Natural Selection (T4)

Question 1

What are six key points of Charles Darwin’s theory of evolution?

Answer 1

• organisms tend to produce more offspring than are needed to replace them
• despite the numbers of offspring produced, established populations of organisms tend to remain the same size
• members of the same species are not identical, they vary. These variations among a species result from genetic differences
• individuals possessing characteristics which are most suited to the environment are more likely to survive and reproduce. Through this reproduction, the genes which allowed these individuals to be successful are passed onto their offspring
• however individuals less suited to their environment are less likely to survive and reproduce, which means that their genes are less likely to be passed into their offspring
• given enough time a species will gradually evolve

Question 2

In a sentence describe the theory of natural selection..

Answer 2

The theory of natural selection proposes that some factors in the environment essentially ‘select’ which form of a species will survive and reproduce under certain conditions.

Question 3

How is the peppered moth a classic example of natural selection?

Answer 3

The peppered moth has two forms; a white variety and a dark one. Initially nearly all moths were of the white form. The first record of the dark variety was in England in 1848. By 1895, 98% of the moths were dark.

The explanation is that prior to the industrial revolution in Britain the moths were of the pale variety as this helped them to camouflage against pale birch trees while the darker variety was easily picked out by birds and predators. As a result of pollution, the bark of the trees and buildings became blackened with soot and now the black variety of moth was now camouflaged. This tipped the balance in the black varieties favour and their numbers increased.

The distribution of the two forms of the moth was directly linked to the degree of industrialisation.

Question 4

How is antibiotic resistance an example of evolution by natural selection?

Answer 4

• mutations happen all the time, especially in the case of microorganisms such as bacteria and viruses
• in bacteria a chance mutation could take place and make the bacteria resistant to antibiotics
• this resistance can provide an advantage to these bacteria over non-resistant bacteria
• the resistant bacteria will survive and multiply in greater numbers than the non-resistant bacteria
• under the right conditions a bacterium can reproduce in 20 minutes meaning there could be 72 generations of the bacterium in a single day
• this can result in more and more resistant bacteria and eventually the entire bacterium population will be antibiotic resistant