EVOLUTION NOTES
Evolution is the gradual change or development of something.
(It can be used in various senses in social or economic structures and general use).
GRADE 10 REVISION:
• Universe started 13.7 bya (Big Bang Theory).
• The earth is very old – 4550 million (4.6 billion) years old.
• Earth’s crust has been built up in layers over millions of years. The layers have been
successfully laid down by either water (sedimentary rocks) or by volcanic activity (volcanic
rocks). Each layer is therefore of a different age, oldest layers at the bottom.
• Dating of fossils – relative dating and radiometric dating (absolute dating) can determine the
age of a rock layer, and therefore the age of fossils embedded in that rock.
• By studying fossils one:
▪ Learns about ancient forms (eg: trilobites), and the appearance and extinction of
organisms, from individual species to whole taxonomic groups (eg: the dinosaurs).
▪ Understands that life-forms changed ad gradually became more similar to present-
day life-forms.
▪ Gains evidence to support the idea that species change, ie: have undergone
evolution.
• South Africa is very rich in fossils with some important finds, for example:
▪ Stromatolites (cyanobacteria) in Barberton.
▪ Glossopteris ferns in KZN.
▪ Coelacanth.
▪ Mammal-like reptiles in the Karoo.
▪ Humankind’s earliest direct ancestors – Australopithecus africanus and Homo
ergaster.
▪ New find: Homo Naledi.
BIOLOGICAL EVOLUTION (descent with modification):
Change in the gene pool of a population during the course of time due to processes such as
mutation, natural selection, and genetic drift.
Why is it important that we study biological evolution?
• It is the unifying concept that acts as a foundation for understanding Biology.
• It supports and explains many aspects of everyday lives.
• It challenges people to think for themselves.
,EVIDENCE FOR EVOLUTION:
Today it is accepted that evolution has occurred and is still happening. This is well supported by
multiple lines of evidence from different sources. By using a combination of these sources, scientists
have been able to:
• Develop detailed histories of the evolution of life forms.
• Demonstrate the evolutionary relationships among organisms that are currently alive
(extant).
Sources which act as evidence for evolution:
1. Fossil records:
• Fossils found all over the earth are a significant source of evidence for evolution.
• Known as paleontological evidence and shows both micro- and macro-evolution.
• Paleontology = study of prehistoric life.
• By using radiometric dating that dates the rocks, the age of fossils can usually be
worked out.
How does fossil evidence show that evolution has occurred?
The fossil record provides detailed information and evidence of systematic change through time – of
descent through modification. Different fossils are found in the different rock layers with the oldest
fossils in the oldest layers. Modern species can be traced back through time as they show similarities
with fossil species that became extinct over hundreds of thousands of years ago.
What can be seen in the fossil record?
Fossil records indicate that evolution has taken place as they show:
• Increase in complexity – simplest organisms appear first.
• Increase in diversity – 1.4 to 1.7 million species of organisms.
• More extinct species as one moves back in time.
• Existence of intermediate forms between groups (transitional fossils) -
transitional fossils have a mixture of traits that show a link between groups.
• Overall increase in size - first organisms were tiny unicellular bacteria.
2. Modification by descent:
• Genes are being passed from one generation to the next.
• Genes are constantly changing.
3. Evidence of biogeography to show that evolution has occurred:
• Biogeography is the study of where species (both present-day and extinct) occur,
and why.
• It is the study of geographical distributions of biological organisms. It provides
information about how and when species may have evolved. Fossils provide
evidence of long- term evolutionary changes, documenting the past existence of
species that are now extinct.
• Many geographical features (oceans, rivers, mountains, and islands) provide barriers
to species, allowing scientists to observe how they evolved separately from one
another.
The conventional explanation that species had been created with adaptions made no sense to either
Charles Darwin or Alfred Russel Wallace. They had noticed during their various voyages that
different regions with similar climatic conditions contained very different animals and plants.
Darwin was so struck by this that he used biogeographical patterns as one of his principal proofs of
his theory of evolution.
,What were these evolutionary patterns?/examples of biogeography:
• Distinct species only found on certain land masses and nowhere else.
• Species are distributed around earth in a pattern that reflects their genetic relationships
to one another. Eg: several species of zebra on one continent (Africa).
• Different regions with similar climatic conditions had
different fauna (animals) and flora (plants).
• Species on islands (eg: Galapagos), appeared to be
closely related to the species on the nearest
continent. Darwin concluded that the animals on
these isolated islands must have been originally from the
nearby continent (South America), but because they were
separated from the other species on the continent, they
gradually evolved into something different over thousands
of years.
• The distribution of fossils. Fossils of extinct species resemble
living species in the same region. Eg: Extinct glyptodonts
found in South America resemble living armadillos in the
same areas. (Shows clearly that the modern species replaced
and evolved from the fossil forms).
