5. Natural Selection

Question 1

Who is usually given the credit for being the first to realise that species evolve by natural selection?

Answer 1

Charles Darwin - he was the first to publish a detailed account of it

Question 2

How many years of research did Darwin do? Why did he delay publication? What eventually spurred him to publish?

Answer 2

• more than 20 years
• feared a hostile reaction (creationist backlash)
• Alfred Wallace, another biologist, wrote to him in 1858 suggesting very similar ideas

Question 3

When was ‘On The Origin of Species’ published?

Answer 3

1859

Question 4

What did ‘On The Origin of Species’ change?

Answer 4

f*****g everything

- the way biologists think about the living world and the place of humans in it

Question 5

Explain the theory of evolution through a series of observations and deductions. (7 steps)

Answer 5

• species tend to produce more offspring than the environment can support
• there is a struggle for existence in which some individuals survive and some die
• in natural populations there is variation between the individuals
• some individuals are better adapted than others. An adaption is a characteristic that makes an individual suited to its environment and way of life.
• individuals that are better adapted tend to survive and produce more offspring, while less well adapted individuals tend to die or produce fewer offspring so each generation contains more offspring of better adapted than less well adapted individuals.
• the frequency of characteristics that make individuals better adapted increases and the frequencies of other characteristics decrease, so species change and become better adapted.

Question 6

What do living organisms acquire during their lifetime?

Answer 6

characteristics - e.g. an amputated leg

Question 7

Why are characteristics not passed on to offspring?

Answer 7

characteristics are not heritable so they are lost when an individual dies. This also means, therefore, that characteristics cannot increase in a species by natural selection

Question 8

Give an example of characteristics not being passed on.

Answer 8

Tennis players:

• right handed tennis players develop bigger muscles in their right arms
• genes that influence muscles have not been altered
• so children of right handed tennis players do not have a bigger right arm

Question 9

When, and only when, can natural selection occur?

Answer 9

• if there is variation among members of a species

- if the environment cannot support

Question 10

Name three sources of variation.

Answer 10

• Mutation
• Meiosis
• Sexual reproduction

Question 11

Explain ‘mutation’ as a source of variation.

Answer 11

• the original source of variation

- new alleles are produced by gene mutation, which enlarges the gene pool of a population

Question 12

Explain ‘meiosis’ as a source of variation.

Answer 12

• produces new combinations of alleles by breaking up existing combinations in a diploid cell
• every cell produced in meiosis is likely to carry a different combination of alleles, because of crossing-over and the independent orientation of bivalents

Question 13

Explain ‘sexual reproduction’ as a source of variation.

Answer 13

• involves the fusion of male and female gametes
• the gametes usually come from different parents, so the offspring has a combination of alleles from two individuals. This contributes to variation in a species