How Homology Is Different from Convergent Evolution Biology

How Homology Is Different from Convergent Evolution Biology

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How Homology Is Different from Convergent Evolution Biology

Question 1

Pine trees that are too tall or too short do not do as well as pine trees that are average

in height. The short trees do not get as much light as tall or average trees. The tall trees

are more likely to break off in storms. Tell how this is an example of stabilizing selection.

Be sure to define stabilizing selection in your answer.

Your response must be at least 75 words in length.

Question 2

There is a moth in England called the peppered moth. Before Britain's industrial

revolution, these moths were usually salt and pepper colored. Because of their coloring,

they blended in well with the tree trunks on which they tended to rest. The coloring

helped them hide from the birds that ate them. During the British industrial revolution,

industry expelled a lot of soot from the burning of coal into the environment. This soot

darkened the tree trunks, and it was noted that black-colored moths were becoming

predominant. The idea is that with soot in the environment, black-colored moths fared

better than light-colored moths. There is some debate as to whether this is actually the

case or not, but for the sake of this question, let's assume it is.

the observations were in the text book i sent you under 12.2. I copied the text here but

it’s not really reader friendly in this format. Can you please adjust question #2

appropriately? Thanks in advance

12.2 Natural Selection Causes Evolution In the Origin of Species, Charles Darwin put

forth two major ideas: the theory of common descent (Chapter 11) and the theory of

natural selection. Darwin’s presentation of the theory of common descent—that all

species living today appear to have descended from a single ancestor—was thorough

and convincing.

Within 20 years of the publication of his book, the theory of common descent had been

accepted by most scientists. However, it was another 60 years before the scientific

community accepted Darwin’s theory of natural selection, which explains in large part

how organisms evolved from a common ancestor to become the great variety we see

today.

Darwin proposed that through the process of natural selection, the physical or

behavioral traits of organisms that lead to increased survival or reproduction become

common within their population, while less favorable traits are lost. The changes

accumulating within populations via natural selection can lead to the development of

new species.

Darwin reasoned that the process of natural selection is an inevitable consequence of

the competition for survival among variable individuals in a population. Today, natural

selection is considered one of the most important causes of evolution (although others,

such as the processes of genetic drift and sexual selection as described in Chapter 13,

also cause populations to change over time).

Darwin’s Observations The theory of natural selection is elegantly simple. It is an

inference based on four general observations: 1. Individuals within Populations Vary

Observations of groups of humans support this statement—people do come in an

enormous variety of shapes, sizes, colors, and facial features. It may be less obvious

that there is variation in nonhuman populations as well.

For example, in a litter of gray wolves born to a single female, individuals may vary in

coat color, while in a field of flowers, one plant may bloom earlier than others (Figure

12.6). We can add all kinds of less obvious differences to this visible variation; for

example, the amount of caffeine produced in the seeds of a coffee plant varies among

individuals in a wild population. Each different type of individual in a population is called

a variant. Visualize This Under what conditions might it be an advantage for an

individual plant to bloom earlier than other nearby flowers? Figure 12.6 Observation 1:

Individuals within populations vary. (a) Gray wolves vary in coat color, even within a

single litter of animals. (b) Flowers may vary in blooming time, with some individual

plants blooming much earlier than others of the same species. Figure 12.6 Full

Alternative Text 2. Some of the Variation among Individuals Can Be Passed on to Their

Offspring Although Darwin did not understand how it occurred, he observed many

examples of the general resemblance between parents and offspring. He also noticed

that people took advantage of the inheritance of variation in other species.

Pigeon fanciers in Darwin’s time clearly recognized the inheritance of variation; they

could see, for instance, that pigeons with neck ruffs were more likely to produce

offspring with neck ruffs than were pigeons without ruffs. Thus, when enthusiasts

wanted to produce a ruffed variety of pigeon, they encouraged breeding among the

birds with this trait (Figure 12.7). Darwin hypothesized that offspring tend to have the

same characteristics as their parents in natural populations as well. Figure 12.7

Observation 2: Some of the variation among individuals can be passed on to their

offspring.

Darwin noted that breeders could create flocks of pigeons with fantastic traits by using

as parents of the next generation only those individuals that displayed these traits. For

several decades after the Origin of Species was published, the observation that some

variations were inherited was the most controversial part of the theory of natural

selection. Because scientists could not adequately explain the origin and inheritance of

variation, many were unwilling to accept that natural selection could be a mechanism for

evolutionary change. When Gregor Mendel’s work on inheritance in pea plants (Chapter

8) was rediscovered in the 1900s, the mechanism for this observation became

clear—natural selection operates on genetic variation that is passed from one

generation to the next. 3.

