Chapter 22: An Introduction to Evolution PDF

CHAPTER 22: An Introduction to Evolution The Theory of Evolution - Evolution: Heritable change in one or more characteristics of a population or species from one generation to the next. - Microevolution: changes in a single gene in a population over time - Macroevolution: formation o...

CHAPTER 22: An Introduction to Evolution The Theory of Evolution - Evolution: Heritable change in one or more characteristics of a population or species from one generation to the next. - Microevolution: changes in a single gene in a population over time - Macroevolution: formation of new species or groups of species - Species: group of related organisms that share a distinctive form. Among species that reproduce sexually, members of the same species are capable of interbreeding to produce viable and fertile offspring. - Population: members of the same species that are likely to encounter each other and thus have the opportunity to interbreed. History of the Theory of Evolution - Empirical Thought relies on observation to from an idea or hypothesis, rather than trying to understand life from a non-physical or spiritual point of view. Geology and Population Growth - Uniformitarianism hypothesis from geology: slow geological processes lead to substantial change Earth was much older than 6,000 years. - Charles Darwin: his theory shaped by several different fields of study geology, economics, and Voyage of the Beagle. He noticed distinctive traits of island species that allowed them to better exploit their environment. Example: Galapagos Island finches. Saw similarities in species yet noted differences that provided them with specialized feeding strategies. Descent with modification Evolution based on - Variation within a given species n Traits heritable – passed from parent to offspring n Genetic basis was not yet known - Natural selection n More offspring produced than can survive n Competition from limited resources n Individual with better traits flourish and reproduce Evidence of Evolutionary Change - Fossil record Fishapod (Tiktaalik roseae) illuminates steps leading to evolution of tetrapods. Transitional form – provides link between earlier and later forms. Evolution of Whales from Terrestrial Mammals: fossil record spans 50 million years. (if believed that decay rate is constant) Terrestrial tetrapod to aquatic animals lacking hind limbs. Order Cetacea  n Whales n Dolphins n Porpoises - Biogeography: the study of geographical distribution of extinct and modern species. Isolated continents and island groups have evolved their own distinct plant and animal communities. Endemic – naturally found only in a particular location. Example: Island fox (Urocyon littoralis) evolved from mainland gray fox (Urocyon cinereoargenteus) - Convergent evolution: two different species from different lineages show similar characteristics because they occupy similar environments; species are not closely related evolutionarily. Examples: n Giant anteater and echidna both have long snouts and tongues to feed on ants. n Aerial rootlets for clinging in English ivy and wintercreeper n Antifreeze proteins in different, very cold-water fish - Selective breeding: programs and procedures designed to modify traits in domesticated species. Also called artificial selection. Darwin influenced by pigeon breeders. Nature chooses parents in natural selection while breeders choose in artificial selection. Made possible by genetic variation. Breeders choose desirable phenotypes. Example: dog breeds, Brassica plants, and corn. - Homologies: fundamental similarity due to descent from a common ancestor. n Anatomical: same set of bones in the limbs of modern vertebrates has undergone evolutionary change for many different purposes. Homologous structures are derived from a common ancestor. Vestigial structures are anatomical structures that have no apparent function but resemble structures of presumed ancestors. Ear wiggling muscles. n Developmental: species that differ as adults often bear striking similarities during embryonic stages. Presence of gill ridges in human embryos indicates that humans evolved from an aquatic animal will gill slits. Human embryos have long bony tails. n Molecular: similarities in cells at the molecular level show that living species evolved from a common ancestor. All living species use DNA to store information. Certain biochemical pathways are found in all or nearly all species. Molecular homology: The same type of gene is often found in diverse organisms. Example: p53 gene encodes the p53 protein, a cell cycle checkpoint protein. Certain genes are found in a diverse array of species. Sequences of closely related species tend to be more similar to each other than to distantly related species. The Molecular Processes That Underlie Evolution - Homologous genes: two genes derived from the same ancestral gene. Orthologs occur in separate species. - Reveals molecular details of evolutionary change - Two sequences may be similar, but not identical due to the independent accumulation of different random mutation. Gene duplications produce gene families - Paralogs: homologous genes within a single species. - Gene duplication can lead to a gene family. Two or more paralogs within the genome of a single organism. Example: Globin genes – allows for specialized function, expression at different times or in different tissues. Horizontal gene transfer - exchange of genetic material among different species. - Surprisingly common phenomenon - Can transfer n From prokaryotes to eukaryotes n From eukaryotes to prokaryotes n Between prokaryotes n Between eukaryotes - Widespread among bacteria Evolution also occurs at the genomic level involves changes in chromosome structure and number. Compare three largest chromosomes in humans and apes. Similar due to close evolutionary relationship. Humans have one large chromosome 2 while apes have it divided into two separate chromosomes. Chromosome 3 very similar but orangutans have large inversion. May have established orangutans as a new species. Questions: 1. The long snout of the giant anteater, Myrmecophaga tridactyl of South America, and the echidan, Tachyglossus aculeatus, of Australia, are animals of different evolutionary lineages that are both adapted to ating ants. Example of convergent evolution. 2. The bacterium Bacillus tumefaciens has been harmed in biotechnology because it can insert a gene from one species of plant into another. This also occur in nature and referred to as horizontal gene transfer. 1. The main differences between the finches on the Galapagos Islands are indeed their beak size and shape. These differences evolved due to natural selection driven by competition for food resources. Finches with beak shapes that were better suited to specific food types (such as seeds, insects, or flowers) had a survival advantage in their respective  environments, leading to the diversification of species. This is a classic example of adaptive radiation. 2. Vestigial structures are non-functional structures left over from an organism’s evolutionary past. 3. In England during the 1850’s higher levels of industrial pollution darkened the trunks of trees found around industrial areas. The effect did this have on the local moth populations is that dark winged moths experienced less predation from birds and become more common due to camouflage. 4. Since the 1970’s researcher has been tracking change in beak depth of one particular species of finch on one of the Galapagos Islands. Their data demonstrated that during dry years birds with large beaks have the advantage and the average beak size increases in the next generation; the trend is reversed during wet years. 5. Lamarck theorized that acquired characteristics are passed onto offspring. This has been shown to be incorrect. Because acquired characteristics are not passed onto offspring. But changed in DNA can be passed on to offspring. 6. If a person wanted to produce dogs with extremely thick coats for surviving in cold climates, he could do this by only allowing dogs with the thickest coats to breed. This is an example of Artificial selection. 7. Horizontal gene transfer occurs when genes are exchanged across unrelated taxa. 8. When comparing amino acid sequences of proteins found in several different species, more closely related species should have fewer differences in amino acid sequence. Evidence of Evolution Comparative anatomy = Homologous structure (Structures shared by different species due to common ancestry, like the limb bones of mammals.) Dog breeds and domesticated plants = Artificial selection (Humans selecting traits over time to breed specific animals or plants.) Non-functional leftovers = Vestigial organs (Organs or structures that have lost most or all of their original function, like the human appendix.) DNA sequence similarity = Molecular biology (Using genetic information to trace evolutionary relationships.) Island organisms differing from mainland = Biogeography (Study of the geographic distribution of species, like Darwin’s observations on the Galápagos Islands.)  Tiktaalik and Archeopteryx = Transitional forms (Fossils that show intermediate traits between ancestral and modern species.) Change over geological time = Evolution of horses (An example of gradual evolutionary changes documented in the fossil record.) Darwin’s finches = Biogeography (Shows adaptation to different environments in close proximity, leading to speciation.)