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How do beneficial features evolve in species without progressing through detrimental stages?

How do beneficial features evolve in species without progressing through detrimental stages?


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I'm thinking in particular of wings on birds that would - I'm guessing - have to progress through stages during which they confer no particular advantage. Or is it that all evolved features must have followed a path of incremental benefit therefore imposing a fundamental limit on what evolution through natural selection can "achieve"? (features that are not beneficial while gradually appearing cannot be evolved)


Features can evolve (or change already present features) which have no negative effect under the current conditions. You can very well have neutral changes which have no purpose. They can then prove positive later (or in a different environment). Changes are usually small and take place over very long time periods.

An example would be bacteria which mutated one of their enzymes for a energy pathway. Before the mutation the enzyme could only metabolize nutrient A, after it, it is a bit less specific for A, but can also metabolize B. As long as the living conditions are so, that only A is present, this will not change anything. If the conditions are so, that A and B are present and A gets limited, these cells will have a profound advantage over cells, which can only utilize A.


There are some interesting hypotheses that wings initially evolved for display, not flight. Then at some point, the winged dinosaurs also had a locomotive advantage, at which point the wings could further evolve with selection for even better locomotion and eventually full flight.

Here is an article about Darla Zelenitsky's work on this: http://phenomena.nationalgeographic.com/2012/10/25/bird-mimic-dinosaur-hints-that-wings-evolved-for-show-not-flight/

There is also an article by Richard Prum in a recent Scientific American that mentions this.https://www.scientificamerican.com/article/dinosaur-feathers-came-before-birds-and-flight/


Can postfertile life stages evolve as an anticancer mechanism?

Affiliation Centre de Recherches Ecologiques et Evolutives sur le Cancer/Centre de Recherches en Ecologie et Evolution de la Santé, Unité Mixte de Recherches, Institut de Recherches pour le Développement 224-Centre National de la Recherche Scientifique 5290-Université de Montpellier, Montpellier, France

Affiliation Centre de Recherches Ecologiques et Evolutives sur le Cancer/Centre de Recherches en Ecologie et Evolution de la Santé, Unité Mixte de Recherches, Institut de Recherches pour le Développement 224-Centre National de la Recherche Scientifique 5290-Université de Montpellier, Montpellier, France

Affiliation Centre de Recherches Ecologiques et Evolutives sur le Cancer/Centre de Recherches en Ecologie et Evolution de la Santé, Unité Mixte de Recherches, Institut de Recherches pour le Développement 224-Centre National de la Recherche Scientifique 5290-Université de Montpellier, Montpellier, France

Affiliations Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Victoria, Australia, School of Natural Sciences, University of Tasmania, Hobart, Tasmania, Australia

Affiliations Centre de Recherches Ecologiques et Evolutives sur le Cancer/Centre de Recherches en Ecologie et Evolution de la Santé, Unité Mixte de Recherches, Institut de Recherches pour le Développement 224-Centre National de la Recherche Scientifique 5290-Université de Montpellier, Montpellier, France, Unité mixte internationale de Modélisation Mathématique et Informatique des Systèmes Complexes, Unité Mixte de Recherches, Institut de Recherches pour le développement/Sorbonne Université, France, Departamento de Etología, Fauna Silvestre y Animales de Laboratorio, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México (UNAM), Ciudad de México, México

Affiliations Centre de Recherches Ecologiques et Evolutives sur le Cancer/Centre de Recherches en Ecologie et Evolution de la Santé, Unité Mixte de Recherches, Institut de Recherches pour le Développement 224-Centre National de la Recherche Scientifique 5290-Université de Montpellier, Montpellier, France, CHU Arnaud de Villeneuve, Montpellier, France

Affiliation ISEM, Université de Montpellier, CNRS, IRD, EPHE, Montpellier, France

Contributed equally to this work with: Jean-François Lemaitre, Alexandra Alvergne

Affiliation Centre National de la Recherche Scientifique, Unité mixte de recherche 5558, Laboratoire de Biométrie et Biologie Evolutive, Université Lyon 1 Villeurbanne, France

Contributed equally to this work with: Jean-François Lemaitre, Alexandra Alvergne

Affiliations ISEM, Université de Montpellier, CNRS, IRD, EPHE, Montpellier, France, Institute of Social and Cultural Anthropology, School of Anthropology and Museum Ethnography, University of Oxford, United Kingdom


How do beneficial features evolve in species without progressing through detrimental stages? - Biology

Unfortunately, many students have persistent misconceptions about evolution. Some are simple misunderstandings — ideas that develop in the course of learning about evolution. Other misconceptions may stem from purposeful attempts to misrepresent evolution and undermine the public's understanding of this topic. Whatever their source, the ideas with which your students come to the classroom will impact what they gain from your teaching. Being aware of inaccurate preconceptions can help you respond to student queries appropriately, avoid reinforcing such misconceptions, and develop instructional materials and strategies that correct these ideas. To learn more about your students' misconceptions, you may wish to administer our Evolution Misconceptions Diagnostic. This 12-item test addresses some of the most commonly held misconceptions.

