The theory of evolution by natural selection

Explain biological diversity in terms of the Theory of Evolution by Natural Selection by examining the changes in and diversification of life since it first appeared on the Earth.


Biological diversity

Bio refers to life and diversity refers to difference. Therefore, biodiversity is a term which describes the difference in the genetic makeup in a species.

Biodiversity applies;

  • within a species – most humans look different to one another despite us all being apart of the same species, hence we are biologically different from others.
  • between species – different species are radically different to other species
  • between ecosystems – this is looking at biodiversity with more of a macro-perspective, but different ecosystem are different to other ecosystem even if they share the same conditions.

It is important to remember that all living things are made up of proteins, these proteins are encoded by genetic information which is found in every cell and is passed on through reproduction.

Diversity between species is a result of evolution this creates a genetic difference which is large enough for a new species to be classified. The theory of evolution as proposed by Darwin states that the individuals within a species will be selected by the environment so the most suitable individuals will be selected. This can be classified into 5 stages.

The 5 stages of evolution:

The first step in evolution is variation in the population. When ever an organism reproduces it will produce more offspring then will reach the stage when they will be able to reproduce. This over production means that different brothers and sisters will look radically different to one another creating variation in the population. This can be seen for giraffes where the offspring all differ by the length of their necks.

The second phase is a change in the environment, this can be a biotic or abiotic change this change in the environment acts as a selective pressure which screens for a favorable trait. In he case of the giraffe, this would be that all the lower down leaves are no longer available so the only food source is higher up.

The third step in evolution is survival of the most suitable individuals in the species to the selective pressure. This eliminates the variants in the population which can not survive the new selective pressure leaving the most suited individuals to grow up. In the case of the giraffes, the giraffes with the shortest necks would die, leaving the tall neck giraffes which were able to reach the higher branches.

Reproduction is the forth phase in Darwinian evolution, the individuals which survived the selective pressure will reproduce with other individuals who were also suited to the environment. This would be the giraffes which contained the long neck genes reproducing.

The final phase is passing on the genetic information to future generations. The genes which were favorably selected by the environment will become more common in the gene pool. This means that future generations will resemble the survivors of previous generations and the characteristics which were not suitable to the selective pressure will be lost.

This process occurs over very short periods of time in the case of micro evolution e.g. the cane toad or extremely long periods of time such as that of the human evolving from apes.


Question 1:

Define the term biological diversity and provide examples. [2 marks]

Question 2:

Explain how the process of evolution created biodiversity between different species. [3 marks]

Question 3:

Gather information to explore the diversity in life from the beginning of life and some of the selective pressures which resulted in natural selection. Present the information in a flow chart. [not so much an exam style question]

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