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Evolution 15
The Big Idea
The theory of natural selection explains evolution and the diversity of life.
Main Idea #1Charles Darwin developed a theory of evolution based on natural selection.
The 1st Scientific Hypothesis of Evolution
• French biologist Jean Baptiste de Lamarck offered the first complete explanation of evolution in 1809.
• He was the first to argue that fossils were the remains of extinct animals.
• His concept was transformational, meaning individuals transform their own traits in order to evolve.
Uniformitarianism• Geologist Sir Charles Lyell - the principle of uniformitarianism.
• Two parts:
• laws of physics and chemistry remain the same throughout earth’s history
• past geological events occurred by natural processes similar to those that observed today
• He said Earth’s age must be measured in millions of years.
Charles Robert Darwin1809-1882
• In 1831, Darwin sailed aboard the very small ship the HMS Beagle.
• During his 5-year voyage, he collected a wide variety of flora and fauna from South America and surrounding islands.
• He found long extinct fossils, including seashells in the Andes Mountains at an altitude of 13,000 feet.
• He also witnessed earthquakes and severe erosion that helped to confirm his ideas about geology.
Darwin & The Galapagos Islands
• These volcanic islands are on the equator, 600 miles west of Ecuador.
• Each island varied in tortoises, iguanas, mockingbirds, and ground finches.
• The islands had similar climate, but varied greatly in vegetation.
• Darwin inferred that island species originated in South America, and were modified over many years under the varying conditions of different islands.
• Darwin conducted the remainder of his work at home in England, where all of his notebooks had been sent home ahead of him in October 1836.
• His travel journal, The Voyage of the Beagle, was published three years later, but he continued his research on the evolution of species by natural selection.
• Darwin first presented his ideas in a paper in 1844, but did not began writing the larger volume until 1856. By 1858, he had received a manuscript from Alfred Russel Wallace summarizing his ideas on natural selection.
• Geologist Lyell was instrumental in convincing Darwin to publish a joint paper with Wallace.
• Darwin’s book On the Origin of Species by Means of Natural Selection was published in 1859. All printed copies sold out in one day.
Darwin (continued...)
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• Darwin’s work actually included 5 separate theories
• Perpetual Change is the basic theory of evolution on which the others are based stating that the world is constantly changing.
• Common Descent (controversial theory) states that all forms of life descended from a common ancestor.
• Multiplication of Species - species divide and split into different species, which can no longer interbreed
• Gradualism - large differences actually originate from an accumulation of many smaller differences
• Natural Selection - explains the selective processes of the environment, through a phenomenon called adaptation.
Darwin’s Theory of Evolution
Natural Selection & Speciation
Natural Selection
• The Ideas Behind Natural Selection
1. Individuals in a population show variations.
2. Variations can be inherited.
3. Organisms have more offspring than can survive on available resources.
4. Variations that increase reproductive success will have a greater chance of being passed on.
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Types of Evidence of Evolution
1. Fossil Record
2. Comparative Anatomy
• Homologous Structures - similar structures inherited from a common ancestor
• Vestigial Structures - structures that are reduced forms of functional structures in other organisms; get smaller over generations
• Analogous Structures - structures that have similar function, but not similar shapes; not inherited from a common ancestor
Evidence (continued...)
3. Comparative Embryology - many embryos share characteristics that are not alike in the adult form
4. Comparative Biochemistry - the more closely related two species are, the more amino acid sequences they will share
5. Geographic Distribution - evolution may be closely linked to climate and geographical characteristics
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Speciation• Speciation is the evolutionary process by which new
biological species arise.
• Allopatric speciation - a physical barrier divides one population into one or more populations
• mountain ranges, lava flows, channels between islands, wide rivers
• believed to be the most common type of speciation
• Sympatric speciation - no physical barrier separates the populations
• the ancestor species and new species live side by side
Types of Evolution
• Chemical Evolution - formation of organic molecules from inorganic substances
• primordial soup; chemicals in the early ocean giving rise to organic, and eventually, living matter
• Organic Evolution - changing of a species into something different by the accumulation of small changes over time