Evolution at its most fundamental level simply describes a cumulative change in something over a passage of time

• For living organisms, this change relates to the occurrence of a specific trait within a particular species

Biological evolution refers to the cumulative changes that occur within the heritable characteristics of a given population

• Only traits encoded by DNA can be transferred from one generation to the next – acquired traits cannot be passed on
  

• The frequency of the trait is recorded across successive generations – therefore, evolution is measured at a population level

For evolution to occur within a species, there must be pre-existing variation within a population which is then exposed to a mechanism of change

• This change can be due to random events (genetic drift), environmental pressures (natural selection) or human intervention (artificial selection)
  

Change Over Time