Natural selection and adaptation

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What is Natural Selection?

**Natural selection** is the process where individuals with traits better suited to their environment are more likely to survive and reproduce.
It is a key mechanism of **evolution**, changing the heritable traits in a population over generations.
Charles Darwin and Alfred Russel Wallace jointly presented the concept in 1858, and Darwin's 1859 book×On the Origin of Species×explained it in detail.
Natural selection is **not intentional**; it contrasts with artificial selection where humans choose desired traits.

Key Requirements for Natural Selection

**Variation**: Individuals in a population have different traits (genotypic and phenotypic).
**Inheritance**: Traits are passed from parents to offspring through genetic material.
**Differential survival and reproduction**: Individuals with advantageous traits are more likely to survive and have more offspring.
Over time, advantageous traits become more common in the population.

Adaptation

An **adaptation** is a heritable trait that increases an organism's fitness in its environment.
Adaptations result from natural selection acting on variation over many generations.
Examples: camouflage, beak shape in finches, antibiotic resistance in bacteria.
Adaptations can be structural, behavioral, or physiological.

Types of Selection

**Stabilizing selection** favors intermediate traits, reducing variation (e.g., human birth weight).
**Directional selection** favors one extreme trait (e.g., larger beak size during drought).
**Disruptive selection** favors both extremes, leading to two distinct groups (e.g., small and large seeds).
**Sexual selection** favors traits that increase mating success (e.g., peacock's tail).

Evidence for Natural Selection

**Fossil record**: Shows gradual changes in species over time.
**Comparative anatomy**: Homologous structures (e.g., forelimbs of mammals) indicate common ancestry.
**Molecular biology**: DNA comparisons reveal evolutionary relationships.
**Observed evolution**: Examples like peppered moths, antibiotic resistance, and Darwin's finches.

Common Misconceptions

Natural selection does **not** create perfect organisms; it only favors traits that are 'good enough' for survival.
Individuals do **not** evolve; populations evolve over generations.
Evolution is **not** goal-directed; it responds to environmental pressures.
Not all traits are adaptive; some are neutral or result from genetic drift.

Natural selection: brown rabbits are better camouflaged against predators, so they survive and reproduce more than white rabbits.

Punnett square showing inheritance of fur color in rabbits. Brown (B) is dominant over white (b).

Energy pyramid showing trophic levels. Energy decreases at each level, favoring efficient adaptations.

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Practice questions

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1.What is natural selection?
Easy
- AThe differential survival and reproduction of individuals due to differences in their traits
- BThe intentional breeding of organisms by humans
- CThe random change in allele frequencies in a population
- DThe process by which organisms acquire traits during their lifetime
2.Who popularised the term 'natural selection'?
Easy
- ACharles Darwin
- BAlfred Russel Wallace
- CGregor Mendel
- DJean-Baptiste Lamarck
3.Which of the following is necessary for natural selection to occur?
Easy
- AVariation of traits within a population
- BAll individuals in a population are identical
- CTraits are acquired during an organism's lifetime
- DThe environment remains constant forever
4.In natural selection, traits that are more likely to be passed on to the next generation are those that:
Medium
- AFacilitate survival and reproductive success
- BAre most common in the population at the start
- CAre acquired through use during the organism's life
- DAre the result of random mutations only
5.What is the difference between natural selection and artificial selection?
Medium
- ANatural selection is intentional; artificial selection is not
- BArtificial selection is intentional; natural selection is not
- CNatural selection involves humans; artificial selection does not
- DThere is no difference; they are the same process
6.What is the primary explanation for adaptive evolution according to modern biology?
Medium
- ARandom genetic drift
- BNatural selection
- CAcquired characteristics
- DCatastrophism
7.Which of the following best describes the modern synthesis in evolutionary biology?
Hard
- AThe union of Darwinian natural selection with Mendelian genetics
- BThe replacement of natural selection by genetic drift
- CThe combination of Lamarckism and Darwinism
- DThe discovery that evolution occurs only through mutations
8.According to the source, what did Empedocles and Lucretius propose that anticipates natural selection?
Hard
- ANature produces a huge variety of creatures randomly, and only those that survive and reproduce persist
- BAll organisms are perfectly designed by a creator
- CSpecies are fixed and unchanging
- DOrganisms evolve by striving to improve themselves

