Evolution Summary

EVOLUTION SUMMARY EVOLUTION DEFINITIONS   Essentialism (stasis) The concept that a species is immutable and merely an imperfect copy of a superior ideal. Two coexisting worlds- perfect world (intellect), imperfect world (senses). A view by Plato (427-347BC) Teleology Belief in a divine order and purpose to life. All things can be arranged in a hierarchy from simple à complex. Look at final causes not efficient causes. A view from Aristotle (384-322BC) Metaphysic view Belief in something other than what we experience. Catastrophism The theory that the major changes in the earth’s crust are due to catastrophic events rather than gradual change (ie biblical flood)- Georges Cuvier Gradualism The theory that changes in the earth arise from gradual changes- accumulation of slow continuous processes. (this conflicted with age of earth- biblical views). (ie new species arising from ancestral species by gradual accumulation of genetic changesà continuity from micro to macro) Uniformatarism The earth is very old. Geological processes occur today in much the same way as they did in the past. Transformism Organisms arise spontaneously from inanimate matter by spontaneous generation then evolve to greater complexity along the Scala Naturae. Evolve according to the changes in environment. Inheritance of acquired characteristics depends on use or disuse by parents. Darwins theory 05 principles of natural selection- influenced by particular people. 01. Organisms beget like organisms. 02. Surviving offspring < original produced. 03. Chance variation. 04. Favourable characteristics, increase survival, more likely to be passed on. 05. Accumulation of characteristics à speciation. Didn’t explain the mechanism for hereditary (04 points) Natural selection Inherited favourable variation tends to become more common from one generation to the next. Differential reproduction of genotypes resulting from interacting between individual organisms and their environments. The phenotype is selected Hypothetico-deductive method Modern scientific method. Not experimental rather observational. Facts à hypothesis à further observations à refute or accept. Adaptive change Transition of form Origin of Species Darwin’s notebook- began in 1837- published in 1859. Artificial selection The process horticulturists and animal breeders choose which individuals would be represented in the next generation (this can show natural selection at work. Heritable characteristics and variation within species) Microevolution Altering individuals within a species. Below the level of species. Population change, genetic drift, genetic diversity, recombination, mutation Macroevolution Above the level of species or speciation. Biogeography, diversity and abundance of species, fossil records (Darwin believed showed continuity and descent with modification), homologous characteristics, adaptation Biogeography The geographical distribution of species. Eg endemic plants between S America and Africa à oceanic currents, plate tectonics, continental drift. Homologous structures Structures that are a result of common ancestry. Same structure, different function (generally). Eg vertebrate forelimb Phylogeny Evolutionary development and history of a species. Common ancestry. Phylogenetic classification takes into account the similarities that are homolgous. Convergent evolution Two species become alike due to same environment. Not necessarily homologous structures. Ontogeny Origin and development from fertilized egg to mature form. Imperfect adaptation Eg. Whale tiny pelvis and femur. Retained homologous structures, not hindering survival. Vestigial organs Rudimentary structures with little or no use to an organism Atavism Occasional expression of a characteristic that was thought to be lost in the phylogeny- due to development abnormality (ie dolphin rear flippers) Evolution The change of allele frequencies over time. Trait heritable, there must be variation within the population and environmental change (selection pressures). Population is the unit. Pops evolve not individuals Blending inheritance Darwin believed inheritance was a result of blending of parents bloods. No mechanism for recovering parental types or spread of favourable traits. Mendel’s theory Inheritance of a trait through genes, passed on to offspring unchanged, one from each parent, a recessive trait may not show up in an offspring but can still be passed onto next generation. Particulate inheritance Basis of Mendel’s theory The Modern synthesis Medellin genetics and Darwinian theories reconciled. (05 principles) 01. Genetic variation arises à mutation, recombination. 02. Genetic evolution influenced by natural selection as well as gene flow and random genetic drift. 03. Adaptive genetic variation à small stepwise changes in phenotypes 04. Divergence of geographically isolated populationsà speciation. 