Browse the lists below to learn about common misconceptions regarding evolution, as well as clarifications of these misconceptions. Also, note that many of these misconceptions are related to common teaching pitfalls. Read more about these pitfalls and confusing terminology at different grade levels: K-2, 3-5, 6-8, 9-12, undergrad.


Misconceptions about evolutionary theory and processes

Misconceptions about natural selection and adaptation

Misconceptions about evolutionary trees

Misconceptions about population genetics

Misconceptions about evolution and the nature of science

Misconceptions about the acceptance of evolution

Misconceptions about the implications of evolution

Misconceptions about evolution and religion

Misconceptions about teaching evolution

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.

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.

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, 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.

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.

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 below.

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.

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:

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.

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:

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.

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.

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.

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.

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. It 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 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.

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.

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.

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.

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.

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 below, 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 advanced tutorial on the topic.

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 advanced tutorial on the topic.

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 below, 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 advanced tutorial on the topic.

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 advanced tutorial on the topic.

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 advanced tutorial on the topic.

MISCONCEPTION: Each trait is influenced by one Mendelian locus.

CORRECTION: Before learning about complex or quantitative traits, students are usually taught about simple Mendelian traits controlled by a single locus — for example, round or wrinkled peas, purple or white flowers, green or yellow pods, etc. Unfortunately, students may assume that all traits follow this simple model, and that is not the case. Both quantitative (e.g., height) and qualitative (e.g., eye color) traits may be influenced by multiple loci and these loci may interact with one another and may not follow the simple rules of Mendelian dominance. 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.

CORRECTION: Before learning about complex traits, students are usually taught about simple genetic systems in which only two alleles influence a phenotype. 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.

MISCONCEPTION: Evolution is not science because it is not observable or testable.

CORRECTION: This misconception encompasses two incorrect ideas: (1) that all science depends on controlled laboratory experiments, and (2) that evolution cannot be studied with such experiments. 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. Second, though we can't run an experiment that will tell us how the dinosaur lineage radiated, we can study many aspects of evolution with controlled experiments in a laboratory setting. In organisms with short generation times (e.g., bacteria or fruit flies), we can actually observe evolution in action over the course of an experiment. 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.

CORRECTION: This misconception stems from a mix-up between casual and scientific use of the word theory. 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. Evolution is a well-supported and broadly accepted scientific theory it is not 'just' a hunch. To learn more about the nature of scientific theories, visit the Understanding Science website.

CORRECTION: This misconception stems from a misunderstanding of the nature of scientific theories. 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. While we don't know everything there is to know about evolution (or any other scientific discipline, for that matter), we do know a great deal about the history of life, the pattern of lineage-splitting through time, and the mechanisms that have caused these changes. 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.g., that treating AIDS patients with a cocktail of medications should slow the evolution of the virus), and has proven itself time and time again in thousands of experiments and observational studies. To date, evolution is the only well-supported explanation for life's diversity. To learn more about the nature of scientific theories, visit the Understanding Science website.

CORRECTION: While it's true that there are gaps in the fossil record, this does not constitute evidence against evolutionary theory. 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. If evolutionary theory were true, then we'd expect there to have been transitional forms connecting ancient species with their ancestors and descendents. 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. Many organisms don't have any body parts that fossilize well, the environmental conditions for forming good fossils are rare, and of course, we've only discovered a small percentage of the fossils that might be preserved somewhere on Earth. 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.

MISCONCEPTION: The theory of evolution is flawed, but scientists won't admit it.

CORRECTION: Scientists have studied the supposed "flaws" that anti-evolution groups claim exist in evolutionary theory and have found no support for these claims. These "flaws" are based on misunderstandings of evolutionary theory or misrepresentations of the evidence. As scientists gather new evidence and as new perspectives emerge, evolutionary theory continues to be refined, but that doesn't mean that the theory is flawed. Science is a competitive endeavor, and scientists would be eager to study and correct "flaws" in evolutionary theory if they existed. For more on how evolutionary theory changes, see our misconception on this topic above.

CORRECTION: Evolutionary theory is not in crisis scientists accept evolution as the best explanation for life's diversity because of the multiple lines of evidence supporting it, its broad power to explain biological phenomena, and its ability to make accurate predictions in a wide variety of situations. 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.

CORRECTION: It is true that we have learned a lot about evolution since Darwin's time. 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. It's important to keep in mind that elaboration, modification, and expansion of scientific theories is a normal part of the process of science. For more on how evolutionary theory changes, see our misconception on this topic above.

MISCONCEPTION: Evolution leads to immoral behavior.

