EVOLUTION BY NATURAL SELECTION 0
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Abstract
Grade 12 life sciences paper 2 notes on human evolution designed to help learners understand the
work revise effectively and prepare for tests and exams
(FISHIEFIRE)
NOTES4U
, (GRADE 12 LIFESCIENCE NOTES)
NOTES4U
© 2026 [NOTES4U]. All Rights Reserved.
This study material is protected by copyright. No part of this document may be reproduced, copied, distributed, resold,
uploaded, shared, modified, or redistributed in any form without prior written permission from the copyright owner.
For personal educational use only. Purchase of this document does not transfer ownership or reproduction rights to
the purchaser.
© 2026 [NOTES4U] | Grade 12 Human Evolution Notes | All Rights Reserved
, (GRADE 12 LIFESCIENCE NOTES)
EVOLUTION BY NATURAL SELECTION AND
HUMAN EVOLUTION.
- SUMMARY -
Evolution by Natural Selection
Origins of Ideas about Origins
Evolution refers to the process by which populations change over time, in response to a change in their environment.
Evolution can also be artificially induced, for example domestic dogs originated from the domestication of wolves.
Biological evolution: the process through which the characteristics of organisms change over successive generations, by means of genetic
variation and natural selection.
Population: a group of individuals of the same species that form a breeding unit and occupy the same habitat at the same time.
Evolution is often referred to as a theory.
Theory: an explanation of a phenomenon that can be tested using rigorous scientific methods at different times, in different locations and by
different people. Theories are not static. As new evidence becomes available, theories can be modified or changed.
Belief: an explanation for a phenomenon that is based on religious or cultural values and that is not usually supported by scientific evidence.
Hypothesis: a possible, or temporary explanation of a phenomenon, that can be tested using observations and/or experiments.
Evidence for Evolution
Palaeontology is the study of fossils. Millions of fossils have been found around the world. By recording the position of fossils in the geological
strata, palaeontologists are able to deduce the relative age of the fossils. The oldest rock strata are found deepest in the earth, whilst the
youngest rocks occur near the surface.
1. The fossil record
Homologous structures
• Structures or body parts that are similar in structure, but have different functions.
• Organisms that have homologous structures share a common ancestor.
Diagram of a generalized forelimb of all vertebrates, with limbs of selected vertebrates for comparison
© 2026 [NOTES4U] | Grade 12 Human Evolution Notes | All Rights Reserved
, (GRADE 12 LIFESCIENCE NOTES)
Analogous structures
Body parts of organisms that have the same function but differ in structure, e.g. a bird's wing and an insect's wing.
2. Modification by descent
Evolutionary scientists compare the anatomy of fossils, as well as the skeletons of living species, to identify trends in the adaptation of living
species.
The fact that all mammals have the same pentadactyl limb structure, suggests that all mammals are descended, or originated, from a common
ancestor and that the limbs have been modified over time in the different species.
Modification of skeletons by descent is further evidence to support the theory of evolution.
3. Biogeography
The effect of continental drift on biogeography is that it provides evidence for the evolution of ancient species.
Biogeography also provides evidence that many modern species have evolved from a common ancestor. The modern distribution of different
species of flightless birds suggests that they probably evolved from a common ancestor that was present before Gondwana split.
4. Genetics
Some of the strongest evidence for evolution comes from the study of Genetics. Through the sequencing of genes on DNA and RNA,
evolutionary geneticists are able to precisely map the relationships between different species. Species which have very similar sequences of
genes on their DNA or RNA will be closely related, while species which have very different sequences of genes will be distantly related.
The Graphical Representation of Evolutionary Relationships
The evolutionary relationships between different species can be represented on a phylogenetic tree (also called an evolutionary tree). An
evolutionary tree is a type of graph which represents the relationships amongst a particular group of organisms.
A cladogram is a type of phylogenetic tree that represents the relationships amongst species based on their genetic characteristics. Each split
on the cladogram represents the evolution of a new characteristic that is not present in the earlier species.
