Evolution Chapters 13, 14, 15, 19 (Human Evolution) PDF

Concepts of Evolution Chapters 13, 14, 15, 19 (Human Evolution) Darwin’s Theory of Evolution (13.1) Charles Darwin – “Father of Evolution” Childhood & Education Conventional view of Earth and life – accepted Aristotle’s view that species were...

Concepts of Evolution Chapters 13, 14, 15, 19 (Human Evolution) Darwin’s Theory of Evolution (13.1) Charles Darwin – “Father of Evolution” Childhood & Education Conventional view of Earth and life – accepted Aristotle’s view that species were fixed Accepted Judeo- Christian belief using literal interpretation of Genesis, estimating age of Earth being 6,000 years At age of 22, travels  Darwin’s Sea Voyage Darwin spent most of his time on shore collecting specimens of fossils and living plants and animals Kept detailed observations Noted characteristics that made the organisms well suited to the diverse environments His observations indicated geographic proximity is a better predictor of relationships among organisms than similarity of environment Plants and animals living in temperate regions of S. America more closely resembled those living in tropical regions of S. America than species in temperate regions in Europe Fossils looked very different than the living organisms but resembled the living ones on the same continent Ex. Fossilized armor plates resembled those of living armadillos; paleontologists later determined the fossils belonged to an extinct armadillo (the size of a Volkswagen Beetle!)  Darwin was intrigued by the geographic distribution of organisms on the Galapagos Islands. Most animals here are found nowhere else in the world. (ex. Marine Iguanas and the Giant Tortoises) Darwin was influenced by other scientists Charles Lyell (“Principles of Geology”) Earth shaped over millions of years by gradual, natural processes that still occur today Darwin’s Writings Darwin now doubted that the Earth was only a few thousand years old He concludes that present-day species are descendants of ancient ancestors He hypothesized that descendants spread and accumulated adaptations (modifications) that fit them to a specific environment. He writes an essay about his Theory of Natural Selection but delays publishing He finally publishes when he learns Alfred Wallace had a nearly identical hypothesis Darwin publishes “The Origin of Species” 13.2 The study of fossils provides strong evidence for evolution Fossils are the imprints or remains of organisms that once lived in the past Some fossils are not actual remnants of organisms. Types of fossils: casts, imprints, hard parts (teeth, bones, etc), coprolites (fossilized feces), amber trapped insects, organisms frozen in ice, etc.  Many fossils are found in sedimentary rock (layers called strata) Paleontology – study of fossils Fossil record is incomplete (conditions did not necessarily favor fossil formation) Figure 13.2c Strata of sedimentary rock at the Grand Canyon 13.3 Transitional forms support Darwin’s theory Many fossils link early extinct species with species living today. Paleontologists unearthed transitional fossils and thought that whales arose from a wolf-like carnivore. Molecular biologists found a close relationship between whales and hippopotamuses and hypothesized that whales and hippos were both descendants of a cloven-hoofed ancestor. Two fossils discovered in 2001 provided the answer. Both Pakicetus and Rodhocetus had the distinctive ankle bone of a cloven- hoofed mammal. Thus, as is often the case in science, scientists are becoming more certain about the evolutionary origin of whales. 13.4 Homologies provide strong evidence for evolution Evolution is a process of descent with modification. Evolution is a remodeling process. Related species can have characteristics that have an underlying similarity yet function differently. Similarity resulting from common ancestry is known as homology. Structural and molecular homologies reveal evolutionary relationships Molecular homologies can include similarities in DNA, in proteins, etc.  Vestigial Structures and Analogous Structures “Left over” structures that are of marginal or perhaps no importance to the organism are called vestigial structures. Examples: Small pelvis and hind-leg bones of ancient whales Eye remnants buried under scales in blind species of cave fishes Genes can be present but have lost their function Analogous structures are those that serve the same function but have different structures. They DO NOT indicate common ancestry. 13.5 Homologies indicate patterns of descent that can be shown on an evolutionary tree Evolutionary trees are hypotheses reflecting our current understanding of patterns of evolutionary descent. Some are supported by a strong combination of fossil, anatomical, and molecular data. Others are more speculative because few data are available. 