Darwin and Natural Selection born in Shrewsbury, England, in 1809 studied medicine at Edinburgh University (1825-1827) where the sight of blood and surgery without anesthetics repulsed him studied to become a clergyman at Cambridge University (1827-1831) After Cambridge, Charles was recommended for a surveying trip on the HMS Beagle. He sailed aboard the Beagle for 5 years, working as a naturalist. The Beagle sailed around the world. This voyage lasted from 1831 to 1836. At the time Darwin made his trip, the majority of people believed the Earth and all of its forms of life had been created only a few thousand years in the past. People also believed that the Earth had not changed during those few thousand years. People also believed in fixity of species; in other words, species never changed. After careful observation and study of new scientific discoveries, Darwin began to The first dinosaur to be described scientifically was Megalosaurus by think otherwise. William Buckland in 1824. James Hutton Darwin was influenced by geologist James The Father of Geology Hutton’s writings that described geologic forces he thought had changed and were still changing the earth. Hutton proposed that the Earth had to be much more than a few thousand years old. Darwin was also influenced by geologist Charles Lyell who wrote Principia Geologica. Lyell’s book proposed that tremendous geologic processes had shaped the Earth such as seen in volcanoes active in the present. On the voyage, Patterns in the species Darwin noticed suggested that the that everywhere he species had changed went, the animals over time and had given and plants differed rise to new and different vastly. species. Many of Darwin’s conclusions were based on observations of wildlife in the Galapagos Islands. The Galapagos Islands lie 500 miles west of Ecuador in the Pacific Ocean, directly on the equator. “Galapagos” means turtle. Darwin noticed on these islands, there were several types of finches. In particular, Darwin observed something odd about the finches: they all looked like a bird he had seen on the South American continent. Darwin wondered if the birds and other animals had been created to match their environment, why didn’t these birds look like the birds of the African continent, since the environments of both the Galapagos and Africa were similar? Darwin guessed that some of the birds from South America migrated to the Galapagos. Once on the islands, the birds must have changed over the years. large ground finch woodpecker finch cactus finch This would explain the numerous species of birds present. Darwin concluded: Each species has descended, with changes, from other species over time. Darwin called this… Descent With Modifications or (change in species over time) Darwin based his theory on his own observations and the writings of Thomas Malthus. Malthus was a British social scientist who made these observations about humans: People have more children than are able to survive. There are built-in population checks: disease, famine, and war. Darwin extended these principles to biology, which helped him form his theory of… …or Survival of the Fittest. Darwin published his ideas in the book On The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life Five basic components of 1. All species have genetic variation. Every species is different, even within itself. Look around you…are you all the same? 2. Organisms produce more offspring than can survive. Many that survive do not produce offspring. The female green sea turtle lays a clutch of about 110 eggs. She may lay several clutches. It is likely that less than 1% of the hatchlings will ever reach sexual maturity. 3. Since more organisms are produced than can survive, there is competition (struggle for existence). Competition exists WITHIN and AMONG species. Within and Among Species for food water shelter space And Within a Species for mates The constant struggle for survival is affected by short-term natural disasters. (drought, fires, floods, snowstorms, hurricanes, and tornadoes) The constant struggle for survival is also affected by long-term changes in the environment. (ice ages, biome shifts, etc) 4. Survival of the fittest Some organisms are more suited to their environment as a result of variations in the species. Fitness: the ability of an individual to survive and reproduce in its specific environment. Fitness is a result of adaptations. Individuals that are fit to their environment survive and leave more offspring than those who aren’t. He who spreads the most genes wins! 1st 5. Decent with modification: Living species today are descended with modifications from common ancestral species that lived in the past. Characteristics of fit individuals increase in a population over time. Over time, genes for less favored characteristics will be eliminated from the gene pool. Example: giraffes and their increasingly longer necks. Natural Selection: Survival of the Fittest An adaptation is any inherited characteristic (a genetic variation) that can increase an organism’s chance of survival. An the variation exists first. change organism does not because of need or desire to the environment changes. survive. The organism either already has the variation that a variation may give an advantage survive environmental change. toenables it to survive or it dies. Species • A group of organisms that are closely related and naturally mate to produce fertile offspring. Speciation • The process by which new species form. – Separate populations of a single species often live in different environments – In each environment, natural selection acts on populations – If environments different enough, separate populations can become dissimilar Different genes favor survival in different habitats – As two groups become more different over time, they may be unable to breed= new species Speciation • What keeps new species separate? • Reproductive Isolation- two populations of the same species do not mate with each other- can be due to… – Geographic isolation – Temporal isolation – Physical differences – Hybrid sterility Ex. Garter snakes- some live in water, some are terrestrial Ex. Courtship behaviors Ex. Eastern spotted skunk (late winter) and western spotted skunk (late summer) Ex. Differences in blossoms attract different pollinators Ex. Gametes of red and purple sea urchins are unable to fuse Ex. Hybrid salamanders do not complete development, those that do develop are frail Ex. Donkey + horse = mule- sterile Ex. Even if the first generation of hybrids is viable and robust, subsequent generations are weak or sterile- rice As the environment changes, organisms must have variations that allow them to survive (adapt) to those changes or die If an entire population of a species cannot adapt, that species becomes extinct. Many scientists say that the earth is currently experiencing a mass extinction crisis. It is estimated that 1/5 or more of the world’s species will become extinct if the rainforests are destroyed. If we are in a period of mass extinction . . . What animals will your grandchildren be able to see in the wild? Visit the World Photos by MartinHarvey Wildlife Fund website World Wildlife for more information Fund International on endangered species.
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