The peacock provides a classic example of sexual selection, the force behind nature's extravagances. From Evolution: "Why Sex?"

Bonnie Chen builds on students' prior knowledge of mutations to lead her class through a simulation of wading birds feeding.

Marilyn Havlik leads students through a simulation of the Hardy-Weinberg Principle to develop their understanding of population genetics.

This article introduces ARKive, a digital library of photographs and videos of the world's wildlife. The library gives special priority to at-risk species. The author notes how this interactive resource can be used by K-5 teachers to support other activities connected to the theme of this issue of the free, online magazine Beyond Weather and the Water Cycle -- We Depend on Earth's Climate.

In this video adapted from KUAC-TV and the Geophysical Institute at the University of Alaska, Fairbanks, learn how tectonic plate movement is responsible for building mountains, such as the Wrangell and St. Elias Mountains.

This interactive activity produced for Teachers' Domain shows the relationship between tectonic boundaries and the locations of earthquake events and volcanoes around the world.

In this transcript of an interview filmed for Evolution: "Great Transformations," Ted Daeschler and Neil Shubin describe the discovery and significance of some of their key fossil finds.

Why do teenagers act the way they do? This video segment from FRONTLINE: Inside the Teenage Brain explores the work scientists are doing to explain some of the mysteries of teenage behavior.

Watch the ZOOM cast discover which insulator -- newspaper or aluminum foil -- is better at keeping an ice cube frozen longer.

In this video segment adapted from ZOOM, cast members show you how to make your very own electroscope. You can use it to find out if an object is electrically charged.

This illustration from Evolution by Monroe W. Strickberger shows the remarkable similarities between the bones in the forelimbs of various tetrapods, all of whose limbs serve very different functions.

This interactive activity from the NOVA Web site challenges you to think like Einstein and understand how time travel might be possible.

This illustrated essay from the NOVA Web site answers questions about irregularities in the tides.

John Noble Wilford, a New York Times science writer, outlines various hypotheses on the origin of bipedalism.

All cells, organs and tissues of a living organism are built of molecules. Some of them are small, made from only a few atoms. There is, however, a special class of molecules that make up and play critical roles in living cells. These molecules can consist of many thousands to millions of atoms. They are referred to as macromolecules (or large biomolecules).

Watch the ZOOM cast build a chair out of newspaper by making good use of the strength of triangles.

In this video segment adapted from ZOOM, the cast tries to design and build a bridge made out of drinking straws that will support the weight of 200 pennies.

This interactive activity, from the Building Big Web site, explores tunneling and the tools and methods used to do the job.

This list of children's books recommends nonfiction titles that supplement basic information found in lessons and activities of this themed issue of the online magazine Beyond Weather and the Water Cycle. The books are grouped by topic -- water, weather and climate, and atmosphere. Each book is described by its content, reading level, and possible uses in the classroom. Covers are pictured. The online magazine is produced for elementary school teachers and is structured around the essential principles of climate sciences and climate literacy.

PowerPoint module leading students through creation and manipulation of spreadsheet to forward model an example of exponential decay -- the number of remaining unpopped kernels of popcorn in a bag of popping popcorn.

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