3B1 Theories and Mechanisms of Evolution

Question 2

What is natural selection?

Answer 2

The process where organisms with favorable traits survive and reproduce.

Natural selection is a key mechanism of evolution. Organisms best suited to their environment are more likely to pass on their traits to the next generation, increasing their reproductive success.

Question 3

Who proposed the theory of natural selection?

Answer 3

Charles Darwin

He introduced natural selection in his 1859 book On the Origin of Species, describing how species evolve through differential survival and reproduction.

Question 4

True or False:

Natural selection always leads to perfectly adapted organisms.

Answer 4

False

Natural selection improves fitness relative to the environment, but it does not result in “perfect” adaptations because environments change, and genetic variation has limits.

Question 5

Fill in the blank:

Traits that enhance an organism’s ability to survive and reproduce are called __________.

Answer 5

adaptations

These are physical or behavioral traits shaped by natural selection to improve survival and reproduction in specific environments.

Question 6

What is reproductive fitness?

Answer 6

The ability to survive, reproduce, and pass on genes.

It measures how well an organism’s traits contribute to its ability to leave offspring compared to others in the population.

Question 7

What causes variation within a population?

Answer 7

• Mutations
• Genetic recombination
• Gene flow

Genetic variation is the raw material for natural selection. Without it, populations cannot adapt to changing environments or evolve over time.

Question 8

True or False:

All individuals in a population have an equal chance of survival and reproduction.

Answer 8

False

Natural selection acts on differences in traits within a population. Individuals with beneficial traits have a higher chance of survival and reproduction.

Question 9

What is directional selection?

Answer 9

A type of natural selection favoring one extreme trait.

Individuals with traits at one end of the spectrum have higher fitness. For example, larger beak size may help birds crack tough seeds.

Question 10

Fill in the blank:

Natural selection acts on ________, not on individuals.

Answer 10

populations

While selection occurs through individuals, its effects are observed in populations over generations as allele frequencies change.

Question 11

What is stabilizing selection?

Answer 11

Selection that favors intermediate traits over extremes.

Stabilizing selection reduces variation by favoring average traits. For example, human birth weight tends to center around an optimal range.

Question 12

What type of selection favors both extreme traits over the average?

Answer 12

Disruptive

Disruptive selection can split a population into two subgroups. For example, light and dark-colored mice may survive better than intermediate-colored mice in patchy environments.

Question 13

True or False:

Adaptations occur because organisms need them to survive.

Answer 13

False

Adaptations arise due to genetic variation and are selected for because they provide advantages. Natural selection does not plan or anticipate needs.

Question 14

What is speciation?

Answer 14

The formation of new and distinct species.

It occurs when populations of a single species become so different that they can no longer interbreed, often due to isolation and selection pressures.

Question 15

What are the two main types of speciation?

Answer 15

1. Allopatric speciation
2. Sympatric speciation

Allopatric speciation occurs due to geographic isolation, while sympatric speciation happens without physical barriers, often through ecological or genetic factors.

Question 16

Fill in the blank:

________ isolation prevents gene flow between populations, leading to speciation.

Answer 16

Reproductive

Reproductive isolation includes barriers like behavioral, temporal, or mechanical differences that prevent successful breeding.

Question 17

What is allopatric speciation?

Answer 17

Speciation due to geographic isolation.

In allopatric speciation, physical barriers like mountains or rivers divide a population, leading to genetic divergence over time.

Question 18

True or False:

Sympatric speciation occurs only in plants.

Answer 18

False

Sympatric speciation can occur in both plants and animals, although it is more common in plants due to mechanisms like polyploidy.

Question 19

What is extinction?

Answer 19

The permanent loss of a species.

Extinction happens when species fail to adapt to environmental changes, competition, or catastrophic events, leading to their disappearance.

Question 20

Fill in the blank:

A ________ extinction affects a large number of species globally over a short period.

Answer 20

mass

Mass extinctions are rapid, widespread events caused by factors like asteroid impacts, volcanic activity, or climate changes.

Question 21

What is adaptive radiation?

Answer 21

The rapid evolution of many species from a common ancestor.

It occurs when species adapt to different ecological niches, such as Darwin’s finches evolving various beak shapes.

Question 22

What are selection pressures?

Answer 22

Environmental factors that influence survival and reproduction.

They can include predation, climate, food availability, and competition, which drive evolutionary changes.

Question 23

True or False:

Human activities can act as selection pressures.

Answer 23

True

Deforestation, pollution, and overhunting create selection pressures that force species to adapt, migrate, or face extinction.

Question 24

What is the fossil record?

Answer 24

The preserved remains or traces of organisms from the past.

These finds provide chronological evidence of how species have changed over time and reveal transitional forms linking ancestors to modern species.

Question 25

How does the fossil record support evolution?

Answer 25

It shows gradual changes in species over time.

Fossils document evolutionary changes by displaying traits in extinct species that are similar to, but distinct from, modern organisms.

Question 26

What are **homologous** structures?

Answer 26

Structures with the **same origin, but different functions**. ## Footnote For example, a bat’s wing and a human’s arm share a common ancestry, which shows evidence of divergent evolution.

Question 27

# Fill in the blank: \_\_\_\_\_\_\_\_\_ structures have similar **functions** but different evolutionary origin.

Answer 27

Analogous ## Footnote *Analogous structures*, like bird wings and insect wings, arise through convergent evolution but do not share common ancestry.

Question 28

What do homologous structures **suggest** about species?

Answer 28

They share a **common ancestor**. ## Footnote *Homologous structures* point to evolutionary relationships where different species evolved from a shared ancestor but adapted to different environments.

