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The universe started 13.7 billion years ago because of the Big Bang theory
South Africa is rich in fossils
o Earliest organism (fossilised Cyanobacteria found in Mpumalanga)
o Primitative land plants found in KwaZulu Natal
o Coelacenth
o Mammal-like reptiles found in the Karoo
o Humankind’s earliest direct ancestors, Australopithecus africanus and
Homo ergaster found in the Sterkfontein Caves at the Cradle of Mankind
What is evolution?
- Evolution is the change in the gene pool of a population over time due to genetic
mutation, natural selection and genetic drift (in smaller populations).
What is biological evolution?
- Evolution is the change in the gene pool of a population over time due to genetic
mutation, natural selection and genetic drift (in smaller populations).
- Biological evolution is simply modification by decent (decent with modification –
change that happens over time.)
A. Before 1700
Scientists accepted that:
Species remained unchanged and were not related.
The earth was still young
There were no fossils formed or genetic studies yet.
B. 1700 to early 1800
Erasmus Darwin, Charlie’s grandfather and Jean-Baptiste Lamarck became aware of the
diversity of organisms and started studying fossil records. They were then convinced
that:
Species have changed gradually over time
The earth was a million years old.
Erasmus Darwin
He came up with the statement that organisms have a common ancestor, the problem is
he didn’t know why. He said species must have changed over time, which he called it
transformation (evolution).
Jean-Baptiste Lamarck
1
,Lamarck noticed about a decade later that there was definitely a change over time. He
reached this conclusion:
Living organisms are different from fossil records
Domestication and selective breeding resulted in animals and plants changing
Cross-breeding often led to new characters appearing
He tried explaining 2 theories of how species acquired change:
The theory of use and disuse of body parts
The more an organ is used, the larger it becomes.
The less an organ is used, the smaller it becomes and eventually disappears
E.g.) Vestigial organs
Inheritance of acquired traits
The traits acquired by parent will be passed down to the next generation.
C. Early 1800 to early 1900
Charles Darwin
Diversity among organisms
Variation of individuals
Earth is extremely old
Common ancestor
Changes happened by natural selection which is a mechanism whereby the
environment selects the fittest to survive – acts on variation.
Natural Selection
A mechanism of evolution whereby the environment selects the fittest to survive – acts
on variation.
(Change in environment + variation for n.s to occur)
2
, Those that have the ability to adapt to change in environmental conditions will
survive.
It can only happen variation occurs, which is caused by reproduction.
Explaining natural selection
1. Organisms reproduce in large numbers; variation occurs (sometimes is a desired
trait)
2. Environmental pressure (the cause of change) will continue to ‘apply pressure’
3. Organisms with desired trait will survive the pressure.
4. Organisms without desired trait will become extinct (eaten and all die)
5. The organism with desired trait will reproduce
Evidence of Evolution
Fossil Evidence
Increases diversity – after accumulating adaptations the ancestors formed, by
branching, a variety of modified descendants. This type of descent is called
cladogenisis.
Increases size
Increases complexity
Modification of decent
Transition fossil – Fossils that have a mixture of traits that show a link between
groups and are also referred to as “missing links”.
Biogeography
Biogeography is the study of where species occur and why
Genetics
All organisms descended from a common ancestor because they all have DNA
and RNA. There are genes in organisms that are encoded to make identical
proteins
Organisms are related to one another by varying degrees – more sequences
shared, the more closed related the species are and the more recently they
diverged from a common ancestor and vice versa
Greater number of genetic markers shows the older the population
Comparative Anatomy
Homologous anatomy – these are similar in
fundamental structure, position and
development but different functions
Analogous anatomy – structures that are
similar in different organisms because they
evolved in a similar environment, rather than
being from a common ancestor, but these
structures have similar functions
3
, Embryology
In vertebrates it is difficult to tell the difference in the early embryos of fish, pigs,
humans or bird. This supports the idea of them sharing a common ancestor
Vestigial Organs
These are organs that serve little to no purpose in some organisms but may have
served one in earlier organisms, which suggests a shared ancestor in which the
homologous structure was functional
Macro Evolution
- Change on or above the level of species over long periods of time
e.g.) transition from amphibians to reptiles or reptiles to mammals
(big changes)
Micro Evolution
- Small changes that take place on a species level over time
- Fossils studying can be helpful in
dating (finding out how old a rock
is) and understanding that life forms
changed and gradually became
similar to present-day life-forms. Gradualism – changes that
Fossils also support the idea that occur over time.
species change have undergone Punctuated equilibrium –
evolution. change in a specific point in
time, much change happened,
then become equilibrium
(stayed the same)
Convergent Evolution – evolve in a
similar environment but no common
ancestor.
4
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