The adjustment or changes in behavior, physiology, and structure of an organism to become more suited to an environment. According to Charles Darwin's theory of evolution by natural selection, organisms that possess heritable traits that enable them to better adapt to their environment compared with other members of their species will be more likely to survive, reproduce, and pass more of their genes on to the next generation.

A double stranded DNA molecule that contains a series of specific genes along its length. In most sexually reproducing organisms, chromosomes occur in pairs, with one member of the pair being inherited from each parent.

Deoxyribonucleic acid. A large biological molecule composed of subunits known as nucleotides strung together in long chains. The sequences of these nucleotides contain the information that cells need in order to grow, to divide into daughter cells, and to manufacture new proteins. Changes in DNA result in mutations, which may be beneficial, neutral, or deleterious to the organism. If these changes occur to DNA in sperm or egg cells, they could be passed onto the next generation.

Evolution consists of changes in the heritable traits of a population of organisms as successive generations replace one another. It is populations of organisms that evolve, not individual organisms.

In science, a "fact" typically refers to an observation, measurement, or other form of evidence that can be expected to occur the same way under similar circumstances. However, scientists also use the term "fact" to refer to a scientific explanation that has been tested and confirmed so many times that there is no longer a compelling reason to keep testing it or looking for additional examples.

A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded, and preserved in the Earth's crust, usually in stratified rock.

A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation. Scientific hypotheses must be posed in a form that allows them to be rejected.

A recent branch of genetics that studies organisms in terms of their complete genetic material, including genes and their functions.

Large-scale evolution occurring over geologic time that results in the formation of new species and broader taxonomic groups.

Changes in the traits of a group of organisms within a species that do not result in a new species.

In biology, mimicry is the superficial resemblance of one species of organism to another species or to a natural object in its surroundings. Some kinds of mimicry result in a selective advantage for concealment and protection from predators. Another type of mimicry enables protection to the mimic through its resemblance to another species that is toxic or in some other way dangerous.

A change in the sequence of one or more nucleotides in DNA. Such changes can alter the structure of proteins or the regulation of protein production. In some cases mutations result in the organism possessing these altered traits to have a greater or lesser chance of surviving and reproducing in a given environment than other members of its species.

Differential survival and reproduction of organisms as a consequence of the characteristics of the environment.

A scientist who studies fossils to learn about ancient organisms.

A large molecule consisting of a chain of smaller molecules called amino acids. The sequence of amino acids and the molecule's three-dimensional structure are coded by the instructions in DNA and determine a protein's specific function in cells or organisms.

A group of organisms of the same species that are in close enough proximity to allow them to interbreed.

Ribonucleic acid. A molecule related to DNA that consists of nucleotide subunits strung together in chains. RNA serves a number of cellular functions, including providing a template for the synthesis of proteins and catalyzing certain biochemical reactions. The structure of RNA is determined by the sequence of nucleotides on DNA.

The use of evidence to construct testable explanations and predictions of natural phenomena, as well as the knowledge generated through this process.

Rocks formed of particles deposited by water, wind, or ice.

The intentional breeding of organisms with desirable traits in an attempt to produce offspring with enhanced characteristics or traits that humans consider desirable. This process is also known as "artifical selection" (compare with "natural selection").

The evolutionary processes through which new species arise from existing species.

In sexually reproducing organisms, species consist of individuals that can interbreed with each other.

A term that refers to the survival of only those organisms best able (fittest) to obtain and utilize resources, resulting in the evolution of organisms that are best adapted to the environment. Darwin used metaphorically to describe "natural selection." The phrase was invented by the 19th century philosopher Herbert Spencer It has been misapplied through history to explain and justify social and economic inequities in human populations ("social Darwinism") or as a method for improving the human condition through selective breeding (eugenics). Survival alone is insufficient for evolution - it's reproduction - passing on of genes that really counts. Most modern biologists no longer use this term when describing or discussing natural selection.

A plausible or scientifically acceptable, well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena and predict the characteristics of as yet unobserved phenomena.