CORRECTION: Evolution does not make ethical statements about right and wrong. Some people misinterpret the fact that evolution has shaped animal behavior (including human behavior) as supporting the idea that whatever behaviors are "natural" are the "right" ones. This is not the case. It is up to us, as societies and individuals, to decide what constitutes ethical and moral behavior. Evolution simply helps us understand how life has changed and continues to change over time — and does not tell us whether these processes or the results of them are "right" or "wrong". 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.

CORRECTION: In the nineteenth and early twentieth centuries, a philosophy called Social Darwinism arose from a misguided effort to apply lessons from biological evolution to society. 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. Pre-existing prejudices were rationalized by the notion that colonized nations, poor people, or disadvantaged minorities must have deserved their situations because they were "less fit" than those who were better off. 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. Visit the Talk Origins Archives for more information on Social Darwinism.

CORRECTION: Part of evolutionary theory includes the idea that all organisms on Earth are related. 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.

MISCONCEPTION: Evolution and religion are incompatible.

CORRECTION: Because of some individuals and groups stridently declaring their beliefs, it's easy to get the impression that science (which includes evolution) and religion are at war however, the idea that one always has to choose between science and religion is incorrect. 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.g., the belief that the world and all life on it was created in six literal days does conflict with evolutionary theory) however, most religious groups have no conflict with the theory of evolution or other scientific findings. 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.

MISCONCEPTION: Teachers should teach "both sides" of the evolution issue and let students decide — or give equal time to evolution and creationism.

CORRECTION: Equal time does not make sense when the two "sides" are not equal. 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. In contrast, a debate pitting a scientific concept against a religious belief has no place in a science class and misleadingly suggests that a "choice" between the two must be made. The "fairness" argument has been used by groups attempting to insinuate their religious beliefs into science curricula. 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.

CORRECTION: This fallacious argument is based on the idea that evolution and religion are fundamentally the same since they are both "belief systems." This idea is simply incorrect. 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. Other decisions specifically uphold a school district's right to require the teaching of evolution. 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.


Evidence for eye evolution from living animals

Only about a third of all animal phyla contain species with proper eyes, another third contain species with light-sensitive organs only, and a third have no means of light detection, although many can detect heat. 15 Nonetheless, of those animals with eyes, both vertebrates and most invertebrates, an enormous variety of eye designs, placement and sizes exists. 10 The eyeball diameter ranges from less then a tenth of a millimetre in certain water fleas to 370 mm in the giant squid. 16 Eye placement also varies, ranging from the common binocular vision employed by most mammals to the movable eye on each side of the head used by many lizards.

The number of eyes in one animal can also vary from none to eight. In spiders alone the number ranges from zero to eight, always existing in pairs of two. Some eyes contain both a lens and a retina-like structure in a single cell. 17 A complex telephoto lens was identified in the chameleon in 1995. The reason why so many designs exist is because eyes must serve very different life forms that live in very different environments. Animals live in the ground, inside of other animals, in the air, on land, in salt water and in fresh water. Furthermore, animals range in size from a water flea to a whale.

Table 1. Mean numbers of myelinated fibres in the optic nerve of selected vertebrates. Note the enormous difference within each category. For example birds range from 408 to 988 thousand, mammals from 7 thousand to 1.21 million. (From Cousins 50 ). Click for larger view.

Although many kinds of very different eyes are known, no direct evidence exists to support the evolution of the eye and its accessory structures. Furthermore, much evidence contradicts such evolutionary beliefs. For example, note in table 1 that the number of myelinated fibres in the optic nerve does not correlate with putative evolutionary development. A pigeon has almost as many fibres as a human. Many birds, such as the eagle and hawk, have excellent vision yet have half as many fibres as a domestic pig.

Another example is visual pigments. The presumably highest, most evolved form of life, the higher primates, have only two cone photoreceptors, blue and green, but birds have a total of six pigments: four cone pigments plus pinopsin (a pineal photoreceptive molecule) and rhodopsin for black and white vision. 12 , 18 Put another way, chickens, humans and mice all have the rhodopsin pigment mice in addition have blue and green humans have blue, green, and red and birds have these three pigments plus violet and pinopsin. For every colour that humans perceive, birds can see very distinct multiple colours, including ultraviolet light. Birds use infrared light (which we sense as heat) for night vision, allowing them to rapidly visualize their young in a dense, dark tree.

The possibility of classifying eyes in living animals from simple to complex&mdashsimple types existing in simple animals and complex types in complex animals (which we will show cannot be done)&mdashdoes not provide evidence for an evolutionary relationship. A primary problem is that this attempt is based only on eye characteristics as they presently exist. Historical eye evolution cannot be proven by listing a series of existing eyes from simple to complex and then arguing that the complex evolved from the simple because evolution requires that all existing eyes have an equally long evolutionary history.

According to neo-Darwinism, the simplest modern eye in living animals has had the same amount of time and evolutionary history as the most complex eye because life began about 3.5 billion years ago and all life today evolved from this point in history. Although Darwinists argue that many of these eyes are evolutionary dead ends, this would require an admission that these modern &lsquosimple&rsquo eyes are only analogues or &lsquosimilar&rsquo to putative past ancestral eyes (to more complex modern types), which reduces their value as evidence.

