21. Evolution by Natural Selection

Descent with Modification

Evolutionary Structures; Homologous, Analogous, and Vestigial

Why do humans have a third eyelid? - Dorsa Amir

Descent With Modification

The researchers placed white and brown mouse models both in abandoned fields on the mainland (dark soil) and on sand dunes on the islands (light soil) and then measured the percentage of models that were attacked by predators. What is the take-home message of the data? Do the data support or reject the hypothesis that mouse color is adaptive? <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/f2d6aec81e42ffae-1677309539293.jpg" style="width: 300px;">

Convergent Evolution in a Nutshell

Which of the following taxonomic levels contains organisms that share the most recent common ancestor?
a. family;
b. order;
c. phylum;
d. genus;
e. class

A population of snails is preyed on by birds that break the snails open on rocks, eat the soft bodies, and leave the shells. The snails occur in both striped and unstriped forms. In one area, researchers counted both live snails and broken shells. Their data are summarized below: 

Which snail form seems better adapted to this environment? Why? Predict how the frequencies of striped and unstriped snails might change in the future.<img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/0a701037b75573c8-1677716852852.jpg" style="width: 300px;">

Convergent and Divergent Evolution by Natural Selection

 The drug did not work in the way that the developers intended. 

 No. Think about the question in relation to natural selection. 

 Patients did not take the drug as it was prescribed. 

 No. Although this may be a factor in the formation of drug-resistant pathogens, in this situation there is a better answer. 

 The bacterium mutated in response to the drug. 

 No. This is not how drug-resistant pathogens emerge. 

 None of the listed responses is correct. 

 No. One of the listed responses is correct. 

 Some members of the bacteria population must have had genetic variation that made them resistant to antibiotics, and these bacteria had greater reproductive success than sensitive individuals. 

When does a gene for drug resistance develop in a population?

How did some strains of Staphylococcus aureus become resistant to antibiotic drugs?

Vestigial Structures

 mosquitoes that survive spraying develop an immunity to the insecticide 

 No. This is not what would be predicted by natural selection. 

 mosquitoes are deliberately adapting themselves to this human-made change in the environment 

 No. Mosquitoes do not have this ability. 

 the original spraying has caused a permanent mutation, giving the insects genetic resistance to the spray 

 No. It is far too unlikely that the spraying could lead to such an immediate advantageous mutation. 

 many mosquitoes today are descendants of mosquitoes with insecticide-resistant characteristics 

Apply what you have learned about natural selection.

When they were first sold, aerosol insecticides were highly effective in killing flies and mosquitoes. Now, several decades later, a much smaller proportion of these insects die when sprayed. The reason fewer insects die when they are sprayed is that __________.

 there's only one possible way to encode information in a macromolecule 

 No. That only a single system is used does not mean it is the only system that would work. 

 the earliest macromolecules probably arose when lightning struck an oxygen-free atmosphere 

 No. The question is not asking how the very first life-form may have originated. 

 all organisms are descended from a single common ancestor 

If it works, don't fix it.

All known organisms translate genetic information to produce protein molecules via the same genetic code. This finding strongly supports the hypothesis that __________.

 only the best-adapted organisms can survive 

 No. This does not account for similarities among dissimilar organisms. 

 advantageous changes can be passed along to offspring 

 No. Though true, this does not account for similarities among dissimilar organisms. 

 most evolution occurs rapidly following a mass extinction 

 All of the listed responses are correct. 

 No. Only one of the other choices is correct. 

 dissimilar organisms might have evolved from a distant, common ancestor 

Consider what accounts for such homology.

Seemingly dissimilar organisms such as hummingbirds, humans, and whales have similar skeletal structures. This most directly suggested to biologists that __________.

