Final answer:
Darwin's postulate 3 explains that in a population, there is variation among individuals, and this can be seen in the finches of the Galapagos Islands. The finches with beaks that are better adapted to the available food sources are more likely to survive and reproduce, passing on their traits to the next generation.
Step-by-step explanation:
In Darwin's theory of natural selection, postulate 3 states that there will be variation among individuals in a population. One example of this can be seen in the finches of the Galapagos Islands. These finches have different beak shapes and sizes, allowing them to eat different types of food. The finches with beaks that are better adapted to the available food sources are more likely to survive and reproduce, passing on their traits to the next generation. This leads to a higher percentage of finches with beaks that are well-suited for their environment.