Darwinists need to determine the eye designs from which existing eyes have actually descended, one from the other, over time. Duke-Elder and Darwin (1872) before him were unable to do this, yet they offered their list of eyes of varying complexity as evidence of evolution. Cousins wrote:

Croft concluded that the claim that we can line up eyes in an evolutionary sequence from very simple to very complex is false because research on the developmental history of the eye in widely differing species finds

Sinclair also concluded that vertebrates and most invertebrates, including insects and cephalopods (molluscs, including octopuses and squid), all have eyes with common visual elements, including &lsquoa similar photoreceptor design&rsquo, yet have a marked &lsquodissimilarity of their appearance&rsquo. 10

The source of the design and evolution of the eye, Darwinists postulate, was a series of beneficial mutations that had to occur in appropriate unison in order to produce the set of structures required for eyes to function. The new mutation set, Darwinists argue, resulted in a superior structure compared to the old one, and this new and better eye improved the animals&rsquo ability to compete against other forms of life. Some of the many problems with this conclusion were noted by Grassé in his discussion of Myrmelion (ant lion) anatomy:

An organ that did not aid the animal&rsquos survival would use scarce energy, nutrients and body space and, if the organ were not used, would be at high risk for problems such as infection. An eye modification would not be selected until it was not only functional but produced a system demonstratively better than the existing organ. Only then could natural selection operate to choose from existing variations to perfect the organ beyond mere functional effectiveness.

Table 2. Land and Nilsson&rsquos widely used classification system of eye designs. Other systems are also used today, illustrating the problems in arranging eye designs into hierarchies. Also note that the Land and Nilsson system also does not show a clear simple to complex design hierarchy. (From Land and Nilson 12 ). Click for larger view.


Engage: Discovering Changes in Shape during Development

In a homework assignment designed to engage students with the idea that organisms undergo large changes in shape as they grow, students conduct an Internet search about the axolotl, a Mexican salamander that reaches adulthood without undergoing metamorphosis (Zimmer, 1998). The students sketch an adult axolotl and write a brief explanation of why the adult looks juvenile. Their explanations should communicate that the timing of development has changed such that the adult axolotl retains the juvenile features even though it reaches sexual maturity. (Because this is an Internet search, an opportunity for addressing information literacy exists sometimes, I ask students how they determined whether the sources they used were appropriate.) I also ask students to think of other organisms that change shape during development (like dogs) in addition to ones that grow without changing shape (like cats).

The homework assignment concludes with a brief introduction to the work we will do in class. I tell students that we will study chimpanzees (Pan troglodytes), anatomically modern humans (Homo sapiens), and the extinct species Australopithecus afarensis and Homo erectus. I explain that we will test the following hypothesis: Evolution of skull shape within the human lineage took place largely by changing the timing of events in development from a chimpanzee-like ancestor. To assess whether the students understand the hypothesis, I use an online adaptation of a minute-paper for assessment: each student sends me an e-mail message that paraphrases the hypothesis and justifies why it is worth testing.

When we meet in the classroom, we review the tenets of natural selection: that heritable variation exists in a population, that more offspring are born than can survive, and that individuals compete for survival. Students then relate those tenets to the changes they see in the development of the axlotl. They should realize that the change in shape during development (that is, allometry) is a source of heritable variation that can lead to survival of the fittest. This understanding helps students see that large amounts of variation already exist in the genome.

This activity focuses on morphology and not genetics, but it helps students to understand that these two biological disciplines are united by evo-devo (Carroll, 2005). In class, I briefly mention to students that growth from fertilized egg to adult involves a host of complex interactions among genes, molecules, and tissues. Subtle alterations in the time at which one of the genes responsible for these interactions is expressed can have far-reaching consequences that result in a different adult shape (Carroll, 2005). I return to this concept at other points during the term.


Evolutionary Scandals

Panchin knows the idea of cancer-derived animals sounds far-fetched — so much so that, in the paper, he and his co-authors refer to them as Scandals (an acronym for “speciated by cancer development animals”).

At first, Scandals were just a thought experiment. While Panchin was writing about transmissible cancers, he heard his colleagues express surprise at the genes for complex tissues that were turning up in certain unusual but simple parasitic animals. Further conversations led to what Panchin calls the “fantastic” idea that such simple parasites could have cancerous origins. “So we took all the data and we proposed this hypothesis,” he said.

According to Panchin’s three-step scenario, a Scandal would start off as a cancer, but not just any cancer. It would have to be transmissible, so that it wouldn’t die when its host did. Then the cancer would have to spread to other species, and then independently evolve multicellularity. Those steps might seem to present insurmountable barriers, and yet there’s reason to believe each one could have happened.

