All-Natrual matter All-Natural Selection size, every gift to the Museum is critical All-Nayural our scientists' work in understanding and protecting the natural world. Breeding bunniesa classroom activity for grades Which allele gets lost is due to random chance.

Video

The Making of a Theory: Darwin, Wallace, and Natural Selection — HHMI BioInteractive Video

All-Natural Selection -

This could be due in part to the perception, unfortunately reinforced by many biologists, that natural selection is so logically compelling that its implications become self-evident once the basic principles have been conveyed.

The goal of this paper is to enhance or, as the case may be, confirm readers' basic understanding of natural selection. This first involves providing an overview of the basis and one of the general outcomes of natural selection as they are understood by evolutionary biologists Footnote 1.

This is followed by a brief discussion of the extent and possible causes of difficulties in fully grasping the concept and consequences of natural selection. Finally, a review of the most widespread misconceptions about natural selection is provided. It must be noted that specific instructional tools capable of creating deeper understanding among students generally have remained elusive, and no new suggestions along these lines are presented here.

Though rudimentary forms of the idea had been presented earlier e. These are depicted in Fig. The basis of natural selection as presented by Darwin , based on the summary by Mayr Some components of the process, most notably the sources of variation and the mechanisms of inheritance, were, due to the limited available information in Darwin's time, either vague or incorrect in his original formulation.

Since then, each of the core aspects of the mechanism has been elucidated and well documented, making the modern theory Footnote 3 of natural selection far more detailed and vigorously supported than when first proposed years ago. This updated understanding of natural selection consists of the elements outlined in the following sections.

to 2 n after n rounds of reproduction. The enormity of this potential for exponential growth is difficult to fathom. For example, consider that beginning with a single Escherichia coli bacterium, and assuming that cell division occurs every 30 minutes, it would take less than a week for the descendants of this one cell to exceed the mass of the Earth.

Of course, exponential population expansion is not limited to bacteria. Keown cites the example of oysters, which may produce as many as ,, eggs in a single spawn. If all these eggs grew into oysters and produced this many eggs of their own that, in turn, survived to reproduce, then within five generations there would be more oysters than the number of electrons in the known universe.

Clearly, the world is not overrun with bacteria, elephants, or oysters. The reason is simple: Most offspring that are produced do not survive to produce offspring of their own. In fact, most population sizes tend to remain relatively stable over the long term. This necessarily means that, on average, each pair of oysters produces only two offspring that go on to reproduce successfully—and that ,, eggs per female per spawn do not survive see also Ridley Many young oysters will be eaten by predators, others will starve, and still others will succumb to infection.

As he noted, this can be conceived as a struggle not only against other organisms especially members of the same species, whose ecological requirements are very similar but also in a more abstract sense between organisms and their physical environments.

Variation among individuals is a fundamental requirement for evolutionary change. Given that it was both critical to his theory of natural selection and directly counter to much contemporary thinking, it should not be surprising that Darwin expended considerable effort in attempting to establish that variation is, in fact, ubiquitous.

He also emphasized the fact that some organisms—namely relatives, especially parents and their offspring—are more similar to each other than to unrelated members of the population. This, too, he realized is critical for natural selection to operate.

The workings of genetics are no longer opaque. Today, it is well understood that inheritance operates through the replication of DNA sequences and that errors in this process mutations and the reshuffling of existing variants recombination represent the sources of new variation.

Any given mutation is merely a chance error in the genetic system, and as such, its likelihood of occurrence is not influenced by whether it will turn out to be detrimental, beneficial, or most commonly neutral.

As Darwin anticipated, extensive variation among individuals has now been well established to exist at the physical, physiological, and behavioral levels. Thanks to the rise of molecular biology and, more recently, of genomics, it also has been possible to document variation at the level of proteins, genes, and even individual DNA nucleotides in humans and many other species.

Darwin saw that overproduction and limited resources create a struggle for existence in which some organisms will succeed and most will not. He also recognized that organisms in populations differ from one another in terms of many traits that tend to be passed on from parent to offspring.

Darwin's brilliant insight was to combine these two factors and to realize that success in the struggle for existence would not be determined by chance, but instead would be biased by some of the heritable differences that exist among organisms. Specifically, he noted that some individuals happen to possess traits that make them slightly better suited to a particular environment, meaning that they are more likely to survive than individuals with less well suited traits.

As a result, organisms with these traits will, on average, leave more offspring than their competitors. Whereas the origin of a new genetic variant occurs at random in terms of its effects on the organism, the probability of it being passed on to the next generation is absolutely non-random if it impacts the survival and reproductive capabilities of that organism.

The important point is that this is a two-step process: first, the origin of variation by random mutation, and second, the non-random sorting of variation due to its effects on survival and reproduction Mayr Though definitions of natural selection have been phrased in many ways Table 1 , it is this non-random difference in survival and reproduction that forms the basis of the process.

In order to study the operation and effects of natural selection, it is important to have a means of describing and quantifying the relationships between genotype gene complement , phenotype physical and behavioral features , survival, and reproduction in particular environments.

In the most basic terms, one can state that the more offspring an individual produces, the higher is its fitness.

Second, it places undue emphasis on survival: While it is true that dead organisms do not reproduce, survival is only important evolutionarily insofar as it affects the number of offspring produced. Traits that make life longer or less difficult are evolutionarily irrelevant unless they also influence reproductive output.