05. Gradual accumulation of genetic differences à new taxa above level of species. Population genetics The process of change in allele frequency in a population or gene pool Population An interbreeding group of organisms (ie of same species), defined and united by the gene pool (same area) Species (Biological species concept) A group of populations that actually or potentially interbreed in nature and produce fertile, viable offspring are reproductively isolated from other populations Hardy Weinberg equilibrium Non evolving populations. 01. No mutation. 02. No migration/gene flow. 03. No genetic drift.(pop large enough that chance events alone won’t alter gene freq) 04. Mating is random/panmictic 05. No difference in reproductive success, no selection. P + q = 1. p2 + 2pq + q2=1 Polygenic variation Many morphological characteristics are influenced by multiple genes (additive effect, co dominant genes, ie skin colour, 7 phenotypes, 3 loci) enviro + polygenes= continuous variation. Agents of change (other than natural selection) Mutation, Sexual selection (3n (number of unlinked allele pairs) number of recombination events possible), Inbreeding, diploidy, the recessive refuge, Outbreeding, heterozygote advantage, genetic drift, gene flow. Mutation Random changes in an organisms DNA. If in gametes à changes in allele frequency. Recessive refuge Protect deleterious alleles. Due to diploidy sheltering rare recessive alleles. Can never eliminate aa (a allele still present in Aa) Inbreeding Breeding with closely related individuals. Loss of variation. Increased homozygosity, decreased heterozygosity. (2n (n number of generation years)= how closely related) Inbreeding depression Inbreeding results in decreased reproductive success and increased susceptibility to diseases. (common among small captive populations or those that have experienced a population bottleneck) Heterozygote advantage The heterozygote is selected for above either of the homozygote’s if it is superior (promotes variability). Recessive alleles, even those that are fatal in the homozygous state are sometimes selected for, for the heterozygote. Heterosis or Hybrid vigour Result of heterozygote superiority or the masking of the effects of recessive alleles (opposite effect of inbreeding depression) Outbreeding depression Traits not compatible from parents à deleterious Genetic drift Random change in allele frequency due to chance events. Population bottleneck, founder effect (small groups of populations established from one, ie leave) Gene flow Movement of alleles in or out of a local gene pool. May introduce new alleles or alter the allele frequency. Can counteract natural selection and tends to maintain variation and similarity of allele frequency. Sexual selection Another form of selection which is the result of competition for a mateà elaborate mating displays and sexual secondary characteristics. Monogamy (little dimorphism), strongest in polygamous mating systems. Sometimes even opposes natural selection. Female preference can result in extreme ornamentation. Intersexual competition Between the sexes. Eg male tail length to attract females Intrasexual competition Within the sexes. Eg epaulets to intimidate males. Polygamous Polyandry- one female, many males. Polygyny- one male, many females Monogamous One male, one female Promiscuous Whatever Clines (microevolution evidence) Gradual variation that follows a geographical distribution, ie gradient (within species- result of natural variation) at the level of microevolution. Eg altitudinal clines Ecotypes (microevolution evidence) Distinct groups of phenotypes (eg cultural specialisation) same species. Microevolution. Genetically distinct as a result of cultural isolation. Eg killer whales. Can result in reproductive isolation eventuallyà incipient speciation Coevolution (macroevolution evidence) Is the result of selective forces exerted by the interaction between species. Eg predator prey Convergent (macroevolution evidence) Is where unrelated species come to resemble each other in some attribute, due to adaptation to similar selection pressures rather than by common ancestry. Doesn’t have to be geographically overlapping Divergent evolution (macroevolution evidence) Related populations become dissimilar sometimes leading to the formation of a new species. Adaptive radiation Is the rapid formation of many new species from a single ancestral group characteristically to fill a new ecological zone. (macroevolution evidence for speciation) Mullerian Mimicry When two or more harmful species, that are not closely related mimic each other’s warning signals (coevolution- ‘cooperation’) Batesian Mimicry When a harmless species has come to resemble the warning signals of harmful species directed a common predator (coevolution- ‘cheating’) absence of mimicry in allopatry is consistent with coevolution (not convergence). Mimicry as a result of adaptation to a common environment- sympatric (eg nocturnal and diurnal moths) = convergence