Why do gaps in fossil evidence exist

Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Nineteenth-century English social scientist Herbert Spencer made this prescient observation: "Those who cavalierly reject the Theory of Evolution, as not adequately supported by facts, seem quite to forget that their own theory is supported by no facts at all.

When I debate creationists, they present not one fact in favor of creation and instead demand "just one transitional fossil" that proves evolution. When I do offer evidence for example, Ambulocetus natans , a transitional fossil between ancient land mammals and modern whales , they respond that there are now two gaps in the fossil record. Get smart. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Learn More What Is Science? Opponents of evolution point to gaps in the fossil record as proof that the theory is invalid.

They say the fossil record fails to show what are called "transitional forms," generally the in-between stages as one type of creature evolved into another. The fossil record certainly has gaps, mostly because the conditions required to create fossils have been rare ever since life began on Earth. A very small percentage of animals that have lived and died ever became fossils. Thus, many pieces of the puzzle are missing; some will never be found.

Nonetheless, we have many, many fossils that illustrate evolutionary transitions between fish and amphibians, between reptiles and mammals, between dinosaurs and birds, and in many lineages such as whales and horses. These are value judgments that have no place in science. One form of a trait may be ancestral to another more derived form, but to say that one is primitive and the other advanced implies that evolution entails progress — which is not the case.

For more details , visit our misconception on this topic. For example, on the tree below, taxon D may be more or less specialized than taxa A, B, and C. Unfortunately, students may assume that all traits follow this simple model, and that is not the case. Both quantitative e. In terms of evolution, this misconception can be problematic when students are learning about Hardy-Weinberg equilibrium and population genetics. Students may need frequent reminders that traits may be influenced by more than one locus and that these loci may not involve simple dominance.

Because students may not have made connections between Mendelian genetics and the molecular structure of DNA , they may not realize that many different alleles may be present at a locus and so may assume that all traits are influenced by only two alleles. This misconception may be reinforced by the fact that students usually focus on diploid genetic systems and by the use of upper and lowercase letters to represent alleles.

The use of subscripts to denote different alleles at a locus as well as frequent reminders that loci may have more than two alleles can help correct this misconception. First, many scientific investigations do not involve experiments or direct observation. Astronomers cannot hold stars in their hands and geologists cannot go back in time, but both scientists can learn a great deal about the universe through observation and comparison. In the same way, evolutionary biologists can test their ideas about the history of life on Earth by making observations in the real world.

In organisms with short generation times e. And in some cases, biologists have observed evolution occurring in the wild. To learn more about rapid evolution in the wild, visit our news story on climate change , our news story on the evolution of PCB-resistant fish , or our research profile on the evolution fish size in response to our fishing practices.

To learn more about the nature of science , visit the Understanding Science website. In everyday language, theory is often used to mean a hunch with little evidential support. Scientific theories, on the other hand, are broad explanations for a wide range of phenomena. In order to be accepted by the scientific community, a theory must be strongly supported by many different lines of evidence. To learn more about the nature of scientific theories , visit the Understanding Science website.

All scientific theories from evolutionary theory to atomic theory are works in progress. As new evidence is discovered and new ideas are developed, our understanding of how the world works changes and so too do scientific theories. And more will be learned in the future. Evolutionary theory, like any scientific theory, does not yet explain everything we observe in the natural world. However, evolutionary theory does help us understand a wide range of observations from the rise of antibiotic-resistant bacteria to the physical match between pollinators and their preferred flowers , does make accurate predictions in new situations e.

Scientists evaluate hypotheses and theories by figuring out what we would expect to observe if a particular idea were true and then seeing if those expectations are borne out. This expectation has been borne out. Paleontologists have found many fossils with transitional features, and new fossils are discovered all the time. However, if evolutionary theory were true, we would not expect all of these forms to be preserved in the fossil record.

So scientists expect that for many evolutionary transitions, there will be gaps in the fossil record. To learn more about testing scientific ideas , visit the Understanding Science website. To learn more about evolutionary transitions and the fossils that document them , visit our module on this topic. For more on how evolutionary theory changes , see our misconception on this topic above.

Scientists do not debate whether evolution took place, but they do debate many details of how evolution occurred and occurs in different circumstances. Antievolutionists may hear the debates about how evolution occurs and misinterpret them as debates about whether evolution occurs. Evolution is sound science and is treated accordingly by scientists and scholars worldwide. Today, we understand the genetic basis for the inheritance of traits, we can date many events in the fossil record to within a few hundred thousand years, and we can study how evolution has shaped development at a molecular level.

These advances — ones that Darwin likely could not have imagined — have expanded evolutionary theory and made it much more powerful; however, they have not overturned the basic principles of evolution by natural selection and common ancestry that Darwin and Wallace laid out, but have simply added to them.

This is not the case. It is up to us, as societies and individuals, to decide what constitutes ethical and moral behavior. Furthermore, some people erroneously believe that evolution and religious faith are incompatible and so assume that accepting evolutionary theory encourages immoral behavior.

Neither are correct. For more on this topic , check out the misconception below. To learn more about the idea that science cannot make ethical statements , visit the Understanding Science website. Social Darwinism suggests that society should allow the weak and less fit to fail and die and that this is good policy and morally right.

Supposedly, evolution by natural selection provided support for these ideas. In this case, science was misapplied to promote a social and political agenda. While Social Darwinism as a political and social orientation has been broadly rejected, the scientific idea of biological evolution has stood the test of time. The human lineage is a small twig on the branch of the tree of life that constitutes all animals. This means that, in a biological sense, humans are animals.

We share anatomical, biochemical, and behavioral traits with other animals. For example, we humans care for our young, form cooperative groups, and communicate with one another, as do many other animals.

And of course, each animal lineage also has behavioral traits that are unique to that lineage. In this sense, humans act like humans, slugs act like slugs, and squirrels act like squirrels.

It is unlikely that children, upon learning that they are related to all other animals, will start to behave like jellyfish or raccoons. People of many different faiths and levels of scientific expertise see no contradiction at all between science and religion. For many of these people, science and religion simply deal with different realms.

Science deals with natural causes for natural phenomena, while religion deals with beliefs that are beyond the natural world. Of course, some religious beliefs explicitly contradict science e.

In fact, many religious people, including theologians, feel that a deeper understanding of nature actually enriches their faith. Moreover, in the scientific community there are thousands of scientists who are devoutly religious and also accept evolution. For concise statements from many religious organizations regarding evolution, see Voices for Evolution on the NCSE website. To learn more about the relationship between science and religion , visit the Understanding Science website.

Religion and science are very different endeavors, and religious views do not belong in a science classroom at all. In science class, students should have opportunities to discuss the merits of arguments and evidence within the scope of science. For example, students might investigate and discuss exactly where birds branched off of the tree of life: before dinosaurs or from within the dinosaur clade. To learn more about the idea that evolution and religion need not be incompatible , see the misconception above.

To learn more about why religious views on creation are not science and so do not belong in science classrooms , visit the Understanding Science website. Belief in religious ideas is based on faith, and religion deals with topics beyond the realm of the natural world. Acceptance of scientific ideas like evolution is based on evidence from the natural world, and science is limited to studying the phenomena and processes of the natural world.

Supreme Court and other Federal court decisions clearly differentiate science from religion and do not permit the advocacy of religious doctrine in science or other public school classes.

For additional information on significant court decisions involving evolution education , visit the NCSE website. To learn more about the difference between science and religion , visit the Understanding Science website.