unit 5 evolution ch. 15 darwin’s theory of evolution
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Unit 5 Evolution
Ch. 15 Darwin’s Theory of Evolution
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The Puzzle of Life’s Diversity
• Evolution - modern organisms have descended from ancient organisms (change over time)
• Theory - a well-supported, testable explanation of phenomena that have occurred in the natural world
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Voyage of the HMS Beagle
• 1831• Charles Darwin contributed most to our
understanding of evolution• He made observations & collected
evidence that led him to propose a hypothesis about the way life changes over time.
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Voyage of the Beagle
• That hypothesis, now supported by a large amount of evidence, has become the Theory of evolution
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Darwin’s Observations
• Darwin collected the preserved remains of ancient organisms - Fossils
• Some of these fossils resembled organisms that were still alive
• Others looked unlike any creature ever seen
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Darwin’s Observations
• The Galapagos Islands influenced Darwin the most
• He observed that the characteristics of animals & plants varied among the different Islands.
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Darwin’s Observations
• Each island had a different climate although they were very close.
• He studied tortoises.• Each tortoise’s shell had a different shape
depending on which island it came from.
• He wondered if the animals living on different islands were once related….
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Views before Darwin
• Earth was created only a few thousand years ago.
• Since creation, neither earth nor its species had changed
• Darwin was influenced by several individuals.
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An Ancient, Changing Earth
• Hutton & Lyell helped scientists recognize that Earth is millions of years old.
• They also noted that the processes that changed Earth in the past are the same processes that are changing Earth now.
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Lamarck’s Evolution Hypothesis
• The year that Darwin was born, Lamarck published his hypothesis
• He proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime
• Over time, this process led to change in a species
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Lamarck’s Explanation
•Tendency toward perfecton•Use and Disuse•Inheritance of Acquired traits
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Population Growth
• English economist, Malthus, published a book, noting that babies were being born faster than people were dying
• He stated that if the human population continued to grow unchecked, sooner or later there would be insufficient living space & food for everyone
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Darwin Presents His Case
• In 1859, Darwin published the results of his work in a book, On the Origin of Species.
• In his book, he proposed a mechanism for evolution called natural selection.
• He stated that evolution has been taking place for millions of years, & continues in all living things
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Darwin Presents His Case
• Species on Earth today descended from ancestral animals in various habitats.
• Heritable variation- differences that are passed from parents to offspring.
• Variations were thought to be unimportant.
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Inherited Variation & Artificial Selection
• Artificial selection - nature provided the variation, & humans selected those variations that they found useful.
• It has produced diverse plants & animals by selectively breeding for different traits.
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Evolution by Natural Selection
• Struggle for existence - the members of each species compete regularly to obtain food, living space, & other necessities of life– Predators that are faster & better at catching
prey are more likely to survive
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Evolution by Natural Selection
• Fitness - the ability of the organism to survive & reproduce in its specific environ.– Fitness is the result of adaptations
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Evolution by Natural Selection
• Adaptation - any inherited characteristic that increases an organisms’ chance of survival– Successful adaptations allow
organisms to become better suited to their environ. & thus better able to survive
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Evolution by Natural Selection
• Individuals that are better suited to their environ., with adaptations that enable fitness, survive & reproduce most successfully - Survival of the Fittest
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Evolution by Natural Selection
• Since it is similar to artificial selection, Darwin referred to survival of the fittest as - Natural Selection
• In both AS & NS, only certain individuals of a population produce new individuals
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Evolution by Natural Selection
• However, in NS, the traits being selected, & therefore, increasing over time, contribute to an organism’s fitness
• NS takes place without human control or direction
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Evolution by Natural Selection
• NS results in changes in the inherited characteristics of a population, that increase a species’ fitness in its environ.
• Over time, NS produces organisms that have different structures, & occupy different habitats
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Evolution by Natural Selection
• As a result, species today look different from their ancestors
• Each living species has descended, with changes, from other species over time - Descent with Modification
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Evolution by Natural Selection
• Descent with modification also implies that all living organisms are related to each other
• Common descent - all species (living & extinct) were derived from common ancestors
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Evidence of Evolution
• Darwin argued that living things have been evolving on Earth for millions of years
• Evidence of this could be found: in the fossil record, the geographical distribution of living species, homologous structures of living organisms, & similarities in early development
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Evidence of Evolution
• The Fossil Record:– Darwin noticed that the sizes, shapes, &
varieties of related organisms preserved in the fossil record, changed over time
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Evidence of Evolution
• Geographic Distribution of Living Species:– Darwin realized that similar animals in different
locations were the product of different lines of evolutionary descent
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Evidence of Evolution
• Homologous Body Structures:– Homologous structures - structures that have
different mature forms but develop from the same embryonic tissues
– Not all homologous structures serve important functions
– Organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs
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Homologous Structures
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Evidence of Evolution
• Homologous Body Structures:– Vestigial organs - may resemble miniature legs,
tails, or other structures, a trace of a homologous structure
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Evidence of Evolution
• Similarities in Early Development:– The early stages or embryos, of many animals
with backbones are very similar