This aesthetic, in-depth, neatly typed document summarises 4.1 of strand 4 (Evolution) of the IEB grade 12 mind action series textbook: Origin of an idea about origins. It includes the full 4.1 Origin of an idea about origins syllabus as well as additional class notes, own research notes and all re...
- Australopithecus Africanus & Homo Ergaster - Sterkfontein caves & Cradle of Mankind
Origin of an idea about origins:
Evolution: Gradual change in gene pool of population due to mutation, natural selection and genetic
drift (descent with modi cation)
• Micro-evolution: evolution within a species
• Macro-evolution: Descent of di erent species from common ancestor
Mechanisms of evolution: Human-driven evolution:
• Natural selection - Arti cial selection
• Polyploidy - In and out breeding eg. dogs, crops
• Gene ow
• Genetic drift
• Mutations
, Erasmus Darwin: (1731 - 1802)
• Proposed that all life descended from common ancestor and that species have changed over time
Jean-Baptiste Lamarck: (1774 - 1829)
• Concluded that:
- Living species are di erent to fossils, therefore life forms changed
- Domestication and selective breeding resulted in animals & plants changing
- Cross-breeding of plants led to new characteristics
• Suggested that organisms changed in order to survive in new environments and that these
acquired changes were passed to o spring. How change took place:
- Use and disuse of body parts
- Inheritance of acquired characteristics (through use & disuse)
- eg. long neck of gira e (he believed it grew longer as trait was passed onto o spring over
generations)
- Hypothesis was incorrect (phenotypic changes don't altar genotype of egg or sperm cells)
Charles Darwin: (1809 - 1882)
• Realised that:
- Earth is very old = time for species to evolve
- Has been great geological change over time
- Isolation leads to species changing
• Published book: 'The Origin of Species'. Explained 2 hypotheses:
- Descent with modi cation (evolutionary change)
- Natural Selection (Individuals best adapted to environment will survive)
• Darwin's explanation of descent with modi cation:
- All related organisms come from common ancestor
- Ancestral species spread into new habitats & adapted to new conditions = new species
- Diversi cation was by branching
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