14-16yrs - darwin - charles darwin and natural selection - classroom presentation

7/28/2019 14-16yrs - Darwin - Charles Darwin and Natural Selection - Classroom Presentation

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Charles Darwin and Natural SelectionAn idea that would change the world


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Charles Darwin developed his theory of evolution by natural selection

using four important observations which led him to two deductions.

Observations:

1. All organisms produce more offspring than survive to adulthood

2. Populations remain more or less constant in numbers3. Members of the same species show variation in characteristics

4. Some characteristics are inherited and so are passed on to the

next generation

Deductions:

A. All organisms are involved in a struggle for survival and only the

best adapted survive

B. Organisms that survive are more likely to reproduce, and therefore

pass on their useful adaptations to their offspring

Introduction


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2. Populations remain more or less constant in numbers

Darwins second observation was that the numbers of many different

species of animals and plants tend to stay fairly constant over long periods

of time.

For example, herds of many animals live on the plains of Africa, wildebeest,

zebra, gazelles etc. Each year many of the females give birth to young, butthe overall population sizes of these species stay the same.

There are a number of factors which keep the population numbers stable,

including competition for food, predation and disease

Observations
http://www.arkive.org/media/08/080AEE4F-C24E-4375-8313-67F61F8F29B0/Presentation.Large/photo.jpghttp://www.arkive.org/media/5A/5A52FB5A-DA12-46AB-B820-B3242D37A812/Presentation.Large/photo.jpghttp://www.arkive.org/media/D1/D15335C0-95F6-4117-918B-53412928F890/Presentation.Large/photo.jpg


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3. Members of the same species show variation in

characteristics

Darwins third observation was that all living things vary slightly in

colour, shape, size or behaviour.

Below are three different colourings and skin patterns found in thegiraffe.

West African giraffe Reticulated giraffe Thornicrofts giraffe

Observations
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4. Some characteristics are inherited and so

passed on to the next generation

Darwins fourth observation was that many features are passed on

from parent to offspring.

Some inherited characteristics

are quite easy to see in humans:

Eye colour

Hair colour

Some are not so easy to see:

Blood group

Observations


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From his four observations Darwin was able to deduce two main

conclusions.

A. All organisms are involved in a struggle for survival.

B. Some individuals are better adapted to their environment than

others.

Polar bears fighting Pygmy seahorse camouflaged against fan coral

Conclusions
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Survival of the fittest

The individuals that are best adapted to their environment are most

likely to survive and have the chance to reproduce, therefore passingon their useful adaptations to the next generation.

Those individuals that are the least well adapted do not survive long

enough to breed.

These ideas formed the basis of Darwins theory of evolution bynatural selection.

Male African lion Silverback mountain gorilla
http://www.arkive.org/media/04/045415C0-C393-4DA0-8874-5E0FF49A3E20/Presentation.Large/photo.jpghttp://www.arkive.org/media/D1/D1FEE107-DC7F-4DBF-85C9-953D692889D6/Presentation.Large/photo.jpg


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Evolution by natural selection

Darwin concluded that natural selection could explain how organismsgradually change and evolve into new species.

At the time of publishing Darwin found it difficult to get his theory

accepted, as it was difficult to prove.

Other scientists at the time wanted Darwin to provide an explanation

to how individuals passed on their characteristics to their offspring.

Since Darwins time advances in our understanding of genetics have

provided evidence to support and extend Darwins theory.

14-16yrs - darwin - charles darwin and natural selection - classroom presentation

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