Evolution Misconceptions
Because evolution is slow, humans cannot influence it.
As described in the misconception about evolutionary rates above, evolution sometimes occurs quickly. And since humans often cause major changes in the environment, we are frequently the instigators of evolution in other organisms. Here are just a few examples of human-caused evolution for you to explore: — Several species have evolved in response to climate change. — Fish populations have evolved in response to our fishing practices. — Insects like bedbugs and crop pests have evolved resistance to our pesticides. — Bacteria, HIV, malaria, and cancer have evolved resistance to our drugs.
Humans can't negatively impact ecosystems, because species will just evolve what they need to survive.
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.
All traits of organisms are adaptations.
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.
Each trait is influenced by one Mendelian locus.
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.
Each locus has only two alleles.
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.
Evolutionary theory implies that life evolved (and continues to evolve) randomly, or by chance.
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.
Evolution only occurs slowly and gradually.
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
Individual organisms can evolve during a single lifespan.
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.
Evolution is a theory about the origin of life.
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.
Genetic drift only occurs in small populations.
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.
Humans are not currently evolving.
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.
Is this classic image an accurate representation of human evolution?
Humans didn't evolve from the modern day phenotypic apes. The apes have evolved since then from a common ancestor, as well as the humans, leading to their modern day forms. The idea of the evolution of humans from apes is inaccurate, it was humans and apes from a common ancestor.
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.
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.
The fittest organisms in a population are those that are strongest, healthiest, fastest, and/or largest.
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
A long branch on a phylogeny indicates that the taxon has changed little since it diverged from other taxa.
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.
Species are distinct natural entities, with a clear definition, that can be easily recognized by anyone.
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.
Natural selection gives organisms what they need.
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.
Natural selection produces organisms perfectly suited to their environments.
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.
Natural selection involves organisms trying to adapt.
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.
Evolution results in progress; organisms are always getting better through evolution.
One important mechanism of evolution, natural selection, does result in the evolution of improved abilities to survive and reproduce; however, this does not mean that evolution is progressive — for several reasons. First, as described in a misconception below (link to "Natural selection produces organisms perfectly suited to their environments"), natural selection does not produce organisms perfectly suited to their environments. It often allows the survival of individuals with a range of traits — individuals that are "good enough" to survive. Hence, evolutionary change is not always necessary for species to persist. Many taxa (like some mosses, fungi, sharks, opossums, and crayfish) have changed little physically over great expanses of time. Second, there are other mechanisms of evolution that don't cause adaptive change. Mutation, migration, and genetic drift may cause populations to evolve in ways that are actually harmful overall or make them less suitable for their environments. For example, the Afrikaner population of South Africa has an unusually high frequency of the gene responsible for Huntington's disease because the gene version drifted to high frequency as the population grew from a small starting population. Finally, the whole idea of "progress" doesn't make sense when it comes to evolution. Climates change, rivers shift course, new competitors invade — and an organism with traits that are beneficial in one situation may be poorly equipped for survival when the environment changes. And even if we focus on a single environment and habitat, the idea of how to measure "progress" is skewed by the perspective of the observer. From a plant's perspective, the best measure of progress might be photosynthetic ability; from a spider's it might be the efficiency of a venom delivery system; from a human's, cognitive ability. It is tempting to see evolution as a grand progressive ladder with Homo sapiens emerging at the top. But evolution produces a tree, not a ladder — and we are just one of many twigs on the tree.
If we evolved from monkeys, why are there still monkeys around?
Start with the same correction as given in #1—apes are closer relatives than monkeys. And then there is a similar misconception. The theory of evolution does not say that currently existing species came from other currently existing species. The most recent common ancestors between humans and Old World monkeys (those from Africa and Asia) were about 25 million years ago (the New World monkeys in South and Central America split off earlier).
Taxa that appear near the top or right-hand side of a phylogeny are more advanced than other organisms on the tree.
This misconception encompasses two distinct misunderstandings. First, when it comes to evolution, terms like "primitive" and "advanced" don't apply. These are value judgments that have no place in science. One form of a trait may be ancestral to another more derived form, but to say that one is primitive and the other advanced implies that evolution entails progress — which is not the case. For more details, visit our misconception on this topic. Second, an organism's position on a phylogeny only indicates its relationship to other organisms, not how adaptive or specialized or extreme its traits are.
Evolution is not science because it is not observable or testable.
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.
Evolutionary theory is invalid because it is incomplete and cannot give a total explanation for the biodiversity we see around us.
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.
Evolution is 'just' a theory.
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
Natural selection is about survival of the very fittest individuals in a population.
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.
Natural selection acts for the good of the species.
When we hear about altruism in nature (e.g., dolphins spending energy to support a sick individual, or a meerkat calling to warn others of an approaching predator, even though this puts the alarm sounder at extra risk), it's tempting to think that those behaviors arose through natural selection that favors the survival of the species — that natural selection promotes behaviors that are good for the species as a whole, even if they are risky or detrimental for individuals in the population. However, this impression is incorrect. Natural selection has no foresight or intentions. In general, natural selection simply selects among individuals in a population, favoring traits that enable individuals to survive and reproduce, yielding more copies of those individuals' genes in the next generation. Theoretically, in fact, a trait that is advantageous to the individual (e.g., being an efficient predator) could become more and more frequent and wind up driving the whole population to extinction (e.g., if the efficient predation actually wiped out the entire prey population, leaving the predators without a food source). So what's the evolutionary explanation for altruism if it's not for the good of the species? There are many ways that such behaviors can evolve. For example, if altruistic acts are "repaid" at other times, this sort of behavior may be favored by natural selection. Similarly, if altruistic behavior increases the survival and reproduction of an individual's kin (who are also likely to carry altruistic genes), this behavior can spread through a population via natural selection.
Gaps in the fossil record disprove evolution.
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.