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- GCSE Bitesize - Evolution

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Science

Evolution

Evolution has taken place over millions of years and

scientists believe this is the reason why all living things on

Earth exist today. There are different views and theoriesabout the origin of life and the evolutionary process.

English naturalist Charles Darwin wrote one of the f irst

major scientific books on this subject.

Charles Darwin

Charles Darwin was an English naturalist who

studied variation in plants and animals during a

five-year voyage around the world in the 19th

century. He explained his ideas on evolution in

a book called, 'On the Origin of Species',

published in 1859. This shows how species

adapt and change by:

variation in any population of

organisms there will be some differences

over-production many organisms produce more

offspring than necessary

struggle for existence there is competition for survival

and resources between the organisms

survival - those with helpful characteristics are more

likely to survive to breed

useful characteristics inherited by the offspring

gradual change of the species over a period of time asuseful characteristics are passed to offspring.

Darwin's ideas caused a lot of controversy, and this continues

today, because they can be seen as conflicting with religious

views about the creation of the world and the creatures living in

t.

Charles Darwin

(1809 - 1882)

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The basic idea behind the theory of evolution is that all the

different species have evolved from simple life forms. These

simple life forms first developed more than 3 billion years ago

(the Earth is about 4.5 billion years old). The timeline below

shows some of the key events in the evolution of life on Earth,

from the first bacteria [bacteria: Single-celled microorganisms,

some of which are pathogenic in humans, animals and plants.

Singular is bacterium. ] to the first modern humans.

You can see a more detailed history of life timeline on BBC

Nature.

Support for Darwins theory

Antib iot ic-resistant bacteria

Microorganisms such as bacteria

[bacteria: Single-celled

microorganisms, some of which are

pathogenic in humans, animals and

plants. Singular is bacterium. ] and

viruses [viruses: ultramicroscopic

non-cellular organisms that replicate

themselves inside the cells of living

hosts ] reproduce rapidly and can

evolve in a relatively short time. One

example is the bacterium E. coli. Its DNA [DNA : The material

nside the nucleus of cells, carrying genetic information. DNA

stands for Deoxyribonucleic Acid. ] can be damaged or changed

during replication, and most of the time this causes the death of

the cell. But occasionally the mutation is beneficial (to thebacteria). For example, it may allow resistance to certain

antibiotics [antibiotics : Substances that kill bacteria. ]. When

those antibiotics are present, the resistant bacteria have an

advantage over the bacteria that are not resistant. Antibiotic-

resistant strains of bacteria are an increasing problem in

hospitals.

E. coli bacteria (Photo from

Rocky Mountain

Laboratories, NIAID, NIH)

http://www.bbc.co.uk/nature/history_of_the_earth#timelinehttp://www.bbc.co.uk/nature/history_of_the_earth#timelinehttp://www.bbc.co.uk/nature/history_of_the_earth#timelinehttp://www.bbc.co.uk/nature/history_of_the_earth#timeline

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DNA

Scientists can now examine the DNA from different species of

organism and use the data produced to see how closely related

the two species are to each other. By collecting a lot of this data,

scientists can compare the results with conventional ideas about

how organisms have evolved. What they found was that DNA

data supported the conventional theory of evolution.

Validating evidence

Darwins theory of evolution is still known as a theory but it is

widely accepted within the scientific community. This wasnt the

case when it was first published as there was very little scientific

evidence to back up his ideas. Now we have evidence from

DNA and studies on resistant bacteria to help validate (confirm)the theory. All new scientific evidence is assessed by the

scientific community through:

scientific journals

the peer review process

scientific conferences.

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