Indeed, traits that enhance net reproduction may increase in frequency over many generations even if they compromise individual longevity. Conversely, differences in fecundity alone can create differences in fitness, even if survival rates are identical among individuals.

Third, this implies an excessive focus on organisms, when in fact traits or their underlying genes equally can be identified as more or less fit than alternatives.

Lastly, this phrase is often misconstrued as being circular or tautological Who survives? The fittest. Who are the fittest? Those who survive. However, again, this misinterprets the modern meaning of fitness, which can be both predicted in terms of which traits are expected to be successful in a specific environment and measured in terms of actual reproductive success in that environment.

Directional natural selection can be understood as a process by which fitter traits or genes increase in proportion within populations over the course of many generations.

It must be understood that the relative fitness of different traits depends on the current environment. Thus, traits that are fit now may become unfit later if the environment changes. Conversely, traits that have now become fit may have been present long before the current environment arose, without having conferred any advantage under previous conditions.

Finally, it must be noted that fitness refers to reproductive success relative to alternatives here and now —natural selection cannot increase the proportion of traits solely because they may someday become advantageous. Careful reflection on how natural selection actually works should make it clear why this is so.

Though each has been tested and shown to be accurate, none of the observations and inferences that underlies natural selection is sufficient individually to provide a mechanism for evolutionary change Footnote 6.

Overproduction alone will have no evolutionary consequences if all individuals are identical. Differences among organisms are not relevant unless they can be inherited. Genetic variation by itself will not result in natural selection unless it exerts some impact on organism survival and reproduction.

However, any time all of Darwin's postulates hold simultaneously—as they do in most populations—natural selection will occur. The net result in this case is that certain traits or, more precisely, genetic variants that specify those traits will, on average , be passed on from one generation to the next at a higher rate than existing alternatives in the population.

Put another way, when one considers who the parents of the current generation were, it will be seen that a disproportionate number of them possessed traits beneficial for survival and reproduction in the particular environment in which they lived.

The important points are that this uneven reproductive success among individuals represents a process that occurs in each generation and that its effects are cumulative over the span of many generations.

Over time, beneficial traits will become increasingly prevalent in descendant populations by virtue of the fact that parents with those traits consistently leave more offspring than individuals lacking those traits.

If this process happens to occur in a consistent direction—say, the largest individuals in each generation tend to leave more offspring than smaller individuals—then there can be a gradual, generation-by-generation change in the proportion of traits in the population.

This change in proportion and not the modification of organisms themselves is what leads to changes in the average value of a particular trait in the population. Organisms do not evolve; populations evolve. As the name implies, this is the process by which populations of organisms evolve in such a way as to become better suited to their environments as advantageous traits become predominant.

This latter topic is particularly difficult for many to grasp, though of course a crucial first step is to understand the operation of natural selection on smaller scales of time and consequence. For a detailed discussion of the evolution of complex organs such as eyes, see Gregory b.

On first pass, it may be difficult to see how natural selection can ever lead to the evolution of new characteristics if its primary effect is merely to eliminate unfit traits.

Indeed, natural selection by itself is incapable of producing new traits, and in fact as many readers will have surmised , most forms of natural selection deplete genetic variation within populations. How, then, can an eliminative process like natural selection ever lead to creative outcomes?

To answer this question, one must recall that evolution by natural selection is a two-step process. The first step involves the generation of new variation by mutation and recombination, whereas the second step determines which randomly generated variants will persist into the next generation.

Most new mutations are neutral with respect to survival and reproduction and therefore are irrelevant in terms of natural selection but not, it must be pointed out, to evolution more broadly.

The majority of mutations that have an impact on survival and reproductive output will do so negatively and, as such, will be less likely than existing alternatives to be passed on to subsequent generations. However, a small percentage of new mutations will turn out to have beneficial effects in a particular environment and will contribute to an elevated rate of reproduction by organisms possessing them.

Even a very slight advantage is sufficient to cause new beneficial mutations to increase in proportion over the span of many generations. Rather, beneficial mutations simply increase in proportion from one generation to the next because, by definition, they happen to contribute to the survival and reproductive success of the organisms carrying them.

Eventually, a beneficial mutation may be the only alternative left as all others have ultimately failed to be passed on. Again, mutation does not occur in order to improve fitness—it merely represents errors in genetic replication.

This means that most mutations do not improve fitness: There are many more ways of making things worse than of making them better. It also means that mutations will continue to occur even after previous beneficial mutations have become fixed.

As such, there can be something of a ratcheting effect in which beneficial mutations arise and become fixed by selection, only to be supplemented later by more beneficial mutations which, in turn, become fixed.

All the while, neutral and deleterious mutations also occur in the population, the latter being passed on at a lower rate than alternatives and often being lost before reaching any appreciable frequency.

Of course, this is an oversimplification—in species with sexual reproduction, multiple beneficial mutations may be brought together by recombination such that the fixation of beneficial genes need not occur sequentially.

Likewise, recombination can juxtapose deleterious mutations, thereby hastening their loss from the population. Nonetheless, it is useful to imagine the process of adaptation as one in which beneficial mutations arise continually though perhaps very infrequently and with only minor positive impacts and then accumulate in the population over many generations.