13.6 Darwin proposed natural selection as the mechanism of evolution All domesticated plants and animals are the products of selective breeding from wild ancestors. The selective breeding of domesticated plants and animals to promote the occurrence of desirable traits in the offspring is called artificial selection. Darwin observed that All organisms tend to over produce Overproduction leads to competition for resources Some organisms have adaptations that give an “edge in survival” Organisms with the adaptations survive and produce offspring, passing on the adaptation So, natural selection is nature “selecting” the survival of the “fittest” Three Key Points about Evolution by Natural Selection Although natural selection occurs through interactions between individual organisms and the environment, individuals do not evolve,. It is the group of organisms (populations) that evolve over time. Natural selection can only amplify or diminish heritable traits. Evolution is not goal directed to lead to perfectly adapted organisms. 13.7 Observing Natural Selection in Action A plane sprays pesticides on crops. As the pesticide is applied, chromosomes with allele confer resistance to the pesticide. The pests with the resistance survive. Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow. The Evolution of Populations (13.8 – 13.11) Organisms typically show individual variation. Mutations are the ultimate source of the genetic variation that serves as raw material for evolution. In organisms that reproduce sexually, most of the genetic variation in a population results from the unique combination of alleles that each individual inherits. Fresh assortments of existing alleles arise every generation from three random components of sexual reproduction: 1. crossing over, 2. independent orientation of homologous chromosomes at metaphase I of meiosis, and 3. random fertilization.  Evolution occurs within populations A population is a group of individuals of the same species living in the same area and which can potentially interbreed. A gene pool consists of all copies of every type of allele at every locus in all members of the population. The relative frequency of alleles in a population is called allele frequency. A change in a gene pool is called microevolution. 13.10 The Hardy-Weinberg equation can test whether a population is evolving The Hardy-Weinberg equilibrium states that allele and genotype frequencies will remain constant if a population is large, mating is random, and there is no mutation, gene flow, or natural selection. The Hardy-Weinberg equation can be used to test whether evolution is occurring in a population.  Figure 13.10C shows a Punnett square that uses these gamete allele frequencies and the rule of multiplication to calculate the frequencies of the three genotypes in the next generation. Because the genotype frequencies are the same as in the parent population, the allele frequencies p and q are also the same. Thus, the gene pool of this population is in a state of equilibrium— Hardy-Weinberg equilibrium. Hardy-Weinberg Equation General formula for calculating the frequencies of genotypes in a population from the frequencies of alleles in the gene pool: p2 + 2pq + q2 = 1 p represents the frequency of homozygous dominant 2pq represents the frequency of heterozygous q represents the frequency of homozygous recessive For the gene pool: p + q =1 p is the frequency of the dominant allele q is the frequency of the recessive allele For a population to be in Hardy-Weinberg equilibrium, allele and genotype frequencies will remain constant generation after generation To be in Hardy-Weinberg equilibrium, 5 conditions must be satisfied Very large population – The smaller the population, the more likely that the allele frequencies will fluctuate by chance from one generation to the next No gene flow between populations – When individuals move into or out of a population, they add or remove alleles, altering the gene pool. No mutations – by changing, deleting, or duplicating genes, mutations modify the gene pool Random mating – If individuals mate preferentially, random mixing of gametes does not occur and genotype frequencies change No natural selection – The unequal survival and reproductive success of individuals can alter allele frequencies A hypothetical population of 10,000 humans has 6840 individuals with the blood type AA, 2860 individuals with blood type AB and 300 individuals with the blood type BB. 1.What is the frequency of the AA genotype in this population? 2.What is the frequency of the AB genotype in this population? 3.What is the frequency of the BB genotype in this population? 4.What is the frequency of the A allele? 5.What is the frequency of the B allele? 