Evolution that occurs quickly is called

Evolution is usually thought to be a very slow process, something that happens over many generations, thanks to adaptive mutations. But environmental change due to things like climate change, habitat destruction, pollution, etc. is happening very fast. There are just two options for species of all kinds: either adapt to environmental change or become extinct.

So, according to McGill biology professor, Andrew Gonzalez, the question arises, "Can evolution happen quickly enough to help a species survive?" The answer, according to his most recent study, published in Science, is a resounding yes.

By using a long-armed robot working 24/7 over a period of several of months, McGill Professors Graham Bell and Gonzalez were able to track the fate of over 2000 populations of baker's yeast for many generations. Yeast was chosen for the experiment because a lot is known about the genetic makeup of this model organism and because it can reproduce in a matter of hours. Bell and Gonzalez used the robot to submit different yeast populations to varying degrees of environmental stress in the form of salt and so study evolutionary rescue, which is the ability of a population to adapt rapidly through evolution, in real time.

What they observed was that the likelihood of evolutionary rescue depended on the severity and rate of change of the environment and the degree of prior exposure of populations to the environmental stressor (salt). The degree of isolation from neighboring populations also affected the capacity of the yeast populations to adapt through the accumulation of beneficial mutations.

Gonzalez and his team were in effect watching evolution at work. And what they discovered is that it can happen surprisingly fast, within 50 to 100 generations.

"The same general processes are occurring whether it's yeast or mammals," said Gonzalez. "At the end of the day we can't do the experiment with a panda or a moose, for example, because the time it would take to study their evolution is far longer than the time we have given the current rate of environmental change. At some point we have to work at the level of a model and satisfy ourselves that the basic reality we capture is sufficient to extrapolate from." While there has been theoretical work on the subject done in the past, this is the first time anyone has done a practical experiment of this kind, and shown evolutionary rescue at work.

Bell and Gonzalez discovered that a population was more likely to adapt quickly through evolutionary rescue if:

1. There was slow environmental deterioration, i.e. a slow increase in the concentration of salt, along with modest levels of contact with other populations. These populations were then able to adapt to environmental stress that would have been sufficient to eradicate their ancestors.
2. It was connected by dispersal, i.e. had previous contact, with another population that had already experienced environmental change. This population then had a much greater probability of avoiding extinction after a rapid and severe perturbation.

The research was funded by Canadian Foundation for Innovation, the Canada Research Chair Program and the Natural Sciences and Engineering Research Council of Canada.

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Unfortunately, many people have persistent misconceptions about evolution. Some are simple misunderstandings — ideas that develop in the course of learning about evolution, possibly from school experiences and/or the media. Other misconceptions may stem from purposeful attempts to misrepresent evolution and undermine the public’s understanding of this topic.

Browse the lists below to learn about common misconceptions regarding evolution, as well as clarifications of these misconceptions. You can also download a pdf of this section. (links need updating in PDF)

Misconceptions about evolutionary theory and processes

• Evolution is a theory about the origin of life.
• Evolutionary theory implies that life evolved (and continues to evolve) randomly, or by chance.
• Evolution results in progress; organisms are always getting better through evolution.
• Individual organisms can evolve during a single lifespan.
• Evolution only occurs slowly and gradually.
• Because evolution is slow, humans cannot influence it.
• Genetic drift only occurs in small populations.
• Humans are not currently evolving.
• Species are distinct natural entities, with a clear definition, that can be easily recognized by anyone.

Misconceptions about natural selection and adaptation

• Natural selection involves organisms trying to adapt.
• Natural selection gives organisms what they need.
• Humans can’t negatively impact ecosystems, because species will just evolve what they need to survive.
• Natural selection acts for the good of the species.
• The fittest organisms in a population are those that are strongest, healthiest, fastest, and/or largest.
• Natural selection is about survival of the very fittest individuals in a population.
• Natural selection produces organisms perfectly suited to their environments.
• All traits of organisms are adaptations.