A physical or behavioral characteristic of an organism.

Newspaper and television stories sometimes make it seem as though evolution and religion are incompatible, but that is not true. Many scientists and theologians have written about how one can accept both faith and the validity of biological evolution. Many past and current scientists who have made major contributions to our understanding of the world have been devoutly religious. At the same time, many religious people accept the reality of evolution, and many religious denominations have issued emphatic statements reflecting this acceptance.

To be sure, disagreements do exist. Some people reject any science that contains the word "evolution"; others reject all forms of religion. The range of beliefs about science and about religion is very broad. Regrettably, those who occupy the extremes of this range often have set the tone of public discussions. Evolution is science, however, and only science should be taught and learned in science classes.

Acceptance of evolution is not the same as a religious belief. Scientists' confidence about the occurrence of evolution is based on an overwhelming amount of supporting evidence gathered from many aspects of the natural world. To be accepted, scientific knowledge has to withstand the scrutiny of testing, retesting, and experimentation. Evolution is accepted within the scientific community because the concept has withstood extensive testing by many thousands of scientists for more than a century. As a 2006 "Statement on the Teaching of Evolution" from the Interacademy Panel on International Issues, a global network of national science academies, said, "Evidence-based facts about the origins and evolution of the Earth and of life on this planet have been established by numerous observations and independently derived experimental results from a multitude of scientific disciplines" (emphasis in original).

Many religious beliefs do not rely on evidence gathered from the natural world. On the contrary, an important component of religious belief is faith, which implies acceptance of a truth regardless of the presence of empirical evidence for or against that truth. Scientists cannot accept scientific conclusions on faith alone because all such conclusions must be subject to testing against observations. Thus, scientists do not "believe" in evolution in the same way that someone believes in God.

Contrary to a widespread public impression, biological evolution is not random, even though the biological changes that provide the raw material for evolution are not directed toward predetermined, specific goals. When DNA is being copied, mistakes in the copying process generate novel DNA sequences. These new sequences act as evolutionary "experiments." Most mutations do not change traits or fitness. But some mutations give organisms traits that enhance their ability to survive and reproduce, while other mutations reduce the reproductive fitness of an organism.

The process by which organisms with advantageous variations have greater reproductive success than other organisms within a population is known as "natural selection." Over multiple generations, some populations of organisms subjected to natural selection may change in ways that make them better able to survive and reproduce in a given environment. Others may be unable to adapt to a changing environment and will become extinct.

As with all active areas of science, there remain questions about evolution. There are always new questions to ask, new situations to consider, and new ways to study known phenomena. But evolution itself has been so thoroughly tested that biologists are no longer examining whether evolution has occurred and is continuing to occur. Similarly, biologists no longer debate many of the mechanisms responsible for evolution. As with any other field of science, scientists continue to study the mechanisms of how the process of evolution operates. As new technologies make possible previously unimaginable observations and allow for new kinds of experiments, scientists continue to propose and examine the strength of evidence regarding the mechanisms for evolutionary change. But the existence of such questions neither reduces nor undermines the fact that evolution has occurred and continues to occur.

Nor do such questions diminish the strength of evolutionary science. Indeed, the strength of a theory rests in part on providing scientists with the basis to explain observed phenomena and to predict what they are likely to find when exploring new phenomena and observations. In this regard, evolution has been and continues to be one of the most productive theories known to modern science.

Even scientific theories that are firmly established continue to be tested and modified by scientists as new information and new technologies become available. For example, the theory of gravity has been substantiated by many observations on Earth. But theoretical scientists, using their understanding of the physical universe, continue to test the limits of the theory of gravity in more extreme situations, such as close to a neutron star or black hole. Someday, new phenomena may be discovered that will require that the theory be expanded or revised, just as the development of the theory of general relativity in the first part of the 20th century expanded knowledge about gravity.

With evolutionary theory, many new insights will emerge as research proceeds. For example, the links between genetic changes and alterations in an organism's form and function are being intensively investigated now that the tools and technologies to do so are available.