The first step, the emergence of the transmissible cancer, is the most straightforward because we know it happens, although it is rare. Devil facial tumor disease (DFTD) has become notorious as a transmissible cancer devastating Tasmanian devils, who transmit it to one another in their bites. More common but perhaps less famous is canine transmissible venereal tumor (CTVT), a sexually transmitted disease among dogs that, according to a recent analysis by Elizabeth Murchison of the University of Cambridge and her colleagues, has been evolving as a transmissible cancer for as long as 8,500 years. (In a 2014 report, Murchison and her co-authors described CTVT as perhaps “the oldest and most widely disseminated cancer in the natural world.”)

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The Tasmanian devil (left) and the Pacific blue mussel (Mytilus trossulus, right) are two of the species affected by transmissible cancers.

Transmissible cancers are not confined to mammals they have also been found in mollusks. There’s no reason to think it would be impossible for transmissible tumors to arise in a cnidarian too. Cnidarians certainly aren’t immune to cancers in general. If myxosporeans are Scandals, they most likely began as tumors of other cnidarian parasites — such as their Polypodium cousins, for instance.

Although the spread of a cancer to other species might seem unlikely, “it’s not unheard of,” said Athena Aktipis, an assistant professor at Arizona State University. Aktipis, who specializes in the evolution of cancer, points to cases such as that of a man with HIV who was discovered to be infected with tumor cells from a tapeworm. Such worm cancers have turned up repeatedly among people with compromised immune systems, and the known cases likely represent only the small minority of occurrences in which the source of a strange growth was tracked down. If this kind of species hopping happens right before our eyes, “maybe we should also consider the possibility that things that were cancer or cancerlike sometimes, in the right conditions, could become parasites on other species,” she said.

“I think that the field has been way too cautious about talking about when cancer becomes its own species, or its own kind of organism,” Aktipis said. In her view, researchers have seen too many examples of transmissible tumors like CTVT and DFTD. “It’s a parasite. It’s a parasitic organism.”

Perhaps the least likely step in the Scandal hypothesis is the one where the cancerous parasite evolves from a unicellular existence to a multicellular one with distinct hosts and stages. Myxosporeans are simple animals but truly multicellular — so if they arose from a transmissible tumor, that tumor would have had to evolve distinct cell types.

Multicellularity is thought to have evolved at least 25 times in eukaryotes, the domain of life that includes complex single-celled creatures as well as plants, animals and fungi. In animals, though, it’s believed to have arisen just once at the very base of our lineage. Some multicellular branches of the eukaryotes have reverted to unicellularity, but no animals have been known to do so (unless, like some scientists, you consider cancer itself to be a kind of reversion). As yet, there don’t seem to be lineages of any kind in which multicellularity was gained, lost and then gained again, in keeping with the Scandal hypothesis. “We understand that this is a very improbable scenario,” Panchin said.

But that doesn’t mean it couldn’t have happened. “I think it’s certainly possible that clusters of cancer cells that are transmissible could evolve to have something like a life cycle,” Aktipis said. “There’s nothing special about the evolutionary process that says you can only evolve a life cycle if you are a branch of the evolutionary tree that didn’t derive from [a part of] another organism.”


Vascular Tissue: Xylem and Phloem

Xylem and phloem form the vascular system of plants to transport water and other substances throughout the plant.

Learning Objectives

Describe the functions of plant vascular tissue

Key Takeaways

Key Points

  • Xylem transports and stores water and water-soluble nutrients in vascular plants.
  • Phloem is responsible for transporting sugars, proteins, and other organic molecules in plants.
  • Vascular plants are able to grow higher than other plants due to the rigidity of xylem cells, which support the plant.

Key Terms

  • xylem: a vascular tissue in land plants primarily responsible for the distribution of water and minerals taken up by the roots also the primary component of wood
  • phloem: a vascular tissue in land plants primarily responsible for the distribution of sugars and nutrients manufactured in the shoot
  • tracheid: elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts

Vascular Tissue: Xylem and Phloem

The first fossils that show the presence of vascular tissue date to the Silurian period, about 430 million years ago. The simplest arrangement of conductive cells shows a pattern of xylem at the center surrounded by phloem. Together, xylem and phloem tissues form the vascular system of plants.

Xylem and phloem: Xylem and phloem tissue make up the transport cells of stems. The direction of water and sugar transportation through each tissue is shown by the arrows.

Xylem is the tissue responsible for supporting the plant as well as for the storage and long-distance transport of water and nutrients, including the transfer of water-soluble growth factors from the organs of synthesis to the target organs. The tissue consists of vessel elements, conducting cells, known as tracheids, and supportive filler tissue, called parenchyma. These cells are joined end-to-end to form long tubes. Vessels and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at the ends. It is the thick walls of the tracheids that provide support for the plant and allow it to achieve impressive heights. Tall plants have a selective advantage by being able to reach unfiltered sunlight and disperse their spores or seeds further away, thus expanding their range. By growing higher than other plants, tall trees cast their shadow on shorter plants and limit competition for water and precious nutrients in the soil. The tracheids do not have end openings like the vessels do, but their ends overlap with each other, with pairs of pits present. The pit pairs allow water to pass horizontally from cell to cell.

