Final answer:
During a 1977 drought on Daphne Major, small-beaked medium ground finches died out, while large-beaked ones thrived on the available large seeds, illustrating evolution by natural selection. If drought conditions persist and the population remains isolated, larger beak sizes will become more prevalent due to survival and reproductive advantages. This phenomenon is consistent with Charles Darwin's observations and theories regarding variation and adaptation among finch species in the Galápagos.
Step-by-step explanation:
Evolution by Natural Selection in Galápagos Finches
Due to a severe drought in 1977 on Daphne Major, an island in the Galápagos, the finch population experienced natural selection. A reduction in small, soft seeds led to a decline in small-beaked finches, while large-beaked finches prevailed due to their ability to consume the larger, hard seeds that remained available. The Grants observed that within two years, the average beak size of the finch population increased, providing evidence for evolution by natural selection.
If the drought conditions continue and the finch population remains isolated, we can predict that the finch population will trend towards larger beak sizes. This is because birds with larger and broader beaks will have better survival and reproductive success under the conditions favoring consumption of large, tough seeds. Consequently, the inherited trait for larger beak size will become more common in succeeding generations.
Charles Darwin also observed the variation in beak shape among finch species, leading to his theorization of adaptive changes shaping evolution. This principle underscores the importance of varying food sources and environmental pressures as driving forces behind the differentiation in beak shapes and sizes among the finches, each suited to a specific feeding niche.