6.If the next generation contained 25,000 individuals, 13.12 Natural selection, genetic drift, and gene flow can cause microevolution The three main causes of evolutionary change are 1. natural selection, 2. ​genetic drift, and 3. ​gene flow The bottleneck effect and founder effect lead to genetic drift. The bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced. Genetic drift is also likely when a few individuals colonize an island or other new habitat, producing what is called the founder effect. Bottleneck Effect Founder Effect Gene Flow A population gains or loses alleles when fertile individuals move into or out of a population OR when gametes are transferred between populations It reduces the differences between populations Today, humans move more freely about the world than in the past, and gene flow has become an important agent of microevolutionary change in 13.13 Natural Selection is the only mechanism that consistently leads to adaptive evolution Only natural selection Body and consistently leads to adaptive bill evolution—evolution that results streamlined like a in a better fit between torpedo for organisms and their movement in water environment. Its tail is Relative fitness is the used like a break to pull contribution an individual out of a makes to the gene pool of the high-speed dive as it next generation relative to the hits the contributions of other water Large, individuals. webbed feet Blue-Footed As a result of natural selection, Booby make great flippers  13.14 Natural selection can alter variation in a population in 3 ways Natural selection can affect the distribution of phenotypes in a population. Stabilizing selection favors intermediate phenotypes. Directional selection shifts the overall makeup of the population by acting against individuals at one of the phenotypic extremes. Disruptive selection typically occurs when environmental conditions vary in a way that favors individuals at both ends of a phenotypic range over individuals with intermediate phenotypes. 13.15 Sexual Selection Sexual selection is a form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mates. Secondary sex characteristics can give individuals an advantage in mating. Sexual dimorphism occurs in many cases: noticeable differences not Figure 13.15a Extreme sexual directly associated with reproduction dimorphism (peacock and peahen) or survival Males are usually the showier sex, at least in vertebrates  Figure 13.15b A contest for access to In some species, intrasexual selection mates between two male elks occurs, in which individuals compete directly with members of the same sex for mates. Contests may involve physical combat but more often ritualized displays Usually in species where winning individual acquires a harem of mates In a more common type of sexual Figure 13.15c A male gray tree frog selection, called intersexual selection calling for mates (between sexes) or mate choice, individuals of one sex (usually females) are choosy in selecting their mates. Every time a female chooses a mate based on its appearance or behavior, she perpetuates the alleles that influenced her choice 13.17 Diploidy and Balancing Selection Diploidy preserves variation by “hiding” recessive alleles. Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population. Heterozygote advantage is a type of balancing selection in which heterozygous individuals have greater reproductive success than either type of homozygote, with the result that two or more alleles for a gene are maintained in the population. The frequency of the sickle cell allele is generally highest in areas where malaria is a major problem CH 14 – Origin of Species Introduction The Galápagos Islands are home to numerous plants and animals that are found nowhere else on Earth, including about a dozen species of giant tortoise. Lonesome George, discovered in 1971, died in 2012, the last member of his species. He mated with two females who laid eggs but none hatched. He left no known offspring. The story of Lonesome George illustrates the biological species concept, which defines species by their ability to interbreed. 14.1 The origin of species is the source of biological diversity Microevolution is the change in the gene pool of a population from one generation to the next. Speciation, the process by which one species splits into two or more species, accounts for both the unity and diversity of life. Figure 14.1 Sketch made by Darwin as he pondered the origin of species  14.2 There Are Several Ways to Define a Species The biological species concept holds that a species is a group of populations whose members can interbreed in nature and produce fertile offspring with each other but not with members of other species. This concept emphasizes reproductive isolation. There are other instances in which applying the biological species concept is problematic. The morphological species concept is based on observable physical traits and can be applied to asexual organisms and fossils. The ecological species concept defines Figure 14.2a Similarity between two focuses on unique adaptations to particular roles species: the eastern meadowlark in a biological