Misconceptions about evolutionary trees

• Taxa that are adjacent on the tips of phylogeny are more closely related to one another than they are to taxa on more distant tips of the phylogeny.
• Taxa that appear near the top or right-hand side of a phylogeny are more advanced than other organisms on the tree.
• Taxa that are nearer the bottom or left-hand side of a phylogeny represent the ancestors of the other organisms on the tree.
• Taxa that are nearer the bottom or left-hand side of a phylogeny evolved earlier than other taxa on the tree.
• A long branch on a phylogeny indicates that the taxon has changed little since it diverged from other taxa.

Misconceptions about population genetics

• Each trait is influenced by one Mendelian locus.
• Each locus has only two alleles.

Misconceptions about evolution and the nature of science

• Evolution is not science because it is not observable or testable.
• Evolution is ‘just’ a theory.
• Evolutionary theory is invalid because it is incomplete and cannot give a total explanation for the biodiversity we see around us.
• Gaps in the fossil record disprove evolution.

Misconceptions about the acceptance of evolution

• The theory of evolution is flawed, but scientists won’t admit it.
• Evolution is a theory in crisis and is collapsing as scientists lose confidence in it.
• Most biologists have rejected ‘Darwinism’ and no longer agree with the ideas put forth by Darwin and Wallace.

Misconceptions about the implications of evolution

• Evolution leads to immoral behavior.
• Evolution supports the idea of ‘might makes right’ and rationalizes the oppression of some people by others.
• If students are taught that they are animals, they will behave like animals.

Misconceptions about evolution and religion

• Evolution and religion are incompatible.

Misconceptions about teaching evolution

• Teachers should teach “both sides” of the evolution issue and let students decide — or give equal time to evolution and creationism.
• Evolution is itself religious, so requiring teachers to teach evolution violates the first amendment.

Misconceptions about evolutionary theory and processes

• MISCONCEPTION: Evolution is a theory about the origin of life.
  CORRECTION: Evolutionary theory does encompass ideas and evidence regarding life’s origins (e.g., whether or not it happened near a deep-sea vent, which organic molecules came first, etc.), but this is not the central focus of evolutionary theory. Most of evolutionary biology deals with how life changed after its origin. Regardless of how life started, afterwards it branched and diversified, and most studies of evolution are focused on those processes.
• MISCONCEPTION: Evolutionary theory implies that life evolved (and continues to evolve) randomly, or by chance.
  CORRECTION: Chance and randomness do factor into evolution and the history of life in many different ways; however, some important mechanisms of evolution are non-random and these make the overall process non-random. For example, consider the process of natural selection, which results in adaptations — features of organisms that appear to suit the environment in which the organisms live (e.g., the fit between a flower and its pollinator, the coordinated response of the immune system to pathogens, and the ability of bats to echolocate). Such amazing adaptations clearly did not come about “by chance.” They evolved via a combination of random and non-random processes. The process of mutation, which generates genetic variation, is random, but selection is non-random. Selection favored variants that were better able to survive and reproduce (e.g., to be pollinated, to fend off pathogens, or to navigate in the dark). Over many generations of random mutation and non-random selection, complex adaptations evolved. To say that evolution happens “by chance” ignores half of the picture. To learn more about the process of natural selection, visit our article on this topic. To learn more about random mutation, visit our article on DNA and mutations.
• MISCONCEPTION: Evolution results in progress; organisms are always getting better through evolution.
  CORRECTION: One important mechanism of evolution, natural selection, does result in the evolution of improved abilities to survive and reproduce; however, this does not mean that evolution is progressive — for several reasons. First, as described in a misconception below (link to “Natural selection produces organisms perfectly suited to their environments”), natural selection does not produce organisms perfectly suited to their environments. It often allows the survival of individuals with a range of traits — individuals that are “good enough” to survive. Hence, evolutionary change is not always necessary for species to persist. Many taxa (like some mosses, fungi, sharks, opossums, and crayfish) have changed little physically over great expanses of time. Second, there are other mechanisms of evolution that don’t cause adaptive change. Mutation, migration, and genetic drift may cause populations to evolve in ways that are actually harmful overall or make them less suitable for their environments. For example, the Afrikaner population of South Africa has an unusually high frequency of the gene responsible for Huntington’s disease because the gene version drifted to high frequency as the population grew from a small starting population. Finally, the whole idea of “progress” doesn’t make sense when it comes to evolution. Climates change, rivers shift course, new competitors invade — and an organism with traits that are beneficial in one situation may be poorly equipped for survival when the environment changes. And even if we focus on a single environment and habitat, the idea of how to measure “progress” is skewed by the perspective of the observer. From a plant’s perspective, the best measure of progress might be photosynthetic ability; from a spider’s it might be the efficiency of a venom delivery system; from a human’s, cognitive ability. It is tempting to see evolution as a grand progressive ladder with Homo sapiens emerging at the top. But evolution produces a tree, not a ladder — and we are just one of many twigs on the tree.
• MISCONCEPTION: Individual organisms can evolve during a single lifespan.
  CORRECTION: Evolutionary change is based on changes in the genetic makeup of populations over time. Populations, not individual organisms, evolve. Changes in an individual over the course of its lifetime may be developmental (e.g., a male bird growing more colorful plumage as it reaches sexual maturity) or may be caused by how the environment affects an organism (e.g., a bird losing feathers because it is infected with many parasites); however, these shifts are not caused by changes in its genes. While it would be handy if there were a way for environmental changes to cause adaptive changes in our genes — who wouldn’t want a gene for malaria resistance to come along with a vacation to Mozambique? — evolution just doesn’t work that way. New gene variants (i.e., alleles) are produced by random mutation, and over the course of many generations, natural selection may favor advantageous variants, causing them to become more common in the population.
• MISCONCEPTION: Evolution only occurs slowly and gradually.
  
