Problem 2 - Campbell Biology

Question

Which of the following observations helped Darwin shape his concept of descent with modification? (A) Species diversity declines farther from the equator. (B) Fewer species live on islands than on the nearest continents. (C) Birds live on islands located farther from the mainland than the birds' maximum nonstop flight distance. (D) South American temperate plants are more similar to South American tropical plants than to European temperate ones.

Step-by-Step Solution

Answer

D

Step 1: Analyze Each Choice

Read through each of the provided observations and connect them to Darwin's concept of descent with modification.

Step 2: Evaluate Choice A

Consider whether the decline in species diversity farther from the equator relates to the idea of descent with modification. Darwin's concept focuses more on how species adapt and change over time rather than geographic species diversity.

Step 3: Evaluate Choice B

Think about whether having fewer species on islands compared to nearby continents supports Darwin's concept. This point may hint towards isolation and evolutionary change but isn't directly about descent with modification itself.

Step 4: Evaluate Choice C

Evaluate the observation about birds' flight limits and island distance. This might highlight migration and isolation, leading to evolutionary changes, but it does not directly address descent with modification.

Step 5: Evaluate Choice D

Investigate whether the similarity between South American temperate plants and South American tropical plants compared to European temperate plants helps explain descent with modification. This directly showcases how species from a common ancestor can diverge while still retaining similarities due to close genetic relationships and environmental conditions.

Step 6: Select the Best Answer

After evaluating all choices, recognize that Choice D best illustrates Darwin's concept. It showcases that species geographically closer, and likely sharing a more recent common ancestor, are more similar than those separated by larger distances and different environments.

Key Concepts

Species Adaptation

Darwin's concept of 'descent with modification' focuses on how species adapt and change over time, stemming from a common ancestor. The adaptations are driven by environmental pressures.
When a species encounters a new environment, it must adapt to survive. These adaptations can be physical traits, behaviors, or physiological changes. The best-adapted individuals are more likely to survive and reproduce, passing these advantageous traits to their offspring.
Over many generations, these small changes accumulate, resulting in new species. For example, the famous finches Darwin observed in the Galápagos Islands had various beak shapes that were adapted to the types of food available on their specific islands.
Some key points of species adaptation include:

• Adaptation is a response to environmental challenges.
• Natural selection favors advantageous traits.
• Over time, significant changes can lead to the formation of new species.

Understanding species adaptation is crucial to comprehending the broader concept of evolutionary change.

Evolutionary Change

Evolutionary change refers to the process through which species evolve over time. This process is gradual and happens through the accumulation of small genetic changes. These changes can lead to significant biological differences within populations.
Charles Darwin identified natural selection as a primary mechanism of evolutionary change. Natural selection occurs when individuals with traits better suited to their environment tend to survive longer and reproduce more, passing these traits to future generations.
Over prolonged periods, these changes can produce new species. This process explains the diversity of life we observe today.
It is important to note several factors that contribute to evolutionary change:

• Genetic variation within a population.
• Mutations as a source of new genetic variation.
• Gene flow between populations.
• Genetic drift causing random changes in gene frequencies.

Darwin's observation that South American temperate plants are more similar to South American tropical plants than to European temperate plants is an example of evolutionary change due to geographic distribution and shared ancestry.

Geographic Distribution

Geographic distribution is the spatial arrangement of species across different regions. It explains why certain species are found in specific areas and not others. This distribution supports the concept of 'descent with modification' by showing how species that are geographically closer are more similar.
For example, species on islands tend to be unique compared to those on the nearest continents. This uniqueness results from isolation, which leads to species adapting to their specific environments, often evolving independently from their mainland relatives.
Darwin observed that birds living on isolated islands had unique traits tailored to their environments. Such observations led him to conclude that geographic separation could lead to speciation - the formation of new species.
Key points about geographic distribution include:

• Geographical barriers can lead to reproductive isolation.
• Isolation triggers independent adaptations and evolution.
• Species in closer proximity share more similarities due to common ancestry.

Understanding geographic distribution helps explain how environmental factors and isolation contribute to the diversity of life forms on Earth.