Chapter 13 How Populations Evolve PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko 1
CHARLES DARWIN AND THE ORIGIN OF SPECIES Biology came of age on November 24, 1859. Charles Darwin published On the Origin of Species by Means of Natural Selection, an assemblage of facts about the natural world. Darwin made three observations from these facts. 1. Life shows rich diversity. 2. There are similarities in life that allow the classification of organisms into groups nested within broader groups. 3. Organisms display many striking ways in which they are suited for their environments. 2
Figure 13.1 (b) Patterns of similarities (a) The diversity of life (c) An insect suited to its environment 3
CHARLES DARWIN AND THE ORIGIN OF SPECIES In The Origin of Species, Darwin proposed a hypothesis, a scientific explanation for his observations, used hundreds of pages in his book to describe the evidence supporting his hypothesis, made testable predictions, and reported the results of numerous experiments he had performed. 4
CHARLES DARWIN AND THE ORIGIN OF SPECIES Darwin hypothesized that present-day species are the descendants of ancient ancestors that they still resemble in some ways and change occurs as a result of descent with modification, with natural selection as the mechanism. 5
CHARLES DARWIN AND THE ORIGIN OF SPECIES Natural selection is a process in which organisms with certain inherited characteristics are more likely to survive and reproduce than are individuals with other characteristics. As a result of natural selection, a population, a group of individuals of the same species living in the same place at the same time, changes over generations. Natural selection leads to evolutionary adaptation, a population s increase in the. frequency of traits suited to the environment Natural selection thus leads to evolution (Darwin s descent with modification ) 6
The Idea of Fixed Species The Greek philosopher Aristotle held the belief that species are fixed and do not evolve. The Judeo-Christian culture fortified this idea with a literal interpretation of the biblical book of Genesis and the suggestion that Earth may only be 6,000 years old. (a) Snakestone (b) Ichthyosaur skull and paddle-like forelimb 7
Lamarck and Evolutionary Adaptations In the early 1800s, French naturalist Jean Baptiste Lamarck suggested that life evolves, and explained this evolution as the refinement of traits that equip organisms to perform successfully in their environment. 8
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 9 Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Darwin was born on February 12, 1809, the same day that Abraham Lincoln was born. In December 1831, Darwin left Great Britain on the HMS Beagle on a five-year voyage around the world. Darwin in 1840 Galápagos Islands Fernandina 0 0 Isabela 40 km Pinta Marchena Santiago PACIFIC OCEAN Equator Daphne Islands Pinzón 40 miles Santa Cruz Florenza Genovesa Santa Fe San Cristobal Española North America PACIFIC OCEAN ATLANTIC OCEAN South America Tierra del Fuego Great Britain Europe Africa Cape of Good Hope Cape Horn HMS Beagle Asia Equator Australia Tasmania 10 New Zealand
The Voyage of the Beagle On his journey on the Beagle, Darwin collected thousands of specimens and observed various adaptations in organisms. Darwin was intrigued by the geographic distribution of organisms on the Galápagos Islands and similarities between organisms in the Galápagos and those in South America. 11
Figure 13.5 A land iguana (left), and a marine iguana (right), an example of the unique species inhabiting the Galápagos 12
The Voyage of the Beagle Darwin was strongly influenced by the writings of geologist Charles Lyell, who suggested that Earth is very old and was sculpted by gradual geological processes that continue today. Darwin reasoned that the extended time scale would allow for gradual changes to occur in species and in geologic features. 13
Descent with Modification Darwin made two main points in The Origin of Species. 1. Organisms inhabiting Earth today descended from ancestral species. 2. Natural selection is the mechanism for evolution. 14
EVIDENCE OF EVOLUTION Evolution leaves observable signs. We will examine five of the many lines of evidence in support of evolution: 1. the fossil record, 2. biogeography, 3. comparative anatomy, 4. comparative embryology, and 5. molecular biology. 15
The Fossil Record Fossils are imprints or remains of organisms that lived in the past. The fossil record is the ordered sequence of fossils as they appear in rock layers, reveals the appearance of organisms in a historical sequence, and fits with the molecular and cellular evidence that prokaryotes are the ancestors of all life. 16
Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 17
The Fossil Record Paleontologists (scientists who study fossils) have discovered many transitional forms that link past and present. Transitional fossils include evidence that birds descended from one branch of dinosaurs and whales descended from four-legged land mammals. 18
Biogeography Biogeography, the study of the geographic distribution of species, first suggested to Darwin that today s organisms evolved from ancestral forms. 19
