Unit 4: Darwinian mechanisms of evolution

Question 1

What are the 2 main theories of evolution ?

Answer 1

• Descent with modification
• Natural selection

Question 2

What is the theory of descent with modification ?

Answer 2

• Biological populations change over successive generations
• Life evolved from a common ancestor
• History of life is like a tree with branches representing diversity of life

Question 3

What is the theory of natural selection ?

Answer 3

It is gradual or non random processes by which biological traits become more or less common in a population through differential reproductive success

Question 4

What are the 6 propositions that underly Darwins theory of evolution through natural selection ?

Answer 4

1) More individuals are produced than can survive
2) There is therefore a struggle for existence
3) Individuals within a species show variation
4) Those with advantageous traits will survive and reproduce more
5) Favourable traits will accumalate over generations
6) Changes in environment can lead to new traits being advantageous

Question 5

What are the 3 modes of selection ?

Answer 5

1) Stabilising
2) Directional
3) Diversifying

Question 6

What is stabilising selection ?

Answer 6

• Selection that favours average traits and selects against the extremes
• Graph is tall and very narrow in middle

Question 7

What is directional selection ?

Answer 7

• Selection that favours an extreme
• Graph same as typical but over to one extreme (Left or right)

Question 8

What is diversifying selection ?

Answer 8

• Selection that favours individuals with extreme traits at both ends
• Graph looks like u shape with rise then fall then rise again

Question 9

What is sexual selection ?

Answer 9

When animals develop features to help them to maximise their reproductive success

Question 10

What is artificial selection ?

Answer 10

The intentional breeding for certain traits or a combination of traits- typically for domestication