Darwin and Natural Selection

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Questions and Answers

What is the primary diet of Geospiza fortis on Daphne Major?

Fruits

Insects

Nectar

Seeds (correct)

The heritability of a trait varies from 0 to 1.

True

What is the name of the species of finch studied in the example of natural selection?

Geospiza fortis

The population of Geospiza fortis on Daphne Major consists of approximately ______ individuals.

1200 Signup and view all the answers

Match the following concepts with their definitions:

Heritability = Proportion of variation due to genes Natural Selection = Differential reproduction based on heritable variation Directional Selection = Selection that favors one extreme phenotype Variation = Differences among individuals in a population Signup and view all the answers

What type of selection is exemplified by the findings in Darwin's finches?

Directional Selection Signup and view all the answers

What was one of Darwin's primary areas of interest during his voyage on the Beagle?

Biogeography Signup and view all the answers

All individuals of Geospiza fortis tend to move away from Daphne Major after being measured.

False Signup and view all the answers

Darwin and Wallace independently proposed the theory of natural selection.

True Signup and view all the answers

What is the main focus of the studies conducted by the Grants on Geospiza fortis?

Variation and heritable variation Signup and view all the answers

What model of evolutionary change did Darwin establish?

Natural selection Signup and view all the answers

Natural selection is one agent of evolution, while __________ and genetic drift are also agents of evolution.

mutation Signup and view all the answers

Match the following concepts with their definitions:

Variation = Observable differences among individuals Heritable variation = Genetic differences that can be passed to offspring Struggle = Competition for resources among organisms Differential reproduction = Variations that affect the likelihood of survival and reproduction Signup and view all the answers

Which factor did Darwin believe was crucial for evolution to take place?

Struggle for existence Signup and view all the answers

Darwin published his findings on natural selection immediately after his voyage on the Beagle.

False Signup and view all the answers

What significant change in population characteristics does evolution represent?

Changes in genetic characteristics Signup and view all the answers

Darwin argued that the changes in heritable characteristics of a population result in __________ as a necessary consequence.

evolution Signup and view all the answers

What was the primary reaction of the scientific community to Darwin's theory shortly after publication?

Widespread criticism Signup and view all the answers

What was the effect of the major drought in 1977 on the finch population in G. fortis?

Major die-off of finches Signup and view all the answers

Differential survival and reproduction was influenced by beak size in G. fortis during droughts.

True Signup and view all the answers

Name one condition that is necessary for evolution by natural selection.

Variation Signup and view all the answers

The average beak size of offspring of survivors after the drought was _____ than the average of the population before the drought.

larger Signup and view all the answers

Match the following concepts with their definitions:

Variation = Differences in traits within a population Heritability = Traits that can be passed from parents to offspring Struggle = Competition for resources Differential reproduction = Survival rates based on advantageous traits Signup and view all the answers

Which of the following factors contributed to the natural selection observed in G. fortis?

Drought conditions Signup and view all the answers

Natural selection is the only mechanism of evolutionary change.

False Signup and view all the answers

What type of seeds became more available during droughts, impacting the finch population?

Large seeds Signup and view all the answers

What is indicated by a heritability estimate of 0 for a trait in G. fortis?

The trait is entirely influenced by environmental factors. Signup and view all the answers

Which of the following best describes the struggle for existence related to G. fortis?

Finches have limited food sources due to habitat loss. Signup and view all the answers

Which of the following statements is true about the population of G. fortis on Daphne Major?

The population size averages around 1,200 individuals. Signup and view all the answers

What type of selection is demonstrated by changes in beak size in G. fortis due to environmental pressures?

Directional selection Signup and view all the answers

Which aspect of G. fortis was found to vary among individuals on Daphne Major?

Beak dimensions Signup and view all the answers

What role does differential reproduction play in the evolution of G. fortis?

It favors the survival of individuals with advantageous traits. Signup and view all the answers

What factor is most important for understanding heritable variation in G. fortis?

The genetic makeup of the finch population. Signup and view all the answers

Which statement best reflects the concept of natural selection as observed in G. fortis?

It results in gradual changes in heritable traits over generations. Signup and view all the answers

What demographic effect occurred in the G. fortis finches as a result of the 1977 drought?

