This summary contains all the necessary information for Evolution (Darwinism, Lamarckism, Natural Selection, Artificial Selection, etc.)
Part 2 will contain information regarding Human evolution (different species & fossils).
For National Senior Certificate (NSC) Grade 12 Biology (Life Science)
EVOLUTION (part 1)
Evolution Permanent genetic changes in a population through consecutive generations,
over billions of years, due to natural selection.
• All organisms are genetically related
• Common ancestor
• Develop from simple to complex
• Happens to populations, not individuals
Biological evolution Changes in a gene pool over time. Indicates modification in offspring.
Evolution is a scientific theory
Hypothesis Possible solution to a problem/question
• provisional explanation to be proven by observations
• Accepted or rejected
Theory Explains a natural phenomenon with reliable evidence gathered through
experiments. Supported by facts, generalizations, pas hypotheses, models
and laws.
PROOF OF EVOLUTION:
1. Fossil record
• Structural evidence
• Indicates order of evolution
• Incomplete (due to fossils not forming easily)
o Due to decay and the high pressure needed to form fossils
Proves 3 things:
a. Simple organisms developed into more complex
• Fossils found in stone. (simple in oldest & complex in newer
layers)
b. Variety increased over time
• Older rock layers have less biodiversity
• Newer have more
• Proves newer organisms come from common ancestor
c. One group developed from another
• Transitional fossils have mixture of traits from different groups.
2. Changes in offspring
a. Homologous structures
• More related = more homologous structures. Proves common
ancestor.
• Body parts change over time, e.g. Wing in bird and arm in human
– both look the same but have different functions.
b. Species change when environment changes
• New species form due to environmental pressure
• Wrong phenotype = become extinct
3. Biogeographical evidence
• Study of where and why species exist in certain areas.
• Related species come from the same region
o E.g. The common ancestor of ostriches, emu’s, etc. comes from
Gondwanaland. Exist on different continents due to continental drift.
• Speciation = due to continental drift & climate change
Christiaan de Beer (2018)
, 4. Genetic evidence
a. Proves common ancestor
• All organisms have DNA and RNA
• Some have similar genes
b. Organisms are related when the following is in common:
• DNA-structures
• Similar nucleotide sequences
• Similar non-coding DNA
• Similar mitochondrial DNA (mtDNA) mutations.
o more mutations = older species.
5. Cultural evidence (not necessary to know for exam)
• Weapons / tools / language.
VARIATION:
Population Group of organisms from the same species, at a certain time, that lives in an
enclosed area and can reproduce freely.
Species Group of organisms that look/are similar and can reproduce successfully by
producing fertile offspring.
Sources of variation:
1. Crossing over (Prophase I)
• Exchange of genetic material leads to new combinations in each gamete
2. Random alignment(Metaphase I and II)
• Creates new combinations of chromosomes
3. Random fertilization
• Different ovums & sperms leads to different offspring
4. Random mating
• Leads to different offspring
5. Mutations
• Leads to variety in genotype & phenotype
Continuous variation A range of variations with intermediate phenotypes of each
characteristic due to many combinations caused by many genes with
different alleles.
Discontinuous variation A few variations of each characteristic without intermediates
due to combinations caused by a few alleles on only 1 gene.
Evolution theory:
Natural selection is the mechanism of evolution
• Environment puts pressure on organisms
• Genetics determine the phenotype
• Individuals with the right phenotype reproduces and carries over the right
genes.
• Individuals with the wrong phenotype dies and the genes vanish from the
gene pool.
• Therefore influenced by Environmental pressure & Variation
Christiaan de Beer (2018)
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