The process of adaptation in a population is depicted in very basic form in Fig. Several important points can be drawn from even such an oversimplified rendition:. Mutations are the source of new variation. Natural selection itself does not create new traits; it only changes the proportion of variation that is already present in the population.

The repeated two-step interaction of these processes is what leads to the evolution of novel adaptive features. Mutation is random with respect to fitness. Natural selection is, by definition, non-random with respect to fitness. Mutations occur with all three possible outcomes: neutral, deleterious, and beneficial.

Beneficial mutations may be rare and deliver only a minor advantage, but these can nonetheless increase in proportion in the population over many generations by natural selection. The occurrence of any particular beneficial mutation may be very improbable, but natural selection is very effective at causing these individually unlikely improvements to accumulate.

Natural selection is an improbability concentrator. No organisms change as the population adapts. Rather, this involves changes in the proportion of beneficial traits across multiple generations.

The direction in which adaptive change occurs is dependent on the environment. A change in environment can make previously beneficial traits neutral or detrimental and vice versa. Adaptation does not result in optimal characteristics. It is constrained by historical, genetic, and developmental limitations and by trade-offs among features see Gregory b.

As Darwin wrote in a letter to Joseph Hooker 11 Sept. The process of adaptation by natural selection is not forward-looking, and it cannot produce features on the grounds that they might become beneficial sometime in the future. In fact, adaptations are always to the conditions experienced by generations in the past.

A highly simplified depiction of natural selection Correct and a generalized illustration of various common misconceptions about the mechanism Incorrect. Properly understood, natural selection occurs as follows: A A population of organisms exhibits variation in a particular trait that is relevant to survival in a given environment.

In this diagram, darker coloration happens to be beneficial, but in another environment, the opposite could be true. As a result of their traits, not all individuals in Generation 1 survive equally well, meaning that only a non-random subsample ultimately will succeed in reproducing and passing on their traits B.

Note that no individual organisms in Generation 1 change, rather the proportion of individuals with different traits changes in the population.

The individuals who survive from Generation 1 reproduce to produce Generation 2. C Because the trait in question is heritable, this second generation will mostly resemble the parent generation. However, mutations have also occurred, which are undirected i. In this environment, lighter mutants are less successful and darker mutants are more successful than the parental average.

Once again, there is non-random survival among individuals in the population, with darker traits becoming disproportionately common due to the death of lighter individuals D. This subset of Generation 2 proceeds to reproduce.

Again, the traits of the survivors are passed on, but there is also undirected mutation leading to both deleterious and beneficial differences among the offspring E.

F This process of undirected mutation and natural selection non-random differences in survival and reproductive success occurs over many generations, each time leading to a concentration of the most beneficial traits in the next generation.

By Generation N , the population is composed almost entirely of very dark individuals. The population can now be said to have become adapted to the environment in which darker traits are the most successful.

This contrasts with the intuitive notion of adaptation held by most students and non-biologists. In the most common version, populations are seen as uniform, with variation being at most an anomalous deviation from the norm X. It is assumed that all members within a single generation change in response to pressures imposed by the environment Y.

When these individuals reproduce, they are thought to pass on their acquired traits. Moreover, any changes that do occur due to mutation are imagined to be exclusively in the direction of improvement Z.

Studies have revealed that it can be very difficult for non-experts to abandon this intuitive interpretation in favor of a scientifically valid understanding of the mechanism.

Diagrams based in part on Bishop and Anderson In its most basic form, natural selection is an elegant theory that effectively explains the obviously good fit of living things to their environments.

As a mechanism, it is remarkably simple in principle yet incredibly powerful in application. However, the fact that it eluded description until years ago suggests that grasping its workings and implications is far more challenging than is usually assumed.

Three decades of research have produced unambiguous data revealing a strikingly high prevalence of misconceptions about natural selection among members of the public and in students at all levels, from elementary school pupils to university science majors Alters ; Bardapurkar ; Table 2 Footnote 7.

It is particularly disconcerting and undoubtedly exacerbating that confusions about natural selection are common even among those responsible for teaching it Footnote 8. Two obvious hypotheses present themselves for why misunderstandings of natural selection are so widespread.

The first is that understanding the mechanism of natural selection requires an acceptance of the historical fact of evolution, the latter being rejected by a large fraction of the population. While an improved understanding of the process probably would help to increase overall acceptance of evolution, surveys indicate that rates of acceptance already are much higher than levels of understanding.

And, whereas levels of understanding and acceptance may be positively correlated among teachers Vlaardingerbroek and Roederer ; Rutledge and Mitchell ; Deniz et al. The second intuitive hypothesis is that most people simply lack formal education in biology and have learned incorrect versions of evolutionary mechanisms from non-authoritative sources e.

Inaccurate portrayals of evolutionary processes in the media, by teachers, and by scientists themselves surely exacerbate the situation e. However, this alone cannot provide a full explanation, because even direct instruction on natural selection tends to produce only modest improvements in students' understanding e.

There also is evidence that levels of understanding do not differ greatly between science majors and non-science majors Sundberg and Dini Misconceptions are well known to be common with many perhaps most aspects of science, including much simpler and more commonly encountered phenomena such as the physics of motion e.

The source of this larger problem seems to be a significant disconnect between the nature of the world as reflected in everyday experience and the one revealed by systematic scientific investigation e. Intuitive interpretations of the world, though sufficient for navigating daily life, are usually fundamentally at odds with scientific principles.