Fewer small, soft seeds were available. Signup and view all the answers

Which condition did not contribute to the natural selection observed in G. fortis?

Genetic mutations. Signup and view all the answers

How did the drought affect the survival rates of finches based on their beak size?

Finches with larger beaks survived in greater proportions. Signup and view all the answers

What can be inferred about the offspring of the finches that survived the drought?

Their average beak size was larger than the previous population. Signup and view all the answers

Which statement reflects the consequence of natural selection in G. fortis?

Variation in traits leads to different survival outcomes. Signup and view all the answers

Which of the following conditions was essential for natural selection to occur in G. fortis?

Heritability of advantageous traits. Signup and view all the answers

What was a direct result of the major drought in 1977 on the finch population?

Approximately 85% of the finch population died. Signup and view all the answers

How is evolution by natural selection best defined in the context of G. fortis?

It occurs through variations in heritable traits affecting survival. Signup and view all the answers

What is NOT one of the five key pieces of natural selection as described by Darwin?

Genetic drift Signup and view all the answers

What primarily influenced Darwin's understanding of struggle in natural selection?

Malthus's writings Signup and view all the answers

Which statement best describes Darwin's publication approach regarding his theory of natural selection?

He was hesitant to publish and delayed it for years. Signup and view all the answers

How does natural selection contribute to evolution according to Darwin?

It leads to a fit between organisms and their environment. Signup and view all the answers

What distinguishes differential reproduction in natural selection?

Certain traits confer a survival advantage. Signup and view all the answers

What was Darwin's stance on heritable variation before it was fully understood?

It was known but not understood how it occurred. Signup and view all the answers

Which best describes the relationship between Darwin and Wallace?

They independently developed the same evolutionary theory. Signup and view all the answers

What type of evidence did Darwin rely on to support his arguments for evolution?

A broad range of empirical data Signup and view all the answers

Which of the following is NOT considered an agent of evolution?

Differential reproduction Signup and view all the answers

What is one primary factor that drives evolution as defined by Darwin?

Environmental pressures Signup and view all the answers

Study Notes

Darwin and Natural Selection

Darwin was a lifelong naturalist, trained in medicine and for the clergy
He embarked on a five-year voyage on the Beagle at age 22, initially not an evolutionist but interested in variation and biogeography
He developed the basic argument for natural selection: variation (observable but underappreciated), heritable variation (known to occur but not how), struggle (influenced by Malthus), differential reproduction based on heritable variation, and changes in the population's characteristics (evolution).
Darwin was slow to publish his findings due to the intellectual climate, likening it to confessing murder.
He amassed evidence and conducted experiments over 15 years.

Alfred Russel Wallace

Wallace independently developed a similar theory of evolution, co-publishing his findings with Darwin.

Darwin's Accomplishments

Established evolution, providing overwhelming evidence and a clear argument for an old idea.
Proposed a plausible mechanism for evolutionary design, widely accepted after 1859.

Natural Selection

Evolution: changes in genetic characteristics of a population over time.
Natural Selection: one agent of evolution that leads to a fit between traits and surroundings.
Other agents of evolution include mutation, migration, and genetic drift.

Five Key Components of Natural Selection

Variation: There must be variation in traits within a population.
Heritability: The variation must be heritable, passed down from parents to offspring.
Struggle: Organisms compete for resources, facing challenges for survival.
Differential Reproduction: Individuals with advantageous traits survive and reproduce more successfully, passing on those traits to their offspring.
Evolution: As a consequence of the first four factors, the population evolves, changing its genetic makeup over generations.

Darwin's Finches

14 species of finches on the Galapagos Islands, similar in appearance but differing in beak dimensions.
Their beak size has evolved as a response to their environment and the available food sources.

Geospiza fortis (Medium Ground Finch)

Studied by the Grants, et al. on Daphne Major island in the Galapagos.
This population is well-documented and serves as an example of natural selection.
The finches are primarily seed eaters and live on a small island with a relatively stable population.
The Grants have been able to track and measure almost all individuals on the island.

Variation in Geospiza fortis

Variation exists in beak dimensions among the finches.

Heritability in Geospiza fortis

The variation in beak dimensions is heritable.
Heritability is measured as the proportion of variation due to genes, ranging from 0 (variation entirely environmental) to 1 (variation entirely genetic).
Researchers can estimate heritability by comparing offspring traits to their parents.