Tracheids and vessel elements: Tracheids (top) and vessel elements (bottom) are the water conducting cells of xylem tissue.

Phloem tissue is responsible for translocation, which is the transport of soluble organic substances, for example, sugar. The substances travel along sieve elements, but other types of cells are also present: the companion cells, parenchyma cells, and fibers. The end walls, unlike vessel members in xylem, do not have large openings. The end walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous connections are called sieve plates. Despite the fact that their cytoplasm is actively involved in the conduction of food materials, sieve-tube members do not have nuclei at maturity. The activity of the sieve tubes is controlled by companion cells through plasmadesmata.


Some Examples of Beneficial Mutation

Beneficial mutation is retained in the population and accumulates in the form of adaptations in the course of evolution, whereas deleterious is not retained and is removed by means of natural selection. Neutral mutation, on the other hand, does not cause significant effects in the population. Generally, neutral mutations are accumulated through genetic drift. The effects of mutation vary depending upon the environment. Let’s take a look at some of the examples of favorable mutations that promote the fitness of the organisms.

Nylonase is an example of beneficial mutation in bacteria. The nylonase bacteria can eat short molecules of nylon (nylon-6). The mutation in these bacteria involves insertion of a single nucleotide in the genetic material. It is estimated that this frameshift mutation might have occurred in the 1940s when nylon was invented. Nylonase can be used in wastewater treatment plants.

Antibiotics are used for the treatment of diseases caused by bacteria. Constant use of antibiotics leads to the development of resistance among the targeted bacteria. Many a time, the antibiotic resistance reduces the fitness of the particular bacterial population, when they are exposed to non-antibiotic environment. These resistant bacteria do not possess the ability to reproduce as fast as those without mutation, thus slowing down the disease progression.

Almond seeds from wild species contain amygdalin, a bitter chemical that converts into cyanide inside the human body. According to researchers, consuming wild almonds is fatal. A single gene mutation in wild almond trees resulted in a variety that no longer synthesizes amygdalin. When humans discovered this non-bitter almond species, they cultivated them, which is continued till today.

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Murray Gray is a cattle breed, obtained accidentally from a traditional cow species. The calves produced by the specific cow were more productive than those produced by the others. Farmers soon noticed the difference and started breeding from the offspring. This way, the Murray breed with some of the most positive characteristics has become popular all over Australia, which then spread to various other countries.

Cysteine-cysteine chemokine receptor 5 (CCR5) is a receptor molecule, located in the membranes of white blood cells (WBCs) and nerve cells. In a cell, CCR5 permits the entry of chemokines that signals the inflammatory response to any foreign particles. The gene responsible for coding CCR5 is present in the human chromosome 3. A mutation in this gene called CCR5-delta32 (involving deletion of 32 base pairs) affects the normal functioning of the CCR5.

In the initial stages of HIV infection, the virus normally enters through CCR5. However, a mutated CCR5 blocks the entry of HIV. People carrying homozygous mutated CCR5-delta32 are resistant to HIV, while heterozygous ones are beneficial, as they slow down the disease progression. Thus, CCR5-delta32 provides partial or complete immunity to HIV.

Although, the CCR5-delta32 mutation has one drawback. It is strongly associated with a chronic liver disease called primary sclerosing cholangitis (PSC). A long-term progressive liver and gallbladder disorder characterized by inflammation and fibrosis of the intrahepatic and extrahepatic bile ducts causing the bile to drain from the gallbladder.

There is no doubt that some of the most productive plants and animals are evolved as a result of mutation. The effects of mutation are well explained by natural selection in which favorable changes persist in the population, while the harmful alterations are eliminated over a period of time.

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Cultural Evolution and Culture-Gene Coevolution

Once a species is sufficiently reliant on learning from others for at least some aspects of its behavioral repertoire, cultural evolutionary processes can arise, and these processes can alter the environment faced by natural selection acting on genes. To develop models of cultural evolution, we begin by taking the theoretically-grounded and empirically-tested hypotheses about our learning psychology—who people learn from and what they tend to infer while learning—to construct models that examine what happens when lots of individuals are learning in these ways, and interacting over generations. Because of their fidelity and frequency of use, human cultural learning abilities are probably unique in giving rise to cumulative cultural evolution, the process through which learning accumulates successful modifications and lucky errors over generations. Cumulative cultural evolution builds complex adaptive practices, tools, techniques, and bodies of knowledge (e.g., about animal behavior and edible plants) that continue to improve over centuries and millennia (Boyd & Richerson, 1996 Boyd, et al., 2011a Henrich, 2004b).

