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

This media-rich series of interviews from the NOVA: "Stationed in the Stars" Web site explores the unique challenges faced by astronauts doing construction work in outer space.

Did you know that air has weight? This illustrated essay from the NOVA Web site explores conditions that affect air density and atmospheric pressure.

This illustration from Biology by Kenneth R. Miller and Joseph Levine describes the steps of the electron transport chain, the second stage in the process of cellular respiration.

Often referred to as the powerhouses of the cell, mitochondria provide the energy that powers nearly every cellular process. This essay by university lecturer John Ross describes in detail the structures and functions of these amazing...

There are almost as many types of bird beaks as there are types of food that birds like to eat. This collection of images shows a wide range of beaks and the types of foods handled by each.

For animals, bright, flashy coloration can serve as a warning or as an invitation. Either way, colorful skin, feathers, and scales yell, "Notice me!" This collection of images shows examples of some of the world's most colorful creatures.

This interactive feature from the NOVA: "Odyssey of Life" Web site explores the often unwitting relationship we share with the billions of "creepy crawlies" that reside in our bodies and in our homes.

What is it that distinguishes a living organism from a nonliving object? This collection of images presents examples that aren't as clear-cut as one might think, enticing students to question the meaning of life.

These images of duckweed (Lemna spp.) illustrate the basic anatomy and environment of these fast-growing plants.

In this interview filmed for Evolution: "Darwin's Dangerous Idea," biologist Chris Schneider discusses the relationship between conservation and speciation.

In this text excerpted from Chapter 3, "Struggle for Existence," of Charles Darwin's "On the Origin of Species," Darwin draws on firsthand and historical information for his observations about evolution.

This graphic illustrates some of the marsupial mammals in Australia and placental mammals in North America. Even though they are not closely related, these mammals look alike because they have adapted to similar ecological roles. From...

This group of letters is a sample of the extensive correspondence Darwin carried on with a wide group of friends and colleagues as he collected evidence to support his theory of evolution by natural selection. From Charles Darwin's...

In this excerpt from the PBS series "Evolution," award-winning science journalist Carl Zimmer describes how gene duplication may have been the key to the rapid evolution of the early stages of life on Earth.

This Web quest from the PBS series "Evolution" will help you investigate a variety of types of evidence for evolution.

Are nature's complex forms evidence of "intelligent design"? In this Evolution essay, biologist Kenneth Miller explains how the processes of evolution account for complex structures such as the human eye.

This video segment from Evolution: "Darwin's Dangerous Idea" shows biologists Chris Schneider and Tom Smith studying hummingbirds and other animals in Ecuador. Their research is investigating the processes by which new species are formed.

This Evolution video segment describes how the famous track fossils known as the Laetoli footprints might have been formed and what they can reveal about the creatures who left them.

In this graphic and article from "The Human Evolution Coloring Book" by Adrienne Zihlman, four different proteins from humans and horses are compared and the reasons each protein evolves at its own characteristic rate are discussed.

This video segment from Evolution: "Why Sex?" explores the "sweaty T-shirt experiment," which showed that humans may unconsciously be drawn toward a specific kind of genetic variation in a mate.

This image of polydactyly illustrates one symptom of Ellis-van Creveld syndrome, which is commonly found in the Amish. Ellis-van Creveld is one example of the founder effect and genetic drift.

The homeobox genes that define the basic body plan of mice and fruit flies are illustrated in this graphic from The Human Evolution Coloring Book by Adrienne Zihlman. The accompanying article describes how these genes act as "molecular...

In this article by An Meeker-O'Connell, discover how DNA evidence is processed before it goes to court.