If common sense were more than superficially accurate, scientific explanations would be less counterintuitive, but they also would be largely unnecessary. It has been suggested by some authors that young students simply are incapable of understanding natural selection because they have not yet developed the formal reasoning abilities necessary to grasp it Lawson and Thompson This could be taken to imply that natural selection should not be taught until later grades; however, those who have studied student understanding directly tend to disagree with any such suggestion e.

Overall, the issue does not seem to be a lack of logic Greene ; Settlage , but a combination of incorrect underlying premises about mechanisms and deep-seated cognitive biases that influence interpretations.

These tend to persist unless replaced with more accurate and equally functional information. In this regard, some experts have argued that the goal of education should be to supplant existing conceptual frameworks with more accurate ones see Sinatra et al.

Other authors suggest that students do not actually maintain coherent conceptual frameworks relating to complex phenomena, but instead construct explanations spontaneously using intuitions derived from everyday experience see Southerland et al.

Though less widely accepted, this latter view gains support from the observation that naïve evolutionary explanations given by non-experts may be tentative and inconsistent Southerland et al. In some cases, students may attempt a more complex explanation but resort to intuitive ideas when they encounter difficulty Deadman and Kelly In either case, it is abundantly clear that simply describing the process of natural selection to students is ineffective and that it is imperative that misconceptions be confronted if they are to be corrected e.

Whereas the causes of cognitive barriers to understanding remain to be determined, their consequences are well documented.

It is clear from many studies that complex but accurate explanations of biological adaptation typically yield to naïve intuitions based on common experience Fig. As a result, each of the fundamental components of natural selection may be overlooked or misunderstood when it comes time to consider them in combination, even if individually they appear relatively straightforward.

The following sections provide an overview of the various, non-mutually exclusive, and often correlated misconceptions that have been found to be most common.

All readers are encouraged to consider these conceptual pitfalls carefully in order that they may be avoided. Teachers, in particular, are urged to familiarize themselves with these errors so that they may identify and address them among their students.

Much of the human experience involves overcoming obstacles, achieving goals, and fulfilling needs. In fact, it has been argued that the default mode of teleological thinking is, at best, suppressed rather than supplanted by introductory scientific education. Teleological explanations for biological features date back to Aristotle and remain very common in naïve interpretations of adaptation e.

On the one hand, teleological reasoning may preclude any consideration of mechanisms altogether if simply identifying a current function for an organ or behavior is taken as sufficient to explain its existence e. On the other hand, when mechanisms are considered by teleologically oriented thinkers, they are often framed in terms of change occurring in response to a particular need Table 2.

Obviously, this contrasts starkly with a two-step process involving undirected mutations followed by natural selection see Fig.

A related conceptual bias to teleology is anthropomorphism, in which human-like conscious intent is ascribed either to the objects of natural selection or to the process itself see below.

Gould described the obvious appeal of such intuitive notions as follows:. Since the living world is a product of evolution, why not suppose that it arose in the simplest and most direct way? The penchant for seeing conscious intent is often sufficiently strong that it is applied not only to non-human vertebrates in which consciousness, though certainly not knowledge of genetics and Darwinian fitness, may actually occur , but also to plants and even to single-celled organisms.

Anthropomorphism with an emphasis on forethought is also behind the common misconception that organisms behave as they do in order to enhance the long-term well-being of their species. Once again, a consideration of the actual mechanics of natural selection should reveal why this is fallacious.

All too often, an anthropomorphic view of evolution is reinforced with sloppy descriptions by trusted authorities Jungwirth a , b , ; Moore et al. Consider this particularly egregious example from a website maintained by the National Institutes of Health Footnote 10 :.

As microbes evolve, they adapt to their environment. If something stops them from growing and spreading—such as an antimicrobial—they evolve new mechanisms to resist the antimicrobials by changing their genetic structure. Changing the genetic structure ensures that the offspring of the resistant microbes are also resistant.

Fundamentally inaccurate descriptions such as this are alarmingly common. As a corrective, it is a useful exercise to translate such faulty characterizations into accurate language Footnote For example, this could read:.

Bacteria that cause disease exist in large populations, and not all individuals are alike. If some individuals happen to possess genetic features that make them resistant to antibiotics, these individuals will survive the treatment while the rest gradually are killed off.

As a result of their greater survival, the resistant individuals will leave more offspring than susceptible individuals, such that the proportion of resistant individuals will increase each time a new generation is produced. When only the descendants of the resistant individuals are left, the population of bacteria can be said to have evolved resistance to the antibiotics.

Many students who manage to avoid teleological and anthropomorphic pitfalls nonetheless conceive of evolution as involving change due to use or disuse of organs. This view, which was developed explicitly by Jean-Baptiste Lamarck but was also invoked to an extent by Darwin , emphasizes changes to individual organisms that occur as they use particular features more or less.

Modern evolutionary theory recognizes several reasons that may account for the loss of complex features e. This is because the cells that are involved in reproduction the germline are distinct from those that make up the rest of the body the somatic line ; only changes that affect the germline can be passed on.

New genetic variants arise through mutation and recombination during replication and will often only exert their effects in offspring and not in the parents in whose reproductive cells they occur though they could also arise very early in development and appear later in the adult offspring.

Correct and incorrect interpretations of inheritance are contrasted in Fig. A summary of correct left and incorrect right conceptions of heredity as it pertains to adaptive evolutionary change.

