Which evolves individuals or populations

This is apparent in the populations around us: for example, a plant may not have the genes to flourish in a drought, or a predator may not be quite fast enough to catch her prey every time she is hungry.

For example, living things are made up of traits resulting from a complicated set of trade-offs — changing one feature for the better may mean changing another for the worse e. And of course, because organisms have arisen through complex evolutionary histories not a design process , their future evolution is often constrained by traits they have already evolved. For example, even if it were advantageous for an insect to grow in some way other than molting, this switch simply could not happen because molting is embedded in the genetic makeup of insects at many levels.

To learn more about the limitations of natural selection , visit our module on misconceptions about natural selection and adaptation.

Some may be the chance results of history. There is nothing special about the relationship between GGC and glycine. Others traits may be by-products of another characteristic. For example, the color of blood is not adaptive. To read more about explanations for traits that are not adaptive , visit our module on misconceptions about natural selection and adaptation. To learn more about what traits are adaptations , visit another page in the same module.

Organisms that share a more recent branching point i. For example, on the tree here, taxon A is adjacent to B and more distant from C and D. However, taxon A is equally closely related to taxa B, C, and D. Similarly, in the tree below, taxon B is adjacent to taxon A, but taxon B is actually more closely related to taxon D. The following phylogenies are all equivalent. Even though each phylogeny below has a different order of taxa at the tips of the tree, each portrays the same pattern of branching.

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.

Fossil: 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. Hypothesis: 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.

Genomics: A recent branch of genetics that studies organisms in terms of their complete genetic material, including genes and their functions. Macroevolution: Large-scale evolution occurring over geologic time that results in the formation of new species and broader taxonomic groups. Microevolution: Changes in the traits of a group of organisms within a species that do not result in a new species. Mimicry: 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.

Mutation: 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.

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Packard AS. Another driving force behind evolution is genetic drift, which describes random fluctuations in allele frequencies in a population. Eventually, genetic drift can cause a subpopulation to become genetically distinct from its original population.

Indeed, over a long period of time, genetic drift and the accumulation of other genetic changes can result in speciation, which is the evolution of a new species. Further Exploration Concept Links for further exploration synteny gene trait genotype Hardy-Weinberg equilibrium allele speciation Hardy-Weinberg equation population bottleneck species allele frequency natural selection genetic drift sexual reproduction neutral theory of evolution.

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