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19 Descent with Modification
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EVOLUTION Evolution: the processes that transformed life on Earth from earliest forms to the diversity of today Charles Darwin: Father of Evolution 1859 published On the Origin of Species Focused on adaptations to different environments as the origin of new species Made 2 points: Using Darwin’s phrase descent with modification Now known as adaptive evolution (change) Current species are descendants of ancestral species Natural Selection: mechanism for adaptive evolution i.e. differential reproductive success © 2016 Pearson Education, Inc. 2
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Concept 19.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species Aristotle: viewed species as fixed and arranged them on a scala naturae (scale of nature) Consistent with the Old Testament Species were individually designed by God and therefore perfect © 2016 Pearson Education, Inc. 3
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TAXONOMY Linnaeus: Father of Taxonomy
Branch of biology that organizes species into a classification system of increasingly general categories Developed the binomial format for naming species (for example, Homo sapiens) Called binomial nomenclature Linnaeus ascribed the resemblance among species to the pattern of creation, rather than evolution © 2016 Pearson Education, Inc. 4
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Ideas About Change over Time
Paleontology: the study of fossils Cuvier is Father of Paleontology Fossils: remains or traces of organisms from the past Usually found in sedimentary rock, which appears in layers or strata Speculated that each boundary between fossils helped to lay the groundwork for Darwin’s ideas Geologists Hutton and Lyell saw that changes in Earth’s surface can result from slow, continuous actions still operating today This view strongly influenced Darwin’s thinking © 2016 Pearson Education, Inc. 5
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Strata Younger stratum with more recent fossils Older stratum
Figure 19.3 Strata Figure 19.3 Formation of sedimentary strata with fossils Younger stratum with more recent fossils Older stratum with older fossils © 2016 Pearson Education, Inc.
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Lamarck’s Hypothesis of Evolution
Lamarck hypothesized that: Species evolve through use and disuse of body parts and the Inheritance of acquired characteristics The mechanisms he proposed are unsupported by evidence © 2016 Pearson Education, Inc. 7
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Concept 19.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life Darwin took an unpaid position as naturalist on a 5-year around-the-world voyage on the Beagle He observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions Darwin perceived adaptation (change) to the environment and the origin of new species as closely related processes Natural selection is a process in which individuals with favorable inherited traits are more likely to survive and reproduce (differential reproductive success) © 2016 Pearson Education, Inc. 8
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Darwin in HMS Beagle in port 1840, after his return from the voyage
Figure 19.5 Darwin in 1840, after his return from the voyage HMS Beagle in port Great Britain EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA PACIFIC OCEAN PACIFIC OCEAN Pinta Genovesa Equator SOUTH AMERICA Equator Malay Archipelago Marchena Santiago Mtns. Chile Brazil AUSTRALIA Fernandina Figure 19.5 The voyage of HMS Beagle (December 1831–October 1836) PACIFIC OCEAN Andes Cape of Good Hope Isabela Santa Cruz Santa Fe San Cristobal Argentina Tasmania Floreana Kilometers Española Cape Horn New Zealand © 2016 Pearson Education, Inc.
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Darwin’s Focus on Adaptation
Figure 19.6 Darwin’s Focus on Adaptation (a) Cactus-eater (c) Insect-eater Figure 19.6 Three examples of beak variation in Galápagos finches (b) Seed-eater Conclusion: diverse group of Galápagos finches arose from an ancestral form by the gradual accumulation of adaptations to different environments © 2016 Pearson Education, Inc.
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Ideas from On the Origin of Species
Darwin published his ideas in On the Origin of Species Explained 3 broad observations about life: The unity of life The diversity of life The match between organisms and their environment The phrase descent with modification summarized Darwin’s perception of the unity of life Refers to the view that all organisms are related through descent from an ancestor that lived in the remote past © 2016 Pearson Education, Inc. 11
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Figure 19.8 TREE OF LIFE In the Darwinian view, the history of life is like a tree with branches representing life’s diversity Fossils of extinct species help to “fill in” the morphological gaps between present-day groups Figure 19.8 “I think . . .” © 2016 Pearson Education, Inc.
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Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) †Moeritherium
Figure 19.9 Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) †Moeritherium †Barytherium †Deinotherium †Mammut †Platybelodon †Stegodon †Mammuthus Figure 19.9 Descent with modification Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) 60 34 24 Millions of years ago Years ago © 2016 Pearson Education, Inc.
