Natural Selection

Question 1

Who

Answer 1

Charles Darwin proposed the theory of natural selection in 1858

Question 2

Darwin’s Theory

Answer 2

In this theory things change gradually over thousands of generations as a result of natural evolution

Question 3

Why does NS occur

Answer 3

NS occurs because an environmental factor acts on a population and results in some organisms having more offspring than others

Question 4

Why does natural selection occur

Answer 4

The environmental factor that causes this is called a selective agent. The result of this selective agent is selective pressure on the population

Question 5

Biotic & Abiotic selective pressure

Answer 5

Biotic selective pressure is that pressure on a population that favours one characteristic of that population via a living selective agent (eg a bacterial infection causes death). Abiotic selective pressure is the same pressure on a population but caused by a non living selective agent (eg the water supply is removed from a population)

Question 6

Favoured & Unfavoured

Answer 6

Those of the population that survive (survival of the fittest) are favoured by this selective agent and thus they produce offspring that have the favourable characteristics for the next generation

Question 7

Features of Natural Selection

Answer 7

1. There must be variation in the population
2. There will be one characteristic that is favoured as a result of selective pressure and the others are not favoured
3. The favoured part of the population survives, and breeds and passes on the favoured characteristics
4. The unfavoured part of the population does not survive and therefore that characteristic does not get passed to the next generation

Question 8

Difference / Definition of Natural Selection & Evolution

Answer 8

EVOLUTION is a gradual change in the inherited traits of a population over many generations. NATURAL SELECTION is a mechanism where the members of a population best suited to their environment have the best chance of surviving to pass on their genes.

Question 9

Homologous Structures

Answer 9

Appear to have similar structure, but different functions

Question 10

Speciation: how would you know that two organisms that look similar are no longer a part of the same species ? (eg horse & donkey = mule scenario)

Answer 10

• If they breed and produce fertile offspring then they are the same species
• If they breed and produce infertile or no offspring then they are NOT the same species

Question 11

Why is variation necessary before natural selection can happen ?

Answer 11

There are selective agents in an environment that favour ONE variant over another. If there is no variation then all members of the population are treated equally by the selective agent