These mini-lessons are illustrated with interactive Web animation. (The Adobe Flash plug-in is required for many of these online click and learn features. Download it free from Adobe.com.)

Now available: a Click & Learn App for iPhone/iPod touch/iPad! (Internet connection required for streaming video.) Click here to find out more!

Deep History of Life on Earth

NEW! The record of life on Earth stretches over 3 billion years, with evidence ranging from chemical signatures in rocks and ancient biological molecules to fossils of colossal dinosaurs and early humans. Developed in support of the 2012 HHMI Holiday Lectures on Science Changing Planet: Past, Present, Future.

Paleoclimate: A History of Change

NEW! The history of Earth's climate over millions of years, during both warmer and colder periods, sheds light on the causes implications, and severity of current climate change. Developed in support of the 2012 HHMI Holiday Lectures on Science Changing Planet: Past, Present, Future.

The Geologic History of O₂

NEW! Early Earth’s atmosphere lacked oxygen gas, yet the planet was teeming with microbes!  Explore the changes in O₂ levels throughout Earth’s history and discover their impact on life. Developed in support of the 2012 HHMI Holiday Lectures on Science Changing Planet: Past, Present, Future.

Creating Phylogenetic Trees from DNA Sequences

DNA sequences can be used to generate phylogenetic trees, diagrams of relatedness among organisms. This Click and Learn explains how DNA sequences can be used to generate such trees, and how to interpret them.

From Birds to People: The West Nile Virus Story

West Nile virus infects mosquitoes, birds, and people—with very different consequences. Drs. Laura Kramer and Marm Kilpatrick discuss their research on the virus life cycle and how factors like temperature and climate affect spread.

Download the accompanying worksheet (PDF) for students to complete as they go through the Click and Learn.

Skeletons Reveal Human and Chimpanzee Evolution

Comparing features of a 4.4-million-year-old fossil skeleton to those of human and chimpanzee skeletons sheds light on our evolutionary history. Also featured on the HHMI DVD Stones, Bones, and Genes: The Origins of Modern Humans, available free from HHMI. Order DVDs here.

Recent Adaptations in Humans

Lactose tolerance, sickle cell anemia, and bitter taste perception are three examples of recently evolved human traits. Also featured on the HHMI DVD Stones, Bones, and Genes: The Origins of Modern Humans, available free from HHMI. Order DVDs here.

Download the accompanying worksheet (PDF) for students to complete as they go through the Click and Learn.

Regulation of the Lactase Gene

Lactase persistence results from a mutation that changes how transcription factors interact, thereby affecting gene expression. Also featured on the HHMI DVD Stones, Bones, and Genes: The Origins of Modern Humans, available free from HHMI. Order DVDs here.

Download the accompanying worksheet (PDF) for students to complete as they go through the Click and Learn.

Using the Scientific Process to Study Human Evolution

Paleoanthropology provides an excellent example of the scientific process at work. Also featured on the HHMI DVD Stones, Bones, and Genes: The Origins of Modern Humans, available free from HHMI. Order DVDs here.

Stopping Mosquito-Borne Disease

Learn about the nature of vector-borne diseases, and the life cycle of the dengue vector mosquito, Interactively explore how to control mosquito-borne diseases. Also featured on the HHMI DVD, Viral Outbreak: The Science of Emerging Disease, available free from HHMI. Order DVDs here.

DNA Sequence Assembly

Learn the principles of how DNA is sequenced and assembled into whole genomes using the Sanger method, shotgun sequencing, or ultra-deep sequencing. Also featured on the HHMI DVD, Viral Outbreak: The Science of Emerging Disease, available free from HHMI. Order DVDs here.

Virochip DNA Microarray

Answer interactive questions to explore the logic of the Virochip microarray design, particularly how evolutionary relationships can be used to detect new viruses. Also featured on the HHMI DVD, Viral Outbreak: The Science of Emerging Disease, available free from HHMI. Order DVDs here.

Sorting Seashells

Explore principles of taxonomy by sorting seashells according to their morphological characteristics and constructing an evolutionary tree. Also featured on the HHMI DVD, Exploring Biodiversity: The Search for New Medicines, available free from HHMI. Order DVDs here.