Question 29

# True or False: Comparative embryology reveals **similarities** in the early development of different species.

Answer 29

True ## Footnote Embryos of vertebrates, for example, share features like gill slits and tails, which suggest common *ancestry* during early development stages.

Question 30

How do nucleotide sequences **support** evolution?

Answer 30

Similar sequences **indicate** shared ancestry. ## Footnote Species with more similar DNA sequences are more closely related, as mutations accumulate over time at a relatively constant rate.

Question 31

# Fill in the blank: \_\_\_\_\_\_\_\_ evolution **occurs** when unrelated species develop similar traits due to similar environments.

Answer 31

Convergent ## Footnote *Convergent evolution* leads to analogous structures, where traits evolve independently in different lineages due to similar selection pressures.

Question 32

What is **comparative embryology**?

Answer 32

The study of **similarities in embryos** of different species. ## Footnote This research shows that embryos of related species share common features during development, supporting *shared* ancestry.

Question 33

# True or False: Fossils can provide evidence of **soft tissues**.

Answer 33

False ## Footnote Fossilization typically preserves *hard structures* like bones, but under rare conditions, impressions of soft tissues may form.

Question 34

What is **artificial selection**?

Answer 34

The process where humans **selectively breed organisms** for desired traits. ## Footnote Humans control reproduction to amplify traits such as size, color, or productivity in plants and animals. A great example is dog breeding, where humans purposefully select certain dogs to mate and reproduce with each other.

Question 35

How does artificial selection **differ** from natural selection?

Answer 35

Humans, not nature, **determine** which traits are favored. ## Footnote While natural selection depends on environmental pressures, artificial selection is driven by human preference for specific traits.

Question 36

# True or False: Artificial selection can **lead** to rapid changes in a species.

Answer 36

True ## Footnote *Artificial selection* can quickly enhance traits across generations due to controlled breeding.

Question 37

What is an example of artificial selection in **plants**?

Answer 37

**Selective breeding** of corn for larger kernels. ## Footnote Farmers have artificially selected traits like yield, disease resistance, and kernel size over thousands of years.

Question 38

What is an example of artificial selection in **animals**?

Answer 38

**Breeding dogs** for specific traits, like size or temperament. ## Footnote Dog breeds, such as golden retrievers or dachshunds, were developed through artificial selection for desired characteristics.

Question 39

What is **contemporary evolution**?

Answer 39

Evolution occurring over **short** timescales, observable in human lifetimes. ## Footnote Contemporary evolution, or *rapid microevolution*, happens when species adapt quickly to changing environments or human influences.

Question 40

What is an example of contemporary evolution in **insects**?

Answer 40

Insects developing **resistance** to pesticides. ## Footnote Overuse of pesticides applies strong selection pressure, leading to resistant individuals surviving and reproducing.

Question 41

# Fill in the blank: Artificial selection often **focuses** on \_\_\_\_\_\_\_\_ traits in a species.

Answer 41

beneficial | (or desirable) ## Footnote Traits selected in artificial selection include productivity (crops), appearance (animals), or behavior.

Question 42

# True or False: Artificial selection is **always** beneficial for a species’ survival.

Answer 42

False ## Footnote While traits may benefit human goals, they can **weaken** a species' ability to adapt to environmental changes.

Question 43

What is **genetic diversity**?

Answer 43

The **variety** of genetic traits within a population. ## Footnote Genetic diversity is crucial for the *adaptability* and survival of a species, allowing it to respond to environmental changes.

Question 44

How do mutations **contribute** to genetic diversity?

Answer 44

It introduces **new** genetic variations. ## Footnote *Mutations* are random changes in DNA that can create new traits, increasing diversity within a population.

Question 45

# True or False: Mutations are **always** harmful to a species.

Answer 45

False ## Footnote While many mutations are neutral or harmful, **some** mutations can provide beneficial traits that enhance survival or reproduction.

Question 46

What is the **role** of sexual reproduction in genetic diversity?

Answer 46

It **combines** genes from two parents, creating unique offspring. ## Footnote This process allows for new genetic combinations, increasing variation within a population.

Question 47

# True or False: Asexual reproduction **increases** genetic diversity.

Answer 47

False ## Footnote Asexual reproduction results in offspring that are genetically identical to the parent, **limiting** genetic diversity.

Question 48

What is **genetic drift**?

Answer 48

A random **change** in allele frequencies within a population. ## Footnote Genetic drift can significantly *affect* small populations, leading to the loss of alleles by chance rather than selection.

Question 49

How does genetic drift **affect** small populations?

Answer 49

It can **cause** a greater loss of genetic variation. ## Footnote In *small populations*, alleles can be lost quickly due to random events, reducing overall genetic diversity.

Question 50

# Fill in the blank: \_\_\_\_\_\_ \_\_\_\_\_ is the **movement** of individuals into or out of a population, affecting genetic diversity.

Answer 50

Gene flow ## Footnote Gene flow *introduces* new genetic material into a population, which can increase genetic diversity.

Question 51

What is a **bottleneck effect** in genetic drift?

Answer 51

A sharp population **reduction**, decreasing genetic diversity. ## Footnote This can occur due to natural disasters or other events, leaving only a small, genetically limited population to recover.

Question 52

How does **inbreeding** affect genetic diversity?

Answer 52

It **reduces** genetic diversity. ## Footnote Mating between closely related individuals increases the chances of homozygous recessive traits, potentially leading to *genetic disorders*.

Question 53

# Fill in the blank: The \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_ theory **explains** how small, isolated populations can accumulate genetic differences over time due to genetic drift.

Answer 53

founder effect ## Footnote This theory emphasizes the *importance* of initial genetic variation in the founding individuals, which may influence the population's genetic diversity.