community. (left) and western meadowlark The phylogenetic species concept defines a (right) species as the smallest group of individuals that share a common ancestor and thus form one branch of the tree of life. Beefalo (Buffalo + Cow) Liger ( Male Lion + Female Tiger) Zonkey (Zebra + Donkey) 14.3 Visualizing the Concept: Reproductive Barriers Keep Species Separate Reproductive barriers serve to isolate the gene pools of species and prevent interbreeding. Depending on whether they function before or after zygotes form, reproductive barriers are categorized as prezygotic or postzygotic. Figure 14.3_1 Figure 14.3_2 Figure 14.3_3 Figure 14.3_4 Figure 14.3_5 Figure 14.3_6 Figure 14.3_7 Figure 14.3_8 14.4 In Allopatric Speciation, Geographic Isolation Leads to Speciation Geographically separated from other populations, a small population may become genetically unique as its gene pool is changed by natural selection, mutation, or genetic drift. Figure 14.4a Allopatric speciation of geographically isolated antelope squirrels 14.6 Sympatric speciation takes place without geographic isolation Sympatric speciation occurs when a new species arises within the same geographic area as the parent species Accidents can occur during cell division that result in extra sets of chromosomes (polyploidy). More common in plants Most polyploid species arise from hybridization of two different species Tetraploid plants can mate with other Gene flow has been tetraploid or self-pollinate BUT cannot mate reduced between flies with parent plant that feed on different Triploid organisms are sterile since they food varieties, even cannot make normal gametes though they both live in the same Sympatric speciation can also occur with geographic area. continued sexual selection or because of habitat differentiation 14.8 Isolated islands are often showcases of speciation Isolated islands are often inhabited by unique species. Islands that have physically diverse habitats and are far enough apart to allow populations to evolve in isolation but close enough to allow occasional dispersals to occur are often the sites of multiple speciation events. The evolution of many diverse species from a common ancestor is known as adaptive radiation. Ex. Finch species in the Galapagos islands Figure 14.8 Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific diet 14.11 Speciation can occur rapidly or slowly Darwin's supported the idea that evolution occurred gradually, over long periods of time. Many fossil species appear suddenly in a layer of rock and persist essentially unchanged through many layers and then disappear suddenly. Punctuated equilibrium describes these long periods of little apparent structural change interrupted by relatively 15.1 Conditions on early Earth made origin of life possible Physicists have evidence that before the universe existed as it does today, all matter was concentrated in one mass which seems to have blown apart with a "big bang" 12 -14 billion years ago. Evidence indicates the Earth formed about 4.6 billion years ago from a vast swirling cloud of dust that surrounded a young sun. Immense heat was generated by impact of meteorites and compaction by gravity Earthy probably began as a molten mass that sorted into layers; the surface solidifying into a thin crust. When & How Life Arose Earliest evidence of life comes from fossils about photo of a cross section 3.5 billion years old. of a fossilized stromatolite Rock formations called stromatolites were built up by ancient photosynthetic prokaryotes. It is likely that significant time elapsed before stromatolites formed, meaning life probably arose as early as 3.9 billion years ago. Scientists hypothesize chemical and physical processes on early Earth produced simple cells in four stages 1. Abiotic synthesis of small organic molecules (amino acids, nitrogen bases) 2. Joining of the small molecules into polymers 3. Packaging the polymers into "protocell" droplets with membranes 4. Origin of self-replicating molecules that eventually made inheritance possible.(RNA before DNA) 15.2 Experiments show abiotic synthesis of organic molecules is possible 1920's – Oparin and Haldane propose that conditions on early Earth could have produced organic molecules 1953 – Stanly Miller and Harold Urey test this hypothesis Showed formation of hydrocarbons, amino acids possible Doesn’t PROVE hypothesis but supports it 15.4 - 15.6 Major Events in the History of Life Macroevolution refers to the evolutionary change above the species level. Earth's history can be divided into four eons of geologic time: Hadean Archaean Proterozoic Phanerozoic Hadean Eon The Hadean Eon, named after the Greek god and ruler of the underworld Hades, is the oldest eon and dates from 4.5–4.0 billion years ago. During this time, the planet was characterized by a partially molten surface, volcanism, and asteroid impacts. The hypothesis for the origin of Earth’s water is