| 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 |