, 4. DNA and molecular biology (evidence from genetics):
- All organisms have similar DNA and RNA molecules.
- All organisms have proteins made of the same 20 amino acids.
- The same genetic code (sequence of nucleic acids) is used to make the same proteins.
- The functions of many proteins are similar.
Genetics is the science of heredity, which includes the study of genes and the inheritance of
variation and traits of living organisms. It deals with resemblances and differences of related
organisms which is why it is valuable in giving evidence for evolution.
- Evidence of evolution can be seen by studying and comparing chromosomal DNA and
mitochondrial DNA (mtDNA).
- Not only do they show that all organisms have descended from a common ancestor but
also shows how closely organism are related to each other.
The following information shows that all organisms must have originated and evolved from a
common ancestor and must be genetically related:
• All organisms have descended from a common ancestor because:
▪ All organisms have DNA and RNA molecules.
▪ There are many genes in all living organisms that are encoded to make identical
proteins (eg: the enzymes used in cellular respiration, which are proteins).
• Organisms are related to each other by varying degrees:
The evidence of evolution shown by molecular biology goes even further. Scientists can use the
similarity of sequences of chromosomal DNA and mtDNA nucleotides to work out how related species
are.
▪ The more sequences shared, the closer the relationship between two species and
the more recently they have diverged from a common ancestor.
▪ The fewer sequences shared, the more distant the relationship between the two
species, and the further in the past the species diverged from a common ancestor.
▪ Example: In humans and chimpanzees, the protein molecule called
cytochrome c, which serves a vital function in respiration within the cells of
all forms of life, consists of the same 104 amino acids in exactly the same
order.
▪ The similarity shows how recent common ancestry was between humans
and chimpanzees.
▪ Thus, the evidence for evolution, which Darwin drew from biogeography,
paleontology, homology and embryology, can be confirms by molecular
studies of chromosomal DA and mtDNA (ie: genetics).
5. Homologous structures (comparative anatomy evidence):
By comparing external and internal structures, scientists can find out how related two organisms
are. This is known as comparative anatomy and provides evidence for evolution.
- The reason for this is that organisms with similar structures or characteristics might have
acquired these features from a common ancestor and therefore are on the same
evolutionary lineage.
- Such features are known as homologies.
- The number of shared homologous features between any one species and another indicates
how recently those two species diverged from a shared lineage.
Evolution is the gradual change or development of something.
(It can be used in various senses in social or economic structures and general use).
GRADE 10 REVISION:
• Universe started 13.7 bya (Big Bang Theory).
• The earth is very old – 4550 million (4.6 billion) years old.
• Earth’s crust has been built up in layers over millions of years. The layers have been
successfully laid down by either water (sedimentary rocks) or by volcanic activity (volcanic
rocks). Each layer is therefore of a different age, oldest layers at the bottom.
• Dating of fossils – relative dating and radiometric dating (absolute dating) can determine the
age of a rock layer, and therefore the age of fossils embedded in that rock.
• By studying fossils one:
▪ Learns about ancient forms (eg: trilobites), and the appearance and extinction of
organisms, from individual species to whole taxonomic groups (eg: the dinosaurs).
▪ Understands that life-forms changed ad gradually became more similar to present-
day life-forms.
▪ Gains evidence to support the idea that species change, ie: have undergone
evolution.
• South Africa is very rich in fossils with some important finds, for example:
▪ Stromatolites (cyanobacteria) in Barberton.
▪ Glossopteris ferns in KZN.
▪ Coelacanth.
▪ Mammal-like reptiles in the Karoo.
▪ Humankind’s earliest direct ancestors – Australopithecus africanus and Homo
ergaster.
▪ New find: Homo Naledi.
BIOLOGICAL EVOLUTION (descent with modification):
Change in the gene pool of a population during the course of time due to processes such as
mutation, natural selection, and genetic drift.
Why is it important that we study biological evolution?
• It is the unifying concept that acts as a foundation for understanding Biology.
• It supports and explains many aspects of everyday lives.
• It challenges people to think for themselves.
,EVIDENCE FOR EVOLUTION:
Today it is accepted that evolution has occurred and is still happening. This is well supported by
multiple lines of evidence from different sources. By using a combination of these sources, scientists
have been able to:
• Develop detailed histories of the evolution of life forms.
• Demonstrate the evolutionary relationships among organisms that are currently alive
(extant).
Sources which act as evidence for evolution:
1. Fossil records:
• Fossils found all over the earth are a significant source of evidence for evolution.
• Known as paleontological evidence and shows both micro- and macro-evolution.
• Paleontology = study of prehistoric life.
• By using radiometric dating that dates the rocks, the age of fossils can usually be
worked out.
