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On the Galapagos Islands he noticed the slight variations that made tortoises from different islands recognizably distinct. The population of the next generation will contain a higher frequency of those types that most successfully survive and reproduce under the existing environmental conditions.
The inferior disadvantaged members of the same species would gradually die out, leaving only the superior advantaged members of the species. It struck him that as population outgrew resources, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed.
If so, it will become more prevalent in the next generation and spread throughout the population.
This is called "microevolution. Some politicians and religious leaders denounce the theory of evolution, invoking a higher being as a designer to explain the complex world of living things, especially humans. He wrote of the giraffe: "We know that this animal, the tallest of mammals, dwells in the interior of Africa, in places where the soil, almost always arid and without herbage, obliges it to browse on trees and to strain itself continuously to reach them.
Take the example of whales — using evolution as their guide and knowing how natural selection works, biologists knew that the transition of early whales from land to water occurred in a series of predictable steps. However, natural selection is "blind" in the sense that changes in phenotype can give a reproductive advantage regardless of whether or not the trait is heritable.
Darwin developed his theory through Darwin was influenced by observations made during his youthful voyage as naturalist on the survey ship Beagle.