these documents consist of evolution notes according to the SAGs documents. It includes, but not limited to, the different theories and evidence. Hominid evolution is not included but can be purchased separately.
EVOLUTION
Background info
- Universe started 13.7 bya
(billion years ago)
- Dating of fossils include
relative dating and
radiometric/absolute
dating
- There has been at least 5
mass extinctions
- By studying fossils one
can learn about ancient
forms, understand that
life-forms changed and
gradually became more
similar to present-day
life-forms and it gains
evidence to support the
idea that species change
- SA is very rich in fossils
with some important finds
such as:
1. Earliest organisms
(3.5bya) like the
Stromatolites
2. Primitive land plants such
as the fern
3. The Coelacanth (fish
group ancestral to
amphibians)
4. Mammal-like reptiles (a
bridge between reptiles
and mammals)
5. Austalopithicus Africanus
and Homo Ergaster
,Development of the theory of evolution
What evolution is
- The change in DNA in an organism over time by mutations
- Gradual change or development
What biological evolution is
- The change in the gene pool of a population during the course of time by
processes such as mutations, natural selection and genetic drift
- Basically is descent with modification
- Population = the same species close enough to produce fertile offspring
- Bigger gene pool = more variation
Micro-evolution = evolution within a species (allele changes)
Macroevolution = the descent of different species from a common ancestor over many
generations (gene changes)
Descent with modification = Charles Darwin -> selective pressures
Speciation = forming a few species
Palaeontology -> studying fossils
Pentadactyl limb = homologous limb
Importance of biological evolution
Biological evolution:
1. Has become the unifying concept that acts as a foundation for understanding all
biology
2. Supports and explains many aspects of our everyday life
3. Challenges people to really think for themselves
How life originated
- Current scientific opinion us that there was a single origin of life
How species diversity originated
BEFORE 1700 SCIENTISTS ACCEPTED:
- Species were unrelated and remained unchanged
- Earth was young and static (unchanging)
,1700 TO EARLY 1800
- Erasmus Darwin (Charles’s grandfather) and Jean-Baptiste Lemarck began to
challenge these concepts
- They became convinced that species has changed gradually over time and the
earth was millions of years old
Erasmus Darwin
- Successful doctor, scientist, philosopher, inventor
- Famous book, Zoonomia, put forward the idea that life on earth descended from
a common ancestor
- It also suggested that species must have changed over time but offered no
mechanism for what he termed ‘transformation’ (evolution)
Jean-Baptiste Lamarck
- French naturalist
- Around a decade later, he put forward his ideas on evolution in his book,
Philosophie Zoologique, and also proposed that species were not fixed
- Reached this conclusion as a result of making various observations like:
1. Living species are different to fossil types
2. Domestication and selective breeding resulted in animals and plants changing
3. Cross-breeding of plant species often led to new characters appearing
HOW LAMARCK SUGGESTED THIS
- He proposed that change was a natural phenomenon and not a result of divine
intervention
- Suggested organisms changed during their lifetime so they could survive in new
environments
- And these acquired changes were then passed onto offspring
1. Use and disuse of body parts
- Believed that when environment changed, the organism would actively
respond by changing so it could adapt to new environment
2. Inheritance of acquired characteristics
- Physical (phenotypes) changes acquired by parents during their lifetime
were passed on to their offspring which is how new species were formed
, Example:
- Suggested long neck and
legs of modern giraffes
were result of
generations of
short-necked and
short-legged ancestors
stretching their necks to
feed on leaves at
progressively higher
levels
- Thought that acquired
characteristics (longer
legs and necks) were passed onto offspring of each generation until eventually a
new species of giraffe with very long legs and necks appeared
Was Lamarck correct?
- Lamarck's belief that environment can produce phenotypic changes in an
individual was correct
- He was incorrect in thinking this caused evolutionary change
- Eg. bodybuilding will increase muscle size, however this does not alter the
genotype of gametes, therefore cannot be passed onto offspring
EARLY 1800 TO EARLY 1900
- Charles Darwin and Alred Russel Wallace
Charles Darwin
- Began formulating theories after 5 year expedition to southern hemisphere where
he studied, observed and documented info
His info he collected made him aware of the:
1. Immense diversity among organisms both living and extinct
2. Variation of individuals of the same species, suggesting species were not
unchangeable
3. Often puzzling distribution of different species
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