Aims:

b) acquire an understanding of scientific ideas, how they develop, the factors which may affect their development and their power and limitations

(Adapted from page 13)

13.3

We can learn from fossils how much (or how little) different organisms have changed since life developed on Earth.

The theory of evolution states that all species of living things which exist today – and many more which are now extinct –have evolved from simple life-forms which first developed more than three billion years ago.

Evolution occurs via natural selection:

• individual organisms within a particular species may show a wide range of variation because of differences in their genes;
  
• predation, disease and competition cause large numbers of individuals to die;
  
• individuals with characteristics most suited to the environment are more likely to survive to breed successfully;
  
• the genes which have enabled these individuals to survive are then passed on to the next generation.
  

*Candidates should be able to:

• explain how fossils provide evidence for the theory of evolution;
  
• explain how over-use of antibiotics can lead to the evolution of resistant bacteria.
  

...
Candidates should be able, when provided with additional information, to interpret evidence relating to evolutionary theory.
The environment that species need to be able to survive may change or successful new predators, new diseases or new competitors may arise. Unless evolution occurs and species become better adapted to survive these changes they may become extinct.

New forms of genes result from changes (mutations) in existing genes.

Mutations occur naturally. The chance of mutations occurring is increased by:

• exposure to ionising radiations, including ultra-violet light, X-rays and radiation from radioactive substances; the greater the dose of radiation, the greater the chance of mutation;
  
• certain chemicals.

*Candidates should be able, when provided with appropriate information, to:

• suggest reasons why Darwin’s theory of natural selection was only gradually accepted;
  

…

• identify the differences between Darwin’s theory of evolution and conflicting theories, e.g. Lamarck’s;
  
• suggest reasons for the different theories.
  

…
Most mutations are harmful:

• if mutations occur in reproductive cells, young may develop abnormally or die at an early stage of their development;
  
• if mutations occur in body cells, these may start to multiply in an uncontrolled way and invade other parts of the body; this is cancer.

Some mutations are neutral in their effects and, in rare cases, a mutation may increase the chances of survival of an organism and any offspring which inherit the mutant gene.

*Through these contexts candidates should be able to apply the following ideas appropriately to information they are given about historically important scientific discoveries and to currently controversial scientific and technological issues:

1. that scientists report their findings to other scientists in special journals. The reports are not published unless other scientists feel the scientific research is of good quality and the findings are not usually accepted unless they can be repeated by other scientists;
   
2. that members of the public depend on the mass media (TV, newspapers, radio etc.) to keep them informed about issues involving science and technology. These may be biased but have a big influence on the issues that are discussed;the points of view people take on these issues; decisions about what research should be funded.
   
3. that to explain their findings scientists need to use their imaginations, so there can be more than one explanation of the same findings;
   
4.  that scientists, like other people, are reluctant to give up explanations that have served them well in the past; have scientific, moral, religious and social views that are influenced by the views in the society in which they live;
   
5.  that a new explanation is more likely to be accepted if it can be used to make predictions which are then tested and observed to be correct;
   
6. that scientists may be uncertain about whether or not a factor increases the chance of a particular outcome. This is especially likely in complex situations when the evidence is based on a small number of cases if it is difficult to explain how the factor could cause the outcome;
   
7. that science-based technology provides people with many of the things they most value in life but can also, usually unintentionally, harm people and the environment so that benefits always need to be weighed against costs (economic, environmental and social);
   
8. That even when there is full scientific agreement about the likely effects of some technological process, there may be a further (moral) question about whether, on balance, it should be allowed. (Adapted from pages 22-23)