  
  CORRECTION: Evolution occurs slowly and gradually, but it can also occur rapidly. We have many examples of slow and steady evolution — for example, the gradual evolution of whales from their land-dwelling, mammalian ancestors, as documented in the fossil record. But we also know of many cases in which evolution has occurred rapidly. For example, we have a detailed fossil record showing how some species of single-celled organism, called foraminiferans, evolved new body shapes in the blink of a geological eye, as shown here.

Similarly, we can observe rapid evolution going on around us all the time. Over the past 50 years, we’ve observed squirrels evolve new breeding times in response to climate change, a fish species evolve resistance to toxins dumped into the Hudson River, and a host of microbes evolve resistance to new drugs we’ve developed. Many different factors can foster rapid evolution — small population size, short generation time, big shifts in environmental conditions — and the evidence makes it clear that this has happened many times. To learn more about the pace of evolution, visit Evolution 101. To learn more about rapid evolution in response to human-caused changes in the environment, visit our news story on climate change , our news story on the evolution of PCB-resistant fish, or our research profile on the evolution of fish size in response to our fishing practices.

• MISCONCEPTION: Because evolution is slow, humans cannot influence it.
  CORRECTION: As described in the misconception about evolutionary rates above, evolution sometimes occurs quickly. And since humans often cause major changes in the environment, we are frequently the instigators of evolution in other organisms. Here are just a few examples of human-caused evolution for you to explore:
  — Several species have evolved in response to climate change.
  — Fish populations have evolved in response to our fishing practices.
  — Insects like bedbugs and crop pests have evolved resistance to our pesticides.
  — Bacteria, HIV, malaria, and cancer have evolved resistance to our drugs.
• MISCONCEPTION: Genetic drift only occurs in small populations.
  CORRECTION: Genetic drift has a larger effect on small populations, but the process occurs in all populations — large or small. Genetic drift occurs because, due to chance, the individuals that reproduce may not exactly represent the genetic makeup of the whole population. For example, in one generation of a population of captive mice, brown-furred individuals may reproduce more than white-furred individuals, causing the gene version that codes for brown fur to increase in the population — not because it improves survival, just because of chance. The same process occurs in large populations: some individuals may get lucky and leave many copies of their genes in the next generation, while others may be unlucky and leave few copies. This causes the frequencies of different gene versions to “drift” from generation to generation. However, in large populations, the changes in gene frequency from generation to generation tend to be small, while in smaller populations, those shifts may be much larger. Whether its impact is large or small, genetic drift occurs all the time, in all populations. It’s also important to keep in mind that genetic drift may act at the same time as other mechanisms of evolution, like natural selection and migration. To learn more about genetic drift, visit Evolution 101. To learn more about population size as it relates to genetic drift, visit this advanced article.
• MISCONCEPTION: Humans are not currently evolving.
  CORRECTION: Humans are now able to modify our environments with technology. We have invented medical treatments, agricultural practices, and economic structures that significantly alter the challenges to reproduction and survival faced by modern humans. So, for example, because we can now treat diabetes with insulin, the gene versions that contribute to juvenile diabetes are no longer strongly selected against in developed countries. Some have argued that such technological advances mean that we’ve opted out of the evolutionary game and set ourselves beyond the reach of natural selection — essentially, that we’ve stopped evolving. However, this is not the case. Humans still face challenges to survival and reproduction, just not the same ones that we did 20,000 years ago. The direction, but not the fact of our evolution has changed. For example, modern humans living in densely populated areas face greater risks of epidemic diseases than did our hunter-gatherer ancestors (who did not come into close contact with so many people on a daily basis) — and this situation favors the spread of gene versions that protect against these diseases. Scientists have uncovered many such cases of recent human evolution. Explore these links to learn about:
  — genetic evidence regarding recent human evolution
  — the recent evolution of adaptations that allow humans to thrive at high altitudes
  — the recent evolution of human genetic traits that protect against malaria
  — the recent evolution of lactose tolerance in humans
• MISCONCEPTION: Species are distinct natural entities, with a clear definition, that can be easily recognized by anyone.
  CORRECTION: Many of us are familiar with the biological species concept, which defines a species as a group of individuals that actually or potentially interbreed in nature. That definition of a species might seem cut and dried — and for many organisms (e.g., mammals), it works well — but in many other cases, this definition is difficult to apply. For example, many bacteria reproduce mainly asexually. How can the biological species concept be applied to them? Many plants and some animals form hybrids in nature, even if they largely mate within their own groups. Should groups that occasionally hybridize in selected areas be considered the same species or separate species? The concept of a species is a fuzzy one because humans invented the concept to help get a grasp on the diversity of the natural world. It is difficult to apply because the term species reflects our attempts to give discrete names to different parts of the tree of life — which is not discrete at all, but a continuous web of life, connected from its roots to its leaves. To learn more about the biological species concept, visit Evolution 101. To learn about other species concepts, visit this side trip.

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Misconceptions about natural selection and adaptation