Models of cumulative cultural evolution suggest two important, and perhaps non-intuitive, features of our species. First, our ecological success, technology, and adaptation to diverse environments is not due to our intelligence. Alone and stripped of our culture, we are hopeless as a species. Cumulative cultural evolution has delivered both our fancy technologies as well as the subtle and unconscious ways that humans have adapted their behavior and thinking to tackle environmental challenges (Henrich & Henrich, 2010). The smartest among us could not in a single lifetime devise even a small fraction of the techniques and technologies that allow any foraging society to survive (Boyd, et al., 2011a Henrich, 2008). Second, the available formal models make clear that the effectiveness of this cumulative cultural evolutionary process depends crucially on the size and interconnectedness of our populations and social networks. It’s the ability to freely exchange information that sparks and accelerates adaptive cultural evolution, and creates innovation. At the population level, it is much better to be social than it is to be smart. Such approaches help us understand archaeological and ethnographic cases in which isolated populations gradually lose their most complex technologies. Sustaining complex technologies depends on maintaining a large and well-interconnected population of minds (Henrich, 2004b, 2006, 2009b Powell, Shennan, & Thomas, 2009).

These cultural evolutionary models also help us to understand how our cognitive processes for cultural learning give rise to many sociological phenomena, like social classes, castes (Henrich & Boyd, 2008), cultures of honor (McElreath, 2003), ethnic groups (Boyd & Richerson, 1987 Henrich & Henrich, 2007: Chapter 9 McElreath, Boyd, & Richerson, 2003) and large-scale cooperation (Boyd, Richerson, & Henrich, 2011b Henrich, 2004a). In the case of ethnic groups, for example, such models explore how genes and culture coevolve. This shows how cultural evolution will, under a wide range of conditions, create a landscape in which different social groups tend to share both similar behavioral expectations and similar arbitrary “ethnic markers” (like dialect or language). In the wake of this culturally constructed world, genes evolve to create minds that are inclined to preferentially interact with and imitate those who share their markers. This guarantees that individuals most effectively coordinate with those who share their culturally learned behavioral expectations (say about marriage or child rearing). These purely theoretical predictions were subsequently confirmed by experiments with both children (Kinzler, Dupoux, & Spelke, 2007 Kinzler, Shutts, Dejesus, & Spelke, 2009 Shutts, et al., 2009) and adults (Efferson, Lalive, & Fehr, 2008).

This approach also suggests that cultural evolution readily gives rise to social norms, as long as learners can culturally acquire the standards by which they judge others (Chudek & Henrich, 2010). Many models robustly demonstrate that cultural evolution can sustain almost any behavior or preference that is common in a population (including cooperation), if it is not too costly (e.g., Boyd & Richerson, 1992 Henrich, 2009a Henrich & Boyd, 2001). This suggests that different groups will end up with different norms and begin to compete with each other. Competition among groups with different norms will favor those particular norms that lead to success in intergroup competition (Boyd & Richerson, 2002 Boyd, et al., 2011b Henrich, 2004a). My collaborators and I have argued that cultural group selection has shaped the cultural practices, institutions, beliefs and psychologies that are common in the world today, including those associated with anonymous markets (Henrich et al., 2005 Henrich et al., 2010), prosocial religions with big moralizing gods (Atran & Henrich, 2010 Shariff, Norenzayan, & Henrich, 2010), and monogamous marriage (Henrich, Boyd, & Richerson, forthcoming). Each of these cultural packages, which have emerged relatively recently in human history, impacts our psychology and behavior. Priming “markets” and “God” (Shariff & Norenzayan, 2007), for example, increase trust and giving (respectively) in behavioral experiments, though “God primes” only work on theists. Such research avenues hold the promise of explaining, rather than merely documenting, the patterns of psychological variation observed across human populations (Henrich, Heine, & Norenzayan, 2010)

The cultural evolution of norms over tens or hundreds of thousands of years, and their shaping by cultural group selection, may have driven genetic evolution to create a suite of cognitive adaptations we call norm psychology (Chudek & Henrich, 2010 Chudek, Zhao, & Henrich, forthcoming). This aspect of our evolved psychology emerged and coevolved in response to cultural evolution’s production of norms. This suite facilitates, among other things, our identification and learning of social norms, our expectation of sanctions for norm violations, and our ability to internalize normative behavior as motivations.

The coevolved norms psychology hypothesized by these models unites much work from across the social sciences. It proposes that learners should act as though they live in a world governed by social rules they need to acquire, many of which are prosocial. Young children show motivations to conform in front of peers (Haun & Tomasello, in press), spontaneously infer the existence of social rules in one trial learning, react negatively to deviations by others to a rule learned in one trial, spontaneously sanction norm violators (Rakoczy, Warneken, & Tomasello, 2008) and selectively learn norms (that they later enforce) in the predicted ways (Rakoczy, Hamann, Warneken, & Tomasello, 2010 Rakoczy, Warneken, & Tomasello, 2009).

