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Descent with Modification: A Darwinian View of Life CHAPTER 22.

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Presentation on theme: "Descent with Modification: A Darwinian View of Life CHAPTER 22."— Presentation transcript:

1 Descent with Modification: A Darwinian View of Life CHAPTER 22

2 22.1 – The darwinian revolution challenged traditional views of a young earth inhabited by unchanging species Historical Setting – Earlier views 1) Scala naturae (Aristotle 384-322 BC) Life-forms could be arranged on a scale of increasing complexity 2) Old Testament Perfect species were individually created by God

3 3) Carolus Linnaeus (1707-1778) Grouped species into general categories based on the pattern of their creation Taxonomy Naming and classification Binomial Nomenclature 2 part naming system that includes Genus species

4 HISTORICAL SETTING (CONTD.) 4) Georges Cuvier(1769-1832) Opposed evolution Advocated catastrophism – the events in the past happened suddenly and by different mechanisms then today 5) Charles Lyell (1797-1875) Uniformitarianism Earth’s processes have not changed – Earth must be OLD Darwin studied his work

5 6) Jean-Baptiste de Lamarck (1744-1829) Early evolution: 1) use and disuse 2) inheritance of acquired characteristics

6 22.2 – Descent with modification by natural selection explains the adaptations of organisms and the unity & diversity of life Darwin’s voyage on the HMS BEAGLE from 1831-1836 was the time that he developed his theory of evolution by natural selection Darwin’s idea focused on natural selection vs. Lamarck’s idea focused on inheritance of acquired traits

7 Natural selection describes how adaptations arise: Adaptation = characteristics that enhance organisms’ ability to survive & reproduce in specific environments Example: desert foxes have big ears, arctic foxes have small ears Natural selection = process in which individuals that have heritable characteristics survive & reproduce at a higher rate than others individuals Over time, NS can increase the match between organisms & environment NS may result in adaptations to new conditions, potentially giving rise to new species

8 Artificial selection The process by which species are modified by humans Example: selective breeding for milk or meat production, etc Individuals do not evolve. POPULATIONS evolve




12 Origin of Species published in 1859 Darwin developed two main ideas: Descent with modification explains life”s unity and diversity Natural selection is a cause of adaptive evolution

13 Tree of life Branches represent diversity

14 Darwin describe four observations of nature and drew 2 conclusions from these Observation #1: Members of a population often vary greatly in their traits Observation #2: Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than the environment can support Observation #4: Due to lack of food or other resources, many of these offspring do not survive

15 Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations

16 SUMMARY OF NATURAL SELECTION Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals Natural selection increases the adaptation of organisms to their environment over time If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

17 22.3 EVOLUTIONARY EVIDENCE Evidence for Evolution Direct Observations The Fossil Record HomologyBiogeography

18 DIRECT OBSERVATIONS 1) Intense predation of wild guppies results in more drably colored mates 2) Evolution of drug-resistant viruses and antibiotic-resistant bacteria


20 THE FOSSIL RECORD Traces of organisms from the past Commonly found in sedimentary rock Paleontology = the study of fossils Fossils show evolutionary changes that have occurred over time & the origin of major new groups of organisms



23 HOMOLOGY & CONVERGENT EVOLUTION 1) Homology Characteristics in related species can have similarities even with different functions 2) Homologous Structures Anatomical sign of evolution Examples – forelimbs of mammals that are now used for various purposes Flying in bats Swimming in whales Once used for walking


25 3) Embryonic homologies Comparison of early stages of animal development reveals homologies in embryos that are not present in adults All vertebrate embryos have a post-anal tail & pharyngeal pouches


27 Vestigial organs Structures of marginal importance Remnants of structures that were useful in ancestors Remnants of pelvis & leg bones in snakes


29 5) Molecular homologies Shared characteristics on the molecular level All life forms use DNA & RNA 6) Convergent evolution Explains why distantly related species can resemble one another Has taken place when two organisms developed similarities as they adapted to similar environmental challenges Known as analogous “Similar problem, similar solution”


31 BIOGEOGRAPHY The geographic distribution of species 1) species in a discrete geographic area tend to be more closely related to each other South American desert animals are more closely related to local animals in other habitats than they are to the desert animals of Asia

32 2) Continental drift The movement of the tectonic plates The break-up of Pangaea Explains the relation of species on different continents


34 3) Endemic species Found at a certain geographic location and nowhere else Marine iguanas are endemic to the Galapagos 4) Darwin’s theory of evolution through natural selection explains the succession of forms in the fossil record Transitional fossils have been found that link ancient organisms to modern ones

35 SUMMARY 1) Evolution is change in species over time 2) Heritable variations exist within a population 3) These variations can result in differential reproductive success 4) Over generations, this can result in changes in the genetic composition of the population INDIVIDUALS DO NOT EVOLVE – POPULATIONS DO

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