Struggle for Existence in Geospiza fortis

There is always a struggle for existence, especially during periods of environmental stress.
Droughts can lead to starvation on Daphne Major, causing a significant die-off of finches (up to 85%).

Differential Survival/Reproduction in Geospiza fortis

During droughts, smaller seeds are less abundant, favoring finches with larger beaks better suited to eating larger seeds.
Finches with larger beaks survived the drought in greater proportions, illustrating differential survival/reproduction.

Evolution in Geospiza fortis

The Grants demonstrated the five components of natural selection in Geospiza fortis: variation, heritability, struggle, differential survival/reproduction, and resulting evolutionary change.
The average beak size of surviving offspring was larger than the average of the population before the drought.

Summary: Natural Selection

Natural selection is a powerful agent of evolutionary change.
Evolution is an inevitable consequence of variation, heritability, struggle, and differential reproduction.
These components can be studied in the field (e.g., finches) and in lab settings.

Charles Darwin

A lifelong naturalist who studied medicine and the clergy
In 1831, at 22, boarded the Beagle for a five-year voyage
Darwin started out not believing in evolution, but took interest in variation and biogeography during his journey

Darwin's Theory of Natural Selection

Darwin recognized that populations display variation in their traits, some of which are inherited.
Darwin believed there was a struggle for existence, influenced by Malthus who described how populations grow exponentially while resources remain limited
He observed that individuals with specific inheritable traits are better suited for survival and reproduction
According to Darwin, the changes in inheritable traits (evolution) are a consequence of differential reproduction, and were passed down through generations

Darwin's Delay and Impact

Darwin delayed publishing his theory, as it went against established religious views
He belonged to a group of intellectuals, and worried the impact of his theory (comparing it to confessing murder)
Darwin gathered extensive evidence and experimented for 15 years after his voyage
Darwin's work led to the widespread acceptance of the concept of evolution, though the mechanism for evolutionary change was not universally accepted

Alfred Russel Wallace - Joint Publication

Wallace independently developed the same theory as Darwin
Darwin and Wallace co-published their theories
Wallace's work is also celebrated and fascinating, as described in Quammen's "Song of the Dodo"

Evolution & Natural Selection

Evolution is defined as changes in the genetic characteristics of a population over time
Natural selection is one agent of evolution and leads to organisms' characteristics being better suited to the environment
Other drivers of evolution include mutation, migration, and genetic drift

Five Easy Pieces of Natural Selection

Variation within a population is necessary
Variation must be inheritable
There must be a struggle for existence
Differential reproduction occurs based on inherited variation
Changes in the heritable characteristics of the population - evolution is the natural outcome

Evolution of Darwin's Finches

Finches on the Galapagos islands are intensely studied, specifically the medium ground finch (Geospiza fortis)
The Grants and their team document real-world natural selection through these finches, described in Jonathan Weiner's "The Beak of the Finch"

Darwin's Finches - Variation and Heritability

Darwin's finches show variation in their bill dimensions
Studies show that at least some of this variation is heritable, meaning it can be passed down to offspring

Darwin's Finches - Struggle for Existence

Finches experience a struggle for existence, particularly during droughts as food is scarce
Drought in 1977 on Daphne Major, an island in the Galapagos, resulted in a significant drop in food availability
This drought led to the death of almost 85% of the finch population

Darwin's Finches - Differential Reproduction

Finches with larger beaks survive better during droughts because they are successful at eating larger, harder seeds
This leads to a higher survival rate and increased reproduction for larger-beaked finches

Darwin's Finches - Evolution

The offspring of finches who survived had larger beaks than the average of previous generations
This is evolution in action - the population's genetic characteristics have changed over time driven by natural selection

Natural Selection as an Agent for Change

Natural selection is a powerful driver of evolution
The four conditions of natural selection are variation, heritability, struggle, and differential reproduction, and can be studied in the field (e.g. finches) and in laboratory settings

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Description

Explore the contributions of Charles Darwin and Alfred Russel Wallace to the theory of natural selection. Understand the key concepts of variation, heritable traits, and differential reproduction that shaped evolutionary biology. This quiz tests your knowledge of their theories and findings.