Download 3.3 Speciation and Evolution

3.3 Speciation and Evolution
Think of three different species of bird?
What makes them different from each other?
We are going to be learning about
1.
2.
3.
4.
5.
What is evolution?
How does evolution happen?
What is and is not a species?
How does speciation happen?
What evidence is there to support the theory of evolution?
Evolution
Darwin proposed that natural selection could result in the formation of
a new species. He called this ‘modification by dissent’. The term
evolution was applied by other scientists.
Look at the kingfishers at the top of p85.
The Origin of Tetrapods
What is a species?
Initially the definition of a species was defined if two organisms could
interbreed to produce fertile offspring.
Male Donkey
Female Donkey
Species
=
Donkey
Donkey
What is a species?
Female Horse
Male Horse
Species
=
Horse
Horse
What is a species?
Male Donkey
Female Horse
Species
=
Mule
Not a species – Mule is infertile
What is a species?
The horse reproduces with other horses to produce more animals of
the same species, as does the donkey. However, when they are cross
bred they produce a mule. A mule is sterile and cannot reproduce
therefore, not a species.
Nowadays, scientist compare DNA when comparing species.
Speciation
Speciation is the process by which one species splits into two or more
separate species.
Darwin first discovered this by comparing Finch species.
Sorting Finch Species
Speciation
Speciation Occurs by the following steps:
1. Variation
2. Isolation
3. Selection
Speciation explained
Evidence for evolution - Fossils
From the first fossils to later examples it can be seen that organisms
become more and more complex. This is expect as new alleles and
genes develop from mutation. This eventually leads to speciation.
Translational fossils fossils have also been recovered. These show one
group of organisms changing to another.
Evidence for evolution – Comparative
anatomy
Comparing the anatomy of living creatures to fossils from that species
can tell us about speciation events that have lead to evolution.
Try Activity Book 3.5.
Evidence for evolution – DNA and protein
structure
• Many organisms share similar DNA.
• The gene in humans that is responsible for cell energy release shares
70% of the same DNA as the gene that does the same job in fungi.
• Animals that look the same often have very similar DNA. Humans
have 96% of the same DNA as chimpanzees.
Evidence for evolution – Distribution of
current species
Many unique species occur on isolated islands. As the species was
originally isolated from its parent species you would expect it to evolve
and adapt to its environment. Australia has been isolated from other
land masses for 40 million years. This has lead to the evolution of
unique species.
Evidence for evolution - embryology
Embryology - The
study of the
development and
structure of embryos.
Vertibrate embryos
have structures that
appear to be
homologous on the
basis of anatomy.
Summary
Create six summary sentences about what you have learned about
evolution.
Unit Review 3.3
Do Unit review 3.3