What changes were observed in the beaks of finches on Daphne Major, and how did they relate to natural selection?

SouravNovember 8, 2024

Answer

The changes observed in the beaks of finches on Daphne Major, particularly the medium ground finch (Geospiza fortis), provide a clear example of natural selection in action. Here’s a summary of the key changes and how they relate to natural selection:

Observed Changes in Beak Size

1. Drought Conditions: In 1977, a significant drought affected the vegetation on Daphne Major, leading to a drastic reduction in available food sources. The drought resulted in fewer small, soft seeds and a predominance of larger, harder seeds.
2. Survival of the Fittest: During this period, finches with larger beaks were better equipped to crack open the tough seeds that remained available. As a result, these birds had higher survival rates compared to those with smaller beaks, which struggled to access food.
3. Increase in Beak Size: Following the drought, studies conducted by Peter and Rosemary Grant revealed that the average beak depth of the medium ground finch population increased significantly from 1976 to 1978. The average beak depth rose from approximately 9.55 mm to about 10.55 mm within just two years, illustrating rapid evolutionary change due to natural selection.

Relation to Natural Selection

1. Natural Selection Mechanism: The changes in beak size exemplify directional selection, where individuals with traits (larger beaks) that confer advantages in survival and reproduction become more common in the population over time .
2. Heritability of Traits: The larger beak size was heritable; thus, the surviving large-billed birds produced offspring with similar traits. This heritability ensured that the advantageous trait was passed on to future generations .
3. Rapid Evolutionary Change: The swift increase in beak size within such a short timeframe demonstrates how natural selection can lead to significant evolutionary changes in response to environmental pressures. This case is notable because it provides direct evidence of evolution occurring in real-time.
4. Adaptive Radiation: The finches on Daphne Major are also an example of adaptive radiation, where different species evolve distinct adaptations (in this case, various beak shapes) based on their ecological niches and available food sources