Populations of Organisms Produce More Offspring than Will Survive This observation is

clear to most of us—the trees in the local park make literally millions of seeds every

summer, but only a small fraction of these survive to germinate, and only a few of the

seedlings live for more than a year or two. In the Origin of Species, Darwin gave a

graphic illustration of the difference between offspring production and survival. In his

example, he used elephants, animals that live long lives and are very slow breeders.

A female elephant does not begin breeding until age 30, and she produces about 1 calf

every 10 years until around age 90. Darwin calculated that even at this very low rate of

reproduction, if all the descendants of a single pair of African elephants survived and

lived full, fertile lives, after about 500 years their family would have more than 15 million

members (Figure 12.8)—many more than can be supported by all the available food

resources on the African continent! Visualize

This Predict what will happen to the elephant population as a result of limited resource

availability when Generation 4 is produced. Figure 12.8 Observation 3: Populations of

organisms produce more offspring than will survive. Even slow-breeding animals like

elephants are capable of producing huge populations relatively quickly. Figure 12.8 Full

Alternative Text 4. Survival and Reproduction Are Not Random In other words, the

subset of individuals that survives long enough to reproduce is not an arbitrary group.

Some variants in a population have a higher likelihood of survival and reproduction than

other variants do; that is, there is differential survival and reproduction among

individuals in the population.

The survival and reproduction of one variant compared with others in the same

population is referred to as its relative fitness. Traits that increase an individual’s relative

fitness in a particular environment are called adaptations. Individuals with adaptations to

a particular environment are more likely to survive and reproduce than are individuals

lacking such adaptations; in other words, these individuals have higher relative fitness.

Darwin referred to the results of differential survival and reproduction as natural

selection.

Adaptations are “naturally selected” in the sense that individuals possessing them

survive and contribute offspring to the next generation. Although Darwin used the word

selection, which implies some active choice, natural selection is a passive process that

is simply determined by differences among individuals and their success in their

particular environment. For example, among the birds called medium ground finches

living on an island in the Galápagos archipelago, scientists have observed that when

rainfall is scarce, a large bill is an adaptation that can be observed.

The large bill can be explained because birds with this attribute are able to crack open

large, tough seeds—the only food available during severe droughts. As shown in Figure

12.9, the 90 survivors of a 1977 drought had an average bill depth that was 6% greater

than the average bill depth of the original population of 751 birds. In these

environmental conditions, a large bill increases survival. Working with Data Use the

graph to determine how the total population size of ground finches changed between

1976 and 1978. Figure 12.9 Observation 4: Survival and reproduction are not random.

The pale purple curve summarizes bill depth in ground finches on Daphne Island in the

Galápagos in 1976. The dark purple curve below it represents the population in 1978,

after the drought of 1977. These data indicate that survivors of the drought had a larger

average bill depth than the predrought population. The change in the population’s

average bill size occurred because finches with larger-than-average bills had higher

fitness than did small-billed birds during the drought. Figure 12.9 Full Alternative Text

Adaptations are not only traits that increase survival.

Any trait possessed by an individual that increases the number of offspring it produces

relative to other individuals in a population is also an adaptation. For example, flowers in

a meadow may have a relatively limited number of potential insect pollinators. More

pollinator visits generally result in more seeds being produced by a single flower, so any

trait that increases a flower’s attractiveness to pollinators, such as a brighter color or

greater nectar production, should be favored by natural selection (Figure 12.10). Figure

12.10 Adaptations are not about survival only. Variations that increase a flower’s

attractiveness to a pollinator can increase its reproductive success by increasing the

number of seeds it produces. Darwin’s Inference: Natural Selection Causes Evolution

