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Summary EVOLUTION NOTES - ACCORDING TO SAG DOCUMENT
Notes based on the SAG document for 2017, for Life Sciences Paper 2. Evolution
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Origin of an idea about originsWhat is evolution?
Evolution is the gradual change or development of something.
What is biological evolution?
Biological evolution is the change in the gene pool of a population during the course of time by mutation,
natural selection and genetic drift. Simply put, biological evolution is descent with modification.
Note: a gene is a group of nucleotides that produce a specific protein that causes a specific trait
Why is it so important that we know about biological evolution?
Biological evolution:
Has become the unifying concept that acts as a foundation for understanding all biology
Supports and explains aspects of our every-day lives
Challenges people to think for themselves
How did life originate?
The current scientific opinion is that there was a single origin of life – this idea is supported by the fact that al
life shares the same genetic code.
A. Before 1700
Scientists accepted that:
Species were unrelated and remained unchanged
The earth was young
B. 1700 to early 1800
Erasmus Darwin and Jean-Baptiste Lamarck began to challenge these concepts. They became convinced that:
Species had changed gradually over time
The Earth was millions of years old
Erasmus Darwin
Erasmus Darwin was a country doctor, a scientist, philosopher, inventor, poet and an author. He put forward
the idea that Earth descended from a common ancestor. In addition, he suggested that species must have
changed over time.
Jean-Baptiste Lamarck
Jean-Baptiste Lamarck suggested that species were not fixed. He reached this
conclusion as a result of making observations such as:
Living species are different to fossil types
Domestication and selective breeding resulted in animals and plants
changing
, Cross-breeding often led to new characters appearing
How did Lamarck suggest that species changed?
He proposed that change was a natural phenomenon and suggested that organisms changed during their
lifetime. These acquired changes were then passed on to their offspring. His hypothesis on how change took
place was as follows:
Use and disuse of body parts – Lamarck believed that when the environment changed, the organism
would adapt to the new environment
Inheritance of acquired characteristics – physical changes acquired by parents were passed on to the
offspring and a new species was formed.
Was Lamarck’s mechanism for evolution correct?
Lamarck’s belief that the environment can produce
phenotypic changes in an individual was correct, but
he was incorrect in thinking this caused evolutionary
change. The characteristic acquired during life
cannot be passed on to the offspring.
C. Early 1800 to early 1900
Charles Darwin
Charles Darwin observed and documented vast
amounts of information about geology, biogeography and fossils. The data he
collected made him aware of the:
Immense diversity among organisms
Variation of individuals
Often puzzling distribution of different species
Darwin realised that:
The earth is extremely old
There has been great geological change
Isolation leads to species changing
Darwin put forward his hypotheses in his famous book, The Origin of Species. This is one of the most influential
scientific books and contains two vitally important hypotheses:
Modification with descent – species had modified gradually from ancient ancestors unlike themselves
Natural selection – the essence of natural selection is that individuals best adapted to the
environment will leave the most offspring.
How did Darwin explain descent with modification?
All related organisms descended from a common ancestor
Species adapted to the new local conditions so they became modifies and thus turned into new
species
The diversification was by branching
Some species died out
,Alfred Russel Wallace
Alfred Russel Wallace was a collector of wildlife and an author who accepted the
concept of evolution. He noticed that organisms in the former were more like
those on the Asian mainland while those in the latter were more like
those in Australia. He suggested that the ancestors of the modern species
would have become isolated from each other by water and evolved
differently.
An amazing co-incidence
Darwin and Wallace read an article by Thomas Malthus. The essence of the essay was that competition and
thus a struggle for existence existed between members of a population. This influenced both men and led
them to come up with similar ideas. Wallace put forward his ideas to Darwin asking for his comments as well as
for assistance in getting it published. Darwin was amazed to realize Wallace’s hypothesis was nearly the same
as his. This led to them publishing a joint paper. Wallace and Darwin share the reputation for having discovered
natural selection although Darwin gained greater credit as he developed it in more detail and was responsible
for it being published.
Evidence of the theory of evolution
1. Fossil evidence indicates that evolution has occurred
Fossils are a significant source of evidence. It is known as paleontological evidence and shows both
microevolution and macroevolution.
How does the fossil evidence show that evolution has occurred?
Fossil records provide detailed information ad evidence
of descent with modification. Different fossils are found in
different rock layers with the oldest fossils in the oldest
layers. Modern species can be traced back through
time. A classic example is the development of the
modern horse.
What can be seen in the fossil record?
Increase in complexity
Increase in diversity
More extinct species
Existence of intermediate forms
between groups
Overall increase in size
Increase in complexity over time
When fossils are arranged in order of time, succession of changes can be seen. Fossils of the simplest
organisms are found in the oldest rocks and progressively gave rise to more complex organisms, which are
found in the newer rocks.
, Beginning of some 545 million years ago, a rapid diversification over a relatively short period of 5 million to 10
million years led to the appearance of a huge diversity of complex, multi-celled organisms. This is known as the
Cambrian period and is when most of the modern major marine groups of animals first appear in the fossil
record.
Increase in diversity
Evolutionists believe that newer organisms descended from common ancestors adapted to a variety of
environments by branching, forming a variety of modified decedents. This type of decent is known as
cladogenesis. Species occurred as a result of the development of novelties or key innovations (something new
and original).
More extinct species as one moves back in time
Species have become extinct because they have not adapted to changing conditions. New species are filling the
niches left vacant. It has been estimated that a typical species becomes extinct within 1 million to 10 million
years of its first appearance. Some species (living fossils) have survived virtually unchanged for hundreds of
millions of years. It is estimated that 99.9% of the species that have ever lived on earth are now extinct.
Intermediate forms between groups – transition fossils
These fossils have a mixture of traits that show a link between groups. They suggest that one group may have
given rise to the other by evolutionary processes. Examples of these forms would be mammal-like reptiles.
In many ways the fossil record is somewhat biased and incomplete because:
Few individuals become fossils
Hard-bodied organisms are more likely to form fossils
Most fossils are of aquatic animals
In addition, it can be predicted that no reversals will be found in future fossil studies.
2. Evidence from biogeography to show evolution has occurred
Darwin and Wallace noticed that different regions with similar climatic conditions contained very different
animals and plants.
What were these evolutionary patterns?
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