Variation
Variation refers to the differences in the genotype and phenotype amongst individuals of a particular species. Factors contributing to variation:
• Crossing over: During meiosis (prophase I) there is the exchange of genetic material between maternal and paternal chromosomes.
• Random arrangement of chromosomes during meiosis (metaphase 1 and 2).
• Random fertilisation: Differences in genetic makeup of sperm and ova will result in zygotes (and offspring) having different genetic make-up.
• Mutation: Changes in gene/chromosome structure result in a different genotype of an organism which influences the phenotype of the
organism.
• Random Mating: Random Mating between organisms within a species results in a different set of offspring from each mating pair.
Variation types
• Discontinuous variation refers to variation of particular characteristics that occur as discrete classes, for example: blood type.
• Continuous variation occurs when phenotypes are determined by multiple genes, for example, height and skin colour.
Evolution tends to occur more quickly when natural selection affects those responsible for discontinuous characteristics than those responsible
for continuous characteristics.
A Brief History of the Theories of Evolution
1. Lamarckism
Jean-Baptiste Lamarck believed that individual organisms had the ability to change their appearance and that these changes would also occur
in any offspring they produced. Lamarck proposed two “laws” to explain how these changes caused species to evolve.
I) The Law of Use and Disuse
The parts of the body that are used regularly will become better developed, while the parts which are not used will shrink and may disappear
altogether in the offspring.
II) The Law of Inheritance of Acquired Characteristics
The characteristics acquired by an organism during its lifetime are passed on (or inherited) by its offspring. (He used the giraffe's long neck to
explain.)
Lamarck's two “laws” have been rejected by evolutionary biologists because there is no scientific evidence to prove either of them. His
explanations are incorrect.
© 2026 [NOTES4U] | Grade 12 Human Evolution Notes | All Rights Reserved
SCAN FOR MORE NOTES
(GRADE 12
LIFESCIENCE NOTES)
(Grade 12 Human Evolution- Complete
summary & Exam notes)
Abstract
Grade 12 life sciences paper 2 notes on human evolution designed to help learners understand the
work revise effectively and prepare for tests and exams
(FISHIEFIRE)
NOTES4U
, (GRADE 12 LIFESCIENCE NOTES)
NOTES4U
© 2026 [NOTES4U]. All Rights Reserved.
This study material is protected by copyright. No part of this document may be reproduced, copied, distributed, resold,
uploaded, shared, modified, or redistributed in any form without prior written permission from the copyright owner.
For personal educational use only. Purchase of this document does not transfer ownership or reproduction rights to
the purchaser.
© 2026 [NOTES4U] | Grade 12 Human Evolution Notes | All Rights Reserved
, (GRADE 12 LIFESCIENCE NOTES)
EVOLUTION BY NATURAL SELECTION AND
HUMAN EVOLUTION.
- SUMMARY -
Evolution by Natural Selection
Origins of Ideas about Origins
Evolution refers to the process by which populations change over time, in response to a change in their environment.
Evolution can also be artificially induced, for example domestic dogs originated from the domestication of wolves.
Biological evolution: the process through which the characteristics of organisms change over successive generations, by means of genetic
variation and natural selection.
Population: a group of individuals of the same species that form a breeding unit and occupy the same habitat at the same time.
Evolution is often referred to as a theory.
Theory: an explanation of a phenomenon that can be tested using rigorous scientific methods at different times, in different locations and by
different people. Theories are not static. As new evidence becomes available, theories can be modified or changed.
Belief: an explanation for a phenomenon that is based on religious or cultural values and that is not usually supported by scientific evidence.
Hypothesis: a possible, or temporary explanation of a phenomenon, that can be tested using observations and/or experiments.
