Problem 8 - Biology

Question

Which of the following is least likely to have occurred after a small population of finches reached the Galapagos Islands from the South American mainland? (a) after many generations, the finches became increasingly different from the original population (b) over time, the finches adapted to their new environment (c) after many generations, the finches were unchanged and unmodified in any way (d) the finches were unable to survive in their new home and died out (e) the finches survived by breeding with other species.

Step-by-Step Solution

Answer

The least likely outcome is (c) the finches were unchanged and unmodified.

Step 1: Understand the Question Context

The question is exploring the likely evolutionary outcomes for a small population of finches arriving at the Galapagos Islands from the mainland. We need to consider evolutionary principles such as natural selection, adaptation, and genetic drift.

Step 2: Analyze the Choices

Identify the outcomes suggested: (a) Increasingly different from original population (b) Adapted to new environment (c) Unchanged over generations (d) Failed to survive (e) Breeding with other species.

Step 3: Apply Evolutionary Concepts

First, consider natural selection (options a and b). Both suggest change over time, which is likely as finches face new environmental pressures. Next, consider option d, which involves survival, and option e, which involves gene flow.

Step 4: Evaluate Unlikely Outcomes

Option c suggests the population remains unchanged, which is unlikely due to natural selection favoring traits suited to the new environment. Option e suggests interbreeding with other species, which is less common as reproductive barriers maintain species separation.

Step 5: Identify Least Likely Outcome

Between options (c) and (e), evolutionary principles suggest that staying completely unchanged (option c) is least likely, given the new selection pressures and the tendency for at least some level of adaptation over many generations.

Key Concepts

Natural Selection

In evolutionary biology, natural selection is a key process that fuels the evolution of species. It operates on the premise that individuals with traits that enhance their survival and reproduction are more likely to pass these advantageous traits to the next generation. Over time, this can lead to populations evolving as advantageous traits become more common.
Natural selection plays a crucial role when a small population, like the finches on the Galapagos Islands, faces new environmental conditions. For instance, different food sources or predators can exert new pressures. Finches with beak shapes suited to the available food might survive better.

• It results in the thriving of individuals with favorable traits.
• Over generations, this could lead to significant changes in the population.

In our exercise, options suggesting adaptation through trait selection are more plausible than remaining unchanged, due to the continuous influence of natural selection in new environments.

Genetic Drift

Genetic drift refers to random changes in the frequency of alleles (gene variants) within a population. Unlike natural selection, these changes are not due to environmental pressures or the traits' influence on survival. Instead, they occur by chance and are more pronounced in small populations.
When the finches arrived at the Galapagos Islands, the population was likely very small, meaning genetic drift could have had a substantial impact on their genetic makeup. Random events could lead to certain alleles becoming more common or being lost entirely. This effect is independent of the environment and can lead to diversity without adaptation.

• Genetic drift can cause dramatic genetic changes in small populations.
• It can lead to differences between populations without any adaptive significance.

This concept helps explain why small populations of finches might have evolved differently from their ancestors, even without any obvious environmental selection pressure.

Adaptation

Adaptation in an evolutionary context refers to the process through which populations become better suited to their environments over many generations. This occurs through natural selection, where individuals with favorable traits are more likely to reproduce.
In the case of the Galapagos finches, adaptation would involve changes in traits like beak shape or size to enhance survival. For example, if the available seeds were tough and required a strong beak to crack, finches with stronger beaks would have a survival advantage.

• Adaptation is a gradual process driven by natural selection.
• It results in populations that are better equipped for survival and reproduction in specific environments.

This process implies that remaining unchanged (as in option 'c') is unlikely, given the strong pressures to adapt to the new conditions on the islands.

Speciation

Speciation is the process by which populations evolve to become distinct species. This can occur when groups of the same species become reproductively isolated and undergo evolutionary changes over time, leading them to become so different they can no longer interbreed.
On the Galapagos Islands, the finches' isolation from their mainland relatives, combined with different environmental pressures, may have led to the emergence of new species. This is known as allopatric speciation.

• Speciation is often driven by geographic isolation and differing selection pressures.
• It involves accumulating changes that result in reproductive isolation over time.

Understanding speciation helps explain how the diverse finch species on the Galapagos could have evolved from a common ancestor after being isolated from the mainland.