Why did sex evolve? The likely answers, in this essay for the Evolution Web site by science journalist Matt Ridley, may surprise you.
Recommended for: Grades 9-12 ***Access to Teacher's Domain content now requires free login to PBS Learning Media.

This video from the series Faces of America details the process of documenting family history and tracing lineage back through maternal and paternal lines.

In this Evolution Web feature, test your skills at judging who's who on the tree of life while you learn about the tools and methods of cladistics.

This video segment from the Secret of Life School Video: "Genetic Medicine: Tinkering with Our Genes" explores the potential for gene therapy to cure diseases like Alzheimer's.

An estimated 15 million Americans will suffer from Alzheimer’s by 2050. QUEST visits with researchers at San Francisco’s Gladstone Institutes who have found that a gene may hold the key to a cure for this debilitating affliction.

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 architects in all animal species. ***Access to Teacher's Domain content now requires free login to PBS Learning Media.

It takes a thick skin to withstand the hardships that life has to offer. This collection of images shows a variety of animals, each with a slightly different type of protective covering.

How long does a baby elephant stay with her mother? What do you call a baby goat? Young children learn some interesting facts about the lives of baby animals in this original video from KET.

This video segment explores the benefits and pitfalls of cloning as a means of reproduction. From Evolution: "Why Sex?"

In this video from Nature researchers from the University of Washington conduct a long-term experiment to see if crows can pass information down from one generation to the next.

Join students as they observe mosquitoes in different stages of development and learn about the insect's life cycle in this video from Curious George.

Students compare the processes of selective breeding and transgenic manipulation of plants. They consider the pros and cons of growing genetically modified crops.

By examining the developmental stages of animals, students learn about the life cycles of living things.

In this video segment, adapted from NOVA, Dr. Judah Folkman uses the scientific method to discover how cancer cells induce the formation of new blood vessels, which in turn nourish those cancer cells.

This lesson from Nature uses the eagle to model universal avian life stages.

Both sexes can use this interactive feature that lets you use DNA information from the Y chromosome to complete a male family tree. From the NOVA: "Lost Tribes of Israel" Web site.

In this video segment adapted from NOVA scienceNOW, scientists discuss a family of genes called FOXO that can significantly extend life span in worms—and in humans.

This interactive feature describes some of the most important structures and functions of the cell membrane.

This video segment from Nature examines American Eagles along the Upper Mississippi River and their struggle to protect their eggs from predators as well as from the cold, extreme weather.