Natural selection model

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blue and green are poor temperature regulators; white and yellow, which reflect heat, are more likely to survive.

Slide 17

It is a particularly hot summer, blue and green are poor temperature regulators; white and yellow, which reflect heat, are more likely to survive.

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When food is plentiful

again the remainder mate and produce 5 offspring some white and some yellow.

Slide 19

When food is plentiful again the remainder mate and produce 5 offspring some white and some yellow.

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A scientist finds this population

and reports that this species occurs in two colours. He says they have adapted to their habitat. What does he mean?

What is the population?

Has it changed?

Slide 21

Slide 22

In outline,

Darwin stated the following

Many more individuals are born than can possibly survive.

Individuals within a population vary slightly from one another.

There is a frequent recurring struggle for existence.

Some individuals will have a better chance of surviving than others (they will be naturally selected).

Any selected variety will tend to propagate its form.

Q.What did the individuals in our population compete for in the struggle to survive?

Q.Which individuals were naturally selected?

Slide 23

Lamarck (a french biologist) proposed

During a life, structures or characteristics may be used or not used.

Extensive use would lead to increased size and/or efficiency.

Characteristics acquired during a lifetime could be inherited and so passed on to any offspring.

Q.Does our population show any evidence to contradict or support Lamark?

To test Lamarck’s theory, Weismann cut off the tails of mice for successive generations.

Q.What should have happened if Lamarck’s ideas were to be supported?

Q.What do you think did happen?