This approach also predicts that humans ought to be inclined to “over-imitate” for two different evolutionary reasons, one informational and the other normative (Henrich & Henrich, 2007). The informational view hypothesizes that people over-imitate because of an evolved reliance on cultural learning to adaptively acquire complex and cognitively-opaque skills, techniques and practices that have been honed, often in nuanced and subtle ways, over generations. In support of this view, children and adults from diverse societies accurately imitate adults’ seemingly unnecessary behaviors (they ‘over-imitate’) even though they are capable of disregarding them (Lyons, Young, & Keil, 2007 Nielsen & Tomaselli, 2010). However, because individuals should also “over-imitate” because human societies have long been full of arbitrary norms (behaviors) for which the “correct” performance is crucial to one’s reputation (e.g., rituals, etiquette), we expect future investigations to reveal two different kinds of over-imitation. This lays a theoretical foundation for research on natural pedagogy by suggesting that humans are programmed to attend to cues that activate an expectation of learning normative information (Topal, Gergely, Miklosi, Erdohegyi, & Csibra, 2008).

The selection pressures created by reputational damage and punishment for norm-violation may also favour norm-internalization. Neuroeconomic studies suggest that social norms are in fact internalized as intrinsic motivations in people’s brains. Both cooperating and punishing in locally normative ways activates the brain’s rewards or reward anticipation circuits in the same manner as does obtaining a direct cash payment (de Quervain et al., 2004 Fehr & Camerer, 2007 Tabibnia, Satpute, & Lieberman, 2008).

A broad range of recent findings can be explained by recognizing that experimental games tap culture-specific norms, often involving monetary transactions with strangers. First, measures of fairness and willingness to punish from standard bargaining experiments vary dramatically across societies in a manner that covaries with market integration and community size, respectively (Chudek, et al., forthcoming Henrich, Ensminger, et al., 2010). Second, framing the games to cue local norms can alter behavior in predictable ways (Henrich, et al., 2005 Herrmann, Thoni, & Gächter, 2008), including findings showing that the same frames have different effects in different populations (Goerg & Walkowitz, 2010 Pillutla & Chen, 1999 Poppe, 2005 Ross & Ward, 1996). Third, game behaviors can be experimentally influenced by observational learning (Cason & Mui, 1998), and prosocial behavior emerges gradually over development (unlike reciprocity), not plateauing until people reach their mid-twenties (Sutter & Kocher, 2007). Finally, non-human primates—who lack norms or coevolution—fail to reveal the prosocial preferences toward strangers so puzzling in the largest-scale human societies (Jensen, Call, & Tomasello, 2007 Jensen, Hare, Call, & Tomasello, 2006 Silk et al., 2005).

The thrust of this line of research is that cultural evolution was likely a dominant force driving our species’ genetic evolution over the last few hundred thousand years. Through its autocatalytic processes (Chudek & Henrich, 2010), ever accumulating cultural elements may have driven our brain expansion, cognitive specializations (Herrmann, Call, Hernandez-Lloreda, Hare, & Tomasello, 2007), social psychology (Henrich & Henrich, 2007) and physiological changes in our guts, teeth, hands and bones (Wrangham, 2009). Understanding and theorizing how cultural processes have shaped human evolution provides a framework that unifies and underpins research programs across the social, biological, and historical sciences.


Reproductive isolation driving evolution of species

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Evolution of species remains a hot topic since Darwin’s theory of natural selection. A European initiative addressed the issue of speciation from the viewpoint of reproductive isolation.

There are many theories regarding the emergence of new species – known as speciation – depending on the level of geographic isolation between the two emerging species. Also, speciation can occur due to reproductive isolation. This can be caused by mating differences, sterility or environmental barriers that eventually lead to the adaptive splitting into two species. However, reproductive isolation is not sufficient but internal barriers to gene flow are required for speciation to evolve.

Recent studies suggest that natural selection and adaptation may play a more significant role in the early stages of divergence and the evolution of reproductive isolation than previously thought. This adaptive speciation may be particularly common where there is partial spatial separation between habitats, such as on the steep environmental gradients that characterise sea-shore habitats.

The key objective of the EU-funded ‘Evolution of reproductive barriers and its implications for adaptive speciation’ (Adaptive Speciation) project was to understand the mechanism of adaptive speciation. The marine snail Littorina saxatilis, which shows evidence of progression towards speciation, was used as a model. In particular, the two morphs (E and S) of L.saxatilis, which inhabit different environments, were studied.

Scientists examined how genetic differentiation and phenotypic plasticity can contribute to species adaptation and reproductive isolation between these two morphs. Using genetic tools such as amplified fragment length polymorphism (AFLP) markers and morphometric analysis, scientists wished to analyze transects on two separate small islands as estimates of gene flow and selection. Additionally, they tested the possibility that enforced mating between the two morphs in the hybrid zone may affect local adaptation.

Adaptive speciation provided important insight into the field of evolutionary biology and more specifically into the role of reproductive isolation in driving speciation. Results are expected to contribute to our understanding on the reasons and processes that cause species diversity.