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Artificial Selection, Natural Selection, and Adaptation
Figure 19.10 Artificial Selection, Natural Selection, and Adaptation Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection Darwin argued that a similar process occurs in nature Cabbage Selection for apical (tip) bud Brussels sprouts Selection for axillary (side) buds Broccoli Selection for flowers and stems Figure Artificial selection Selection for stems Selection for leaves Kale Wild mustard Kohlrabi
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Darwin drew 2 inferences from 2 observations
Observation #1: Members of a population often vary in their inherited traits © 2016 Pearson Education, Inc. 15
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Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce © 2016 Pearson Education, Inc. 16
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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 If some heritable traits are advantageous, these will accumulate in a population over time, and this will increase the frequency of individuals with these traits This process explains the match between organisms and their environment © 2016 Pearson Education, Inc. 17
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Key Features of Natural Selection
Individuals with certain heritable traits (best suited/adapted to that environment) will survive and reproduce at a higher rate than other individuals; differential reproductive success Over time, natural selection increases the frequency of adaptations that are favorable in a given environment If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species NOTE: individuals do not evolve; populations evolve over time Natural selection can only increase or decrease heritable traits that vary in a population The traits that are adaptive will vary with different environments © 2016 Pearson Education, Inc. 18
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Concept 19.3: Evolution is supported by an overwhelming amount of scientific evidence
New discoveries continue to fill the gaps identified by Darwin in On the Origin of Species There are 4 types of data that document the pattern of evolution Direct observations Homology The fossil record Biogeography © 2016 Pearson Education, Inc. 19
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Direct Observations of Evolutionary Change
2 modern examples provide evidence for natural selection: Natural selection in response to introduced species Evolution of drug-resistant bacteria © 2016 Pearson Education, Inc. 20
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Homology Evolution is a process of descent with modification
Related species can have characteristics with underlying similarity that function differently Homology is similarity resulting from common ancestry © 2016 Pearson Education, Inc. 21
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Figure 19.16 Homologous structures: anatomical similarities that represent variations on a structural theme present in a common ancestor Humerus Radius Ulna Carpals Metacarpals Figure Mammalian forelimbs: homologous structures Phalanges Human Cat Whale Bat © 2016 Pearson Education, Inc.
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Figure 19.17 Comparative embryology: reveals anatomical homologies not visible in adult organisms Pharyngeal arches Post-anal tail Figure Anatomical similarities in vertebrate embryos Chick embryo (LM) Human embryo © 2016 Pearson Education, Inc.
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Vestigial structures are remnants of features that served important functions in the organism’s ancestors © 2016 Pearson Education, Inc. 24
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A Different Cause of Resemblance: Convergent Evolution
Convergent evolution is the evolution of similar or analogous features; NOT from a common ancestor but due to their same jobs in life Convergent evolution does not provide information about ancestry © 2016 Pearson Education, Inc. 25
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Convergent Evolution: Analogous Structures
Figure 19.18 Convergent Evolution: Analogous Structures Sugar glider NORTH AMERICA AUSTRALIA Figure Convergent evolution Flying squirrel © 2016 Pearson Education, Inc.
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The Fossil Record The fossil record provides evidence of
The extinction of species The origin of new groups Changes within groups over time Fossil evidence shows that living cetaceans and their close relatives, the even-toed ungulates, are more different from each other today than were early cetaceans and even-toed ungulates © 2016 Pearson Education, Inc. 27
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Fossils can document important transitions
Figure 19.20 Fossils can document important transitions For example, the transition from land to sea in the ancestors of cetaceans Pelvis and hind limb bones Other even-toed ungulates Hippopotamuses †Pakicetus †Rodhocetus Common ancestor of cetaceans †Dorudon Figure The transition to life in the sea Living cetaceans 70 60 50 40 30 20 10 Key Pelvis Femur Tibia Foot Millions of years ago © 2016 Pearson Education, Inc.
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Biogeography Biogeography: the scientific study of the geographic distribution of species Provides evidence of evolution Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift Endemic species: species that are not found anywhere else in the world Islands have many endemic species that are often closely related to species on the nearest mainland or island Darwin explained that species on islands gave rise to new species as they adapted to their new environments © 2016 Pearson Education, Inc. 29
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What Is Theoretical About Darwin’s View of Life?
In science, a theory accounts for many observations and explains and integrates a great variety of phenomena The predictions of a scientific theory must stand up to continual testing by experimentation and observation Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions Ongoing research adds to our understanding of evolution © 2016 Pearson Education, Inc. 30
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Individuals in a population vary in their heritable characteristics.
Figure 19.UN02 Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals. Figure 19.UN02 Summary of key concepts: natural selection and Over time, favorable traits accumulate in the population. © 2016 Pearson Education, Inc.
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