More questions

9.What is meant by 'fecundity selection'?
Medium
- ASelection based on traits that confer the lowest cost to reproductive health
- BSelection of traits that are actively preferred by mating partners
- CSelection for the largest body size
- DSelection that occurs only in females
10.Which of the following is an example of sexual selection?
Hard
- APeacocks with bright tail feathers are more likely to attract mates
- BCacti have spines to reduce water loss
- CBacteria become resistant to antibiotics
- DMice that run faster escape predators
11.What happens to a population when the environment changes?
Easy
- AIndividuals with traits better suited to the new environment are more likely to survive and reproduce
- BAll individuals adapt equally to the change
- CThe population remains unchanged
- DIndividuals can choose to change their traits
12.In the context of natural selection, what does 'fitness' refer to?
Medium
- AThe ability of an organism to survive and reproduce in its environment
- BThe physical strength of an organism
- CThe speed at which an organism can run
- DThe number of offspring an organism produces in its lifetime
13.In a population of beetles, some are green and some are brown. The beetles live on tree trunks that are covered in brown bark. Which color beetle is more likely to survive and reproduce?
Medium
- AGreen beetles, because they are easier to see
- BBrown beetles, because they are camouflaged from predators
- CBoth colors have equal survival chances
- DGreen beetles, because they stand out to mates
14.A population of birds has an average beak depth of 10 mm. After a drought that produces only large, hard seeds, the average beak depth in the next generation is 12 mm. What is the most likely explanation?
Hard
- AIndividual birds grew larger beaks to crack the seeds and passed this change to offspring
- BBirds with larger beaks survived better and reproduced more, passing the large-beak allele to more offspring
- CThe drought caused a mutation for larger beaks in all birds
- DBirds with smaller beaks learned to crack large seeds and their beaks grew
15.Which of the following best describes the relationship between genetic variation and natural selection?
Medium
- ANatural selection creates genetic variation
- BGenetic variation provides the raw material for natural selection to act upon
- CNatural selection reduces genetic variation to zero
- DGenetic variation is not necessary for natural selection
16.A farmer breeds cows to produce more milk. This is an example of:
Easy
- ANatural selection
- BArtificial selection
- CSexual selection
- DFecundity selection
17.In a population of flowers, red flowers produce more seeds than white flowers. However, white flowers are more attractive to pollinators. What is likely to happen to the frequency of the white allele over time?
Hard
- AIt will decrease because white flowers produce fewer seeds
- BIt will increase because pollinators prefer white flowers
- CIt will stay the same because both traits are equally beneficial
- DIt will increase only if white flowers also have higher survival
18.A scientist observes that a population of mice living in a desert has thicker fur than mice from the same species living in a forest. Which statement best explains this difference?
Medium
- AThe desert mice evolved thicker fur because they needed it
- BNatural selection favored thicker fur in the desert because it helps mice survive cold nights
- CThe forest mice lost their thick fur because they didn't need it
- DThe desert mice grew thicker fur after moving to the desert
19.What is the term for the process where individuals with traits better suited to the environment are more likely to survive and reproduce?
Easy
- AArtificial selection
- BNatural selection
- CSexual selection
- DGenetic drift
20.A population of rabbits has two fur colors: brown and white. The environment changes from snowy to mostly brown soil. Which outcome is most likely?
Medium
- AThe brown rabbits will become more common because they are better camouflaged
- BThe white rabbits will become more common because they are more visible
- CBoth colors will remain equally common
- DThe rabbits will change color to match the soil
21.In a population of fish, body size is determined by a single gene with two alleles: L (large) and S (small). The large allele is dominant. In a pond with many predators that eat small fish, what is expected to happen to the frequency of the S allele over generations?
Hard
- AIt will increase because small fish are easier to hide
- BIt will decrease because small fish are more likely to be eaten
- CIt will remain constant because predators have no effect on allele frequency
- DIt will increase because the S allele is recessive
22.Charles Darwin proposed natural selection as a mechanism for evolution. Which of the following is NOT a key component of natural selection?
Easy
- AVariation among individuals
- BInheritance of traits
- CUse and disuse of organs
- DDifferential survival and reproduction
23.A scientist measures the beak sizes of finches on an island before and after a drought. After the drought, the average beak size is larger. Which conclusion is best supported?
Medium
- AThe drought caused beaks to grow larger in each finch
- BFinches with larger beaks were more likely to survive the drought and reproduce
- CFinches with smaller beaks migrated to another island
- DThe drought did not affect beak size
24.In a population of insects, some are resistant to a pesticide. After the pesticide is applied, most insects die, but a few survive and reproduce. The next generation is mostly resistant. This is an example of:
Hard
- AArtificial selection by the pesticide
- BNatural selection acting on pre-existing variation
- CMutation caused by the pesticide
- DAcquired resistance passed to offspring
25.In an experiment, a student places 50 green and 50 brown beetle models on a brown tree trunk. After 10 minutes, a bird is released and allowed to eat for 2 minutes. The student records the number of each color eaten. Which variable is the independent variable in this experiment?
Medium
- AThe color of the beetle models
- BThe number of beetles eaten
- CThe color of the tree trunk
- DThe time the bird is allowed to eat
26.A population of grasshoppers lives in a meadow. Some are green, some are brown. A drought turns the grass brown. After several generations, most grasshoppers are brown. Which of the following best describes the process that caused this change?
Hard
