Lecture 1 Flashcards
Explain fully where the earth started
- Earth and other planets formed about 4.6 billion years ago
- The earth cooled enough to form a crust 4.2 to 4.1 BYA. Surface temperature ranged from 500 to 1000deg Celsius
- Earth originally had primitive atmosphere
H2O, N2, CO2, H2 & CO were the gasses present. - It was a reducing atmosphere lacking free O2
- The geological time scale in the next slide gives us a good idea of when life started and when oxygen was introduced into the atmosphere.
What did the presence of O2 inhibit
Formation of complex organic molecules
What is the central idea of biological evolution
All life on Earth shares a common ancestor
What is speciation
- It is the splitting of one species in to two or more species, or the transformation of one species into a new species over time.
- It is the final result of changes in the in gene pool allele and genotype frequencies
- The one requires geographic isolation while the other one does not.
What are the 3 branches of speciation
- Parapatry
- Sympatry
- Allopatry
Explain natural selection in evolution
- The mechanism by which species change over time –some of this was discussed by Darwin
- Inheritance of acquired characteristics-Lamarck is a name that comes to mind
- This deals with modifications in an individual caused by its environment or disuse of a structure –it could be inherited by its offspring-causing a change in a species
eg ) Finches from Galapagos Archipelago
When can natural selection take place
- Natural selection can only take place if there is variation among individuals in a population.
- Genetic diversity in a population has two sources: Mutation and sexual reproduction
What are the patterns of evolution
- Divergent evolution
- Convergennt evolution
- Analogous evolution
Source of a mutation
- A mutation can affect the phenotype that may cause reduced fitness- resulting in fewer offspring.
- Mutation may produce a phenotype with a beneficial effect on fitness
- Neutral mutations that have no effect on fitness
Explain homologous structures
- Are related to each other through common descent but may differ in structure and function
e.g) the forelimbs of a horse and the wings of a bat
Explain analogous structures
- Have the same function but not derived from the same organ in a common ancestor
e.g. the wings of an insect and the wings of a bat
What does homology indicate
Species belong to related group
What is evolution
- The process that is responsible for the changes in characteristics of species and how new species arise
Explain parallel evolution
- Produces similar characters in related lineages without occurring in a common ancestor
Explain convergent evolution fully
- Similar biological traits evolves in two unrelated species as a result of exposure to similar environments. Eg Wings of birds and wings of bats
- Acquisition of similar trait in distantly related lines of descent as a result of adaptation to similar environmental conditions
Explain adaptive radiation
When a single ancestral species rapidly gives rise to a radiation of new species as each adapts to a specific environment
Eg ) The Galapagos finches
What is macroevolution
- Is part of the history of life on earth and involves speciation
- Speciation involves the splitting of one species into two or more species
What are the 3 concepts of species
- Morphological species concept
- Evolutionary species concept
- Phylogenetic species concept
Explain each of the 3 concepts of species
- Morphological species concept: Species identified on the basis of appearance or morphology
- Evolutionary species concept: Species differentiated on the basis a specific evolutionary pathway
- Phylogenetic species concept: A species is the smallest set of interbreeding organisms-usually a population, shares a common ancestor
What are reproductive isolating mechanisms
Two major operators that makes sure that species remain separate
Explain prezygotic isolators
- Habitat isolation
- Temporal – time differences in mating strategy
- Behavioural – courtship differences
- Mechanical – incompatible reproductive organs
- Gamete – gametes not able to form zygote
Explain postzygotic isolating mechanisms
- Prevents hybrid offspring from reproducing
- Zygote may be formed but hybrid zygote not able to undergo mitosis
- Hybrid zygote may develop into sterile adult. Gamete formation prevented during meiosis
- F2 fitness-offspring are fertile but F2 generation is sterile
Explain the cenozioc era
- This is the present era. Mammals diversified and human evolution commenced
- Three periods: Palaeogene and Neogene and Quartenary
- Mammalian diversification
- Evolution of Primates
Explain the paleozoic era
- Era lasted 300 million years
- All extant (living) taxa trace origins to Cambrium or earlier
- Richness due to development of external skeletons eg. Trilobites
Explain the precambrium
- History of life is divided into Eras, Periods, Epochs
- Oldest biological era is the Precambrium
- Lasted 87% of geological time
4.5 BYA - formation of Earth
3.5 BYA – Oldest known fossils
2.5 BYA – O2 accumulates in atmosphere
2.0 BYA – Oldest eukaryote fossils
1.4 BYA – Protists evolve and diversify
600 MYA – Ediacarian animals
543 MYA – Cambrium animals
Explain allopatric speciation fully
- Speciation by geographic isolation
- Something extrinsic to the organisms prevents two or more groups from mating with each other regularly, eventually causing that lineage to speciate.
- Isolation might occur because of great distance or a physical barrier, such as a desert or river.
Explain allopatric speication and gene flow
- Can occur even if the barrier is a little “porous,” that is, even if a few individuals can cross the barrier to mate with members of the other group.
- In order for a speciation even to be considered “allopatric,” gene flow between the soon-to-be species must be greatly reduced making mating impossible
Explain parapatric speciation fully
- No specific extrinsic barrier to gene flow.
- The population is continuous, yet population does not mate randomly.
- Individuals more likely to mate with geographic neighbours than with individuals in a different part of the population’s range.
- Divergence may happen due to reduced gene flow within the population and varying selection pressures aross the population’s range.
eg ) The grass species Anthoxanthum odoratum
Explain sympatric speciation
- Large-scale geographic distance not required to reduce gene flow between parts of a population.
- How? Ability to exploit a new niche may automatically reduce gene flow with individuals exploiting another niche.
Example, herbivorous insects try out a new host plant.
Explain examples of sympatric speciation
- Fish of lake Malawi – Fish in different parts of the lake evolved to become different species.
- They end up occupying different parts of the lake and feed on different types of organisms.
- Adaptive radiation through ecological release. Species evolve because of competition for food and resources
Explain autoploidy and allopdoidy in plants
- Autoploidy: small diploid seeded bananas produces diploid gametes because of nondisjunction. They would then produce a polyploidy which is sterile
- Alloploidy: Reproduction between two species of plants to produce a sterile hybrid. Doubling of this chromosome number produce a fertile 3rd species, that can only breed with itself.
Explain the factors influencing evolution
- Continental drift
The earth’s crust divided into tectonic plates that move because of seafloor spreading at ocean ridges - Mass extinctions
Caused by climatic changes after meteoric events and/or after continents drift into new positions - Domestication
Human induced selection of plants and animals (think of cattle, grains, dogs) - Vicariant events
Are speciationeventswhere a species’ distribution becomes segmented and the separated populations evolve due to different selecting factors, causing the populations to become unique species
Expalin examples of vicariant events
- The present day continental masses of Australasia, Antarctica, Africa, Madagascar, India and South America were once a great, single continent that geologists call Gondwanaland or Gondwana.
- Evidence of the Gondwanaland connection is still seen in some of the living flora and fauna of those land masses
