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Essential Science for Teachers: Life Science

Variation, Adaptation, and Natural Selection

What causes variation among a population of living things? How can variation in one generation influence the next generation? In this session, variation in a population will be examined as the "raw material" upon which natural selection acts.

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Learning Goals

Natural variation

During this session, you will have an opportunity to build understandings to help you:

  • Recognize how populations vary with regard to inherited traits
  • Distinguish between DNA, chromosomes, and genes
  • Relate genes to variation in populations
  • Describe the process of adaptation through natural selection

Video Overview

How is it that life always seems to find a way? Changes–both large and small–are ever-present in the environment that surrounds life. But despite sometimes extreme challenges to survival, life forms persist from generation to generation. In the last two sessions, we focused on life cycles and their connection to DNA, and we began to look at life at the level of populations. The next two sessions build upon this as we focus on the fundamentals of evolution: how populations change over time and how this can lead to new life forms. Session 5 starts with an exploration of variation, adaptation, and natural selection.

Video Outline

Where do we find variation in the living world? Our Bottle Biologist, Dr. Paul Williams, switches hats for this program. As the developer of Wisconsin Fast Plants, he has firsthand experience observing variation and how it provides the raw material for change in populations over time. Using the curriculum resource Exploring with Wisconsin Fast Plants, the sixth graders in Dr. Kathy Vandiver’s class in Lexington, Massachusetts, assess variation in plant height and think about its causes.

Dr. Robert Murray and Dr. Georgia Dunston, of the National Human Genome Center, introduce us to the role of genes as a source of variation. We hear of one example that applies to humans–PTC tasting–and we are presented later with a scenario in which the ability to taste PTC is an advantage that leads to change in a population. The role of genes is emphasized as mutation is introduced as one cause of new variation in populations.

As a contrast to natural selection, Dr. Williams describes how he developed Fast Plants through artificial selection. A bit of evolutionary history is next highlighted as we introduce Charles Darwin’s contributions and focus on the meaning of adaptation through natural selection. Throughout the program, we visit the Science Studio, where a new group of children composed of fourth and fifth graders gives us insight into children’s ideas.

And Bottle Biology returns as Dr. Williams features a bottle system for studying the fundamentals of evolution.

Series Directory

Essential Science for Teachers: Life Science


Produced by Harvard-Smithsonian Center for Astrophysics. 2003.
  • Closed Captioning
  • ISBN: 1-57680-730-4