- AIndividual grasshoppers changed color to match the brown grass and passed that change to their offspring.
- BBrown grasshoppers were more likely to survive and reproduce, passing on the brown color allele.
- CThe drought caused a mutation that made all grasshoppers brown.
- DGreen grasshoppers migrated to a different meadow.
27.A scientist measures the beak depth of finches on an island before and after a drought. Before the drought, average beak depth was 9 mm. After the drought, average beak depth was 12 mm. Which conclusion is best supported by this data?
Medium
- AThe drought caused finches to grow larger beaks.
- BFinches with larger beaks were more likely to survive the drought and reproduce.
- CAll finches with small beaks died during the drought.
- DBeak depth is not influenced by natural selection.
28.Which of the following is required for natural selection to occur in a population?
Easy
- AThe population must be very large.
- BIndividuals must vary in their traits.
- CAll individuals must be identical.
- DThe environment must be unchanging.
29.In a species of fish, females prefer to mate with males that have bright orange spots. Over many generations, the average number of orange spots in males increases. This is an example of:
Hard
- ANatural selection due to predation
- BSexual selection
- CArtificial selection
- DGenetic drift
30.A farmer sprays a pesticide on a field of insects. Most insects die, but a few survive. The next generation of insects is also resistant to the pesticide. Which statement best explains this?
Medium
- AThe pesticide caused the insects to become resistant.
- BSome insects were already resistant before the pesticide was applied, and they survived and reproduced.
- CThe resistant insects learned to avoid the pesticide.
- DThe pesticide made the insects mutate to become resistant.
31.A scientist studies two populations of the same plant species. One population lives in a dry desert, the other in a wet forest. The desert plants have thicker leaves. Which experiment would best test whether the thick leaves are an adaptation to dry conditions?
Medium
- AMeasure the water loss from leaves of both populations in a controlled environment.
- BCount the number of seeds each population produces.
- CCross-breed the two populations and observe the offspring.
- DCompare the DNA sequences of the two populations.
32.In a population of rabbits, fur color is determined by a single gene with two alleles: B (brown, dominant) and b (white, recessive). The environment changes from snowy to mostly brown soil. Which outcome is most likely after many generations?
Hard
- AThe frequency of the B allele will increase.
- BBoth alleles will become equally common.
- CThe rabbits will change fur color during their lifetime.
33.A student sets up an experiment with two groups of bacterial colonies on agar plates. One plate has an antibiotic, the other does not. After 24 hours, the student counts the number of colonies on each plate. What is the purpose of the plate without antibiotic?
Medium
- AIt is a control to show that bacteria can grow normally without antibiotic.
- BIt is used to test if the antibiotic kills all bacteria.
- CIt is a replicate to ensure accuracy.
- DIt is used to grow a different species of bacteria.
34.A population of birds has a range of beak sizes. After a drought, only large, hard seeds are available. The average beak size in the next generation is larger than before. Which of the following is a valid conclusion?
Hard
- AThe drought caused birds to develop larger beaks.
- BBirds with larger beaks had higher fitness in the drought conditions.
- CAll birds with small beaks died of starvation.
- DBeak size is not inherited.
35.Which of the following best describes the difference between natural selection and artificial selection?
Medium
- ANatural selection is driven by human choice; artificial selection is driven by environmental factors.
- BNatural selection occurs without human intervention; artificial selection is guided by humans.
- CNatural selection only affects plants; artificial selection only affects animals.
- DThere is no difference; the terms are interchangeable.
36.A scientist observes that a population of mice living in a desert has thicker fur than mice from the same species living in a forest. Which statement best explains this observation?
Hard
- AThe desert mice grew thicker fur because it was cold at night, and they passed this change to their offspring.
- BMice with thicker fur were better able to survive the desert conditions and reproduced more, so the trait became more common.
- CThe forest mice have thinner fur because they need to stay cool.
- DThicker fur is always an advantage, so it evolved in both populations.
37.What is the term for the differential survival and reproduction of individuals due to differences in their traits?
Easy
- ANatural selection
- BArtificial selection
- CSexual selection
- DFecundity selection
38.In a population of flowers, red flowers produce more seeds than white flowers. However, white flowers are more attractive to pollinators. What is likely to happen to the frequency of the red flower trait over generations?
Hard
- AIt may increase if seed production has a greater effect on fitness
- BIt will definitely decrease because white flowers attract more pollinators
- CIt will remain constant because both traits are equally fit
- DIt will disappear because white flowers are more attractive
39.In a population of plants, some individuals produce many small seeds and others produce few large seeds. After a drought, the soil becomes very dry and only the large seeds have enough stored water to germinate. Over several generations, which change is most likely to occur?
Medium
- AThe average number of seeds per plant will increase.
- BThe average seed size will increase.
- CThe plants will produce seeds of both sizes equally.
- DThe plants will stop producing seeds.
40.A scientist measures the running speed and tail length of a population of lizards. She finds that lizards with longer tails run faster and escape predators more often. Over 10 generations, the average tail length increases by 15%. Which of the following best explains this change?
Hard
- ALizards with longer tails are more likely to survive and reproduce, passing on the long-tail alleles.
- BLizards stretch their tails by running, and this acquired trait is passed to offspring.
- CThe environment causes mutations that produce longer tails in all lizards.
- DLong-tailed lizards mate more often because they are more attractive.

