During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time. Wherever the ship anchored, Darwin went ashore to collect plant and animal specimens that he added to an ever-growing collection.
Although the islands were close, they had very different climates. The smallest, lowest islands were hot, dry, and nearly barren. The higher islands had greater rainfall and a different assortment of plants and animals. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited. Darwin observed that the characteristics of many animals and plants varied noticeably among the different Galapagos islands.
Hutton and Lyell helped scientists recognize 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. He proposed that geological forces have shaped earth and that layers of rock form very slowly. Some rocks are moved up by forces beneath earth's surface while others are buried and other form mountain ranges. This results in rocks being shaped by a variety of natural forces.
He wrote Principles of Geology. Stressed that scientists must explain past events in terms of processes that they can observe. His work explained how geological features could be built up or torn down over long periods of time.
Principle of Geology
Written by Charles Lyell. Helped Darwin appreciate the significance of geological phenomena that he had observed and helped Darwin understand how geological processes could have raised rocks from sea floor to the mountaintop. Understanding of geology influenced Darwin in two ways- If the earth could change overtime, might life change as well? Then he realized that it would have taken many years for life to change.
Jean Baptiste Lamarck
Publishes his hypotheses of the inheritance of acquired traits. The ideas are flawed, but he is one of the first to propose a mechanism explaining how organisms change over time. First to recognize that living things have changed over time and that all species were descended from other species. Also realized that organisms were somehow adapted to their environments. 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.
In 1798, published book in which he noted that babies were being born fast than people were dying. Reasoned that if the human population continued to grow unchecked, soon or later there would be insufficient living space and food for everyone. Darwin realized that this reasoning applies to plants and animals more than it does to humans because humans produce little offspring.
"Essay on the Principles of Population"
Malthus predicts that the human population will grow faster than the space and food supplies needed to sustain it.
Alfred Russel Wallace
Write to Darwin speculating on evolution by natural selection, based on his studies of the distribution of plants and animals. Darwin present's his essay to the Linnanen Society. Did field work in Malaysia and was a naturalist.
On the Origin of Species by Means of Natural Selection
Essay summarized the thoughts on evolutionary change that Darwin had been mulling over for almost 25 years. Proposed a mechanism for evolution that he called natural selection and then presented evidence that evolution has been taking place for millions of years and continues in all living things.