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C2.2 · Research factors that influence evolutionary processes

Learn to research factors that influence evolutionary processes through clear examples and targeted practice.

Ontario Grade 11 Biology

Evolution

Researching how populations change over generations

In a population of insects, some individuals may be harder for predators to see than others. If the environment changes, the less visible insects might survive and reproduce more often. If their differences can be inherited, the population may change over generations. This is one example of evolution. Evolution does not mean that an individual changes because it needs to. It describes changes in inherited characteristics across generations in a population. In SNC2D, you studied cells, systems, and how evidence can be used to investigate questions. Here, use those inquiry skills to research which factors can influence evolutionary processes and how scientists support their explanations.

What you will learn

Explain evolution as a change in inherited characteristics within a population over generations.
Describe how natural selection, mutation, gene flow, genetic drift, and mate choice can influence evolutionary change.
Use evidence to distinguish an observed pattern from an explanation of that pattern.
Evaluate whether a research claim is supported by relevant evidence and whether other explanations remain possible.

From a biological question to evidence

A population is a group of the same kind of organism living in the same area. Individuals in a population can differ. A characteristic is an observable feature, such as body colour or beak shape. Some differences are inherited, meaning they can be passed from parents to offspring. Evolutionary change concerns inherited differences across generations, not changes an individual makes during its lifetime.

A useful research question names a population, a factor, and a possible change. For example: “Did a change in tree colour influence the frequency of dark and light moths in a population?” Frequency means how common a type is in the group. The question does not assume the explanation is true. Researchers need evidence that addresses it.

An observation is a recorded pattern, such as a rise in the proportion of dark moths. An explanatory model is an account of why that pattern occurred. A pattern alone does not prove its cause. Researchers compare evidence, consider other explanations, and check whether the evidence is reliable. A source should identify what was observed, when and where it was studied, and how the conclusion follows from the evidence.

Evolution describes inherited change in a population across generations.
A pattern is not the same thing as an explanation.
A strong research question can be investigated using relevant evidence.

Factors that can influence evolutionary change

Natural selection occurs when individuals with some inherited characteristics survive and reproduce more successfully in a particular environment. Over generations, those characteristics may become more common. The environment does not give an organism a useful characteristic because it needs one. Instead, selection acts on differences that already exist in the population.

Mutation is a change in inherited information. Mutations can create new inherited differences, although not every mutation affects an observable characteristic. A mutation is not necessarily helpful. Its effect depends on the organism and conditions. Mutation can provide new variation, but a mutation does not appear because the population needs it.

Gene flow is the movement of inherited differences between populations when organisms move and reproduce in a new population. It can make populations more similar or introduce a difference into a population. Genetic drift is a change in how common inherited differences are because of chance. Chance can have a greater effect in a small population. Unlike natural selection, drift does not require a difference to improve survival or reproduction.

Mate choice, sometimes called sexual selection, occurs when some individuals are more likely to find mates because of particular characteristics. If those characteristics are inherited, they may become more common over generations, even if they do not help an organism avoid predators. These factors can interact. For example, movement between populations can bring in variation, and environmental conditions can then affect which individuals reproduce more successfully.

Selection is linked to differences in survival or reproduction in a particular environment.
Mutation can introduce inherited variation; it is not directed by need.
Gene flow involves movement between populations; drift involves chance.
Mate choice can influence which inherited characteristics are passed on.

Researching patterns and evaluating explanations

Scientists can investigate evolutionary processes by comparing records from different times, comparing populations, or examining published studies. A comparison is useful when it makes clear what differs and what stays similar. For example, a study might compare moth colour frequencies before and after tree surfaces became darker. That comparison shows a pattern. To support natural selection as an explanation, evidence should also connect colour with survival or reproduction under the relevant conditions.

A well-known example is the peppered moth in Britain. Industrial pollution darkened some tree surfaces, and researchers reported changes in the relative frequency of light and dark moth forms. Bernard Kettlewell’s 1950s research examined moth survival in relation to bird predation and background colour. Later work, including Majerus’s field study published in 2009, provided further evidence about predation and moth colour. The research supports natural selection as an explanation for changes in moth frequencies, but a careful account distinguishes the observed changes from the proposed cause and considers the conditions under which the evidence was collected.

When researching, prefer sources that name the study and describe its evidence. A scientific article, a university or museum explanation that cites research, or a government science resource can be more useful than an unsupported online claim. Check whether the evidence concerns the same population and conditions as the claim. Also ask what the evidence cannot show. A change in frequency by itself may be consistent with selection, drift, or movement between populations; additional evidence is needed to judge which factor best explains it.

Compare observations with the explanation offered for them.
Ask whether evidence directly connects a factor to inherited change.
Check study conditions, source quality, and alternative explanations.

Build a clear evidence-based conclusion

A concise research conclusion can follow three steps: state the observed pattern, identify the factor proposed to explain it, and describe evidence that links the two. Then note a limitation or another possible explanation. This structure avoids claiming more than the evidence supports.

For example, saying “dark moths increased, so pollution caused evolution” skips important reasoning. A stronger conclusion says that dark moths became more common in the studied setting, that darker backgrounds may have reduced their visibility to predators, and that evidence about predation supports natural selection. It should also identify limits, such as whether the observations cover enough locations or generations to rule out other influences.

Separate the pattern, the proposed factor, and the supporting evidence.
Use cautious language when evidence supports but does not prove an explanation.
State a relevant limitation.

Worked example

Interpreting a moth study

A report describes more dark moths in an industrial area after tree surfaces became darker. It also reports that birds more often captured moths that contrasted with the tree surface. What pattern is observed, and what evolutionary factor is supported?