In all diagrams, a set of nine squares represents an individual multicellular organism and each square represents a type of cell of which the organisms are constructed. In the left panels, the organisms include two kinds of cells: those that produce gametes the germline, black and those that make up the rest of the body the somatic line, white.

In the top left panel , all cells in a parent organism initially contain a gene that specifies white coloration marked W A. A random mutation occurs in the germline, changing the gene from one that specifies white to one that specifies gray marked G B. This mutant gene is passed to the egg C , which then develops into an offspring exhibiting gray coloration D.

The mutation in this case occurred in the parent specifically, in the germline but its effects did not become apparent until the next generation.

In the bottom left panel , a parent once again begins with white coloration and the white gene in all of its cells H.

During its lifetime, the parent comes to acquire a gray coloration due to exposure to particular environmental conditions I.

However, because this does not involve any change to the genes in the germline, the original white gene is passed into the egg J , and the offspring exhibits none of the gray coloration that was acquired by its parent K.

In the top right panel , the distinction between germline and somatic line is not understood. In this case, a parent that initially exhibits white coloration P changes during its lifetime to become gray Q.

Under incorrect views of soft inheritance, this altered coloration is passed on to the egg R , and the offspring is born with the gray color acquired by its parent S.

In the bottom right panel , a more sophisticated but still incorrect view of inheritance is shown. Here, traits are understood to be specified by genes, but no distinction is recognized between the germline and somatic line. In this situation, a parent begins with white coloration and white-specifying genes in all its cells W.

A mutation occurs in one type of body cells to change those cells to gray X. A mixture of white and gray genes is passed on to the egg Y , and the offspring develops white coloration in most cells but gray coloration in the cells where gray-inducing mutations arose in the parent Z. Intuitive ideas regarding soft inheritance underlie many misconceptions of how adaptive evolution takes place see Fig.

Studies have indicated that belief in soft inheritance arises early in youth as part of a naïve model of heredity e. That it seems intuitive probably explains why the idea of soft inheritance persisted so long among prominent thinkers and why it is so resistant to correction among modern students.

Unfortunately, a failure to abandon this belief is fundamentally incompatible with an appreciation of evolution by natural selection as a two-step process in which the origin of new variation and its relevance to survival in a particular environment are independent considerations.

Thirty years ago, widely respected broadcaster Sir David Attenborough aptly described the challenge of avoiding anthropomorphic shorthand in descriptions of adaptation:. Darwin demonstrated that the driving force of [adaptive] evolution comes from the accumulation, over countless generations, of chance genetical changes sifted by the rigors of natural selection.

In describing the consequences of this process it is only too easy to use a form of words that suggests that the animals themselves were striving to bring about change in a purposeful way—that fish wanted to climb onto dry land, and to modify their fins into legs, that reptiles wished to fly, strove to change their scales into feathers and so ultimately became birds.

Unlike many authors, Attenborough admirably endeavored to not use such misleading terminology. However, this quote inadvertently highlights an additional challenge in describing natural selection without loaded language.

Darwin himself could not resist slipping into the language of agency at times:. It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life.

We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were. Being, as it is, the simple outcome of differences in reproductive success due to heritable traits, natural selection cannot have plans, goals, or intentions, nor can it cause changes in response to need.

For this reason, Jungwirth a , b , bemoaned the tendency for authors and instructors to invoke teleological and anthropomorphic descriptions of the process and argued that this served to reinforce misconceptions among students see also Bishop and Anderson ; Alters and Nelson ; Moore et al.

That said, a study of high school students by Tamir and Zohar suggested that older students can recognize the distinction between an anthropomorphic or teleological formulation i. Moore et al. Some authors have argued that teleological wording can have some value as shorthand for describing complex phenomena in a simple way precisely because it corresponds to normal thinking patterns, and that contrasting this explicitly with accurate language can be a useful exercise during instruction Zohar and Ginossar In any case, biologists and instructors should be cognizant of the risk that linguistic shortcuts may send students off track.

Intuitive models of evolution based on soft inheritance are one-step models of adaptation: Traits are modified in one generation and appear in their altered form in the next. This is in conflict with the actual two-step process of adaptation involving the independent processes of mutation and natural selection.

Unfortunately, many students who eschew soft inheritance nevertheless fail to distinguish natural selection from the origin of new variation e.

Whereas an accurate understanding recognizes that most new mutations are neutral or harmful in a given environment, such naïve interpretations assume that mutations occur as a response to environmental challenges and therefore are always beneficial Fig.

For example, many students may believe that exposure to antibiotics directly causes bacteria to become resistant, rather than simply changing the relative frequencies of resistant versus non-resistant individuals by killing off the latter Footnote Again, natural selection itself does not create new variation, it merely influences the proportion of existing variants.

Most forms of selection reduce the amount of genetic variation within populations, which may be counteracted by the continual emergence of new variation via undirected mutation and recombination.

Misunderstandings about how variation arises are problematic, but a common failure to recognize that it plays a role at all represents an even a deeper concern. Not surprisingly, transformationist models of adaptation usually include a tacit assumption of soft inheritance and one-step change in response to challenges.

A proper understanding of natural selection recognizes it as a process that occurs within populations over the course of many generations. It does so through cumulative, statistical effects on the proportion of traits differing in their consequences for reproductive success.