Some who oppose the teaching of evolution sometimes use quotations from prominent scientists out of context to claim that scientists do not support evolution. However, examination of the quotations reveals that the scientists are actually disputing some aspect of how evolution occurs, not whether evolution occurred.

This is an important question because evolution of the wide variety of organisms currently existing on Earth required a very long period of time. Several independent dating techniques indicate that the Earth is billions of years old. Measurements of the radioactive elements in materials from the Earth, the Moon, and meteorites provide ages for the Earth and the solar system. These measurements are consistent with each other and with the physical processes of radioactivity. Additional evidence for the ages of the solar system and the galaxy includes the record of crater formation on the planets and their moons, the ages of the oldest stars in the Milky Way, and the rate of expansion of the universe. Measurements of the radiation left over from the Big Bang also support the universe's great age.

Nothing is wrong with teaching critical thinking. Students need to learn how to reexamine their ideas in light of observations and accepted scientific concepts. Scientific knowledge itself is the result of the critical thinking applied by generations of scientists to questions about the natural world. Scientific knowledge must be subjected to continued reexamination and skepticism for human knowledge to continue to advance.

But critical thinking does not mean that all criticisms are equally valid. Critical thinking has to be based on rules of reason and evidence. Discussion of critical thinking or controversies does not mean giving equal weight to ideas that lack essential supporting evidence. The ideas offered by intelligent design creationists are not the products of scientific reasoning. Discussing these ideas in science classes would not be appropriate given their lack of scientific support.

Recent calls to introduce "critical analysis" into science classes disguise a broader agenda. Other attempts to introduce creationist ideas into science employ such phrases as "teach the controversy" or "present arguments for and against evolution." Many such calls are directed specifically at attacking the teaching of evolution or other topics that some people consider as controversial. In this way, they are intended to introduce creationist ideas into science classes, even though scientists have thoroughly refuted these ideas. Indeed, the application of critical thinking to the science curriculum would argue against including these ideas in science classes because they do not meet scientific standards.

There is no scientific controversy about the basic facts of evolution. In this sense the intelligent design movement's call to "teach the controversy" is unwarranted. Of course, there remain many interesting questions about evolution, such as the evolutionary origin of sex or different mechanisms of speciation, and discussion of these questions is fully warranted in science classes. However, arguments that attempt to confuse students by suggesting that there are fundamental weaknesses in the science of evolution are unwarranted based on the overwhelming evidence that supports the theory. Creationist ideas lie outside of the realm of science, and introducing them in science courses has been ruled unconstitutional by the U.S. Supreme Court and other federal courts.

"Creationism" is a very broad term. In the most general sense, it refers to views that reject scientific explanations of certain features of the natural world (whether in biology, geology, or other sciences) and instead posit direct intervention (sometimes called "special creation") in these features by some transcendent being or power. Some creationists believe that the universe and Earth are only several thousand years old, a position referred to as "young Earth" creationism. Creationism also includes the view that the complex features of organisms cannot be explained by natural processes but require the intervention of a nonnatural "intelligent designer." The "Additional Readings" section following these questions contains several books that describe the various ways in which the word "creationism" is used.

The goal of science education is to expose students to the best possible scholarship in each field of science. The science curriculum is thus the product of centuries of scientific investigation. Ideas need to become part of the base of accepted scientific knowledge before they are appropriately taught in schools. For example, the idea of continental drift to explain the movements and shapes of the continents was studied and debated for many years without becoming part of the basic science curriculum. As data accumulated, it became clearer that the surface of the Earth is composed of a series of massive plates, which are not bounded by the continents, that continually move in relation to each other. The theory of plate tectonics (which was proposed in the mid-1960s) grew from these data and offered a more complete explanation for the movement of continents. The new theory also predicted important phenomena, such as where earthquakes and volcanoes are likely to occur. When enough evidence had accumulated for the concept of plate tectonics to be accepted by the scientific community as fact, it became part of the earth sciences curriculum.