Based on his observations, Darwin reasoned that the result of natural selection is that

inherited variations that are favorable within a given environment tend to increase in

frequency in a population over time, while variations that are unfavorable within a given

environment tend to be lost within the population. In other words, adaptations become

more common in a population as the individuals who possess them contribute larger

numbers of their offspring to the succeeding generation. Natural selection results in a

change in the traits of individuals in a population over the course of generations—that

is, evolution. Although there are other factors, such as genetic drift and migration of

individuals, that can cause populations to evolve over time, natural selection is the only

force that can lead to the adaption of a population to its environment. It is a testament to

the power of the theory of natural selection that today it seems self-evident to us. But

the theory of natural selection only became so powerful after it was tested and shown to

work—in nature—in the manner Darwin described. Natural selection proved such a

powerful idea that it has influenced how we think about many phenomena, from the

success of particular brands of soft drinks to the relationships among nations. Natural

selection also explains the emergence of XDR-TB. Testing Natural Selection Darwin

proposed a scientific explanation of how evolution occurs, and like all good hypotheses,

it needed to be tested. All of the tests described next illustrate that natural selection is

an effective mechanism for evolutionary change. Artificial Selection Selection imposed

by human choice is called artificial selection. It is artificial in the sense that humans

deliberately control the survival and reproduction of individual plants and animals to

change the characteristics of the population. Individuals with preferred traits are

permitted to breed, whereas those that lack preferred traits are not allowed to breed.

The fancy pigeons that Darwin studied arose by artificial selection, and the great variety

of domestic dogs we see today also resulted from this process. In each case, different

breeds evolved through selection by breeders for various traits (Figure 12.11). These

examples demonstrate that differential survival and reproduction change the

characteristics of populations. However, because of the direct intervention of humans

on the survival and reproduction of these organisms, artificial selection is not exactly

equivalent to natural selection. Can change in populations occur without direct human

intervention? Visualize This What would this sequence of changes look like if the

selection was for dogs with a particular behavioral trait, for instance, pointing at a prey

animal? Figure 12.11 Artificial selection can cause evolution. When breeders select

dogs with certain traits to produce the next generation of animals, they increase the

frequency of that trait in the population. Over generations, the trait can become quite

exaggerated. Dachshunds are descendants of dogs that were selected for the

production of very short legs. Figure 12.11 Full Alternative Text Natural Selection in

the Lab Another test of the effectiveness of natural selection is to examine whether

populations living in artificially manipulated laboratory environments change over time.

An example of this kind of experiment is one performed on fruit flies placed in

environments containing different concentrations of alcohol. High concentrations of

alcohol cause cell death in fruit flies. Many organisms, including fruit flies and humans,

produce enzymes that metabolize alcohol—that is, they break it down, extract energy

from it, and modify it into less-toxic chemicals. There is variation among fruit flies in the

rate at which they metabolize alcohol. In a typical laboratory environment, most flies

process alcohol relatively slowly, but about 10% of the population possesses an

enzyme variant that allows those flies to metabolize alcohol twice as rapidly as the more

common variant. In an experiment (Figure 12.12), scientists divided a population of fruit

flies into two randomized groups. Initially, these two groups had the same percentage of

fast and slow alcohol metabolizers. One group of flies was placed in an environment

containing typical food sources; the other group was placed in an environment

containing the same food spiked with alcohol. After 57 generations, or about two years

in the laboratory, the percentage of fast alcohol-metabolizing flies in the environment

with only typical food sources was the same as at the beginning of the

experiment—10%. But after the same number of generations, the percentage of fast

alcohol-metabolizing flies in the alcohol-spiked environment was 100%. Because all of

the flies in this environment were now of the fast alcohol-metabolizing variety, the

average rate of alcohol metabolism in the population in this environment was much

higher in generation 57 than in generation 1. The population had evolved. Working with

Data This data can be represented as a line graph as well as a bar graph. Sketch the

line graph. Figure 12.12 Natural selection in laboratory conditions. When fruit flies are

placed in a high-alcohol environment, the percentage of flies that can rapidly metabolize

alcohol increases over many generations because of natural selection. In the normal

laboratory environment, there is no selection for faster alcohol processing, so the

average rate of alcohol metabolism does not change. Figure 12.12 Full Alternative Text

The evolution of the fruit flies in this experiment was a result of natural selection. In an

environment where alcohol concentrations were high, individuals that were able to

metabolize alcohol relatively rapidly had higher fitness. Because they lived longer and

were less affected by alcohol, the fast alcohol-metabolizing flies left more offspring than

the slow alcohol- metabolizing flies did. Thus, each generation had a higher frequency

of fast alcohol-metabolizing individuals than the previous generation did. After many

generations, flies that could rapidly metabolize alcohol predominated in the population.

