B2f: Natural Selection

The concept of evolution is well known. However, the mechanism of evolution by natural selection is commonly misunderstood. This item discusses evidence for evolution as well as its mechanism. It also looks at how scientific theories develop and why some become accepted and some do not. 

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What happens when some environments change?
Some plants and animals species survive evolve but many become extinct.
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What is evolution?
When groups of organisms change over a long period of time.
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Why are individuals that are poorly adapted to their environment are less likely to survive?
They are also less likely to reproduce, which means their genes are less likely to be passed to the next generation.
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How many theories have been put forward to try and explain evolution?
Many!
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Which theory of evolution do most scientists now accept?
Natural Selection - proposed by Charles Darwin
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What are the key points of natural selection?
Individuals in a species show a wide range of variation cuz of differences in their genes.Ones w/ characteristics most suited to environment are more likely to survive&reproduce.Genes that allow these to be successful are passed to their offspring.
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What are adaptations controlled by? What does this mean can happen?
Adaptations are controlled by genes, that these genes can be passed on to the next generation.
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What is speciation?
When over a long period of time, organisms change so much because of natural selection a completely new species is formed.
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What can reproductive isolation cause?
by Geographic isolation.
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When does speciation happen?
When populations of the same species change enough to become reproductively isolated.
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What does reproductive isolation mean?
When a species can't interbreed to produce fertile offspring.
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Explain reproductive isolation being caused by geographic isolation.
A physical barrier divides a population.Different mutations create new features in the 2 groups.Natural selection works on the new features.Conditions on each side of barrier will be different,so beneficial features will be different for each group.
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Describe the final stage in reproductive isolation caused by geographic isolation.
Eventually, individuals from the two different populations will have such different features that they won't be able to breed together to produce fertile offspring. They'll become reproductively isolated and will be separate species.
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Give an example of a physical barrier that could divide a population of a species
A river changes its course.
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Explain the point in reproductive isolation caused by geographic isolation 'Natural Selection works on the new features'
If the new features are of benefit, they spread through each of the populations.
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For which two reasons is natural selection now widely accepted?
It explains a wide range of observations and it has been discussed and tested by a wide range of scientists.
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What are the three reasons why the theory of evolution by natural selection was met with an initially hostile response?
It conflicted with religious views that God made all plants and animals, it didn't have enough evidence at the time and 50 years after the theory was discovered the way inheritance and variation works was discovered.
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Who came up with Lamarck's theory? What did he do?
Jean-Baptiste Lamarck, a French scientist who developed an alternative theory at the beginning of the 19th century.
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Describe Lamarck's theory.
A characteristic that was used a lot by an animal would become more developed. There acquired characteristics could be passed onto the animal's offspring.
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Why was Lamarck's theory discredited?
People eventually concluded that acquired characteristics don't have a genetic basis - so they're unable to be passed on to the next generation.
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Give an example of what Lamarck's theory would mean could happen - rabbit legs.
If a rabbit did a lot of running and developed big leg muscles, its offspring would also have big leg muscles.
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State a difference between Darwin's and Lamarck's theories.
Lamarck's theory implies that all organisms would gradually become complex, and simple organisms disappear. On the other hand, Darwin's theory can account for the continued presence of simple organisms.
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Card 2

Front

What is evolution?

Back

When groups of organisms change over a long period of time.

Card 3

Front

Why are individuals that are poorly adapted to their environment are less likely to survive?

Back

Preview of the front of card 3

Card 4

Front

How many theories have been put forward to try and explain evolution?

Back

Preview of the front of card 4

Card 5

Front

Which theory of evolution do most scientists now accept?

Back

Preview of the front of card 5
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