Revision notes

## Natural Selection & Adaptation Natural selection is the **differential survival and reproduction** of individuals due to differences in their traits. It is a key mechanism of evolution that changes heritable traits in a population over generations. ### Key Ideas - **Variation**: Individuals in a population have different traits (genotypic and phenotypic). - **Inheritance**: Traits are passed from parent to offspring. - **Differential survival & reproduction**: Individuals with traits better suited to the environment are more likely to survive and reproduce, passing on those traits. - **Adaptation**: Over time, beneficial traits become more common in the population, leading to adaptation. ### How It Works 1. **Struggle for existence**: Competition for resources and mates. 2. **Variation exists**: No two individuals are exactly alike. 3. **Some traits are advantageous**: They increase fitness (ability to survive and reproduce). 4. **These traits are passed on**: Offspring inherit them. 5. **Population changes**: The frequency of advantageous traits increases over generations. ### Types of Selection - **Natural selection**: Environment favors certain traits. - **Sexual selection**: Traits favored because they attract mates. - **Fecundity selection**: Traits that improve reproductive success. ### Important Notes - Natural selection is **not intentional**; it is a result of variation, inheritance, and differential success. - It acts on **phenotypes** (observable traits), but changes **genotypes** (genetic makeup) over time. - New species can arise if traits become very different (macroevolution). - Natural selection is the **primary explanation for adaptive evolution**. ### Example In a population of rabbits, some have thicker fur. In a cold environment, thick-furred rabbits survive better and have more offspring. Over generations, the population becomes thicker-furred — an adaptation to cold.