Scientists and science educators have concluded that evolution should be taught in science classes because it is the only tested, comprehensive scientific explanation for the nature of the biological world today that is supported by overwhelming evidence and widely accepted by the scientific community. The ideas supported by creationists, in contrast, are not supported by evidence and are not accepted by the scientific community.

Different religions hold very different views and teachings about the origins and diversity of life on Earth. Because creationism is based on specific sets of religious convictions, teaching it in science classes would mean imposing a particular religious view on students and thus is unconstitutional, according to several major rulings in federal district courts and the Supreme Court of the United States.

Science can neither prove nor disprove religion. Scientific advances have called some religious beliefs into question, such as the ideas that the Earth was created very recently, that the Sun goes around the Earth, and that mental illness is due to possession by spirits or demons. But many religious beliefs involve entities or ideas that currently are not within the domain of science. Thus, it would be false to assume that all religious beliefs can be challenged by scientific findings.

As science continues to advance, it will produce more complete and more accurate explanations for natural phenomena, including a deeper understanding of biological evolution. Both science and religion are weakened by claims that something not yet explained scientifically must be attributed to a supernatural deity. Theologians have pointed out that as scientific knowledge about phenomena that had been previously attributed to supernatural causes increases, a "god of the gaps" approach can undermine faith. Furthermore, it confuses the roles of science and religion by attributing explanations to one that belong in the domain of the other.

Many scientists have written eloquently about how their scientific studies have increased their awe and understanding of a creator. The study of science need not lessen or compromise faith.

Darwin at 200. Editorial by Francisco J. Ayala and John C. Avise, Department of Ecology and Evolutionary Biology, University of California, Irvine published in the Proceedings of the National Academy of Sciences (PNAS), Volume 106, No. 8. Feb. 24, 2009.

From the National Academies - Working Together to Address Challenges to the Teaching of Evolution in Cell Biology Education/Life Sciences Education Volume 7, Fall 2008.

From the National Academies - Understanding Our Audiences: The Design and Evolution of Science, Evolution, and Creationism in Cell Biology Education/Life Sciences Education, Volume 7, Spring 2008

From the National Academies: Ongoing Challenges to Evolution Education: Resources and Activities of the National Academies in Cell Biology Education,Volume 4, Winter 2005.

From the National Academies: Teaching the Science of Evolution in Cell Biology Education Volume 3, Summer 2004.

Sackler Colloquium on Two Centuries of Darwin (2009)
Two Centuries of Darwin is the third collection of the In the Light of Evolution series. Each installment in the series explores evolutionary perspectives on a particular biological topic that is scientifically intriguing but also has special relevance to contemporary societal issues or challenges. In this book of collected work, leading evolutionary biologists and science historians reflect upon and commemorate the Darwinian Revolution. They canvass modern research approaches and current scientific thought on each of the three main categories of selection (natural, artificial, and sexual) that Darwin addressed during his career.

Sackler Colloquium on Biodiversity and Extinction (2007)
This collection of presentations is from the National Academy of Sciences' Sackler Colloquium on the biodiversity crisis and whether a mass extinction of plants and animals is under way. Leading researchers and students discussed recent discoveries and concepts regarding the global abundance and distribution of biodiversity, and compare these patterns with conditions in the near and distant evolutionary past, as well as with those plausible in the near future.

Sackler Colloquium on Adaptation and Complex Design (2006)
This colloquium, part of the Arthur M. Sackler series, synthesizes recent scientific findings on the evolutionary origins of complex biological adaptations as well as conceptual approaches to understanding them.

Sackler Colloquium on Systematics and the Origin of the Species (2004)
The colloquium celebrated the 100th birthday of the eminent evolutionist Ernst Mayr and the 62nd anniversary of the publication of his Systematics and the Origin of Species (1942), one of the four books often considered as the foundations of the modern theory of evolution. The Colloquium explored the main topics in Mayr's book and examined the same (and related) issues in the light of current science, although the focus was be on speciation, rather than on systematics.

