Natural selection

Question 1

Darwins theory of Natural Selection.

Answer 1

• Over 150 years ago Charles Darwin wrote his theory of natural selection to explain how evolution might happen. It says that if animals and plants are better adapted to their environment, they and the following generations are more likely to survive.
• He did not know exactly how adaptations were passed on. We now know that when organisms reproduce, their genes are passed on to the next generation.

Question 2

The modern version of natural selection can be summarised like this:

Answer 2

• Within any species there is variation.
• Organisms produce far more more young than will survive, so there is competition for limited resources such as food.
• Only those best adapted will survive, which is called survival of the fittest.
• Those that survive pass on successful adaptations to the next generation in their genes.

Question 3

Over time, the changes produced by natural selection may result in a new species.

Answer 3

• This only happens if different groups of organisms cannot mate for long time.
• The organisms might be prevented from mating because they live in different areas. This is geographical isolation. They might be prevented from mating because of behavioral isolation.
• If each group evolves differently they might over time become different enough to be classified as seperate species.

Question 4

Natural selection is difficult to study because it usually takes thousands of years to see the effect. Some examples have been studied over shorter time spans:

Answer 4

• More and more bacteria are developing resistance to antibiotics.
• Peppered moths are dark or pale in colour. Dark moths are better camouflaged in polluted areas, so more of them survive.
• Warfarin resistance in rats.

Question 5

At first many people disagreed with Darwin’s ideas:

Answer 5

• Some people thought he did not have enough evidence to back up his theory.
• Many people disagreed because they though God had created all species.

Question 6

Now Darwin’s theory is much more widely accepted. This is because

Answer 6

• It explains lots of observations.
• It has been discussed and tested by a wide range of scientists.

Question 7

Alternative Theory to Darwin’s One

Answer 7

• There have been other attempts to explain evolution. Before Darwin, Jean-Baptiste Lamarck had a different theory, called the law of acquired characteristics. This said, for example, that giraffes acquired long necks to feed, and this characteristic was passed on.
• As we have discovered more about how genes are passed on, theories like Lamarck’s have been proved incorrect and Darwin’s theory had become widely accepted.