that it originated from inside the planet, and emerged as vapor associated with volcanic eruptions  Archaean Eon Archean Eon, Earth finally starts to cool down with a more stable climate.” At the start of the Archean Eon, Earth was without free oxygen. Water molecules had oxygen but they were bonded with Hydrogen. In this eon, Earth's atmosphere was mostly methane and nitrogen gas. First prokaryotes show up around 3.5 billion years ago. They were anaerobic heterotrophs. Eventually, anaerobic cyanobacteria appeared (blue-green algae). These microscopic cyanobacteria converted sunlight to energy. They carried out photosynthesis in the oceans metabolizing their own food. As a waste product, they released oxygen gas. Over time, free oxygen built up in the oceans into banded iron formations. But oxygen poisoned cyanobacteria threatening their very own existence. Evolution of aerobic respiration allowed other prokaryotes to flourish. Proterozoic Eon First eukaryotes appear about 1.8 billion years ago (Endosymbiotic Theory) Toward end of the eon (Pre- Cambrian Time) A great diversity of unicellular eukaryotes followed with multicellular forms including algae, plants, fungi, and invertebrate animals Oldest-known fossils of multicellular eukaryotes of small algae around 1.2 billion years ago Phanerozoic Eon Consists of 3 Eras: Paleozoic, Mesozoic, and Cenozoic Major Paleozoic Era Events Cambrian Period – sudden increase in diversity of many animal phyla ("Cambrian Explosion") Periods that follow saw colonization of land by fugi, plants, and animals (bony fish, amphibians, insects, reptiles, seed plants, etc.) Mesozoic Era of Phanerozoic Eon Triassic Period – cone bearing plants, dinosaurs appear, mammals first appear Jurassic Period - "Age of the Dinosaurs" Cretaceous Period – flowering plants appear, mass extinction – end of the dinosaurs  Cenozoic Era Began with a major radiation of mammals, birds, and pollinating insects Appearance of primates and bipedal humans Homo sapiens appear Includes current time  Mechanisms of Macroevolution (15.7- 15.13) Since multicellular eukaryotes appeared, there have been three times in which the land masses of Earth have come together to form a supercontinent. Each time the masses split, it yielded a different configuration of continents. The theory of plate tectonics describes the drifting of the continents. 250 million yrs ago (end of Paleozoic) - a supercontinent called Pangaea formed (reason for the mass extinction) Pangaea began to break up at start of Mesozoic, causing geographic isolation of colossal proportions and by end of Mesozoic, the modern continents were beginning to take shape. Re-shaping continents affects the distribution Mass Extinctions Five mass extinctions have altered the course of evolution. The vast majority of species that have ever lived are now extinct. Mass extinctions occur when the global environment changes are so rapid and disruptive that 50% or more of Earth's species are eliminated in a short amount of time. Permian Extinction - widespread volcanic eruptions releasing CO2 to warmed climate, oxygen deficit in oceans, etc. (Formation of Pangaea) Cretaceous Extinction - presence of iridium and large crater (Chicxulub) support idea that a meteor struck the Earth (extinction of dinosaurs, etc)  Phylogeny & the Tree of Life (15.14 - 15.19) Taxonomy is the branch of biology concerned with identifying, naming, and classifying species Carolus Linnaeus devised a method of naming species and a hierarchical classifications scheme that put species within progressively broader groups Binomial Nomenclature assigned each species a two-part scientific name (Genus and Species) Taxonomy involves a hierachy with different taxons: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species Phylogenies based on homologies reflect evolutionary history The evolutionary history of a species is called phylogeny. Systematics, which includes taxonomy, is a discipline of biology that focuses on classifying organisms and determining their evolutionary relationships. Phylogenetict trees depict hypotheses about evolutionary histories. Morphological and molecular data is collected and analyzed Fossil evidence is analyzed Genes are homologous if they are descended from genes of a common ancestor Analogous features are not used since they represent convergent evolution (similarities due to simar environments) Cladistics In cladistics, orgnisms are grouped by common ancestry. A clade consists of an ancestral species and all its evolutionary descendants. Shared ancestral characters are common to members of a particular clade, but originated in an ancestor that is not a member of the clade Ex. All mammals have backgones BUT presence of a backbone does not distinguish mammals from other vertebrates Shared derived characters are common to members of a particualr clade and NOT found in ancestors. Ingroups and outgroups are established