The Future of Evolution (2000)
This collection of colloquium papers presented by experts in biology, evolution, genetics, environmental science, and more was originally published in the Proceedings of the National Academy of Sciences. The volume looks at evolution not just as history, but as an active agent that will affect our future.

15 Evolutionary Gems 
PDF of summarizing 15 lines of evidence for evolution by natural selection, provided by the journal Nature.

Ardipithecus Ramidus
Science presents 11 papers, describing an early hominid species, Ardipithecus ramidus, and its environment.

Ardipithecus Ramidus
Science presents 11 papers, describing an early hominid species, Ardipithecus ramidus, and its environment.

Activities, Writings and Resources on Evolution 
Sigma Xi The Scientific Research Society

The AIBS/NCSE Evolution List Server Network 
American Institute of Biological Sciences and the National Center for Science Education

Becoming Human 
NOVA's comprehensive, three-part special, "Becoming Human," examines what the latest scientific research reveals about our hominid relatives. Watch part 1, part 2, and part 3 online.

Darwin 200
Nature provides a 200th anniversary special on Darwin's life, science, and legacy.

Darwin 200: Seed Celebrates the Life and Work of Charles Darwin 
SEED magazine honors Darwin with a curated exploration of the culture of ideas that has arisen as a result of Darwin's life and work.

Darwin: The Genius of Evolution 
In 2009 to mark the 200th anniversary of Charles Darwin's birth and the 150th anniversary of the publication of 'On the Origin of Species', the BBC aired a season of landmark TV and radio programmes.

Evolution: A Journey Into Where We're From and Where We're Going
Public Broadcasting Service (PBS)

Evolution: Constant Change and Common Threads 
Howard Hughes Medical Institute 2005 Holiday Lecture Series

Evolution on the Front Line 
American Association for the Advancement of Science (AAAS) Press Room

Findings magazine Special Evolution Theme Issue 
Findings, a student-oriented magazine that puts a face on science celebrates the Year of Darwin by featuring the exciting work of two evolutionary biologists. Companion multimedia offerings include online evolution games, a videocast, and a podcast.

Judgement Day: Intelligent Design on Trial 
Public Broadcasting Service (PBS)

National Center for Science Education 
Home page

Online Course for Teachers: Teaching Evolution 
Public Broadcasting Service (PBS)

Political Challenges to the Teaching of Evolution 
American Geological Institute

Position Statement on the Teaching of Evolution 
National Science Teacher's Association

Resources for Teaching Evolution 
National Science Teachers Association

Statements from Scientific Organizations

Understanding Evolution 
University of California Museum of Paleontology and the National Center for Science Education

Understanding Science 
University of California Museum of Paleontology and the National Center for Science Education

What Darwin Never Knew
PBS special on breakthroughs in science that confirm the brilliance of Darwin's insights while revealing clues to life's diversity.

What Does it Mean to be Human?
Smithsonian Museum of Natural History's Hall of Human Origins Exhibit web resource.

The Year of Darwin 
Science magazine celebrates the Year of Darwin with a variety of news features, scientific reviews and other special content, all collected here.

Evolution: Education and Outreach 
Editors-in-chief N. Eldredge, G. Eldredg, Springer Press.

The Complete Work of Charles Darwin Online 
by Dr. John van Wyhe, University of Cambridge.

Evolution 
NOVA's special Web compilation of their evolution-related programs and materials.

Your Inner Fish: A Journey into the 3.5-Billion Year History of the Human Body 
Why do we look the way we do? What does the human hand have in common with the wing of a fly? Are breasts, sweat glands, and scales connected in some way? To better understand the inner workings of our bodies and to trace the origins of many of today's most common diseases, we have to turn to unexpected sources: worms, flies, and even fish. In Your Inner Fish, Neil Shubin tells the story of evolution by tracing the organs of the human body back millions of years, long before the first creatures walked the earth. The book won its category in the 2009 Keck Futures Initiative Communications Awards, which recognize excellence in reporting and communicating science, engineering, and medicine to the general public.

