Natural Selection

evolution – The development of new species as a result of natural selection. extinction – The complete disappearance of a species due to changes in its environment that reduce its ability to survive and reproduce. fossil – The preserved remains, impressions or traces of an organism that lived millions of years ago. natural selection – The process where individuals that are well adapted to their environment survive and reproduce at the expense of less well-adapted individuals. trait – A distinguishing and inheritable characteristic of an organism. variation – The natural differences between individual members of a species. Glossary

True or false?

Evolution all around us Darwin said: “It is not the strongest of the species that survives, nor the most intelligent, but rather the one most responsive to change.” The environment today is changing rapidly as a result of habitat destruction, pollution and the artificial control of populations. How is environmental change affecting the evolution of animals, plants and microbes?

Peppered moths rest on tree trunks during the day. Some are light coloured and others are dark. The number of light coloured moths is increasing. Cities are cleaner now. What difference has this made? Peppered moths When cities were very polluted in the 19th century the number of previously rare dark coloured moths increased, as they were better camouflaged against predators on soot-stained trees.

What are superbugs? Some species of bacteria can double in number every 20 minutes. Mutations that offer competitive advantages spread rapidly through the population as a result. A common type of mutation amongst bacteria is to develop resistance to an antibiotic. If bacteria become resistant to several antibiotics, they are known as ‘superbugs’. Infections caused by antibiotic-resistant bacteria are very difficult to treat, especially in patients with weakened immune systems. This is because the range of drugs that can kill the bacteria is so limited.

The evolution of superbugs?

MRSA is ‘Methicillin-resistant Staphylococcus aureus’ – a bacterium that is resistant to several antibiotics. What is MRSA? About 30% of the population carry MRSA without any symptoms. In hospital patients, however, it can cause pneumonia, blood poisoning and even death. The antibiotic vancomycin is used to treat MRSA infection, but resistance to this has evolved, creating VRSA.

What is the risk from bird flu? The concern is that the virus may mutate into a pathogenic strain that can be transmitted between humans. Only a small number of people have died from bird flu, and these were people in close contact with domestic poultry. There are different strains of bird flu – some are more pathogenic (disease- causing) than others. Most pose little risk to humans. Since 1997, the H5N1 avian influenza, or ‘bird flu’, virus has been infecting birds across Asia and Europe.

Summary

The mechanism of natural selection

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