This contrasts with two major errors that are commonly incorporated into naïve conceptions of the process:. Natural selection is mistakenly seen as an event rather than as a process Ferrari and Chi ; Sinatra et al. Events generally have a beginning and end, occur in a specific sequential order, consist of distinct actions, and may be goal-oriented.

By contrast, natural selection actually occurs continually and simultaneously within entire populations and is not goal-oriented Ferrari and Chi Misconstruing selection as an event may contribute to transformationist thinking as adaptive changes are thought to occur in the entire population simultaneously.

In actuality, it is a probabilistic process in which some traits make it more likely—but do not guarantee—that organisms possessing them will successfully reproduce.

Surveys of students at all levels paint a bleak picture regarding the level of understanding of natural selection. Though it is based on well-established and individually straightforward components, a proper grasp of the mechanism and its implications remains very rare among non-specialists.

The unavoidable conclusion is that the vast majority of individuals, including most with postsecondary education in science, lack a basic understanding of how adaptive evolution occurs.

While no concrete solutions to this problem have yet been found, it is evident that simply outlining the various components of natural selection rarely imparts an understanding of the process to students. Various alternative teaching strategies and activities have been suggested, and some do help to improve the level of understanding among students e.

Efforts to integrate evolution throughout biology curricula rather than segregating it into a single unit may also prove more effective Nehm et al. At the very least, it is abundantly clear that teaching and learning natural selection must include efforts to identify, confront, and supplant misconceptions.

Most of these derive from deeply held conceptual biases that may have been present since childhood. Natural selection, like most complex scientific theories, runs counter to common experience and therefore competes—usually unsuccessfully—with intuitive ideas about inheritance, variation, function, intentionality, and probability.

The tendency, both outside and within academic settings, to use inaccurate language to describe evolutionary phenomena probably serves to reinforce these problems.

Natural selection is a central component of modern evolutionary theory, which in turn is the unifying theme of all biology. Without a grasp of this process and its consequences, it is simply impossible to understand, even in basic terms, how and why life has become so marvelously diverse.

The enormous challenge faced by biologists and educators in correcting the widespread misunderstanding of natural selection is matched only by the importance of the task. For a more advanced treatment, see Bell , or consult any of the major undergraduate-level evolutionary biology or population genetics textbooks.

Much of the additional material is available in Darwin and Stauffer Ridley points out that Darwin's calculations require overlapping generations to reach this exact number, but the point remains that even in slow-reproducing species the rate of potential production is enormous relative to actual numbers of organisms.

Humans are currently undergoing a rapid population expansion, but this is the exception rather than the rule. This is because not all evolution occurs by natural selection and because not all outcomes of natural selection involve changes in the genetic makeup of populations. Instructors interested in assessing their own students' level of understanding may wish to consult tests developed by Bishop and Anderson , Anderson et al.

Even more alarming is a recent indication that one in six teachers in the USA is a young Earth creationist, and that about one in eight teaches creationism as though it were a valid alternative to evolutionary science Berkman et al.

Strictly speaking, it is not necessary to understand how evolution occurs to be convinced that it has occurred because the historical fact of evolution is supported by many convergent lines of evidence that are independent of discussions about particular mechanisms.

Again, this represents the important distinction between evolution as fact and theory. See Gregory a. htm , accessed February Likewise, mechanisms involving organisms' conscious desires to change are often incorrectly attributed to Lamarck. For recent critiques of the tendency to describe various misconceptions as Lamarckian, see Geraedts and Boersma and Kampourakis and Zogza It is unfortunate that these mistakenly attributed concepts serve as the primary legacy of Lamarck, who in actuality made several important contributions to biology a term first used by Lamarck , including greatly advancing the classification of invertebrates another term he coined and, of course, developing the first albeit ultimately incorrect mechanistic theory of evolution.

For discussions of Lamarck's views and contributions to evolutionary biology, see Packard , Burkhardt , , Corsi , Humphreys , , and Kampourakis and Zogza Alters B.

Teaching biological evolution in higher education. Boston: Jones and Bartlett; Google Scholar. Alters BJ, Nelson CE. Teaching evolution in higher education. Anderson DL, Fisher KM, Norman GJ.

Development and evaluation of the conceptual inventory of natural selection. J Res Sci Teach. doi: Asghar A, Wiles JR, Alters B. Canadian pre-service elementary teachers' conceptions of biological evolution and evolution education.

McGill J Educ. Attenborough D. Life on earth. Boston: Little, Brown and Company; Banet E, Ayuso GE. Teaching of biological inheritance and evolution of living beings in secondary school.

Int J Sci Edu ;— Bardapurkar A. A critical review of the causal structure of student explanations. Evo Edu Outreach. Barton NH, Briggs DEG, Eisen JA, Goldstein DB, Patel NH. Cold Spring Harbor: Cold Spring Harbor Laboratory Press; Bartov H.

Can students be taught to distinguish between teleological and causal explanations? Teaching students to understand the advantages and disadvantages of teleological and anthropomorphic statements in biology.

Beardsley PM. Middle school student learning in evolution: are current standards achievable? Am Biol Teach. Bell G. The basics of selection.

Selection: the mechanism of evolution. Oxford: Oxford University Press; Berkman MB, Pacheco JS, Plutzer E. Evolution and creationism in America's classrooms: a national portrait. PLoS Biol. Bishop BA, Anderson CW. Evolution by natural selection: a teaching module Occasional Paper No.

