Syllabus Edition
First teaching 2015
Last exams 2025
Biodiversity Arises from Evolutionary Processes
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Biodiversity Arises from Evolutionary Processes
Biodiversity arises from evolutionary processes
Biological variation arises randomly and can either be beneficial to, damaging to, or have no impact on, the survival of the individual
Natural Selection
In any environment, the individuals that have the best adaptive features are the ones most likely to survive and reproduce
This results in natural selection:
Individuals in a species show a range of variation caused by differences in genes
When organisms reproduce, they produce more offspring than the environment is able to support
This leads to competition for food and other resources which results in a ‘struggle for survival’
Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
Therefore the genes resulting in these characteristics are passed on to their offspring at a higher rate than those with characteristics less suited to survival
This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics
This theory of natural selection was put forward by Charles Darwin and became known as ‘survival of the fittest’
Example of Natural Selection
Variation in fur colour exists within rabbit populations
Rabbits have natural predators like foxes which act as a selection pressure
Rabbits with a white coat do not camouflage as well as rabbits with brown fur, meaning predators are more likely to see white rabbits when hunting
As a result, rabbits with white fur are less likely to survive than rabbits with brown fur
The rabbits with brown fur therefore have a selection advantage, so they are more likely to survive to reproductive age and be able to pass on their genes to their offspring
Over many generations, the frequency of the gene for brown fur will increase and the frequency of the gene for white fur will decrease
Selective pressures acting on a rabbit population for one generation - predation by foxes causes the frequency of rabbits with brown fur to increase and the frequency rabbits with white fur to decrease
Remember that organisms better suited to their environments are more likely to survive, but survival is not guaranteed
Organisms that are less suited to an environment are still able to survive and potentially reproduce within it, but their chance of survival and reproduction is lower than the individuals that are better-adapted
Also, it is important to be aware that an environment, and the selection pressures it exerts on an organism, can change over time
When a change occurs then a different characteristic may become more advantageous
Finally, remember that all organisms (not just animals) experience selection pressures as a result of the environment they are in
Another good example of natural selection is the evolution of the peppered moth
Examiner Tips and Tricks
There are many examples of natural selection and you cannot possibly be familiar with all of them, however, they ALL follow the same sequence:
Based on the idea that within a species there is always variation due to chance mutations, some individuals will develop a characteristic that gives them a survival advantage that allow them to live longer, breed more, and be more likely to pass their genes on. Repeated over generations, the advantageous characteristic will become the norm within a population.
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