When Charles Darwin visited the islands in the 1800s, he observed many types of organisms that were similar but lived on different islands. The four species of mockingbirds found on the Galapagos Islands are shown below. Each species lives on a different island. These species are very similar. However, the Hood mockingbird has a longer beak than the other three species. Which of the following best explains this difference?
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The difference in beak length among the four species of mockingbirds in the Galapagos Islands can be best explained by natural selection. Charles Darwin observed that these mockingbirds were similar but had slight variations in their physical characteristics, including beak length.
According to Darwin's theory of evolution, these variations may have arisen from a common ancestor through a process called descent with modification. Over time, the mockingbird populations on the different islands faced different environmental conditions and food sources. As a result, individuals with longer beaks were better suited to obtain certain types of food, such as nectar from long tubular flowers, while individuals with shorter beaks were better adapted to different food sources.
Through natural selection, individuals with favorable traits, in this case, longer beaks, were more likely to survive and reproduce, passing on their advantageous traits to future generations. Over many generations, this selective pressure led to the differentiation of beak length among the mockingbird species on different islands. Therefore, the longer beak of the Hood mockingbird is an adaptation to its specific ecological niche on its respective island.
The best explanation for the difference in beak length among the four species of mockingbirds on the Galapagos Islands is natural selection.
To understand this further, let's break down how natural selection works:
1. Variation: Within a population, there is natural variation, meaning individuals differ in their traits. In this case, the mockingbirds have different beak lengths.
2. Environmental Pressure: The Galapagos Islands have diverse habitats with varying food sources. Each island may have different types of available food, which can put selective pressure on the mockingbirds.
3. Fitness Advantage: In this particular case, let's consider the food sources available on each island. If an island has larger or tougher food items, mockingbirds with longer beaks may be better adapted to feed on those items, thus having a fitness advantage over others.
4. Reproduction and Inheritance: Individuals with longer beaks that can access better food sources are more likely to survive and reproduce. Over time, their genetic traits – including the longer beak – are passed on to succeeding generations.
5. Reproductive Isolation: The four species living on different islands are geographically isolated, meaning they cannot readily interbreed. With time and isolation, genetic differences accumulate, leading to distinct traits in each species.
So, based on this understanding of natural selection, the longer beak of the Hood mockingbird likely evolved because of the selective advantage it offered in accessing specific food sources on the Hood Island.