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Section 15-1: The Puzzle of Life's Diversity
During his travels, Charles Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.
Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos.
Section 15-2: Ideas That Shaped Darwin's Thinking
Hutton and Lyell helped scientists realize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species.
Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.
Section 15-3: Darwin Presents His Case
In artificial selection, nature provides the variation among different organisms, and humans select those variations that they find useful.
Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment.
Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in the fossil record, the geographical distribution of living species, homologous structures of living organisms, and similarities in early development.