• MISCONCEPTION: Natural selection involves organisms trying to adapt.
  CORRECTION: Natural selection leads to the adaptation of species over time, but the process does not involve effort, trying, or wanting. Natural selection naturally results from genetic variation in a population and the fact that some of those variants may be able to leave more offspring in the next generation than other variants. That genetic variation is generated by random mutation — a process that is unaffected by what organisms in the population want or what they are “trying” to do. Either an individual has genes that are good enough to survive and reproduce, or it does not; it can’t get the right genes by “trying.” For example bacteria do not evolve resistance to our antibiotics because they “try” so hard. Instead, resistance evolves because random mutation happens to generate some individuals that are better able to survive the antibiotic, and these individuals can reproduce more than other, leaving behind more resistant bacteria. To learn more about the process of natural selection, visit our article on this topic. To learn more about random mutation, visit our article on DNA and mutations.
• MISCONCEPTION: Natural selection gives organisms what they need.
  CORRECTION: Natural selection has no intentions or senses; it cannot sense what a species or an individual “needs.” Natural selection acts on the genetic variation in a population, and this genetic variation is generated by random mutation — a process that is unaffected by what organisms in the population need. If a population happens to have genetic variation that allows some individuals to survive a challenge better than others or reproduce more than others, then those individuals will have more offspring in the next generation, and the population will evolve. If that genetic variation is not in the population, the population may survive anyway (but not evolve via natural selection) or it may die out. But it will not be granted what it “needs” by natural selection. To learn more about the process of natural selection, visit our article on this topic. To learn more about random mutation, visit our article on DNA and mutations.
• MISCONCEPTION: Humans can’t negatively impact ecosystems, because species will just evolve what they need to survive.
  CORRECTION: As described in the misconception above, natural selection does not automatically provide organisms with the traits they “need” to survive. Of course, some species may possess traits that allow them to thrive under conditions of environmental change caused by humans and so may be selected for, but others may not and so may go extinct. If a population or species doesn’t happen to have the right kinds of genetic variation, it will not evolve in response to the environmental changes wrought by humans, whether those changes are caused by pollutants, climate change, habitat encroachment, or other factors. For example, as climate change causes the Arctic sea ice to thin and break up earlier and earlier, polar bears are finding it more difficult to obtain food. If polar bear populations don’t have the genetic variation that would allow some individuals to take advantage of hunting opportunities that are not dependent on sea ice, they could go extinct in the wild.
• MISCONCEPTION: Natural selection acts for the good of the species.
  CORRECTION: When we hear about altruism in nature (e.g., dolphins spending energy to support a sick individual, or a meerkat calling to warn others of an approaching predator, even though this puts the alarm sounder at extra risk), it’s tempting to think that those behaviors arose through natural selection that favors the survival of the species — that natural selection promotes behaviors that are good for the species as a whole, even if they are risky or detrimental for individuals in the population. However, this impression is incorrect. Natural selection has no foresight or intentions. In general, natural selection simply selects among individuals in a population, favoring traits that enable individuals to survive and reproduce, yielding more copies of those individuals’ genes in the next generation. Theoretically, in fact, a trait that is advantageous to the individual (e.g., being an efficient predator) could become more and more frequent and wind up driving the whole population to extinction (e.g., if the efficient predation actually wiped out the entire prey population, leaving the predators without a food source).

