolution. Explain why transitional forms may be less likely to form fossils according to the punctuated equilibrium model of evolution.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Biology Workbook. Ask students to complete the worksheets alone or in pairs as a review of lesson content.
Have students answer the Review Questions listed at the end of the lesson in the FlexBook®.
Points to Consider
You read in this chapter about adaptive radiation on the Galápagos Islands. A single finch species evolved into many new species to fill all available niches. For example, the species evolved adaptations for a variety of food sources.
- What is a species’ niche? What do you think it might include besides the food a species eats?
- Niche is a term from ecology. What is ecology? How do you think knowledge of ecology might help scientists understand evolution?