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Chapter 15 Evolution What You’ll Learn You will analyze the theory of evolution. You will compare and contrast the processes of evolution. Darwin’s Theory of Natural Selection • Section Objectives: Summarize Darwin’s theory of natural selection. Explain the 4 principles of natural selection Show how natural selection could change a population What is Evolution? • Evolution ~process of change through time – explains how modern organisms have descended from ancient organisms Evolution! Evolution! Why do we accept this as a Scientific Principle? Evolution! Evolution: process of change through time • The change in characteristics of populations through generations. Thus, existing life forms have evolved from earlier life forms • A unifying principle for biology. • Provides an explanation for the difference in structure, function, and behavior among organisms What do we know? • There are many different creatures on Earth • How do we know this? OBSERVATION Biodiversity Diversity ofofLife Lifeon onEarth Earth WhatHow accounts did allfor these all this creatures biological come diversity? about? What do we know? • All creatures have common characteristics • How do we know this? OBSERVATION Unity of Life on Earth cells DNA How could all of life have the same basic features? What do we know? • Creatures have changed over time • How do we know this? OBSERVATION Fossil Record Evolution explains Unity & Diversity • Only evolution explains both – unity of life • similarities between all living things – diversity of life • wide variety of different creatures on Earth DNA Darwin & Evolution by Natural Selection Cactus eater Insect eaters Seed eaters Bud eater 2006-2007 Charles Darwin • Proposed a way how evolution works – How did creatures change over time? – by natural selection • Collected a lot of evidence to support his ideas – 1809-1882 – British naturalist Voyage of the HMS Beagle • Invited to travel around the world – 1831-1836 (22 years old!) – makes many observations of nature • main mission of the Beagle was to chart South American coastline Robert Fitzroy Voyage of the HMS Beagle • Stopped in Galapagos Islands – 500 miles off coast of Ecuador Galapagos Recently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland. 800 km west of Ecuador Darwin found…many unique species Many of Darwin’s observations made him wonder… Why? Darwin asked: Why were these creatures found only on the Galapagos Islands? Darwin found…clues in the fossils Darwin found: Evidence that creatures have changed over time present day Armadillos Darwin asked: ancient Armadillo Why should extinct armadillos & modern armadillos be found on same continent? Darwin found… birds Darwin found: Many different birds on the Galapagos Islands. Finch? He thought he found very different kinds… Sparrow? QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Woodpecker? Warbler? But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Finch?ground Finch? finch Small ground finch Sparrow? Sparrow? QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Darwin asked: If the Galapagos finches came from the mainland, why are they so different now? Warbler finch Woodpecker? Woodpecker? Tree finch Warbler? Warbler? The finches cinched it! beaks are inherited different Darwin found: The differences between species of finches were associated with the different food they ate. variations serve as adaptations that help birds Darwin said:compete for food Ahaaaa! these birds survive & A flock Large Big seed ground eater of South Small ground seed eater finch Finch? Sparrow? reproduce finch American finches were pass on the genes for those stranded on the more fit beaks Galapagos… over time nature selected for different species with different beaks QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Warbler Insect eater finch Woodpecker? Tree & Leaf finch bud eater Warbler? Relationship between species (beaks) & food DARWIN’S THEORY AND THE MODERN SYNTHESIS • Darwin also saw that humans choose organisms with specific characteristics Breeding organisms with specific traits in order to produce offspring with identical traits is called artificial selection. • Darwin hypothesized that there was a force in nature that worked like artificial selection. Darwin proposed natural selection as the mechanism of evolution • Darwin hypothesized that there was a force in nature that worked like artificial selection. • Darwin saw natural selection as the basic mechanism of evolution • Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted – As a result, the proportion of individuals with favorable characteristics increases – Populations gradually change in response to the environment • Organisms without these variations are less likely to survive and reproduce. Darwin’s finches • Darwin’s conclusions – variations in beaks • differences in beaks in the original flock • adaptations to foods available on islands – natural selection for most fit • over many generations, the finches were selected for specific beaks & behaviors – offspring inherit successful traits • accumulation of winning traits: both beaks & behaviors – separate into different species From 1 species to 14 species… Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Large insectivorous tree finch Small ground finch Cactus eater Insect eaters Medium ground finch Seed eaters Vegetarian tree finch variation Bud eater natural selection for best survival & reproduction Large ground finch What do we know? • Populations are a mix of different individuals • How do we know this? Variation OBSERVATION How does that work? Variation Over-Production & Competition Adaptation Nature selects the ones that “fit” the environment better … survive & reproduce Natural Selection What determines survival? • Natural Selection – traits that help individuals survive • • • • survive predators survive disease compete for food compete for territory Adaptations – traits that help individuals reproduce • attracting a mate • compete for nesting sites • successfully raise young Survival & Reproduction of the Fittest Survival & Reproduction of the fittest not the …the fittest! strongest… bravest… fastest… biggest… Adaptations the traits that help an organism fit the environment better to survive & reproduce Survival & reproduction of the fittest bug…