BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 13 How Populations Evolve Modules 13.1 – 13.3

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings All organisms have evolutionary adaptations –Inherited characteristics that enhance their ability to survive and reproduce The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment –Large, webbed feet help propel the bird through water at high speeds Clown, Fool, or Simply Well Adapted?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Aristotle and the culture of the 1800’s believed that species are fixed Fossils suggested that life forms change –This idea was embraced by Lamarck in the early 1800s 13.1 A sea voyage helped Darwin frame his theory of evolution EVIDENCE OF EVOLUTION

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings While on the voyage of the HMS Beagle in the 1830s, Charles Darwin observed –similarities between living and fossil organisms –the diversity of life on the Galápagos Islands, such as blue-footed boobies and giant tortoises Figure 13.1A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The voyage of the Beagle Figure 13.1B North America Great Britain Europe Africa Equator Australia Tasmania New Zealand Cape of Good Hope South America Andes Cape Horn Tierra del Fuego Galápagos Islands Pacific Ocean Atlantic Ocean

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin became convinced that the Earth was old and continually changing –He concluded that living things also change, or evolve over generations –He also stated that living species descended from earlier life-forms: descent with modification

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fossils and the fossil record strongly support the theory of evolution –Hominid skull 13.2 The study of fossils provides strong evidence for evolution Figure 13.2A, B –Petrified trees

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Scorpion in amber –“Ice Man” Figure 13.2E, F

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The fossil record shows that organisms have appeared in a historical sequence Many fossils link early extinct species with species living today –These fossilized hind leg bones link living whales with their land-dwelling ancestors Figure 13.2G, H

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other evidence for evolution comes from –Biogeography –Comparative anatomy –Comparative embryology 13.3 A mass of evidence validates the evolutionary view of life Figure 13.3A HumanCatWhaleBat

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Molecular biology Figure 13.3B HumanRhesus monkeyMouseChickenFrogLamprey Last common ancestor lived 26 million years ago (MYA), based on fossil evidence 80 MYA 275 MYA 330 MYA 450 MYA

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin observed that (Natural Selection) –organisms produce more offspring than the environment can support –organisms vary in many characteristics –these variations can be inherited –organisms that are better adapted leave more offspring 13.4 Darwin proposed natural selection as the mechanism of evolution DARWIN’S THEORY AND THE MODERN SYNTHESIS

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin’s Four Criteria for Natural Selection to Occur Overproduction of offspring leads to more offspring than environment can support Variation in those offspring Variations are inherited Offspring that are better adapted to environment leave subsequently more offspring

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted Darwin saw natural selection as the basic mechanism of evolution –As a result, the proportion of individuals with favorable characteristics increases –Populations gradually change in response to the environment

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment –This is called artificial selection Figure 13.4A Adopt me!!

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms –Example: camouflage adaptations of mantids that live in different environments 13.5 Connection: Scientists can observe natural selection in action Figure 13.5A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The evolution of insecticide resistance is an example of natural selection in action Figure 13.5B Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Insecticide application

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A species is a group of populations whose individuals can interbreed and produce fertile offspring A population is a group of interbreeding individuals living in same place and same time. –Populations evolve, not individuals!!! 13.6 Populations are the units of evolution Figure 13.6

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A gene pool is the total collection of genes in a population at any one time Microevolution is a change in the relative frequencies of alleles in a gene pool 13.7 Microevolution is change in a population’s gene pool over time

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool –To test this, let’s look at an imaginary, nonevolving population of blue-footed boobies 13.8 The gene pool of a nonevolving population remains constant over the generations Figure 13.8A WebbingNo webbing

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Figure 13.8B Phenotypes Genotypes Number of animals (total = 500) WW 320 Ww 160 ww 20 Genotype frequencies 320 / 500 = / 500 = / 500 = W160 W w40 w 800 / 1,000 = 0.8 W 200 / 1,000 = 0.2 w Number of alleles in gene pool (total = 1,000) Allele frequencies

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 13.8C Recombination of alleles from parent generation Next generation: Genotype frequencies Allele frequencies SPERMEGGS 0.64 WW0.32 Ww0.04 ww 0.8 W0.2 w WW p 2 = 0.64 WW qp = 0.16 Ww pq = 0.16 ww q 2 = 0.04 W sperm p = 0.8 w sperm q = 0.2 W egg p = 0.8 w egg q = 0.2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The population is very large The population is isolated Mutations do not alter the gene pool Mating is random All individuals are equal in reproductive success Five conditions are required for Hardy- Weinberg equilibrium

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings What is Hardy-Weinberg Equilibrium???? It just means that the gene pool is in equilibrium. Allele frequency is not changing POPULATION IS NOT EVOLVING!!!

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic drift is a change in a gene pool due to chance –Genetic drift can cause the bottleneck effect There are several potential causes of microevolution Figure 13.11A Original population Bottlenecking event Surviving population

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –or the founder effect Figure 13.11B, C

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gene flow can change a gene pool due to the movement of genes into or out of a population Mutation changes alleles Natural selection leads to differential reproductive success

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Five Fingers of Evolution (Causes of Microevolution) Small population size Non-random mating Mutations Gene flow (migration) Natural selection

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection results in the accumulation of traits that adapt a population to its environment –If the environment should change, natural selection would favor traits adapted to the new conditions Adaptive change results when natural selection upsets genetic equilibrium

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phenotypic variation may be environmental or genetic in origin –But only genetic changes result in evolutionary adaptation Variation is extensive in most populations VARIATION AND NATURAL SELECTION

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many populations exhibit polymorphism and geographic variation Figure 13.13

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Connection: Mutation and sexual recombination generate variation Figure ParentsA1A1 A1A1 A2A2 A3A3 A1A1 A2A2 A3A3 A1A1 A2A2 A1A1 A3A3 and MEIOSIS Gametes FERTILIZATION Offspring, with new combinations of alleles

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection tends to reduce variability in populations –The diploid condition preserves variation by “hiding” recessive alleles –Balanced polymorphism may result from the heterozygote advantage Overview: How natural selection affects variation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some variations may be neutral, providing no apparent advantage or disadvantage –Example: human fingerprints Not all genetic variation may be subject to natural selection Figure 13.16

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment –Studies have shown that cheetah populations exhibit extreme genetic uniformity –Thus they may have a reduced capacity to adapt to environmental challenges Connection: Endangered species often have reduced variation Figure 13.17

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals Production of fertile offspring is the only score that counts in natural selection The perpetuation of genes defines evolutionary fitness

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There are three general outcomes of natural selection Figure Frequency of individuals Original population Phenotypes (fur color) Original population Evolved population Stabilizing selectionDirectional selectionDiversifying selection

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sexual selection leads to the evolution of secondary sexual characteristics –These may give individuals an advantage in mating Sexual selection may produce sexual dimorphism Figure 13.20A, B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This is due to: –historical constraints –adaptive compromises –chance events –availability of variations Natural selection cannot fashion perfect organisms