So what’s the evolutionary explanation for altruism if it’s not for the good of the species? There are many ways that such behaviors can evolve. For example, if altruistic acts are “repaid” at other times, this sort of behavior may be favored by natural selection. Similarly, if altruistic behavior increases the survival and reproduction of an individual’s kin (who are also likely to carry altruistic genes), this behavior can spread through a population via natural selection. To learn more about the process of natural selection, visit our article on this topic.

Advanced students of evolutionary biology may be interested to know that selection can act at different levels and that, in some circumstances, species-level or group-level selection may occur. However, it’s important to remember that, even in this case, selection has no foresight and is not “aiming” at any outcome; it is simply favoring the reproducing units that are best at leaving copies of themselves in the next generation. To learn more about levels of selection, visit our side trip on this topic.

• MISCONCEPTION: The fittest organisms in a population are those that are strongest, healthiest, fastest, and/or largest.
  CORRECTION: In evolutionary terms, fitness has a very different meaning than the everyday meaning of the word. An organism’s evolutionary fitness does not indicate its health, but rather its ability to get its genes into the next generation. The more fertile offspring an organism leaves in the next generation, the fitter it is. This doesn’t always correlate with strength, speed, or size. For example, a puny male bird with bright tail feathers might leave behind more offspring than a stronger, duller male, and a spindly plant with big seed pods may leave behind more offspring than a larger specimen — meaning that the puny bird and the spindly plant have higher evolutionary fitness than their stronger, larger counterparts. To learn more about evolutionary fitness, visit Evolution 101.
• MISCONCEPTION: Natural selection is about survival of the very fittest individuals in a population.
  CORRECTION: Though “survival of the fittest” is the catchphrase of natural selection, “survival of the fit enough” is more accurate. In most populations, organisms with many different genetic variations survive, reproduce, and leave offspring carrying their genes in the next generation. It is not simply the one or two “best” individuals in the population that pass their genes on to the next generation. 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. These individuals may not be the “fittest” in the population, but they are “fit enough” to reproduce and pass their genes on to the next generation. To learn more about the process of natural selection, visit our article on this topic. To learn more about evolutionary fitness, visit Evolution 101.
• MISCONCEPTION: Natural selection produces organisms perfectly suited to their environments.
  CORRECTION: Natural selection is not all-powerful. There are many reasons that natural selection cannot produce “perfectly-engineered” traits. 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.g., a bird with the “perfect” tail plumage to attract mates maybe be particularly vulnerable to predators because of its long tail). 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.
• MISCONCEPTION: All traits of organisms are adaptations.
  CORRECTION: Because living things have so many impressive adaptations (incredible camouflage, sneaky means of catching prey, flowers that attract just the right pollinators, etc.), it’s easy to assume that all features of organisms must be adaptive in some way — to notice something about an organism and automatically wonder, “Now, what’s that for?” While some traits are adaptive, it’s important to keep in mind that many traits are not adaptations at all. Some may be the chance results of history. For example, the base sequence GGC codes for the amino acid glycine simply because that’s the way it happened to start out — and that’s the way we inherited it from our common ancestor. There is nothing special about the relationship between GGC and glycine. It’s just a historical accident that stuck around. Others traits may be by-products of another characteristic. For example, the color of blood is not adaptive. There’s no reason that having red blood is any better than having green blood or blue blood. Blood’s redness is a by-product of its chemistry, which causes it to reflect red light. The chemistry of blood may be an adaptation, but blood’s color is not an adaptation. 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.

