Jean-Baptiste Lamarck proposed a theory of inheritance of acquired characteristics. Environmental pressures and internal "desires" bring about changes in the individual's body. Offspring can inherit these changes. This provided a force for perfection up the Chain of Being.
Charles Lyell's book Principles of Geology proposed that subtle, repetitive processes of change, had shaped the Earth. He challenged the view that Earth was only 6,000 years old.
For example, Darwin noted examples of organisms whose existence challenged the concept of creation.
In Argentina, the fossils of extinct
glyptodonts
were similar to the living
armadillos
he observed.
Thomas Malthus, a clergyman and economist, wrote an essay that Darwin read on his return to England. It argued that as population size increases, resources dwindle, the struggle to live intensifies and conflict increases. Darwin suspected that any population has the capacity to produce more individuals than the environment can support. He reasoned that the variations in traits might affect an individual's ability to secure resources, and to survive and reproduce.
On the Galapagos Islands, he had observed that the finches varied slightly from each other but all resembled the mainland finches to some extent. He attempted to correlate variations in their traits with environmental challenges.
Darwin reasoned that those animals now present could have descended from those living in the past, but with changes. Darwin gradually developed a theory of natural selection to explain how such changes could come about.
Alfred Wallace was a naturalist who arrived at the same conclusions Darwin did. He wrote to Darwin describing his views and prompted Darwin to finally present his ideas in a formal paper.
Darwin and Alfred Wallace published their ideas jointly in 1858. Darwin published his theory in book form in 1859. The book laid out in great detail his evidence in support of the theory of evolution by natural selection. If one species can evolve into another, there should be transitional forms. When Darwin published his work, no such forms were known. He was hoping that "transitional" animals would be found to strengthen his ideas. Almost seventy years later the study of genetics led to substantiation of Darwin's ideas.
This animation (Audio - Important) describes the Galapagos Islands.
This animation (Audio - Important) describes Darwin's finches.
Biological evolution does not change individuals. It changes a population. Traits in a population vary among individuals. Evolution is change in the frequency of traits.
This animation (no audio) describes alleles.
Sources of variation (caused by genes, manifested in phenotype) include:
REVIEW: The place Darwin visited on his trip around the world that had the greatest impact on his
thinking was
REVIEW: Georges Cuvier was a strong proponent of the theory of
REVIEW: In Argentina, Darwin noted the similarity of fossils of glyptodonts to modern
REVIEW: Which of the following evolve?
REVIEW: Darwin saw that populations of Galapagos finches _____ .
a. show variation in traits
b. resemble birds in South America
c. are adapted to different island habitats
d. all of the above
REVIEW: Genetic variation gives rise to variation in _____ traits.
a. morphological
b. physiological
c. behavioral
d. all of the above
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