Fig. 2.7 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2.1 Darwin’s Voyage on HMS Beagle In 1831, Charles Darwin took on the role of naturalist of the ship HMS Beagle Fig. 2.1 The Beagle set sail on a five-year navigational trip around the world Charles Darwin (1809-1882) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2.1 Darwin’s Voyage on HMS Beagle Darwin studied a wide variety of plants and animals across the globe Particularly on the Galapagos Islands In 1859, he published his book On the Origin of Species In it he proposed that evolution occurs through natural selection Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13.1 Evolution: Getting from There to Here Natural selection, the process that leads to evolution, occurs in steps 1. Gene variation exists among individuals in a population 2. This variation is often passed to offspring 3. All populations overproduce offspring 4. Individuals with traits that aid survival and reproduction have a better chance of contributing to the next generation 5. Over time, the population changes such that the traits of the more successful reproducers are more prevalent Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13.1 Evolution: Getting from There to Here Macroevolution Evolutionary change on a grand scale Encompasses the origins of new species and major episodes of extinction Microevolution Evolutionary change on a small scale Encompasses the genetic changes that occur within a species over time These changes are the result of changes in gene frequencies Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13.2 The Evidence For Evolution Evidence for evolution comes from the following Fossil record Molecular record Anatomical record Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fossils have been found linking all the major groups The forms linking mammals to reptiles are particularly well known Fig. 13.4 Whale “missing links” Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The greater the evolutionary distance Fig. 13.5 Molecules reflect evolutionary divergence The greater the number of amino acid differences Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display This same pattern of divergence is seen with DNA sequences, such as that of the cytochrome c gene The changes appear to accumulate at a constant rate This phenomenon is referred to as a molecular clock Fig. 13.6 Note: Different proteins evolve at different rates Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Anatomical Record All vertebrates share a basic set of developmental instructions Fig. 13.7 Relict developmental forms Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13.5 Why Allele Frequencies Change Microevolution – five evolutionary forces can significantly alter the allele frequencies of a population 1. 2. 3. 4. 5. Mutation Migration Genetic drift Nonrandom mating Selection Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mutation Table 13.1 Errors in DNA replication The ultimate source of new variation Mutation rates are too low to significantly alter allele frequencies on their own Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Migration Table 13.1 Movement of individuals from one population to another Immigration: movement into a population Emigration: movement out of a population A very potent agent of change Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Genetic Drift Random loss of alleles Table 13.1 More likely to occur in smaller population Founder effect Small group of individuals establishes a population in a new location Bottleneck effect A sudden decrease in population size to natural forces Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nonrandom Mating Mating that occurs more or less frequently than expected by chance Table 13.1 Inbreeding Mating with relatives Increases homozygosity Outbreeding Mating with non-relatives Increases heterozygosity Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Selection Some individuals leave behind more offspring than others Table 13.1 Artificial selection Breeder selects for desired characteristics Natural selection Environment selects for adapted characteristics Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13.8 Selection on Color in Guppies Poecilia reticulata (guppy) is a popular aquarium fish In nature, it is found in small streams in NE South America and in mountainous streams in Trinidad Due to dispersal barriers, guppies can be found in two different pool environments Below waterfalls, where risk of predation is high Above waterfalls, where risk of predation is low Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 13.19 The evolution of protective coloration in guppies A voracious predator of guppies Rarely preys on guppies Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In low-predation pools, males Display gaudy colors and spots Reproduce at a late age Attain larger adult sizes In high-predation pools, males Exhibit drab coloration Reproduce younger Attain relatively small adult sizes In the absence of predators, larger more colorful fish may produce more offspring In the presence of predators, smaller and less colorful fish are likely favored by selection Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The evolution of these differences in guppies was experimentally tested in laboratory greenhouses Fig. 13.20 Indistinguishable from low-predation controls Same results were obtained in field experiments Smaller and drab in color Thus, natural selection can lead to rapid evolutionary change Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display