NEW: Your Inner Fish is now a three-part series on PBS. The series is based on the best-selling book and hosted by author and evolutionary biologist Dr. Neil Shubin. Follow the adventure now on PBS

Infectious Disease: Evolving Challenges to Human Health 
The Marian Koshland Science Museum of the National Academy of Sciences' Infectious Disease: Evolving Challenges to Human Health exhibit examines impacts of microbial evolution on the spread of disease over the centuries. Visitors can explore characteristics of different bacteria, viruses, and fungi, as well as the diseases that are caused by many of them both virtually and in-house. Explore the exhibit or visit the Koshland Science Museum online.

Infectious Disease Webquest 
The Koshland Museum has developed a series of materials for middle and high school educators relating evolution to current science. Two of the classroom activities focus on the HIV/AIDS epidemic from both biological and public health angles. Students can also explore the potential of an avian influenza epidemic and develop a suggested public policy campaign through the Infectious Disease webquest. Teachers can also bring students to the museum for a facilitated field trip focusing on Infectious Diseases. Download the HIV/AIDS curriculum supplements. Explore the avian influenza webquest. Learn more about the museum's field trip program.

Science, Evolution, and Creationism Podcast (2005) 
Science, Evolution, and Creationism explains the fundamental methods of science, documents the overwhelming evidence in support of biological evolution, and evaluates the alternative perspectives offered by advocates of various kinds of creationism, including "intelligent design." The podcast, from the series Sounds of Science, gives a brief overview of the report, which was released January 4th.

Genesis: The Scientific Quest for Life's Origins (2005) 
Life on Earth arose nearly 4 billion years ago, bursting forth from air, water, and rock. Though the process obeyed all the rules of chemistry and physics, the details of that original event pose as deep a mystery as any facing science. How did non-living chemicals become alive? While the question is (deceivingly) simple, the answers are unquestionably complex. Genesis tells the tale of transforming scientific advances in our quest for life's origins. Written with grace, beauty, and authority, it goes directly to the heart of who we are and why we are here. (Published by Joseph Henry Press, an imprint of the National Academies Press. The views expressed in this book are solely those of the author(s) and do not necessarily reflect the views of the National.)

Darwin's Gift to Science and Religion (2007) 
With the publication in 1859 of On the Origin of Species by Means of Natural Selection, Charles Darwin established evolution by common descent as the dominant scientific explanation for nature s diversity. This was to be his gift to science and society at last, we had an explanation for how life came to be on Earth. In Darwin's Gift, a voice at once fresh and familiar brings a rational, measured perspective to the science of evolution. An acclaimed evolutionary biologist with a background in theology, Francisco Ayala offers clear explanations of the science, reviews the history that led us to ratify Darwin's theories, and ultimately provides a clear path for a confused and conflicted public. (Published by Joseph Henry Press, an imprint of the National Academies Press. The views expressed in this book are solely those of the author(s) and do not necessarily reflect the views of the National.)

Statement on the Teaching of Evolution 
InterAcademy Panel on International Issues

Activities, Writings and Resources on Evolution 
Sigma Xi The Scientific Research Society

Evolution: Constant Change and Common Threads 
Howard Hughes Medical Institute 2005 Holiday Lecture Series

Statements from Scientific Organizations 
National Center for Science Education

Position Statement on the Teaching of Evolution 
National Science Teacher's Association

National Center for Science Education 
Home page

Resources for Teaching Evolution 
National Science Teachers Association

Evolution: A Journey Into Where We're From and Where We're Going 
Public Broadcasting Service (PBS)

Judgement Day: Intelligent Design on Trial 
Public Broadcasting Service (PBS)

Online Course for Teachers: Teaching Evolution 
Public Broadcasting Service (PBS)

Understanding Evolution 
University of California Museum of Paleontology and the National Center for Science Education

The AIBS/NCSE Evolution List Server Network 
American Institute of Biological Sciences and the National Center for Science Education

Evolution on the Front Line 
American Association for the Advancement of Science (AAAS) Press Room

Political Challenges to the Teaching of Evolution
American Geological Institute