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Misconceptions about evolutionary trees

• MISCONCEPTION: Taxa that are adjacent on the tips of phylogeny are more closely related to one another than they are to taxa on more distant tips of the phylogeny.
  
  
  CORRECTION: In a phylogeny, information about relatedness is portrayed by the pattern of branching, not by the order of taxa at the tips of the tree. Organisms that share a more recent branching point (i.e., a more recent common ancestor) are more closely related than are organisms connected by a more ancient branching point (i.e., one that is closer to the root of the tree). 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. The ancestor/branch point shared by A and B is the same as the ancestor/branch point shared by A and C, as well as by A 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. That’s because taxa B and D share a more recent common ancestor (labeled on the tree below) than do taxa B and A.It may help to remember that the same set of relationships can be portrayed in many different ways. 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. The information in a phylogeny is contained in the branching pattern, not in the order of the taxa at the tips of the tree. To learn more phylogenetics, visit our tutorial on the topic.

• MISCONCEPTION: Taxa that appear near the top or right-hand side of a phylogeny are more advanced than other organisms on the tree.
  CORRECTION: This misconception encompasses two distinct misunderstandings. First, when it comes to evolution, terms like “primitive” and “advanced” don’t apply. 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. Second, an organism’s position on a phylogeny only indicates its relationship to other organisms, not how adaptive or specialized or extreme its traits are. For example, on the tree below, taxon D may be more or less specialized than taxa A, B, and C.
  

  It may help to remember that the same set of relationships can be portrayed in many different ways. The information in a phylogeny is contained in the branching pattern, not in the order of the taxa at the tips of the tree. The following phylogenies are all equivalent, but have different taxa positioned at the right-hand side of the phylogeny. There is no relationship between the order of taxa at the tips of a phylogeny and evolutionary traits that might be considered “advanced.” To learn more phylogenetics, visit our tutorial on the topic.

   

• MISCONCEPTION: Taxa that are nearer the bottom or left-hand side of a phylogeny represent the ancestors of the other organisms on the tree.
  
  
  CORRECTION: On phylogenies, ancestral forms are represented by branches and branching points, not by the tips of the tree. The tips of the tree (wherever they are located — top, bottom, right, or left) represent descendents, and the tree itself represents the relationships among these descendents. In the phylogeny here, taxon A is the cousin of taxa B, C, and D — not their ancestor.This is true even if the organisms shown on the phylogeny are extinct. For example, Tiktaalik (shown on the phylogeny below) is an extinct, fish-like organism that is closely related to the ancestor of modern amphibians, mammals, and lizards. Though Tiktaalik is extinct, it is not an ancestral form and so is shown at a tip of the phylogeny, not as a branch or node. The actual ancestor of Tiktaalik, as well as that of modern amphibians, mammals, and lizards, is shown on the phylogeny below. To learn more phylogenetics, visit our tutorial on the topic.
  

