Evolution

Evolution

1. Variation

   • the differences between organisms of the same species
   • comes from
     • sexual reproduction- meiosis
     • physical variety- phenotypes
     • mutations
   • Genetic
     • characteristics determined by genes- inherited from parents
       • genes- codes inside your cells that control how you're made
       • genes are passed on in sex cells (gametes)
       • combining genes from two parents cause genetic variation
         • characteristics determined by genes:
           • eye colour
           • blood type
           • inherited disorders
           • natural hair colour
   • Environmental
     • a difference caused by the conditions something lives in
       • e.g.
         • sun tan
         • injury
   • Genetic and Environmental
     • e.g.
       • Health
         • some people are more likely to get certain disease due to their genes, lifestyle also affects he risk e.g smoking and diet
       • Height
         • max. height is determined by genes, actual height by environment
   • Mutations
     • a random change in an organism's DNA
       • caused by:
         • radiation
         • UV and sunlight
         • x-rays
         • some chemicals
     • gene is altered, so the sequence of amino acids that make up a protein may change
       • therefore protein made may change
     • if the environment changes, and the new the phenotype makes an individual more suited to the environment it becomes common throughout the species through natural selection
     • changes:
       • small change so no effect on phenotype
         • mutation produces a genetic variant that codes for the same amino acid sequence
         • change one amino acid but the change has no effect on the proteins function
       • small influence of phenotype
         • some characteristics controlled by more than 1 gene- eye colour, so there's only a slight change
       • determines a phenotype

2. Theory

   • All of today's species have evolved from simple life forms that first started to develop over 3 billion years ago
     • 'developed' from single cell organisms such as bacteria
   • Charles Darwin - Natural Selection
     • 1. Individuals within a species show wide variation in their characteristics due to the mix of genetic variants in the populations
     • 2. some genetic varient give rise to better suited characteristics to the environment so organisms with these characteristics have a higher chance of survival and are more likely to breed sucessfully
     • 3. So the genetic variants responsible for the useful characteristic are more likely to be passed on to the next generations and over time it will become more common within the populations leading to a change in the species.
   • Evidence
     • the fossil record
       • allows you to see the changes of an organism over time
       • how are fossils formed?
         • hard parts of animals that don't decay e.g. teeth, bones, shells
         • when conditions are absent for decay - ice fossils, peat bog man (rarest fossils)
         • parts of an organism are replaced by other materials as they decay (most common) - rock bones & shells
         • preserved traces of organisms - foot prints

3. Extinction

   • Extinction: When no living individuals of a species remain.
     • e.g. dinosaurs, mammoths
   • Evidence- Fossil record
   • Why do species become extinct?
     • sudden change in environment - e.g destruction of habitat
     • new predator e.g. humans
     • new disease
     • catastrophic event e.g. volcanic eruption/ meteor

4. Darwin V. Lamarck

   • Darwin's theory - controversial:
     • Went against common religious beliefs about how life on earth developed
     • Couldn't explain why these new characteristics appeared or how they were passed on from individual organisms (didn't know about genes or mutations - discovered 50yrs after his theory)
     • not enough evidence to convince many scientists- not many other studies had been done on how organisms changed over time
   • Lamarck
     • argued that changes that an organism acquires during it's lifetime will be passed on to it's offspring
       • thought that if a characteristic was used a lot by an organism, then it would become more developed in it's lifetime and the offspring would inherit it

5. Speciation

   • A Species: a group of similar organism that can reproduce to give fertile offspring (able to rebreed)
   • Speciation: the development of a new species
     • occurs when populations become so different that they can no longer successfully interbreed to produce fertile offspring
   • Isolation
     • where populations of a species are separated
     • happens through a physical barrier
       • geographical barriers (caused by - floods or earthquakes)
     • can lead to speciation
   • Natural selection
     • when two populations are isolated conditions on each side of the barrier will be slightly different e.g. climate
     • because the environments are differnet, different characteristics will become more common in each population due to natural selection
     • eventually, individuals from the different populations will have changed so much that they won't be able to breed with one another and produce fertile offspring - two groups have become different species.