(a) Cynognathus was a carnivorous reptile found in Triassic rocks in South America and Africa. Cynognathus Lystrosaurus (b) Lystrosaurus was a herbivorous reptile found in Triassic rocks in Africa, India, and Antarctica. Biogeography and Continental Drift South America Africa Antarctica India Australia (c) Mesosaurus was a freshwater reptile found in Permian rocks in South America and Africa. Mesosaurus Glossopteris (d) Glossopteris was a seed-bearing tree found in Permian rocks in South America, Africa, India, Antarctica, and Australia. 20 Fig. 18-12, p. 402
Comparative Anatomy Comparative anatomy is the comparison of body structure between different species and attests that evolution is a remodeling process in which ancestral structures become modified as they take on new functions. Homology is the similarity in structures due to common ancestry 21
Figure 13.9 Human Cat Whale Bat 22
Comparative Anatomy Vestigial structures are remnants of features that served important functions in an organism s ancestors and now have only marginal, if any, importance. 23
Comparative Embryology Early stages of development in different animal species reveal additional homologous relationships. Comparative embryology of vertebrates supports evolutionary theory Pharyngeal pouches Post-anal tail Chicken embryo Human embryo 24
Development of different animals 25
Molecular Biology Evolutionary relationships among species can be determined by comparing genes and proteins of different organisms. Primate Chimpanzee Human Gorilla Orangutan Gibbon Old World monkey Percent of selected DNA sequences that match a chimpanzee s DNA 92% 96% 100% 26
Darwin s Theory of Natural Selection Darwin based his theory of natural selection on two key observations. Observation 1: Overproduction and competition All species have the potential to produce many more offspring than the environment can support. This leads to inevitable competition among individuals. 27
Darwin s Theory of Natural Selection Observation 2: Individual variation Variation exists among individuals in a population. Much of this variation is heritable. Inference: Unequal reproductive success (natural selection) Those individuals with traits best suited to the local environment generally leave a larger share of surviving, fertile offspring. 28
Figure 13.15-3 Insecticide application Chromosome with gene conferring resistance to pesticide Survivors Reproduction 29
Figure 13.UN09 Observations Overproduction of offspring Individual variation Conclusion Natural selection: unequal reproductive success 30
Figure 13.17 Common ancestor of lineages to the right Lungfishes 1 Tetrapod limbs 2 Amnion 3 Amphibians Mammals Lizards and snakes Tetrapods Amniotes 4 Crocodiles Homologous trait shared by all groups to the right 5 Feathers 6 Ostriches Hawks and other birds Birds 31
Populations as the Units of Evolution The total collection of alleles in a population at any one time is the gene pool. (a) Two dense populations of trees separated by a lake (b) A nighttime satellite view of North America 32
Genetic Variation in Populations Genetic variation results from processes that both involve randomness: 1. mutations, changes in the nucleotide sequence of DNA, and 2. sexual recombination, the shuffling of alleles during meiosis. 33
MECHANISMS OF EVOLUTION The main causes of evolutionary change are genetic drift, gene flow, and natural selection. Natural selection is the most important, because it is the only process that promotes adaptation. 34
Animation: Causes of Evolutionary Change Right click slide / select Play 35
Genetic drift is a change in the gene pool of a small population due to chance. Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring RR RR rr RR RR Rr Rr RR RR rr RR RR rr RR RR Rr Rr RR RR RR Rr rr RR RR RR Rr Rr Rr RR RR Generation 1 p 0.7 q 0.3 Generation 2 p 0.5 q 0.5 Generation 3 p 1.0 q 0.0 36
The bottleneck effect is an example of genetic drift and results from a drastic reduction in population size. Original population Bottleneck event Surviving population 37
The Founder Effect The founder effect is likely when a few individuals colonize an isolated habitat. 38
Gene Flow Gene flow is another source of evolutionary change, is separate from genetic drift, is genetic exchange with another population, tends to reduce genetic differences between populations. 39
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Three General Outcomes of Natural Selection 1. Directional selection shifts the overall makeup of a population by selecting in favor of one extreme phenotype. 2. Disruptive selection can lead to a balance between two or more contrasting phenotypic forms in a population. 3. Stabilizing selection favors intermediate phenotypes, occurs in relatively stable environments, and is the most common. 41
Figure 13.29 Frequency of individuals Original population Original population Evolved population Phenotypes (fur color) (a) Directional selection (b) Disruptive selection (c) Stabilizing selection 42
Sexual Selection Sexual selection is a form of natural selection in which individuals with certain traits are more likely than other individuals to obtain mates. 43