   

• MISCONCEPTION: Taxa that are nearer the bottom or left-hand side of a phylogeny evolved earlier than other taxa on the tree.
  CORRECTION: It is the order of branching points from root to tip on a phylogeny that indicate the order in which different clades split from one another — not the order of taxa at the tips of the phylogeny. On the phylogeny below, the earliest and most recent branching points are labeled.
  

  Usually phylogenies are presented so that the taxa with the longest branches appear at the bottom or left-hand side of the phylogeny (as is the case in the phylogeny above). These clades are connected to the phylogeny by the deepest branching point and did diverge from others on the phylogeny first. However, it’s important to remember that the same set of relationships can be represented by phylogenies with different orderings of taxa at the tips and that taxa with long branches are not always positioned near the left or bottom of a phylogeny (as shown below).

  

  It’s also important to keep in mind that substantial amounts of evolutionary change may have occurred in a lineage after it diverged from other closely related lineages. This means that the characteristics we associate with these long-branched taxa today may not have evolved until substantially after they were a distinct lineage. For more on this, see the misconception below. To learn more phylogenetics, visit our tutorial on the topic.

• MISCONCEPTION: A long branch on a phylogeny indicates that the taxon has changed little since it diverged from other taxa.
  CORRECTION: In most phylogenies that are seen in textbooks and the popular press, branch length does not indicate anything about the amount of evolutionary change that has occurred along that branch. Branch length usually does not mean anything at all and is just a function of the order of branching on the tree. However, advanced students may be interested to know that in the specialized phylogenies where the branch length does mean something, a longer branch usually indicates either a longer time period since that taxon split from the rest of the organisms on the tree or more evolutionary change in a lineage! Such phylogenies can usually be identified by either a scale bar or the fact that the taxa represented don’t line up to form a column or row. In the phylogeny on the left below,1 each branch’s length corresponds to the number of amino acid changes that evolved in a protein along that branch. On longer branches, the protein collagen seems to have experienced more evolutionary change than it did along shorter branches. The phylogeny on the right shows the same relationships, but branch length is not meaningful in this phylogeny. Notice the lack of scale bar and how all the taxa line up in this phylogeny.
  

  The misconception that a taxon on a short branch has undergone little evolutionary change probably arises in part because of how phylogenies are built. Many phylogenies are built using an “outgroup” — a taxon outside the group of interest. Sometimes a particular outgroup is selected because it is thought to have characteristics in common with the ancestor of the clade of interest. The outgroup is generally positioned near the bottom or left-hand side of a phylogeny and is shown without any of its own close relatives — which causes the outgroup to have a long branch. This means that organisms thought to have characteristics in common with the ancestor of a clade are often seen with long branches on phylogenies. It’s important to keep in mind that this is an artifact and that there is no connection between long branch length and little evolutionary change.

  It may help to remember that often, long branches can be made to appear shorter simply by including more taxa in the phylogeny. For example, the phylogeny on the left below focuses on the relationships among reptiles, and consequently, the mammals are shown as having a long branch. However, if we simply add more details about relationships among mammals (as shown on the right below), no taxon on the phylogeny has a particularly long branch. Both phylogenies are correct; the one on the right simply shows more detail regarding mammalian relationships. To learn more phylogenetics, visit our tutorial on the topic.

  What is it called when evolution occurs rapidly?

  The theory of punctuated equilibrium states that evolutionary change is characterised by short periods of rapid evolution followed by longer periods of stasis in which no change occurs.

  Can evolution ever occur quickly?

  CORRECTION: Evolution occurs slowly and gradually, but it can also occur rapidly. We have many examples of slow and steady evolution — for example, the gradual evolution of whales from their land-dwelling, mammalian ancestors, as documented in the fossil record.

  What is evolution over a short period of time called?

  Evolution that occurs over a short period of time is known as microevolution. It might take place in just a couple of generations. This scale of evolution occurs at the level of the population.

  What causes evolution to be rapidly?

  Rapid Evolution within Populations. In the right conditions, adaptation can happen very rapidly. Where there is existing genetic variation for a trait within a population, and that trait comes under strong selection, the trait can change substantially across just a few generations.