Darwin's Voyage of Discovery

Darwin’s Voyage of Discovery If you’d met young Charles Darwin, you probably wouldn’t have guessed that his ideas would change the way we look at the world. As a boy, Darwin wasn’t a star student. Charles Darwin was born in England on February 12, 1809. He grew up at a time when the scientific view of the natural world was shifting dramatically. Geologists were suggesting that Earth was ancient and had changed over time, and biologists were suggesting that life on Earth had also changed. The process of change over time is called evolution. An Important Time in Biology! Darwin’s Epic Journey Darwin was invited to sail on the HMS Beagle’s five-year voyage mapping the coastline of South America. Darwin planned to collect specimens of plants and animals on the voyage. • • What was Charles Darwin’s contribution to science? Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors. Darwin’s Voyage Observations Aboard the Beagle What three patterns of biodiversity did Darwin note? (1) Species vary globally: Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe. (2) species vary locally: Darwin noticed that different, yet related, animal species often occupied different habitats within a local area. (3) species vary over time: Darwin noticed that some fossils of extinct animals were similar to living species. Species Vary Globally Darwin also noticed that rabbits and other species living in European grasslands were missing from the grasslands of South America and Australia. Australia’s grasslands were home to kangaroos and other animals that were found nowhere else. What did these patterns of geographic distribution mean? Species Vary Locally Darwin’s most interesting observations came from the Galápagos Islands, about 1000 km off the Pacific coast of South America. These islands are close to one another, yet they have different ecological conditions. Several islands were home to distinct forms of giant land tortoises. Darwin saw differences among tortoises and learned from the islands’ governor that the tortoises’ shells varied in predictable ways from one island to another. The shape of the tortoises’ shells corresponds to different habitats. Isabela Island has high peaks, is rainy, and has abundant vegetation that is close to the ground. A tortoise from Isabela Island has a dome-shaped shell and short neck. Hood Island, in contrast, is flat, dry, and has sparse vegetation. A long neck and a shell that is curved and open around the neck and legs allow the Hood Island tortoise to reach sparse, high vegetation. Darwin also observed that different islands had different varieties of mockingbirds, all of which resembled mockingbirds Darwin had seen in South America. In addition, Darwin noticed several types of small brown birds on the islands with beaks of different shapes. He didn’t consider these smaller birds to be unusual or important—at first. Putting the Pieces of the Puzzle Together On the voyage home, Darwin thought about the patterns he’d seen. Darwin sent plant and animal specimens to experts for identification. The Galápagos mockingbirds turned out to belong to three separate species found nowhere else. The little brown birds were actually all species of finches, also found nowhere else, though they resembled a South American finch species. The same was true of Galápagos tortoises, marine iguanas, and many plants that Darwin had collected on the islands. • Darwin was surprised by the number of similar but not identical species that he observed compared to the mainland. Darwin began to wonder whether different Galápagos species might have evolved from South American ancestors. He spent years actively researching and filling notebooks with ideas about species and evolution. The evidence suggested that species are not fixed and that they could change by some natural process. Four Outside Influences that Shaped Darwin’s Thinking: • What did Hutton and Lyell conclude about Earth’s history? Geologists Hutton and Lyell concluded that Earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present. a) Hutton recognized the connections between geological processes and geological features. Certain kinds of rocks are formed from molten lava. Other kinds of rocks form very slowly, as sediments build up and are squeezed into layers. Forces beneath Earth’s surface can push rock layers upward, tilting or twisting them to form mountain ranges. Mountains, in turn, can be worn down by rain, wind, heat, and cold. Hutton introduced gradualism and deep time. b) Lyell, in his book Principles of Geology presented uniformitarianism, the idea that the geological processes we see in action today must be the same ones that shaped Earth millions of years ago. Darwin witnessed a quake was so strong that it lifted a stretch of rocky shoreline more than 3 meters out of the sea—with mussels and other sea animals clinging to it. Sometime later, Darwin observed fossils of marine animals in mountains thousands of feet above sea level. Darwin asked himself, if Earth can change over time, could life change too? • How did Lamarck (1809) propose that species evolve? Lamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. He also suggested that individuals could pass these acquired traits on to their offspring, enabling species to change over time. Lamarck proposed that all organisms have an inborn urge to become more complex and perfect, and to change and acquire features that help them live more successfully in their environments. He thought that organisms could change the size or shape of their organs by using their bodies in new ways. For example, a black-necked stilt could have acquired long legs because it began to wade in deeper water looking for food. As the bird tried to stay above the water’s surface, its legs would grow a little longer. Structures of individual organisms could also change if they were not used. If a bird stopped using its wings to fly, for example, its wings would become smaller. Lamarck also suggested that a bird that acquired a trait, like longer legs, during its lifetime could pass that trait on to its offspring, a principle referred to as inheritance of acquired characteristics. Evaluating Lamarck’s Hypotheses Organisms don’t have an inborn drive to become more perfect. Evolution does not mean that over time a species becomes “better” somehow, and evolution does not progress in a predetermined direction. In addition, traits acquired by individuals during their lifetime cannot be passed on to offspring. However, Lamarck was one of the first naturalists to suggest that species are not fixed. He was among the first to try to explain evolution scientifically using natural processes. He also recognized that there is a link between an organism’s environment and its body structures. • What was Malthus’s view of population growth? Malthus reasoned that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone. In 1798, English economist Thomas Malthus noted that humans were being born faster than people were dying, causing overcrowding. The forces that work against population growth, Malthus suggested, include war, famine, and disease. He reasoned that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone. Darwin realized that Malthus’s reasoning applied even more to other organisms than it did to humans. One oyster can produce millions of eggs each year. However, most offspring die before reaching maturity, and only a few of those that survive manage to reproduce. When Darwin realized that most organisms don’t survive and reproduce, he wondered which individuals survive…and why? • How is inherited variation used in artificial selection? Artificial selection: nature provides the variations, and humans selectively breed those they find useful. Breeders knew that individual organisms vary, and that some of this variation could be passed from parents to offspring and used to improve crops and livestock. Darwin had no idea how heredity worked or what caused heritable variation, but he did know that variation occurs in wild species as well as in domesticated plants and animals. Darwin recognized that natural variation was very important because it provided the raw material for evolution. When Darwin published his scientific explanation for evolution, it changed the way people understood the living world.