Vestigial Traits and Evolutionary Misconceptions

The theory of common descent states that all modern organisms                   .
a. can change in response to environmental change;
b. descended from a single common ancestor;
c. descended from one of many ancestors that originally arose on Earth;
d. have not evolved;
e. can be arranged in a hierarchy from “least evolved” to “most evolved”

Traits that are derived from a common ancestor, like the bones of human arms and bird wings, are said to be                .

 No. This answer is true, but there is a better response. 

 No. The fossils Darwin studied did show definite lines of descent, but there is a better answer. 

 studying adaptations of organisms to their environments 

 No. Darwin was especially interested in the variety of Gal&#225;pagos finch species, but there is a better answer. 

 the unique organisms he saw in the Gal&#225;pagos Islands 

 No. His interest was especially piqued by the Gal&#225;pagos finches, but there is a better response. 

Which of these had a greater impact on the theory of natural selection?

During his voyage around the world, Darwin was inspired to think about evolution by __________.

Most mice living on the mainland of Florida are brown, but the mice that live on the sand dunes of the barrier islands have white fur. The differences in color are heritable, determined by genes such as MC1R. It is intuitive that the light color of beach-dwelling mice is an adaptation for blending into their environment—and thus evading predators.

What is an evolutionary adaptation?

a. a trait that improves the fitness of its bearer, compared with individuals without the trait

b. a trait that changes in response to environmental influences within the individual’s lifetime

c. the ability of an individual to adjust to its environment

d. a trait that an individual wants so that it can survive

A species of crayfish that lives in caves produces eyestalks like its above-ground relatives, but has no eyes. Eyestalks in cave-dwelling crayfish are thus                   .
a. an evolutionary error;
b. a dominant mutation;
c. biogeographical evidence of evolution;
d. a vestigial trait;
e. evidence that evolutionary theory may be incorrect

 an organism's traits affect only its own survival 

 No. An organism's heritable traits will also affect the survival of its offspring. 

 environmental changes have no effect on the organisms living in that environment 

 No. A trait that is advantageous in one environment may be detrimental in another. 

 natural selection operates only when an organism needs to evolve 

 No. Natural selection is always operating. 

 natural selection can improve the match between an organism and its environment 

Think about how descent with modification can improve a species' chances of survival.

In Darwin's view of descent with modification, __________.

The best definition of evolutionary fitness is                   .
a. physical health;
b. the ability to attract members of the opposite sex;
c. the ability to adapt to the environment;
d. survival and reproduction relative to other members of the population
e. overall strength

Some biologists summarize evolution by natural selection with the phrase “mutation proposes, selection disposes.” Mutation is a process that creates heritable variation. Explain what the phrase means.

Convergent vs  Divergent Evolution

What Is Adaptation? | Ecology & Environment | Biology | FuseSchool

True or false? Some traits are considered vestigial because they existed long ago.

DNA sequences in many human genes are very similar to the sequences of corresponding genes in chimpanzees. The most likely explanation for this result is that
a. humans and chimpanzees share a relatively recent common ancestor.
b. humans evolved from chimpanzees.
c. chimpanzees evolved from humans.
d. convergent evolution led to the DNA similarities.

Evolutionary fitness

Which of the following is not an observation or inference on which natural selection is based?
a. There is heritable variation among individuals.
b. Poorly adapted individuals never produce offspring.
c. Species produce more offspring than the environment can support.
d. Only a fraction of an individual’s offspring may survive.

 the passing of acquired characteristics to offspring 

 an individual's ability to adapt to its environment 

 No. Individuals do not evolve. Only populations evolve. 

 a way to classify organisms based on morphological similarities 

 No. Although Darwin's concept of evolution fit well with Linnaeus's classification system, his theory is an explanation of the pattern, not a description of it. 

 No. One of the other choices is correct. 

Darwin was thinking in terms of a process.

Darwin originally defined evolution as __________.

Summarize the key points of Darwin’s theory of descent with modification, including his proposed mechanism of evolution.

