Studying the similarities and differences between organisms helps us to ...
- Classify living organisms depending on whether they are animals , plants or micro-organisms
- understand evolutionary and ecological relationships
Evidence of how organisms have evolved are evident in fossils found in rocks.
Evolutionary trees are models that allows us to map the realtionships between organisms.
There are different theories of evolution because scientists don't always have enough valid or reliable evidence.
Theories of Evolution
Charles Darwin's theory of evolution by natural selection states: all living things that exsist today, and many more that are now extinct, evolved from simple life forms more than three billion years ago.
Darwin's 'The Theory of Evolution by Natural Selection' was published in 1859. It took a long time to be accepted because ...
- it challenged the idea that God made the all the plants and animals that live on the Earth
- there was insufficient evidence at that time to convince many scientists
- the mechanism of inheritance and variation wasn't discovered until 50 years later.
Jean-Baptiste Lamarck described another thoery of evolution ; any change that occurs during the lifetime of an organism will be passsed on and inheritied by their offspring. - We now know that in the vast majority of cases this type of inheritance can't occur.
Evolution by Natural Selection
- is the change in a population over many generations
- may result in the formation of a new species whcih is better adapted to it's environment.
1. Individual organisms within a species show variation because of differences in their genes.
2. Individuals better adapted to their environment are more likely to survive , breed successfully and produce offspring. This is survival of the fittest.
3. The survivors pass on their genes to their offspring, reulting in an 'improved' organisation evolving through natural selection.
Gene mutations may bring about a more rapid change in a species.