East Lansing: Institute for Research on Teaching; Student conceptions of natural selection and its role in evolution. Bizzo NMV. From Down House landlord to Brazilian high school students: what has happened to evolutionary knowledge on the way? Bloom P, Weisberg DS.

Childhood origins of adult resistance to science. CAS Google Scholar. Brem SK, Ranney M, Schindel J. Perceived consequences of evolution: college students perceive negative personal and social impact in evolutionary theory.

Sci Educ. Brumby M. Problems in learning the concept of natural selection. J Biol Educ. Brumby MN. Misconceptions about the concept of natural selection by medical biology students.

Burkhardt RW. The inspiration of Lamarck's belief in evolution. J Hist Biol. The spirit of system. Cambridge: Harvard University Press; Chinsamy A, Plaganyi E. Accepting evolution. Clough EE, Wood-Robinson C.

How secondary students interpret instances of biological adaptation. Corsi P. The age of Lamarck. Berkeley: University of California Press; Coyne JA.

Selling Darwin. Creedy LJ. Student understanding of natural selection. Res Sci Educ. Curry A. Creationist beliefs persist in Europe. Darimont CT, Carlson SM, Kinnison MT, Paquet PC, Reimchen TE, Wilmers CC.

Human predators outpace other agents of trait change in the wild. Proc Natl Acad Sci U S A. Darwin C. Image credit: " Darwin's tree of life ," by Charles Darwin. Photograph by A. Kouprianov, public domain. Darwin proposed that species can change over time, that new species come from pre-existing species, and that all species share a common ancestor.

In this model, each species has its own unique set of heritable genetic differences from the common ancestor, which have accumulated gradually over very long time periods. Repeated branching events, in which new species split off from a common ancestor, produce a multi-level "tree" that links all living organisms.

Darwin's sketch above illustrates his idea, showing how one species can branch into two over time, and how this process can repeat multiple times in the "family tree" of a group of related species. Importantly, Darwin didn't just propose that organisms evolved.

If that had been the beginning and end of his theory, he wouldn't be in as many textbooks as he is today! Instead, Darwin also proposed a mechanism for evolution: natural selection. This mechanism was elegant and logical, and it explained how populations could evolve undergo descent with modification in such a way that they became better suited to their environments over time.

Darwin's concept of natural selection was based on several key observations:. Traits are often heritable. In living organisms, many characteristics are inherited, or passed from parent to offspring.

Darwin knew this was the case, even though he did not know that traits were inherited via genes. A diagram with text reading parents pass on heritable traits to their offspring. On the left a dark blue and a light blue butterfly are crossed to produce offspring with wings of varying shades of blue.

On the right a dark red and a light red butterfly are crossed to produce offspring with wings of varying shades of red. More offspring are produced than can survive. Organisms are capable of producing more offspring than their environments can support. Thus, there is competition for limited resources in each generation.

A diagram with a box reading limited resources. Arrows point away from the box to bubbles reading lack of food, lack of habitat, and lack of mates.

Text below reads …not all individuals will survive and reproduce. A group of 16 butterflies with wings of varying shades of blue and red is shown. A text bubble reading gleep! comes from 4 of the butterflies. Offspring vary in their heritable traits. The offspring in any generation will be slightly different from one another in their traits color, size, shape, etc.

A text bubble reading Hey, are you red? That's pretty sweet! comes from one of the blue butterflies. A text bubble reading Whoa! Love that blue wing color comes from one of the red butterflies. Text at the bottom reads Butterflies do not actually talk!

Cartoon for cute illustration purposes only. A smiley face is shown next to the text. Based on these simple observations, Darwin concluded the following:. In a population, some individuals will have inherited traits that help them survive and reproduce given the conditions of the environment, such as the predators and food sources present.

The individuals with the helpful traits will leave more offspring in the next generation than their peers, since the traits make them more effective at surviving and reproducing.

Because the helpful traits are heritable, and because organisms with these traits leave more offspring, the traits will tend to become more common present in a larger fraction of the population in the next generation.

Over generations, the population will become adapted to its environment as individuals with traits helpful in that environment have consistently greater reproductive success than their peers.

Darwin's model of evolution by natural selection allowed him to explain the patterns he had seen during his travels. For instance, if the Galápagos finch species shared a common ancestor, it made sense that they should broadly resemble one another and mainland finches, who likely shared that common ancestor.

If groups of finches had been isolated on separate islands for many generations, however, each group would have been exposed to a different environment in which different heritable traits might have been favored, such as different sizes and shapes of beaks for using different food sources.

These factors could have led to the formation of distinct species on each island. Example: How natural selection can work. To make natural selection more concrete, let's consider a simplified, hypothetical example.

In this example, a group of mice with heritable variation in fur color black vs. tan has just moved into a new area where the rocks are black. This environment features hawks, which like to eat mice and can see the tan ones more easily than the black ones against the black rock.

Because the hawks can see and catch the tan mice more easily, a relatively large fraction of the tan mice are eaten, while a much smaller fraction of the black mice are eaten.

If we look at the ratio of black mice to tan mice in the surviving "not-eaten" group, it will be higher than in the starting population. A 3-panel cartoon, each showing a hawk flying above a group of mice.

