Chapter 15: Darwin’s Theory of Evolution Charles Robert Darwin ( ) “nothing in biology makes sense except in the light of evolution”-Theodosius Dobzhansky

Evolution On the grandest scale, is all the changes that have transformed life over time. Essentially, it is the biological history of life on Earth. Evolutionary Theory: A collection of facts, observations, and hypotheses about the process by which modern organisms have descended from ancient ones.

15-1: The Puzzle of Life’s Diversity ► In 1831, a 22-yr-old Darwin set sail on the HMS Beagle on a 5 year cruise around the world ► As a naturalist, he studied the geology, plants, and animals encountered on the voyage

Darwin’s Observations ► He observed an immense amount of diversity in the South American plants, animals, and fossils  Many different ways of reproducing and surviving  Life seemed well suited for the environment  Some fossils resembled modern life forms, some had no resemblance ► The Galapagos Islands- islands had similar life forms but varied in climate and vegetation  Darwin inferred that the species on the different islands had once been part of the same mainland species

The Galapagos Tortoises

15-2: Ideas that Shaped Darwin’s Thinking ► Darwin’s voyage occurred during one of the most exciting periods in the history of Western science ► Explorers were traveling the globe, and great thinkers were beginning to challenge established views about the natural world ► At this time, most Europeans believed:  Life was created in its complexity and has remained fixed (or unchanging) since this time  The Earth was about 10,000 years old and also relatively unchanging

Early Influences ► George Buffon (mid-1700s): French naturalist; collected fossils and noticed similarities and differences; suggests Earth is older than 10,000yrs ► James Hutton (1785): English Geologist; suggest geological forces that shape Earth’s surface are slow and require long periods of time (Earth must be millions of years old) ► Jean Baptiste Lamarck (1809): French naturalist; Explains Buffon’s observations by making a hypothesis that life evolves through the inheritance of acquired characteristics

Lamarck’s Hypothesis

Geological Influence ► On the voyage of the Beagle, Darwin read the writings of geologist Charles Lyell (1833) ► Lyell proposed that the geological processes that shape the Earth’s surface today (erosion, deposition, earthquakes, etc.) are the same processes that shaped the Earth in the past ► Encouraged explaining the past in terms of observable present day processes

A Mechanism for Change ► When Darwin returned to England, he could no longer accept the idea of unchanging life ► He began contemplating a mechanism for evolutionary change ► In 1838, he read the work of Thomas Malthus (an economist who wrote an essay on human populations) ► Malthus suggested that human warfare, famine, and disease would limit the growth of the population

Darwin Publishes His Ideas ► In 1844, Darwin wrote a 200- page essay that outlined his idea, but did not publish it in fear of controversy and doubt ► Instead he spent the next decade collecting evidence to support his idea ► Darwin received an essay from a young naturalist, Alfred Wallace, in 1858 proposing the same idea for evolutionary change with similar evidence ► In 1859, Darwin published his book On The Origin of Species by Means of Natural Selection