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What you need to know
Reflections and Exam tips
Evolution is the gradual change in species over time. It is a very slow process which takes millions of years.
Organisms need to keep changing because their environment is always changing, if they do not change to fit prevailing conditions, they may become extinct.
Theories of evolution/the origins of organisms:
1. Charles Darwin's theory: Evolution by Natural Selection
This is the most widely accepted theory in Science and it briefly says:
Evidence for Evolution
Fossils- earliest fossils show that life began around 4 Billion years ago.
Fossils show how organisms or their parts changed over time e.g. the pentadactyl limb (5 digits at the end of each limb).
The incomplete fossil record:
Some organisms are missing from the fossil record so it is incomplete (some may say it's evidence that the Evolution theory is wrong). This is expected as:
2. Lamarck's theory
Jean Baptiste Lamarck proposed that Giraffes developed long necks by constantly stretching them to reach for food on tall trees.
These long necks were then passed to their offspring.
In short, he thought that acquired characteristics like scars, language etc could be passed to offspring. This is not so as we now know that for charactristics to be inherited, they have to be in the genes.
Lamarck's Theory is no longer regarded as credible.
Some people see religious Beliefs as in competition or war with scientific Theories: Evolution V Christianity, Hinduism, Muslims etc. No!
This is because of the following key ways in which the 2 work:
So, this does not mean competition or war, they are just 2 different dimensions of human existence.
Is the permanent loss of an organism- The organism no longer exists.
Mass extinction- Is the large-scale extinction of a species e.g. dinosaurs. Mass extinction may be due to asteroids, floods and volcanic activity. This is mainly possible for endemic species.
Endemic species are organisms mainly found in one geographical area.
Causes of extinction
Speciation- is the origin of a new species through evolution.
Examples of speciation
1. Why was Darwin's Theory controversial when he started bit?
2. Why did it take a very long time to accept it?
3. Find out about other theories that explain the origin of life.
1. Make sure you can explain Darwin's Theory of Evolution step-by-step.
2. Always include the idea of Natural selection.