LF263 Evolution L1-3
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| 🇬🇧 | 🇬🇧 |
| What did people believe at the time of Darwin? | Immutability of species and Neutral Theory. |
| What is evolution and why people think it did not occur? | Evolution is organism change by descent over time; needed to explain: complexity, similar /same species occurring in the same area and how species cannot interbreed |
| Darwins Arguments | Uniformity, Sequence, Consilience and Discordance |
| Variation under Domestication | -Each domesticated species come from a single wild species -Cannot cross true breeds to produce a stable new breed -We produce new races by crossing the same races. |
| Variation under Nature | -Species definition is problematic -Variation occurs in every part of an organism -intraspecific variation is important |
| Struggle for existence | The tendency for geometric expansion through reproduction for all species. Without check they would over run the planet in a very low number of generations; ergo they are in check |
| Natural Selection | The Preservation of favourable variations and the rejection of injurious variations |
| Conditions of Selection | -Large population -Rapid Reproduction -Locally restricted -Isolated |
| Diversions of Character | -Divergence allows new niches to be occupied -Ancestral forms are quickly extinct -Australia is a poor example of diversification |
| Laws of variation | -Law of compensation -Correlation of growth effects of disuse -Analogous variation between related species -Traits in one species will show greater variation than the rest of the genus, because NS(natural selection) still in action |
| Why are species discrete? - Difficulties on theory | -Intermediate forms are outcompeted -More of a problem with hybrid zones |
| Intermediate zone | It is a small zone that cannot produce variants quickly, therefore no intermediate variant becomes established. |
| Large transitions in habitat - Difficulties on theory | -Transition from land to water is minor to explain -Flight is a real problem - no transition allied species -Organs of extreme perfection |
| Instinct | Involved just like organs |
| Hybridism | 2 Categories of sterility: -When species are first crossed, - sterility of hybrids Animals are generally less interfertile No line between the end and start of new species |
| Imperfection of fossils | -Fossils are laid down by specific circumstances -Land loss is a time of extinction -Immigration and emigration can look like extinction and speciation -New forms are likely to be highly fecund and locally restricted |
| Geological Succession of Organic Beings | -Forms of life changed in the world; New World forms resemble European fossils more than extant European forms -Fossils connect ancient lineages to the rest of life -Fossils should approach one another in similarity away from extant forms -Intermediates should occur in mid succession -Later forms should be more developed - Similar fossils and extant forms occur in same areas |
| Geographical Distribution | -Similar climates have different faunas -Barriers correspond to abrupt fauna changes -Niches are filled in parallel in different areas by different species -Disjunct species distributions explained by migration |
| Means of dispersal | -Climate can open close migration routes -Islands are a big problem because they are isolated -Glacial periods are important, contribute to isolation and many doubtful forms and varieties can be seen |
| Geographic distribution Pt2 | -Fewer species on oceanic islands -Endemics explained by isolation -Poor competitors relative to continental invaders -Remote islands deficient in classes - niches with atypical groups |
| Classification: morphology | -Features that are external and adaptive were considered important for classification -Adaptive resemblances give false unity -Aberrant species sit on the end of many extinct intermediates -Use "unity of type" |
| Classification: embryology | -Ancestral forms are present at embryonic stages |
| Classification: rudimentary organs | -Tend to be larger in embryos because of weakness of selection at that stage -Their existence is useless, imperfect and waste |
| What did Darwin Achieve? | - Show species wee not separately created -Natural Selection was the main agent of change |
| 3 alternatives to Darwinism | Lamarckism Saltation Orthogenesis |
| Lamarckism | -Variation was directed -Soft inheritance -Mechanism of adaptation -Popular until genetics rise |
| Orthogenesis | -By William Haacke -Formalist approach to explain embryological development -Variations are directional -Species may be doomed to extinction |
| Saltation 1 | -Francis Galton -Believer of NS -Did not accept that variations need to be small, larger will be more effectively selective -Eugenics |
| Saltation 2 | -William Bateson -Env. variation is continuous -Species are discontinuous, and so change |
| Saltation 3 | -Hugo de Vries -Believer of NS -Larger mutations were selected for and responsible for speciation -Rediscovered Mendel's Laws |
| Hardy-Weinberg Equilibria | -Calculate the expected genotype proportions -The resultant p and q show that do not change from gen to gen -Variation is preserved under particulate inheritance |
| Modern Synthesis | -Phase 1: The fusion of Mendelism and Darwinism -Phase 2: The linking of subdisciplines of biology |
| 1st Strand | -RA Fisher -Darwinism requires a particulate inheritance to work -Large mutations are deleterious -Rate of increase fitness = its genetic variance |
| 2nd Strand | -JBS Haldane -Different species have no adaptive significance -introduced Pluralism -Mutations lead to loss of complexity - didn't have to be small |
| 3rd Strand | -JS Huxley -Pluralist -NS is a major force |
| 4th Strand | -S Wright -Evolution in Mendelian pop. -Genetic drift important for pop. -Adaptive landscapes -Basis of genetics |
| Neo-Darwinism | -Hereditary variation of discontinuous characters is due to particulate genes -Small differences in reproductive fitness can bring evolutionary change -Selection can maintain genetic variation in a pop. -NS is a major force of change |
| Hardy-Weinberg Assumptions | -Panmixis -No selection -Pop. not at equilibrium, then 2 assumptions have been broken |
| Genetic Drift | -More pronounced in small populations and its effects are rapid -small pops are carrying less diversity -Drift removes variation |
| Wright’s fixation indices (Fst) | -To measure structure -Fst gives a measure of how differentiated populations are: range from 0-1 -When a pop is fractured into subpopulations, the heterozygosity decreases -Fst = 1/ (1+4Nm) |
| Inbreeding | -Reduces heterogenicity but allele frequencies are unaffected -F = (Ho-H1) / Ho |
| Founder effects | -The founding of a new population by very few individuals representing fraction of the genetic variation of the source population - Can lead to high frequencies of unexpected genotypes -Proposed as a mechanism for speciation |