Purpose: The purpose of this activity is to understand how new species can form from old species through the mechanisms of evolution covered so far in the unit (mutation, genetic drift, changes in environmental conditions, and natural selection).

Connection to previous activities: Students refer to the mechanisms of mutation (introduced in the last activity), genetic drift (from the activity before that), changes in environmental conditions and natural selection (from two previous activities), to develop the explanations for the outcomes in this activity.

Learning Performances

• Analyze data from a computer investigation applying concepts of statistics and probability to explain why adaptations for reproductive isolation can help reinforce specialized adaptations for survival for different niches within different gene pools in a population. [Emphasis is on analyzing shifts in numerical distribution of traits in a histogram and using these shifts as evidence to support explanations.]

Scientific Principles Discovered in This Activity:

• New species emerge from old species (a group of organisms that is capable of interbreeding only between each other to produce fertile offspring).

• Speciation can occur when specialization for survival in different niches is available to a population; this specialization opportunity can tend to reinforce adaptations that lead to greater reproductive isolation between those populations.

• Speciation can occur when geographic isolation leads to separate populations that through mutation and genetic drift, develop genes and corresponding traits that make descendent from each population less reproductively compatible with each other over time.

Description of the Lesson

The class revisits their definition of a species and discusses whether genetic drift alone could account for why new species emerge.

They then use a computer model of plants in an ecosystem to explore how speciation always could also emerge from a single population over time under certain conditions.

Through discussion, the teacher helps build consensus about why speciation might occur when mutation initiates the pathway to speciation, but natural selection and adaptation are the driving mechanisms that continue to reinforce the emergence of this outcome.

In the homework, they study examples of how speciation has been created in laboratory conditions with human intervention and contrast the mechanisms at work in real world ecosystems when new species emerge. And they read Darwin’s finches on the Galapagos Islands as a real-world example of adaptive radiation.