Identify the pattern
The report says that dark moths became more common in the studied area. This is the observation; it does not by itself identify the cause.
Connect evidence to a factor
Birds captured more moths that contrasted with the background. This links visibility with survival and supports natural selection as an explanation for the change in frequency.
State a limitation
The conclusion applies to the reported conditions. More evidence from other locations or times could help determine whether the same explanation fits elsewhere.

Answer: The observed pattern is an increase in dark moths. The predation evidence supports natural selection because moths that were less visible were captured less often. This evidence supports the explanation for the studied conditions, but it does not automatically explain every moth population.

Check: The answer separates an observed change from the explanation and links the proposed factor to survival.

Worked example

Distinguishing selection from drift

A small island population has fewer individuals with a particular inherited colour after a storm. No evidence is available about whether that colour affected survival during the storm. Which factor is the more cautious explanation, and what evidence would help distinguish the possibilities?

Note the uncertainty
The colour became less common, but the description does not show whether colour affected survival or reproduction. The pattern alone cannot establish natural selection.
Consider chance
Because the population is small and a storm occurred, genetic drift is a reasonable possibility. Drift describes frequency change due to chance, not a demonstrated advantage or disadvantage.
Choose useful evidence
Evidence about which individuals survived and reproduced, and whether colour was connected to that outcome, would help assess selection. Records from further generations could show whether the change continued, but would not alone prove its cause.

Answer: Genetic drift is a cautious possibility because the group is small and the evidence does not connect colour to survival. The available pattern does not establish drift either. Information linking colour to survival or reproduction would help assess natural selection; further evidence is needed to judge the explanation.

Check: The example does not treat chance as proven. It identifies evidence needed to compare explanations.

Worked example

Researching movement between populations

Researchers find that an inherited colour characteristic appears in a population where it was not recorded earlier. They learn that individuals from a nearby population moved into the area and reproduced. What factor is supported, and what should the researchers avoid claiming?

Match the evidence to the factor
Individuals moved between populations and reproduced. This is evidence for gene flow, the movement of inherited differences between populations through movement and reproduction.
Check the strength of the record
The researchers should check how the earlier and later observations were made. If earlier records were incomplete, the characteristic may have been present but not noticed.
Limit the conclusion
The evidence supports gene flow as a possible source of the characteristic. It does not show that the characteristic arose because it was useful, or that movement is the only factor affecting the population.

Answer: Gene flow is supported because individuals from another population moved in and reproduced. Researchers should not claim that the characteristic appeared because the population needed it or that gene flow was the only influence.

Check: The answer uses the evidence about movement and reproduction and avoids claiming a purpose or a single cause.

Common mistakes and how to avoid them

Saying that an individual evolves during its lifetime.

Correction: Evolution describes changes in inherited characteristics in a population across generations.

Saying organisms develop a useful inherited characteristic because they need it.

Correction: Inherited differences can exist before conditions change. Selection can affect which individuals reproduce more successfully.

Treating any change in a characteristic’s frequency as proof of natural selection.

Correction: A frequency change is a pattern. Evidence must connect the characteristic to survival or reproduction to support selection.

Assuming genetic drift always makes a population better suited to its environment.

Correction: Drift is change due to chance. It does not require an advantage.

Lesson summary

Evolution is inherited change in a population over generations.
Natural selection, mutation, gene flow, genetic drift, and mate choice can influence evolutionary processes.
Research conclusions should distinguish observations from explanations and link claims to relevant evidence.
Good research also checks source quality, study conditions, alternative explanations, and limitations.

Check your understanding

Question 1

Which statement best describes genetic drift?

A change in how common inherited differences are because of chance.
A change caused only when a characteristic improves survival.
The movement of individuals between populations followed by reproduction.
A change an individual makes because it needs to survive.

Show answer and explanation

A change in how common inherited differences are because of chance.

Drift is frequency change due to chance. Selection involves differences in survival or reproduction, while movement and reproduction between populations describe gene flow.

Question 2

A report shows that a characteristic became more common but gives no evidence about survival or reproduction. What is the best conclusion?

The characteristic must have been favoured by natural selection.
The pattern is observed, but the factor causing it is not yet established.
The population changed because individuals needed the characteristic.
Gene flow is proven even if no movement was studied.

Show answer and explanation

The pattern is observed, but the factor causing it is not yet established.

A frequency pattern alone does not identify its cause. Additional evidence is needed to evaluate possible explanations.

Question 3

What evidence most directly supports gene flow between two populations?

Individuals move from one population to another and reproduce there.
A storm occurs while the population’s size is small.
A characteristic is linked to higher survival in one environment.
A new inherited difference is recorded in a population.

Show answer and explanation

Individuals move from one population to another and reproduce there.

Gene flow involves movement between populations and reproduction, which can transfer inherited differences.

Key terms

Population: A group of the same kind of organism living in the same area.
Inherited: Passed from parents to offspring.
Natural selection: A process in which inherited characteristics linked to greater survival or reproduction can become more common over generations.
Mutation: A change in inherited information that can introduce a new inherited difference.
Gene flow: Movement of inherited differences between populations when individuals move and reproduce.
Genetic drift: A change in how common inherited differences are because of chance.
Frequency: How common a type or characteristic is in a group.
Mate choice: A pattern in which some individuals are more likely to find mates because of particular characteristics.

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Published by DoAssignment. This reviewed lesson follows Ontario Grade 11 Biology (SBI3U), expectation C2.2. It is a study resource, not an official curriculum publication.

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