Evolution A

Evolution A

1. Theory of evolution - more than 3 billion years ago, life on Earth began as simple organisms from which all the more complex organisms evolved

   • All organisms are related even if only distantly
     • similarities and differences between organisms allows us to classify them into groups
       • plants make their own food and are fixed to the ground
       • animals move and hunt
       • microorganisms are different e.g.bacteria are single-celled
       • studying them can also help us to understand how all living things are related (evolutionary relationships) and how they interact with each other (ecological relationship)
         • ECOLOGICAL
           • if we see organisms in the same environment with similar characteristics (e.g. dolphins and sharks) it suggests they might be in competition (e.g. for food_
             • difference between organisms in the same environment (e.g. dolphins swim in small groups but herring swim in giant shoals) can show predator-prey relationships (e.g. dolphins hunt herring)
         • EVOLUTIONARY
           • species with similar characteristics often have similar genes because they share a recent common ancestor so they're closely related
             • they often look alike and tend to live in similar types of habitats
           • genetically different species might look alike too.
             • e.g. dolphins and shark look similar because they're both adapted to living in the same habitat
               • they're not closely related - they've evolved from different ancestors
           • evolutionary trees show common ancestors and relationships between organisms
           • the more recent the common ancestor the more closely related the two species.

2. EVOLUTION can occur due to MUTATION

   • a MUTATION is a change in an organism's DNA
   • most of the time mutations have no effect, but they can be beneficial by producing a useful characteristic
     • this characteristic may give the organism a better chance of surviving and reproducing
       • if so, this is more likely to be passed on to future generations by NATURAL SELECTION
         • over time the beneficial mutation will accumulate in a population e.g. some species of bacteria have become resistant to antibiotics due to mutation

3. scientists come up with different hypotheses to explain similar observations

   • they may develop different hypotheses because they have different beliefs or they've been influenced by different people
     • only way to find out whose is right is to find evidence to support or disprove each one