(5) Natural Selection leading to evolution

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Explain how natural selection leads to evolution

When a population produces more offspring than the carrying capacity, individuals compete for resources such as food and shelter. 

The variation between the individuals (from independent assortment and crossing over) makes some more successful in this struggle for survival. 

The more successful ones are more likely to reproduce, passing on these genes. 

After one generation, there will be slightly more advantageous genetic traits than the others. 

This situation repeats and after many generations these traits become common. 

As this process continues, other traits might dissapear from the gene pool of the population, and all individuals might be the kind that is more successful. 

This is the "cumulative change in the heritable characteristics of a population" or evolution.

Explain two examples of evolution (in response to environmental change): 

 If a species cannot adapt to changing environment it will die out. Dinosaurs couldnt adapt to cold climates so warm-blooded mammals took their place. 

Antibiotic resistance of bacteria: 

Bacteria can survive in the presence of an antibiotic. 

Many diseases caused by bacteria can be treated with penicillin and other antibiotics. 

But after the Second World War, the use of antibiotics became widespread, many bacteria developed resistance. example: tuberculosis and cholera are both resistant to all antibiotics)

Staphylococcus aureus is a common bacterium found thatlives on the skin. 

They are harmless but can invade the bloodstream - infect tissues in the kidney or bones and become fatal.

There are straints of S.

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