Symbiotic Bioluminescence

Explore the biology of the symbiotic relationship between the Hawaiian Bobtail Squid and bioluminescent bacteria Vibrio fischeri. Also featured on the HHMI DVD, Exploring Biodiversity: The Search for New Medicines, available free from HHMI. Order DVDs here.

Bacterial Quorum Sensing

Understand how quorum sensing works by reasoning through experiments involving genetically-engineered bioluminescent bacteria. Also featured on the HHMI DVD, Exploring Biodiversity: The Search for New Medicines, available free from HHMI. Order DVDs here.

Neural Control of Walking and Running

Different gaits employed by animals and how the nervous system is able to switch between them. Also featured on the HHMI DVD, Making Your Mind: Molecules, Motion, and Memory, available free from HHMI. Order DVDs here.

Electrical Activity of Neurons

Measuring neuronal activity, generating action potentials, and recording the firing of individual neurons. Also featured on the HHMI DVD, Making Your Mind: Molecules, Motion, and Memory, available free from HHMI. Order DVDs here.

Cells of the Immune System

An overview of the immune system, concentrating on the roles played by B and T lymphocytes, and the antigen-presentation system. Also featured on the HHMI DVD, AIDS: Evolution of an Epidemic, available free from HHMI. Order DVDs here.

Retroviruses and Viral Diversity

A brief discussion of what makes a virus a retrovirus, and how they differ from other types of viruses. Also featured on the HHMI DVD, AIDS: Evolution of an Epidemic, available free from HHMI. Order DVDs here.

Drug Adherence and Resistance

Problems associated with adherence to antiviral drugs, and a student activity that mimics adherence to a multi-drug regimen. Also featured on the HHMI DVD, AIDS: Evolution of an Epidemic, available free from HHMI. Order DVDs here.

Tissue Regeneration in Animals

An overview and comparison of different regenerative capabilities in many different organisms. Also featured on the HHMI DVD Potent Biology: Stem Cells, Cloning, and Regeneration, available free from HHMI. Order DVDs here.

Stem-Cell-Based Therapies

An exploration of current and future therapies. Also featured on the HHMI DVD Potent Biology: Stem Cells, Cloning, and Regeneration, available free from HHMI. Order DVDs here.

Visualizing Gene-Expression Patterns

Learn about the different ways scientists are able to detect when genes are being expressed in various tissues. Also featured on the HHMI DVD Evolution: Constant Change and Common Threads, available free from HHMI. Order DVDs here.

Natural and Artificial Selection

Learn about artificial and natural selection. Features multiple clips from the lectures on evolution. Also featured on the HHMI DVD Evolution: Constant Change and Common Threads, available free from HHMI. Order DVDs here.

Genetic Switches

Learn about how gene switches can control expression of genes in different tissues. Also featured on the HHMI DVD Evolution: Constant Change and Common Threads, available free from HHMI. Order DVDs here.

RNA Interference

RNA interference is an exciting new research tool for shutting down genes. It could also yield new medical treatments. Learn how RNA interference was discovered and how it works. Also featured on the HHMI DVD The Double Life of RNA, available free from HHMI. Order DVDs here.

RNA Diversity

RNA is an information molecule that can also function as an enzyme. Learn about the many different forms that RNA can take. Also featured on the HHMI DVD The Double Life of RNA, available free from HHMI. Order DVDs here.

Structure and Function of Telomeres

This mini-lesson covers the research on telomeres that has happened since the 1995 Holiday Lectures. Also featured on the HHMI DVD The Double Life of RNA, available free from HHMI. Order DVDs here.

Measuring Obesity

There is no way to directly measure how much fat a living person has. Learn about the various methods used by researchers and fitness advisors to estimate a person’s body fat. Also featured on the HHMI DVD Science of Fat, available free from HHMI. Order DVDs here.

Molecular Structure of Fat

This slide show delves into the various molecular shapes that fat can take. Also featured on the HHMI DVD Science of Fat, available free from HHMI. Order DVDs here.

