Variation 2 Flashcards
Describe how dawin developed the theory of evolution by natural selection
Charles Darwin, as a result of observations on a round the world
expedition, backed by years of experimentation and discussion and
linked to developing knowledge of geology and fossils, proposed the
theory of evolution by natural selection.
- Individual organisms within a particular species show a wide range of
variation for a characteristic. - Individuals with characteristics most suited to the environment are
more likely to survive to breed successfully. - The characteristics that have enabled these individuals to survive are
then passed on to the next generation
The theory of evolution by natural selection was only gradually accepted
because:
The theory of evolution by natural selection was only gradually accepted
because:
* the theory challenged the idea that God made all the animals and
plants that live on Earth
* there was insufficient evidence at the time the theory was published
to convince many scientists
* the mechanism of inheritance and variation was not known until
50 years after the theory was published.
Lamark’s ideas and why it is incorrect
When a characteristic is regularly used - it becomes more developed
This strengthened characteristic is then passed on to the offspring
We now know that in the vast majority of cases, changes that occur in an organisms lifetime cannot be passed onto offspring
(this type of inheritance cannot occur)
Wallace
Alfred Russel Wallace independently proposed the theory of evolution
by natural selection. He published joint writings with Darwin in 1858
which prompted Darwin to publish On the Origin of Species (1859) the
following year.
Wallace worked worldwide gathering evidence for evolutionary theory.
He is best known for his work on warning colouration in animals and his
theory of speciation.
Alfred Wallace did much pioneering work on speciation but more
evidence over time has led to our current understanding of the theory of
speciation.
Describe speciation - describe how new species form
Speciation is the development of new species
Speciation occurs when populations of the same species become so different they can no longer successfully interbreed toproduce fertilie offspring
Isolation can occur - Isolation is where populations of a species are seperated
Isolation can happen due to a physical/geographical barrier. This isolates some individuals from the main population
There is now no interbreeding between the two groups of snails
Conditions on either side of the barrier will be slightly different e.g. they may have different climates
Because the environment is different, one each side, different characteristics will become more common in each population due to natural selection operating different on the populations
Because there is no interbreeding between the two populations, any mutations that occur cannot spread between the two populations
This means that over may generations, the two populations will begin to change
There will come a time where the phenotype of the two populations are so different, they can no longer reproduce to produce fertile offspring - now the snails are two different species
What is needed for speciation
A geographical barrier to separate a population into two and prevent interbreeding between the two populations
- describe the development of our understanding of genetics including
the work of Mendel
In the mid-19th century Gregor Mendel carried out breeding experiments
on plants.
From his experiments he realised that characteristics are not blended during inheritance
E.g. shape of pea pod has no effect on the colour of the flowers
He said that characteristics are determined by inherited units and these units do not change when passed on to descendents
These units are called genes
He showed that some characteristics can be masked and then reappear in later generations - recessive alleles
One of his observations was that the inheritance of
each characteristic is determined
- understand why the importance of Mendel’s discovery was not
recognised until after his death.
lack of knowledge of DNA
Evidence for evolution
Fossils -remains of organisms from millions of years ago which are found in rocks
Antibiotic resistance in bacteria
How are fossils formed
Fossils can form when parts of the organisms have not decayed
This can happen when conditions needed for decay are absent e.g. if temperature is too cold, if there is not enough oxygen or if there is not enough water
Fossils can form even if an organism decays, if parts of the organism are slowly replaced by minerals during the decay process
Fossils can be the preserved traces of organisms - E.g. animals can leave footprints or burrows, and plants can leave preserved spaces where roots were
problem with fossils
explan why scientsts cannot be certain about how life began on earth
many of the earliest forms of life were soft-bodied organisms. They did not have a shell or a skeleton.
Soft-bodied organisms very rarely form fossils
Many of the fossils that did form have been destroyed by changes to rocks in the Earth’s crust/geological activity
So because there are very few fossils of the early forms of life, scientists cannot be certain how life on Earth began
What do fossils show
Fossils show that a huge number of species have become extinct
When is a species considered extinct
A species is extinct when there are no remaining individuals of that species still alive
Why species become extinct
Species can become extinct due to a catastrophic event. E.g. an asteroid colliding with the Earth eventually led to the extinction of the dinosaurs
A species can become extinct when the environment changes
E.g. changing weather patterns
A new disease or a new predator could kill all of the individuals of a species and make it extinct
A species can become extinct if a new, more successful species evolves and competes with it e.g. for scarce food or water