Complete this concept map describing potential causes of evolutionary change within populations. 
a.
b. 
c. 
d. 
e. 
f. 
g. <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/643b7124a0839857-1677716774352.jpg" style="width: 300px;">

Why don’t the biggest and strongest individuals in a population always produce the most offspring?
a. The biggest and strongest individuals always have higher fitness.
b. In some environments, being big and strong lowers fitness.
c. Sometimes the biggest and strongest individuals may choose to have fewer offspring.
d. Sometimes the number of offspring is not related to fitness.

 No. Lamarck is best known for proposing the inheritance of acquired characteristics. 

 No. Aristotle believed that all living forms could be arranged on a scale or ladder of increasing complexity, the scale of nature. 

 No. Wallace is best known for proposing natural selection independently of Charles Darwin. 

 No. Lyell is best known for uniformitarianism. 

What did this person believe caused the extinctions? ?

The modern idea of extinction as a common occurrence in Earth's history was first proposed in the early-19th-century writings of __________.

 No. Natural selection is differential reproductive success in nature. 

No. Sexual recombination refers to new combinations of alleles resulting from fertilization.

 No. Paleontology is the study of fossils. 

No. Homology refers to organisms sharing traits based on common ancestry.

Consider which of these terms best implies human involvement.

The breeding of plants and animals for particular traits by humans is called __________.

 organisms that are positioned close to each other are closely related 

 No. The positioning of branch points, points at which organisms most recently shared a common ancestor, are better indications of relatedness. 

 scientists are sure of the correct placement and relationships of all organisms 

 No. Evolutionary trees are more like hypotheses for which supporting evidence is still being collected. 

 the concept of descent with modification is not well represented 

 No. The nested pattern is what would be expected from descent with modification. 

 homologous characteristics form a nested pattern 

Think about Darwin's concept of the branching "tree of life."

On an evolutionary tree, __________.

 was rejected by Darwin in favor of catastrophism 

 No. Darwin came to agree with Lyell that processes at work in the present could have produced observed geologic features. 

 was compatible with the idea of Earth being only a few thousand years old 

 No. For present-day earth processes to have produced observed geologic features, those processes would have had to act over millions or billions of years. 

 was similar to Lamarck's theory of inheritance of acquired characteristics 

 No. Lyell was considering geologic processes as opposed to biological processes. 

 states that current geologic processes are very different from those that operated in the past 

 No. Uniformitarianism states that current geologic processes are the same as those that operated in the past. 

 strongly influenced Darwin's view of how living organisms could change over time 

How did this concept influence Darwin's thinking about how organisms could change given enough time?

Lyell's principle of uniformitarianism __________.

According to data presented in this chapter, which of the following are correct? Select True or False for each statement.
T/F When individuals change in response to challenges from the environment, their altered traits are passed on to offspring.
T/F Species are created independently of each other and do not change over time.
T/F Populations—not individuals—change when natural selection occurs.
T/F The traits of populations become more perfect over time.

Fitness, Adaptation, and Artificial Selection

An adaptation is a trait of an organism that increases                   .
a. its fitness;
b. its ability to survive and replicate;
c. in frequency in a population over many generations;
d. A and B are correct;
e. A, B, and C are correct

Define artificial selection, and compare and contrast it with natural selection.

 evidence for Lamarck's theory of use and disuse 

 No. Lamarck's theory of use and disuse referred to body parts that would change in structure and function during an organism's lifetime. 

 one piece of evidence that does not support the theory of evolution 

 No. The presence of vestigial organs does support the theory of evolution. 

 examples of anatomical imperfections such as the human knee 

 No. This is not a term to describe anatomical imperfections. 

 homologies that can only be observed in embryos 

 No. This is not true of vestigial organs. 

 remnants of structures that were useful to an organism's ancestors but that are now nonfunctional or show reduced function 

What is the meaning of the word vestige?