How does fossil evidence show that evolution has occurred?
The fossil record provides detailed information and evidence of systematic change through time – of
descent through modification. Different fossils are found in the different rock layers with the oldest
fossils in the oldest layers. Modern species can be traced back through time as they show similarities
with fossil species that became extinct over hundreds of thousands of years ago.
What can be seen in the fossil record?
Fossil records indicate that evolution has taken place as they show:
• Increase in complexity – simplest organisms appear first.
• Increase in diversity – 1.4 to 1.7 million species of organisms.
• More extinct species as one moves back in time.
• Existence of intermediate forms between groups (transitional fossils) -
transitional fossils have a mixture of traits that show a link between groups.
• Overall increase in size - first organisms were tiny unicellular bacteria.
2. Modification by descent:
• Genes are being passed from one generation to the next.
• Genes are constantly changing.
3. Evidence of biogeography to show that evolution has occurred:
• Biogeography is the study of where species (both present-day and extinct) occur,
and why.
• It is the study of geographical distributions of biological organisms. It provides
information about how and when species may have evolved. Fossils provide
evidence of long- term evolutionary changes, documenting the past existence of
species that are now extinct.
• Many geographical features (oceans, rivers, mountains, and islands) provide barriers
to species, allowing scientists to observe how they evolved separately from one
another.
The conventional explanation that species had been created with adaptions made no sense to either
Charles Darwin or Alfred Russel Wallace. They had noticed during their various voyages that
different regions with similar climatic conditions contained very different animals and plants.
Darwin was so struck by this that he used biogeographical patterns as one of his principal proofs of
his theory of evolution.
,What were these evolutionary patterns?/examples of biogeography:
• Distinct species only found on certain land masses and nowhere else.
• Species are distributed around earth in a pattern that reflects their genetic relationships
to one another. Eg: several species of zebra on one continent (Africa).
• Different regions with similar climatic conditions had
different fauna (animals) and flora (plants).
• Species on islands (eg: Galapagos), appeared to be
closely related to the species on the nearest
continent. Darwin concluded that the animals on
these isolated islands must have been originally from the
nearby continent (South America), but because they were
separated from the other species on the continent, they
gradually evolved into something different over thousands
of years.
• The distribution of fossils. Fossils of extinct species resemble
living species in the same region. Eg: Extinct glyptodonts
found in South America resemble living armadillos in the
same areas. (Shows clearly that the modern species replaced
and evolved from the fossil forms).
, 4. DNA and molecular biology (evidence from genetics):
- All organisms have similar DNA and RNA molecules.
- All organisms have proteins made of the same 20 amino acids.
- The same genetic code (sequence of nucleic acids) is used to make the same proteins.
- The functions of many proteins are similar.
Genetics is the science of heredity, which includes the study of genes and the inheritance of
variation and traits of living organisms. It deals with resemblances and differences of related
organisms which is why it is valuable in giving evidence for evolution.
- Evidence of evolution can be seen by studying and comparing chromosomal DNA and
mitochondrial DNA (mtDNA).
- Not only do they show that all organisms have descended from a common ancestor but
also shows how closely organism are related to each other.
The following information shows that all organisms must have originated and evolved from a
common ancestor and must be genetically related:
• All organisms have descended from a common ancestor because:
▪ All organisms have DNA and RNA molecules.
▪ There are many genes in all living organisms that are encoded to make identical
proteins (eg: the enzymes used in cellular respiration, which are proteins).
• Organisms are related to each other by varying degrees:
The evidence of evolution shown by molecular biology goes even further. Scientists can use the
similarity of sequences of chromosomal DNA and mtDNA nucleotides to work out how related species
are.
▪ The more sequences shared, the closer the relationship between two species and
the more recently they have diverged from a common ancestor.
▪ The fewer sequences shared, the more distant the relationship between the two
species, and the further in the past the species diverged from a common ancestor.
▪ Example: In humans and chimpanzees, the protein molecule called
cytochrome c, which serves a vital function in respiration within the cells of
all forms of life, consists of the same 104 amino acids in exactly the same
order.
▪ The similarity shows how recent common ancestry was between humans
and chimpanzees.
▪ Thus, the evidence for evolution, which Darwin drew from biogeography,
paleontology, homology and embryology, can be confirms by molecular
studies of chromosomal DA and mtDNA (ie: genetics).
5. Homologous structures (comparative anatomy evidence):
By comparing external and internal structures, scientists can find out how related two organisms
are. This is known as comparative anatomy and provides evidence for evolution.
- The reason for this is that organisms with similar structures or characteristics might have
acquired these features from a common ancestor and therefore are on the same
evolutionary lineage.
- Such features are known as homologies.
- The number of shared homologous features between any one species and another indicates
how recently those two species diverged from a shared lineage.