Evidence for Evolution
Palaeontology is the study of fossils. Millions of fossils have been found around the world. By recording the position of fossils in the geological
strata, palaeontologists are able to deduce the relative age of the fossils. The oldest rock strata are found deepest in the earth, whilst the
youngest rocks occur near the surface.
1. The fossil record
Homologous structures
• Structures or body parts that are similar in structure, but have different functions.
• Organisms that have homologous structures share a common ancestor.
Diagram of a generalized forelimb of all vertebrates, with limbs of selected vertebrates for comparison
© 2026 [NOTES4U] | Grade 12 Human Evolution Notes | All Rights Reserved
, (GRADE 12 LIFESCIENCE NOTES)
Analogous structures
Body parts of organisms that have the same function but differ in structure, e.g. a bird's wing and an insect's wing.
2. Modification by descent
Evolutionary scientists compare the anatomy of fossils, as well as the skeletons of living species, to identify trends in the adaptation of living
species.
The fact that all mammals have the same pentadactyl limb structure, suggests that all mammals are descended, or originated, from a common
ancestor and that the limbs have been modified over time in the different species.
Modification of skeletons by descent is further evidence to support the theory of evolution.
3. Biogeography
The effect of continental drift on biogeography is that it provides evidence for the evolution of ancient species.
Biogeography also provides evidence that many modern species have evolved from a common ancestor. The modern distribution of different
species of flightless birds suggests that they probably evolved from a common ancestor that was present before Gondwana split.
4. Genetics
Some of the strongest evidence for evolution comes from the study of Genetics. Through the sequencing of genes on DNA and RNA,
evolutionary geneticists are able to precisely map the relationships between different species. Species which have very similar sequences of
genes on their DNA or RNA will be closely related, while species which have very different sequences of genes will be distantly related.
The Graphical Representation of Evolutionary Relationships
The evolutionary relationships between different species can be represented on a phylogenetic tree (also called an evolutionary tree). An
evolutionary tree is a type of graph which represents the relationships amongst a particular group of organisms.
A cladogram is a type of phylogenetic tree that represents the relationships amongst species based on their genetic characteristics. Each split
on the cladogram represents the evolution of a new characteristic that is not present in the earlier species.
Variation
Variation refers to the differences in the genotype and phenotype amongst individuals of a particular species. Factors contributing to variation:
• Crossing over: During meiosis (prophase I) there is the exchange of genetic material between maternal and paternal chromosomes.
• Random arrangement of chromosomes during meiosis (metaphase 1 and 2).
• Random fertilisation: Differences in genetic makeup of sperm and ova will result in zygotes (and offspring) having different genetic make-up.
• Mutation: Changes in gene/chromosome structure result in a different genotype of an organism which influences the phenotype of the
organism.
• Random Mating: Random Mating between organisms within a species results in a different set of offspring from each mating pair.
Variation types
• Discontinuous variation refers to variation of particular characteristics that occur as discrete classes, for example: blood type.
• Continuous variation occurs when phenotypes are determined by multiple genes, for example, height and skin colour.
Evolution tends to occur more quickly when natural selection affects those responsible for discontinuous characteristics than those responsible
for continuous characteristics.
A Brief History of the Theories of Evolution
1. Lamarckism
Jean-Baptiste Lamarck believed that individual organisms had the ability to change their appearance and that these changes would also occur
in any offspring they produced. Lamarck proposed two “laws” to explain how these changes caused species to evolve.
I) The Law of Use and Disuse
The parts of the body that are used regularly will become better developed, while the parts which are not used will shrink and may disappear
altogether in the offspring.
II) The Law of Inheritance of Acquired Characteristics
The characteristics acquired by an organism during its lifetime are passed on (or inherited) by its offspring. (He used the giraffe's long neck to
explain.)
Lamarck's two “laws” have been rejected by evolutionary biologists because there is no scientific evidence to prove either of them. His
explanations are incorrect.
© 2026 [NOTES4U] | Grade 12 Human Evolution Notes | All Rights Reserved
