rganisms change as they adapt to their environment and thus are "naturally selected" was explained in that work along with his four basic observations that: 1.) More young are produced than necessary. 2.) Offspring differ from one another, allowing the better suited ones to survive. 3.) Better suited traits are passed to the next generation. 4.) Those best suited to their environment survive. Although other scientists of the time had the same idea, Darwin had the solid evidence collected during the Beagle voyage to support his theories. Darwin's health steadily declined and one theory about his ill health is that he contacted Chagas' disease from an insect bite received in Brazil on March 26, 1835 during the voyage of the Beagle. Chagas' disease symptoms include alteration of heart rate, enlarged heart and cardiac arrest occurring 10 to 20 years after being infected. At 73 years of age Charles Robert Darwin died of a heart attack on April 19, 1882.
             On January 11, 1887 Clara and Carl Leopo
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