Allopatry Most common mode of speciation. Occurs through geographical isolation Dispersal A form of allopatry. Chance movement to new habitats. Parent species stay put. Vicariance A form of allopatry. A geographical disruption of distributions. Eg mountains and rivers etc Speciation A new species forming. Through allopatry and sympatry and RIM’s. Genetic differences + mutations, different selection pressures à genetically isolated à can’t interbreed. Sympatry Less common mode of speciation. Occurs if gene flow is reduced between members of species due to polyploidy, disruptive selection and sexual selection. Since there is no geographical barrier, reproductive isolation occurs through genetic or social isolating mechanisms. Polyploidy A form of speciation. More common in plants. An increase in the genome number often coupled with hybridization. No longer can breed with the parent species. Autopolyploidy- same species. More than 2 chromosome sets. Allopolyploidy- Different species. Fertile polyploids can mate with each other but not with parent species Disruptive selection A form of sympatry. More common in animals. Not as common. Preferential mating, habitat differentiation causing genetic discontinuities. Pre zygotic isolating mechanisms Pre-fertilization- Preventing the chance of fertilization occurring in the first place. Spatial- habitat isolation, populations don’t meet. Temporal- mating/flowering occurs at different times of day etc. Behavioural- Courtship, rituals, other behavioural that attracts a mate of same species. Mechanical- Structural differences in genitalia. Gametic- sperm from one species can’t fertilize egg of the other. Gametes are inviable. Post zygotic reproductive isolating mechanisms Post-fertilization. Prevents the hybrid zygote from developing into a viable, fertile adult. Reduced hybrid viability- Genes of different parent species may interact so that hybrid can’t survive or reach sexual maturity. Reduced hybrid fertility- Hybrid may be sterile due to different chromosome numbers eg mules. Hybrid breakdown- First generation is fertile but if they mate with each other or the parent species then the second generation is sterile/feeble. Phyletic change (anagenesis) Gradual, apparently directional change within a single lineage over time, at the Microevolutionary level. (macroevolution evidence for speciation) Cladogenesis Evolutionary change produced by the branching off of populations from each other to form new species. Responsible for diversity. (macroevolution evidence for speciation) Extinction Disappearance of a species from the earth. Low steady rate of extinction interrupted periodically by mass extinction. 5 mass extinctions, most recent at end of age of dinosaursà adaptive radiation of mammals. (macroevolution evidence for speciation) Punctuated equilibrium New species appear in bursts of rapid speciation among small populations. This new species displaces many of the then existing species- ie they become extinct. These then persist for long periods with little change, and then in turn abruptly become extinct. (macroevolution evidence for speciation) Challenged Darwins view that macroevo is gradual Evolutionary systematics Seeks to construct hierarchical groupings of species that reflect their phylogeny (evolutionary history) Taxonomy Discovering, describing and naming organisms Ancestral characteristics Sometimes called primitive. Characteristics inherited with little or no change from remote ancestors Derived character Undergone recent change and may be shared only by closely related species or taxa Analogous structures Structures that have the same function due to adaptation to a similar environment rather than common ancestry (convergent evolution) Traditional taxonomy Relied primarily on morphological similarities and often ranks taxa according to evolutionary grades of anagenic Cladistics The most widely accepted methodology, is based entirely on branching relationships (clades), determined by shared evolutionary novelties (shared derived character states) and ignores overall similarities (ancestral characteristics) Monophyletic Every taxon should consist only of organisms derived from a common ancestor. Cladistics emphasizes this. Polyphyletic Two species derived from different immediate ancestors Paraphyletic Includes some but not all of the species of a common ancestor Grades Groups which have evolved new abilities or organization. From a common ancestor but also share common features however distally related they are to each other. Eg fish are a grade Clades Groups including only monophyletic branching events eg fish can’t be a clade because land mammals also descended from fish. Prosimians (primate) Include bush babies, tarsiers, lemurs and lorises Anthropoids (primate) New world, old world monkeys, and hominoids (apes and humans) Hominins Species more closely related to modern humans than chimpanzees (closest living relative to