Vestigial organs are __________.

 the idea that animals and plants might change over time was absent from Western science 

 No. Several others had at least proposed this idea. 

 the idea of evolution was widely accepted because it could fit into the biblical story of creation 

 No. Evolution is not a part of the biblical story of creation. 

 the idea of evolution was widely accepted by scientists, but Darwin's great impact was to popularize it for the layperson 

 No. Darwin proposed evolution by natural selection some time after his return from the voyage. 

 No. One of the other listed responses is correct. 

 several biologists had proposed that species might change over time, but none had suggested a convincing mechanism that might cause the change 

What prevailing Earth view had Darwin grown up with?

At the time Charles Darwin sailed on HMS Beagle, __________.

Which of the following observations is not part of the theory of natural selection?
a. Populations of organisms have more offspring than will survive;
b. There is variation among individuals in a population;
c. Modern organisms are unrelated;
d. Traits can be passed on from parent to offspring;
e. Some variants in a population have a higher proba­bility of survival and reproduction than other variants do.

Which of the following observations helped Darwin shape his concept of descent with modification?
a. Species diversity declines farther from the equator.
b. Fewer species live on islands than on the nearest continents.
c. Birds live on islands located farther from the mainland than the birds’ maximum nonstop flight distance.
d. South American temperate plants are more similar to the tropical plants of South America than to the temperate plants of Europe.

Most mice living on the mainland of Florida are brown, but the mice that live on the sand dunes of the barrier islands have white fur. The differences in color are heritable, determined by genes such as MC1R. It is intuitive that the light color of beach-dwelling mice is an adaptation for blending into their environment—and thus evading predators.

Compare how evolution by inheritance of acquired characters and the theory of evolution by natural selection would explain the observation of white mice living primarily on light soil and brown mice living primarily on dark soil.

Darwin and Natural Selection: Crash Course History of Science #22

Evaluate this statement: Evolution is said to occur when new traits accumulate over time, increasing complexity.

Even though marsupial mammals give birth to live young, an eggshell forms briefly early in their development. This is evidence that a.marsupials share a common ancestor with some egg-laying species;
b. marsupials are not really mammals;
c. all animals arose from a common ancestor;
d. marsupial mammals were separately created by God;
e. the fossil record of marsupial mammals is incorrect

How can evolutionary fitness be measured? Select True or False for each statement.
T/F Document how long individuals survive.
T/F Count the number of healthy, fertile offspring produced.
T/F Determine which individuals are strongest.
T/F Determine which phenotype is the most common.

A swim bladder is a gas-filled sac that helps fish maintain buoyancy. Evidence indicates that early fish gulped air into primitive lungs, helping them survive in stagnant waters. The evolution of the swim bladder from lungs of an ancestral fish is an example of
a. an evolutionary trend.
b. paedomorphosis.
c. the gradual refinement of a structure with the same function.
d. exaptation.

Evidence of Evolution - Homologous, Analogous, & Vestigial Structures

A team led by evolutionary biologist Hopi Hoekstra set out to test the hypothesis that predators are an agent of natural selection on mouse color. They made 250 plasticine models of mice that were alike in every way except that half were painted white and half were painted brown. Suggest one advantage and one disadvantage of using model mice instead of real mice in this experiment.

Divergent Evolution

Within six months of effectively using methicillin to treat S. aureus infections in a community, all new S. aureus infections were caused by MRSA. How can this best be explained?
a. A patient must have become infected with MRSA from another community.
b. In response to the drug, S. aureus began making drug- resistant versions of the protein targeted by the drug.
c. Some drug-resistant bacteria were present at the start of treatment, and natural selection increased their frequency.
d. S. aureus evolved to resist vaccines.

