The 1977 Daphne Major Drought

A Real, Famous Example of Natural Selection

Introduction & Genetic Variation

In 1977, there was a major drought that severely impacted a population of birds called Darwin’s Finches. These finches lived on the Galápagos Islands and possessed natural biological variations in their beak sizes.

There are finches born with small beaks which naturally excel at eating soft seeds, and finches with strong, bigger beaks which can crack open hard seeds. This divergence in physical traits within the population is completely possible because of how traits are passed down from parent to offspring via genetic inheritance.

Interactive Climate Simulator

Adjust the environmental timeline slider below to simulate the exact resource shift that occurred on Daphne Major in 1977.

How Survival Affects Reproduction

The drought happened because there was not a lot of rain. Because there was not enough rain, there were no more soft seeds.

Now that there are only big and hard seeds left on the island, the big strong beak became adaptive in the new environment. Finches with small beaks were less likely to survive. This process proves how survival affects reproduction, because only the birds strong enough to crack the hard seeds survived long enough to reproduce.

Multi-Generational Prediction

After just two generations, the average beak sizes of the finches increased by 4% compared to their grandparents.

A scientific future prediction could be, if the island's climate is still dry, the small-beak trait will disappear overtime, as an adaptation.