Nancy S - Speciation

Title: What is a Species?

Principle(s) Investigated:

(1)  Biological Species Concept defines a population of individuals that actually or can potentially interbreed in nature to produce fertile offspring.

(2) Species evolve over time.  The millions of species that live on earth today are related by descent from common ancestors.

(3)  The broad patterns of behavior exhibited by animals have evolved by natural selection as a result of reproductive success.

(4)  Scientists have found that the original definition of species as groups of organisms with similar morphology does not reflect underlying evolutionary processes.

Standards :

7.3.1  Identify factors that have contributed to the diversity of species

7.3.2  Explain how new species form

7.3.3  Explain how scientists infer evolutionary relationships among species

7.3.4  Explain what causes the extinction of species


(1)  List of Reproductive Barriers (alternatively use reproductive barrier cards)

(2)  List of 14 Species Examples for analysis (alternatively use species cards)

(3)  Worksheet for students to complete analysis of species examples (alternatively use card match ups)


(1)  Review theory of evolution by natural selection.  In particular that evolution leads to the development of new species over time.

(2)  Introduce definition of biological species concept

(3)  Review each of the 8 reproductive barriers (prevent organisms from meeting biological species concept definition and thereby divert organisms to becoming new species).  Provide students with definition sheet, have them fill in the title of the reproductive barrier as you review.

(4) Place students into groups of 3 students each.  Provide each group with the color hand out of 14 species for analysis

(5)  Using the worksheets from step #3, students read about each of the 14 species, compare it to their reproductive barrier sheet, and determine which barrier applies to each species. (analysis).

(6)  Upon group consensus, students write in the worksheet which barrier applies to each of the species examples.

(7)  When all groups are done, review each of the species as a whole class using the power point version of the example species.

Student prior knowledge:

Theory of evolution by natural selection. 

Evolution leads to the development of new species over time.

Adaptation to changes in environment through gene mutation and natural selection.

Gene flow – the result of interbreeding is the movement of genes

Gene pool – same species share a common group of genes


Students will see the logical and sometimes subtle differences in the reproductive barriers that can lead to speciation.  This activity fills in the gaps in the evolution theory by explaining how different species evolve in conjunction with the previously learned concept of natural selection and adaptation.

Questions & Answers:
1.  Why is appearance alone no longer considered sufficient evidence for classifying organisms?

A.  Although organisms can look similar (as seen in many of the examples), there exist many other reproductive barriers that cause speciation of these similar looking organisms (behavioral, temporal, etc.)

2.  Why must the offspring of breeding organisms be capable of reproducing as well? 

A.  Because the offspring must carry on the gene pool in order for the two organisms to continue as a common species.

3. Can two species have more than one reproductive barrier? 

A.  Yes, an example is the lion and tiger.  They are separated geographically.  In addition, their offspring, the liger, is sterile.  So geographic isolation and hybrid sterility both apply.

Applications to Everyday Life:

1.  Geographic Isolation  – students will view barriers such as the Grand Canyon, oceans, rivers, etc. in a new light now as they can serve as reproductive barriers in nature.

2 – Habitat Isolation – students will understand how different habitats within the same geographic area can be so different as to cause the similar species to not meet and reproduce.  Example:  Birds living on different branches of the same tree.

3 – Behavioral Isolation – students will view animal courtship behaviors in a new light, seeing it as a method of speciation, not just animal characteristic behavior.  Example:  Crickets mating call at different pitch.



Lab-Aids, Inc.  -



Norman Herr,
Apr 27, 2011, 4:00 PM
Norman Herr,
Apr 27, 2011, 4:10 PM