EVOLUTIONARY THEORY

Outcomes 1. Explain how the evolutionary theory unifies biology. 1.1 Describe how individual variations are produced. 1.2 Discuss the action of natural selection on individuals, populations, and species. 1.3 Explain how Darwin's observations led to his inferences about evolution. 1.4 Compare the development of theories of evolutionary change (some examples - Lamarck, De Vries, Weisman). 2.5 Examine broad climatic changes during the earth's history (ice ages, melting of the ice caps) and consider how these changes may have contributed to the changing organisms. 2.6 Examine the effects of migration and mutations on evolutionary change.

Theories of Evolution Carolus Linnaeus ( ) and Taxonomy Taxonomy is the science of classifying organisms; taxonomy had been a main concern of biology. Carolus Linnaeus was a Swedish taxonomist. Linnaeus developed a binomial system of nomenclature (two-part names for each species [e.g., Homo sapiens]). He developed a system of classification for all known plants. Like other taxonomists of his time, Linnaeus believed in the ideas of special creation-each species had an "ideal" structure and function; and fixity of species-each species had a place in the scala naturae, a sequential ladder of life.

Theories of Evolution Georges Louis Leclerc Georges Louis Leclerc, known by his title, Count Buffon ( ), was a French naturalist. He wrote on the natural history of all known plants and animals, provided evidence of descent with modification. His writings speculated on influences of the environment, migration, geographical isolation, and the struggle for existence. Erasmus Darwin Erasmus Darwin ( ) was Charles Darwin's grandfather. He was a physician and a naturalist whose writings on both botany and zoology contained many comments that suggested the possibility of common descent. He based his conclusions on changes undergone by animals during development, artificial selection by humans, the presence of vestigial organs Erasmus Darwin offered no mechanism by which evolutionary descent might occur.

Theories of Evolution Cuvier and Catastrophism George Cuvier ( ), a French vertebrate zoologist, was the first to use comparative anatomy to develop a system of classifying animals He founded the science of paleontology-the study of fossils-and suggested that a single fossil bone was all he needed to deduce the entire anatomy of an animal. To explain the fossil record, Cuvier proposed that a whole series of catastrophes (extinctions) and repopulations from other regions had occurred Catastrophism is the term applied to Cuvier's explanation of fossil history: the belief that catastrophic extinctions occurred, after which repopulation of surviving species occurred, giving an appearance of change through time.

Theories of Evolution Lamarck's Acquired Characteristics Lamarck ( ) was the first to state that descent with modification occurs and that organisms become adapted to their environments. Lamarck, an invertebrate zoologist, held ideas at odds with Cuvier's. Lamarck mistakenly saw "a desire for perfection" as inherent in all living things. Inheritance of acquired characteristics was Lamarck's belief that organisms become adapted to their environment during their lifetime and pass these adaptations to their offspring. Experiments fail to uphold Lamarck's inheritance of acquired characteristics

Theories of Evolution

Darwin’s Finches In 1831 Charles Darwin travel to an island in the Galapagos Darwin identified 13 species of Finches among the Galápagos Islands that were primarily differentiated by beak size. In contrast, only one species of this bird existed on the mainland South America to the east. Darwin correctly concluded that the different beaks were adaptations to different diets available among the islands. Darwin ultimately generalized the observation from the finches that any population consists of individuals that are all slightly different from one another. Furthermore, individual organisms having a phenotype characteristic providing an advantage in staying alive to successfully reproduce will pass their phenotype traits more frequently to the next generation. Over time and generations the traits providing reproductive advantage become more common within the population. Darwin called this process "descent with modification". Adaptive radiation, as observed by Charles Darwin in Galapagos finches, is a consequence of allopatric speciation among island populations.

Darwin’s Finches

Darwin Natural selection is the engine that drives evolution. The organisms best suited to survive in their particular circumstances have a greater chance of passing their traits on to the next generation. But plants and animals interact in very complex ways with other organisms and their environment. These factors work together to produce the amazingly diverse range of life forms present on Earth. Charles Darwin coined the term "natural selection." You'll typically hear it alongside the often misunderstood evolutionary catchphrase "survival of the fittest." But survival of the fittest isn't necessarily the bloody, tooth- and-claw battle for survival we tend to make it out to be (although sometimes it is). Rather, it is a measure of how efficient a tree is at dispersing seeds; a fish's ability to find a safe spawning ground before laying her eggs; the skill with which a bird retrieves seeds from the deep, fragrant cup of a flower; a bacterium's resistance to antibiotics.

Darwin Organisms Have Variations In contrast to the previous worldview where imperfections were to be ignored, variations were essential in natural selection. Darwin suspected, but did not have today's evidence, that the occurrence of variation is completely random New variations are as likely to be harmful as helpful. Variations that make adaptation possible are those that are passed on from generation to generation. Darwin could not state the cause of variations because genetics was not yet established.

Darwin Organisms Struggle to Exist Malthus proposed that human populations outgrow food supply and death and famine were inevitable. Darwin applied this to all organisms; resources were not sufficient for all members to survive Therefore, there is a constant struggle for existence; only certain members survive and reproduce. Organisms Differ in Fitness Organisms whose traits enable them to reproduce to a greater degree have a greater fitness. Darwin noted that humans carry out artificial selection. Darwin noted that humans carry out artificial selection. Early humans likely selected wolf variants; produced the varieties of domestic dogs. Many crop plant varieties can be traced to a single ancestor. Evolution by artificial or natural selection occurs when more fit organisms reproduce and leave more offspring

Darwin Organisms Become Adapted An adaptation is a trait that helps an organism be more suited to its environment Unrelated organisms living in the same environment often display similar characteristics. Because of differential reproduction, adaptive traits increase in each succeeding generation

Individual Variations Mutations - changes in genetic information. Neutral Mutation – a mutation that does not result in any selective advantage or disadvantage Harmful Mutation – any mutation that reduces the reproductive success of an individual and is therefore selected against; harmful mutations do not accumulate over time Beneficial Mutation – any mutation that increases the reproduction success of an organism; beneficial mutations are favorable by natural selection and accumulate over time Migration – is the movement of populations, groups or individuals. In genetic terms, migration enables gene flow: the movement of genes from one population into another. If the two populations originally had different gene frequencies and if selection is not operating, migration (or, to be exact, gene flow) alone will rapidly cause the gene frequencies of the different populations to converge. Migration will generally unify gene frequencies among populations rapidly in evolutionary time. In the absence of selection, migration is a strong force for equalizing the gene frequencies of subpopulations in a species. Provided that the migration rate is greater than zero, gene frequencies will eventually equalize. Even if there is only one successful migrant per generation, gene flow inevitably draws the population's gene frequency to the species' average. Gene flow thus acts to bind the species together.

Discussion How would changes in the climate affect evolution?