How The Body Uses Fat

This slide show explores some of the ways the body processes fat, including digestion, transport, conversion, and energy extraction. Also featured on the HHMI DVD Science of Fat, available free from HHMI. Order DVDs here.

The p53 Gene and Cancer

One of the most important molecules relating to cancer is called p53. It has been called the guardian of the genome. Learn about what p53 does, and how interfering with its function can lead to cancer. Also featured on the HHMI DVD Learning from Patients: The Science of Medicine, available free from HHMI. Order DVDs here.

The Proteasome and Protein Regulation

The proteasome is a large molecular machine that plays an important role in recycling and regulating cellular proteins. Learn about the structure and function of this fascinating cellular machine. Also featured on the HHMI DVD Learning from Patients: The Science of Medicine, available free from HHMI. Order DVDs here.

How to Analyze DNA Microarray Data

DNA microarrays, or gene chips, are an important new technology for genomic research. Learn how researchers use computing to analyze and interpret the huge datasets generated by microarray experiments. Also featured on the HHMI DVD Scanning Life's Matrix: Genes, Proteins, and Small Molecules, available free from HHMI. Order DVDs here.

Using DNA to Trace Human Migration

All living humans originated from populations of ancestors who migrated out of Africa less than 100,000 years ago. Learn how scientists have used genetic markers to trace the migration routes and origins of modern human populations. Also featured on the HHMI DVD Scanning Life's Matrix: Genes, Proteins, and Small Molecules. Available free from HHMI. Order DVDs here.

Small-Molecule Diversity

Small molecules are chemicals that can interact with proteins to affect their functions. Learn about the structure and biological functions of various small molecules like sugar and caffeine. Also featured on the HHMI DVD Scanning Life's Matrix: Genes, Proteins, and Small Molecules. Available free from HHMI. Order DVDs here.

Microarray Manufacturing Technology

How both gene chips and microarray slides are created. Also featured on the HHMI DVD Scanning Life's Matrix: Genes, Proteins, and Small Molecules. Available free from HHMI. Order DVDs here.

Gender Testing of Athletes

At times those responsible for conducting high-stakes athletic competitions like the Olympics have been greatly concerned with gender testing athletes. Learn why verifying a person's gender may be harder than you think.

Test Your Knowledge of Sex Determination

Answer the questions in this online quiz to test your knowledge of what determines the sex of a human, a fruit fly, and a snapping turtle. Includes links to relevant sections from the 2001 Holiday Lectures on sex determination.

Are You a Morning or an Evening Person?

This survey, developed by Horne and Ostberg, will let you determine if you are a morning or an evening person. From the 2000 Holiday Lectures on biological clocks.

Test Your Knowledge of Microbes

Take this quiz to see how well you understand some of the topics covered in the 1999 Holiday Lectures on infectious disease. Includes links to the relevant parts of the lectures and a final score.

Antibiotics Attack

A multimedia presentation covering how antibiotics function to fight invaders. Five major sections with animations cover bacteria, antibiotic structure, pathways of attack, penicillin, and antibiotic resistance.

The Vertebrate Circulatorium

In the Veterbrate Circulatorium you can compare the circulation patterns of different vertebrates. Click on the different animal names on the left to see the overall circulation patterns in "systemic view." More detailed views of the hearts are available by clicking on "To heart detail."

Electrocardiogram Primer

A quick tutorial on the basics of the electrocardiogram machine. Created by one of HHMI's high school interns from Thomas Edison High School of Technology in Montgomery County, Maryland.

Heart Size in Mammals

Explore the relationship between heart size and rate in this multimedia demonstration by one of HHMI's high school interns from Thomas Edison High School of Technology in Montgomery County, Maryland.

Electric Fish

You're probably thinking of an electric eel, sending out 800 volts of electricity—enough to stun or kill a person, even a horse.

But most species of electric fish live in fresh water and are actually harmless. They generate from only a fraction of a volt up to a few volts of electricity with their electric organs located in the tail, which is made up of specialized muscle or nerve tissue.