humans)- The upright walking ape Multiregional hypothesis Also called the candelabra hypothesis. Proposed that geographically distant populations of archaic humans linked by gene flow slowly evolved into modern humans over the last 700,000 or more years. Anagenesis The eve hypothesis Also Noah’s ark model. Proposes that modern humans originated in Africa less than 200,000 years ago and spread rapidly through Europe and Asia replacing the Neanderthals and other archaic humans. Supported by mitochondrial DNA sequences (all living individuals descended forma common maternal ancestor that lived some 200,000 years ago) Cladogenesis. Mass extinction (05 main ones) 65 million years ago asteroid/comet hit earthà destroyed half the life on earth, spread of soot and charcoals (floods, tsunamis, cold and darkness, acid rain) extinction of masters of the animal kingdom, the dinosaurs as well as 70% of species. Mammals explosive phase of evolution and eventually humans arose. Was speciation gradual or punctuated? 01. Silurian extinction (first jawed fish) 02. Carboniferous extinction (first reptiles) 03. Triassic extinction (first dinosaurs) 04. Jurassic extinction (first mammals) 05. K/T extinction (mammals radiate) Extra-terrestrial evidence for end of dinosaurs 01. Iridium layer anomaly 02. Laminar de-formation of quartz grains 03. Basaltic spherules Backs up catastrophism. Mechanism responsible for punctuated equilibrium?     Famous evolution scientists   Plato 427-347BC Essentialism Carolus Linnaeus 1707-1778 Still believed in essentialism and teleology. Sought to better organise the diversity of life- Systema Naturae Impacted our scientific Latin binomial nomenclature system (his was morphologically group not evolutionary). Swedish Naturalist Aristotle 384-322 BC Believed in Teleology. Created Scala Naturae (the great chain of being), accepted essentialism. Copernicus (1473-1543), Galileo (1564-1642), followed by Newton and Descartes Physical sciences- replaced teleological views for the purpose for which events to occur with efficient/material causes which are the mechanisms for which events occur. Eg gravity replaces faith. Georges Cuvier 1769-1832 Fossil record. Despite fossils and extinction he believed in fixity of species and so thought they corresponded with catastrophes rather than evolution- Catastrophism James Hutton 1726-1797 believed in gradualism- changes occurred over time and can be observed today Charles Lyell 1797-1879 Expanded on Hutton’s ideas of gradualism in his book ‘Principles of Geology’- Darwin took this book on the beagle- highly influenced. Thomas Mathus  Essay on principles of population- human growing= shortage of food and limited resources Jean Baptiste Lamarck 1744-1829 Transformism. First systematic theory of evolution Mendel described inheritance/hereditary with his pea plant experiments Julien Huxley- Modern Synthesis         Whale summary: -First though whales (cetaceans) were most closely related to extinct group mesonychians (carnivous hooged mammals) and that these were both related to the artiodactyls (even toed hoof mammals) -Actually closes relatives are in fact the hippos (an artiodactyls) -Similarities of the mesonychids and cetaceans are the result of convergence not homology.     Hominins 3.6-1.4 mya A. afarensis, A. africanus, A. robustus, A. boisei and Homo. habilis. A. afarensis 3.6 mya Laetoli footprints, lucy A. africanus   Skull, ape like but upright walking. Proposed ancestor of modern humans. Expected it to have a larger brain. Early models of hominin evolution emphasized anagenesis, but as more fossils have accumulated cladogenesis is emphasized H. erectus 1.6mya-300,000ya Tall, skeletons represent those of modern humans, heavier skulls, flattened crania, heavy brows, large teeth and jaws and a sloping chin. Used stone tools. Had fire. H. Neanderthalis 350-500,000-30-35,000ya Fire, caves, hunted large animals, clothing, buried dead. Disappeared about 28,000ya (replacement by modern humans) H. sapiens sapiens (cro-magnons)   Anatomically modern humans, appear to have replaced Neanderthals, improved tools and weapons and highly developed symbolic representation. H. Floresiensis Up till 12,000ya H. erectus crossed land bridges from Asia to Java at least 1.5million years ago.     Cheetah summary- microevolution, population bottlenecks: -Originally 4 species and 4 subspecies distributed around Europe, Asia and Africa in the Pleistocene and Pliocene eras. Only one monophyletic cheetah species survivedà limited to Africa. Also 75% of all large mammals in North America, Europe and Australia abruptly become extinct. Environmental change? Epizootics? Human hunting pressure? -Reduced levels of genetic variation (ie MHC gene). Showed ancestors had intensive period of inbreeding due a population bottleneck. Lack of variation 90-99% à physiological impairments, spermatozoa, decreased fertility, high infant mortality, increased sensitivity to diseases.