Selection can change populations in highly regulated laboratory environments. But does

it have an effect in natural wild populations? Natural Selection in Wild Populations The

evolution of M. tuberculosis from being susceptible to antibiotics to being resistant is

one example of natural selection in a wild population; clearly, a change in the

environment (that is, the introduction of antibiotics) caused a change in the bacteria

population. Dozens of other pathogens, organisms that cause disease, have become

resistant to drugs and pesticides in the past 50 years as well. But even these changes

may seem less convincing to some readers because the adaptation is to a human-

imposed environmental change. Although studying adaptation to natural environmental

changes in the field is a significant challenge, the effects of natural selection have also

been observed in dozens of wild populations. A classic example of natural selection in a

natural setting is the evolution of bill size in Galápagos finches in response to drought

(review Figure 12.9). The survivors of the drought tended to be those with the largest

bills, which could more easily handle the tough seeds that were available in the dry

environment. The survival of this nonrandom subset of birds resulted in a dramatic

change in the next generation. The population of birds that hatched from eggs in

1978—the descendants of the drought survivors—had an average bill depth 4 to 5%

larger than that of the predrought population. A more recent example of natural

selection causing evolution has occurred in the past few decades on the eastern coast

of the United States, where an invasive Asian crab species is wreaking havoc on native

mussels. But one species, the blue mussel, has quickly evolved the ability to thicken its

shell when it grows in the presence of the Asian crab, thwarting their attacks (Figure

12.13). Scientists at the University of New Hampshire were able to demonstrate that this

was an evolutionary change by comparing blue mussel populations in regions invaded

by the Asian crab with those in more northerly waters, where the Asian crab cannot

survive. These researchers demonstrated that while both populations of mussels

thicken their shells in response to the presence of native crabs, only the mussels that

had been living with the Asian crabs responded to the presence of this species. Clearly,

natural selection for individual mussels that could recognize this new species of crab as

a predator had caused a change in the mussel population. Figure 12.13 Natural

selection in the wild. (a) Asian shore crabs are recent invaders to the east coast;

because they were unfamiliar predators to the native mussels, they initially devastated

mussel beds. (b) Some populations of blue mussels have evolved the ability to

recognize the presence of the crabs and respond the way they do to native predators,

by adding layers to their shells. Got It? Two of Darwin’s observations that led to the

theory of natural selection are that organisms in a population from each other and that

traits can be on their offspring. The fitness of an individual is defined as its success in

and compared with other individuals in the same population. An adaptation is a trait that

increases an individual’s relative to others in the population who do not have the trait.

When humans manipulate the environment and cause the evolution of traits in a

population of domestic animals or plants it is called . The evolution of rapid alcohol

metabolism in a population of fruit flies in a lab occurred in the presence of high alcohol

levels could occur because individuals in their rate of alcohol metabolism.

In your own words, explain the concepts from the four observations discussed in 12.2

using the moth as an example. In other words, how does the moth illustrate the first

observation, the second observation, etc.?

Your response must be at least 200 words in length.

Question 3

Explain how homology is different from convergent evolution and give examples. Briefly

define homology and convergent evolution in your explanation.

How Homology Is Different from Convergent Evolution Biology

RUBRIC
Excellent Quality 95-100%	Introduction 45-41 points The background and significance of the problem and a clear statement of the research purpose is provided. The search history is mentioned.		Literature Support 91-84  points The background and significance of the problem and a clear statement of the research purpose is provided. The search history is mentioned.			Methodology 58-53 points Content is well-organized with headings for each slide and bulleted lists to group related material as needed. Use of font, color, graphics, effects, etc. to enhance readability and presentation content is excellent. Length requirements of 10 slides/pages or less is met.
Average Score 50-85%	40-38 points More depth/detail for the background and significance is needed, or the research detail is not clear. No search history information is provided.		83-76  points Review of relevant theoretical literature is evident, but there is little integration of studies into concepts related to problem. Review is partially focused and organized. Supporting and opposing research are included. Summary of information presented is included. Conclusion may not contain a biblical integration.			52-49  points Content is somewhat organized, but no structure is apparent. The use of font, color, graphics, effects, etc. is occasionally detracting to the presentation content. Length requirements may not be met.
Poor Quality 0-45%	37-1 points The background and/or significance are missing. No search history information is provided.		75-1 points Review of relevant theoretical literature is evident, but there is no integration of studies into concepts related to problem. Review is partially focused and organized. Supporting and opposing research are not included in the summary of information presented. Conclusion does not contain a biblical integration.			48-1 points There is no clear or logical organizational structure. No logical sequence is apparent. The use of font, color, graphics, effects etc. is often detracting to the presentation content. Length requirements may not be met
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