Natural selection: The differential survival and reproduction of individuals due to differences in their traits, leading to changes in heritable characteristics of a population over generations.
Adaptation: A trait that increases an organism's chance of survival and reproduction in its environment, becoming more common in a population over time through natural selection.
Variation: Differences in traits (genotypic and phenotypic) among individuals in a population.
Fitness: The ability of an individual to survive and reproduce in its environment.
Sexual selection: A form of natural selection where traits are favored because they increase mating success.
Fecundity selection: Selection for traits that improve reproductive output or health.

Flashcards

What is natural selection?

Natural selection is the differential survival and reproduction of individuals due to differences in their traits, leading to changes in heritable characteristics of a population over generations.

Who popularized the term 'natural selection'?

Charles Darwin popularized the term 'natural selection', contrasting it with artificial selection.

What are the three processes that result in natural selection according to Darwin?

Inheritance (passing traits from parent to offspring), variation (differences in traits among individuals), and the struggle for existence (competition and cooperation).

What is variation?

Variation refers to differences in traits (genotypic and phenotypic) among individuals within a population.

How does natural selection affect trait frequencies in a population?

Traits that improve survival and reproduction become more common over generations, while less beneficial traits become less common.

What is an adaptation?

An adaptation is a heritable trait that increases an organism's fitness in its environment, becoming more common through natural selection.

What is the difference between natural selection and artificial selection?

Artificial selection is intentional breeding by humans for desired traits, while natural selection is non-intentional, driven by environmental pressures.

What is sexual selection?

Sexual selection is a form of natural selection where traits are favored because they are preferred by mating partners.

What is fecundity selection?

Fecundity selection favors traits that lower the cost to an organism's reproductive health, often influenced by female choice.

What is the difference between microevolution and macroevolution?

Microevolution is small-scale change within a species due to new traits favored in a specific niche; macroevolution is large-scale change that can lead to new species.

What is the modern synthesis?

The modern synthesis is the union of Darwinian evolution with classical genetics, developed in the mid-20th century.

What is evolutionary developmental biology (evo-devo)?

Evo-devo compares developmental processes across organisms to understand how developmental processes evolved.

What is genetic drift?

Genetic drift is a random change in allele frequencies over time, which can cause evolution but is not driven by natural selection.

What did Charles Darwin's book 'On the Origin of Species' explain?

It explained natural selection as the mechanism for evolution, using evidence from artificial selection and observations of nature.

What is the struggle for existence?

The struggle for existence includes competition for resources and cooperation (mutual aid) among organisms, influencing survival and reproduction.

How does natural selection lead to adaptation?

Natural selection favors traits that improve survival and reproduction in a given environment, causing those traits to become more common and thus the population becomes better adapted.

What is the role of heritability in natural selection?

Heritability ensures that favored traits are passed from parents to offspring, allowing natural selection to change trait frequencies across generations.

What is the difference between genotype and phenotype?

Genotype is the genetic makeup of an organism; phenotype is the observable characteristics resulting from genotype and environment.

What is fitness in the context of natural selection?

Fitness is the ability of an individual to survive and reproduce in its environment, relative to other individuals.

Can natural selection occur without genetic variation?

No, natural selection requires variation in traits; without variation, there is no differential survival and reproduction.

What is an example of natural selection?

Peppered moths: dark-colored moths became more common in polluted areas because they were better camouflaged from predators.

What is the extended evolutionary synthesis?

The extended evolutionary synthesis is a 21st-century update that challenges the gene-centered view, emphasizing organisms' roles in evolution.

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