The researchers placed white and brown mouse models both in abandoned fields on the mainland (dark soil) and on sand dunes on the islands (light soil) and then measured the percentage of models that were attacked by predators. What is the take-home message of the data? Do the data support or reject the hypothesis that mouse color is adaptive? <IMAGE>

What observations did Darwin make on the Galápagos Islands that helped convince him that evolution occurs?
a. the existence of animals that did not fit into Linnaeus’s classification system;
b. the similarities and differences among cacti and tortoises on the different islands;
c. the presence of species he had seen on other tropical islands far from the Galápagos;
d. the radioactive age of the rocks of the islands;
e. fossils of human ancestors

Natural Selection - Crash Course Biology #14

 The predatory fish will evolve smaller mouths so that they do not drive their prey to extinction. 

 No. Natural selection is not goal oriented&#151;in other words, it does not operate in order to bring about some future benefit. 

 The zooplankton will become sexually mature at larger sizes. 

 No. This is exactly the opposite of what one should predict. 

 The predatory fish will evolve poor eyesight so as to preserve their food supply. 

 The first and the third listed responses are both good predictions. 

 No. Natural selection does not operate in order to bring about some future benefit. 

 The population will come to contain adult zooplankton that reach sexual maturity when they are still relatively small. 

Consider what fitness would entail in such a situation.

A population of zooplankton is exposed to a small number of predatory fish that feed on the larger-sized (adult) zooplankton. Which of the following predictions would most likely occur based on the principles of natural selection?

 Individuals within a population vary, yet island species around the world all appear to be related to each other. 

 No. Variation among individuals within a population was a key observation, but Darwin observed that island species seemed to be related to organisms from the closest mainland. 

 Organisms produce more offspring than can be supported by their environment, and adaptations to specific environments increase an organism's ability to survive and reproduce. 

 No. The overproduction of offspring was a key observation, but the differential success of individuals was an inference Darwin made based on his observations. 

 Some individuals leave more descendants than other individuals, but the individuals in a population are essentially identical to each other. 

 No. Individuals in a population vary in their heritable traits. 

 Some individuals within a population have greater success in survival and reproduction than others, and favorable traits within a population will accumulate over generations. 

 No. These are the inferences Darwin made based on his key observations. 

 Organisms within a population vary, and all populations produce more offspring than can be supported by the environment, resulting in competition for survival within the population. 

Consider lines of evidence, not inferences made from that evidence.

Because he was well aware of the effect his theory of evolution would have on the public and on the Church of England, Darwin delayed publishing his work for several decades while he gathered additional evidence. After invoking selective breeding of domesticated species as evidence that groups of organisms are capable of change, he then proposed that natural populations can change as well. On which two lines of evidence did he base this proposal?

Which of the following did not influence Darwin as he synthesized the theory of evolution by natural selection?
a. examples of artificial selection that produce large and relatively rapid changes in domesticated species
b. Lyell’s Principles of Geology, on gradual geologic changes
c. comparisons of fossils with living organisms
d. Mendel’s paper describing the laws of inheritance

 paleontology; believed in catastrophism 

 uniformitarianism; believed that the same geologic forces are operating today that occurred in the past 

 No. This describes James Hutton and Charles Lyell. 

 genetics; described the mechanism for descent with modification 

 evolution; first proposed that acquired characteristics are inherited 

 No. Lamarck first proposed that acquired characteristics are inherited. 

 the binomial classification system; thought that resemblances among different species reflected the pattern of their creation 

Why was Linnaeus interested in the classification of organisms?

Carolus Linnaeus is considered to be the founder of __________, and he __________.

Vestigial Structures | What are Vestigial Structures?

 homologous proteins have arisen independently in many different animal groups 

 No. Homologous features are similar because of their common ancestry and, thus, did not arise independently in many different groups. 

 closely related animal species have similar geographic distributions 

 No. Biogeography is the study of the geographic distribution of life. 

 closely related organisms have similar stages of development 

 closely related organisms have more similar DNA and proteins than more distantly related organisms 

Molecular biology includes the study of proteins and nucleic acids.

Evidence from molecular biology supports the theory of evolution by demonstrating that __________.