In the first panel there are 3 black mice and 6 tan mice. The black mice match the black ground. Text reads A population of mice has moved into a new area where the rocks are very dark. Due to natural genetic variation, some mice are black, while others are tan.

An arrow points from the first panel to the second with text reading Some mice are eaten by birds. In the second panel there are 3 black mice and 2 tan mice. Text reads Tan mice are more visible to predatory birds than black mice. Thus, tan mice are eaten at higher frequency than black mice.

Only the surviving mice reach reproductive age and leave offspring. An arrow points from the second panel to the third with text reading Mice reproduce, giving next generation.

In the third panel there are 7 black mice and 2 tan mice. Text reads Because black mice had a higher chance of leaving offspring than tan mice, the next generation contains a higher fraction of black mice than the previous generation.

Hawk outline traced from " Black and white line art drawing of Swainson hawk bird in flight ," by Kerris Paul public domain. Fur color is a heritable trait one that can be passed from parent to child. So, the increased fraction of black mice in the surviving group means an increased fraction of black baby mice in the next generation.

After several generations of selection, the population might be made up almost entirely of black mice. This change in the heritable features of the population is an example of evolution.

Key points about natural selection. When I was first learning about natural selection, I had some questions and misconceptions! about how it worked. Here are explanations about some potentially confusing points, which may help you get a better sense of how, when, and why natural selection takes place.

Natural selection depends on the environment. Natural selection doesn't favor traits that are somehow inherently superior. Instead, it favors traits that are beneficial that is, help an organism survive and reproduce more effectively than its peers in a specific environment.

Traits that are helpful in one environment might actually be harmful in another. Natural selection acts on existing heritable variation. Natural selection needs some starting material, and that starting material is heritable variation. For natural selection to act on a feature, there must already be variation differences among individuals for that feature.

Also, the differences have to be heritable, determined by the organisms' genes. Heritable variation comes from random mutations. The original source of the new gene variants that produce new heritable traits, such as fur colors, is random mutation changes in DNA sequence.

Random mutations that are passed on to offspring typically occur in the germline, or sperm and egg cell lineage, of organisms. Sexual reproduction "mixes and matches" gene variants to make more variation. Natural selection and the evolution of species.

Let's take a step back and consider how natural selection fits in with Darwin's broader vision of evolution, one in which all living things share a common ancestor and are descended from that ancestor in a huge, branching tree.

What is happening at each of those branch points? In the example of Darwin's finches, we saw that groups in a single population may become isolated from one another by geographical barriers, such as ocean surrounding islands, or by other mechanisms.

Once isolated, the groups can no longer interbreed and are exposed to different environments. In each environment, natural selection is likely to favor different traits and other evolutionary forces, such as random drift, may also operate separately on the groups.

Over many generations, differences in heritable traits can accumulate between the groups, to the extent that they are considered separate species.

Based on various lines of evidence , scientists think that this type of process has repeated many, many times during the history of life on Earth. Evolution by natural selection and other mechanisms underlies the incredible diversity of present-day life forms, and the action of natural selection can explain the fit between present-day organisms and their environments.

Want to join the conversation? Log in. Sort by: Top Voted. Posted 7 years ago. How would have homo sapiens evolved from the apes , why did the characteristics of standing erect dominate over bending forward. would it be a transmission of the lifestyle of apes eating food from the ground to hunting?

Downvote Button navigates to signup page. Flag Button navigates to signup page. Show preview Show formatting options Post answer. Quang Luong. Posted a year ago.

From the Homo Sapiens book, Yuval shared a very simple but reasonable concept that standing on 2 legs on the ground will give more broad and wide of view instead of 4 legs.

Climbing on to the tree will give more advantage but more effort just to check the surroundings. So standing on 2 legs dominated over time for our species to become.

Posted 6 years ago. In the example of the mice and hawks, what if due to natural selection the hawk's ability to spot out black mice increases? Will that cause the mice to 'counter evolve' and will this cycle of evolutions on the prey and predators' part continue?

Natural selection is the process Fat distribution and bodybuilding which species adapt All-Natural Selection their environments. It is the engine that drives evolution. English naturalist Charles All-Natural Selection All-Natkral the All-Natural Selection book outlining his All-Nstural of natural selection, On Selectiin Origin of Species. The book chronicled his studies in South America and Pacific islands. Published inthe book became a best seller. English naturalist Charles Darwin developed the idea of natural selection after a five-year voyage to study plants, animals, and fossils in South America and on islands in the Pacific. Inhe brought the idea of natural selection to the attention of the world in his best-selling book, On the Origin of Species. Natural selection is one of Selechion basic mechanisms of evolution, Seoection with mutation, All-Natutal, and genetic drift. Selecgion you have variation, differential reproduction, and heredity, Lower back pain relief will Selfction evolution Srlection natural Sflection as All-Natural Selection outcome. Natural selection is All-Natural Selection as a All-Natuural by which species of Time-restricted eating research All-Natural Selection plants All-Natural Selection are best adapted to their environment survive and reproduce, while those that are less well adapted die out. Natural selection ensures only the fittest survive to pass their genes on to the next generation. In evolution, the process by which those individuals of a species with characters that help them to become adapted to their specific environment tend to leave more offspring and transmit their characters, while those less able to become adapted tend to leave fewer offspring or die out, so that in the course of generations there is a progressive tendency in the species to a greater degree of adaptation.