variation and evolution important

• genetic variation in a species is due to mutations that have occured
• mutation: a change in the sequence of bases in the DNA - so this changes the genetic code and makes new genes/alleles
• Evolution: a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
• natural selection: individuals with characteristics most suited to the environment are more likely to survive to breed successfully
• natural selection model answer

  1. there's phenotype variation in a population due to mutations
  2. those best adapted to the environment will be more likely to survive
  3. and successfully reproduce
  4. and pass on their genes for the useful characteristic to the next generation
• darwin and religious influences

  darwin lived at a time when religious values were very strong. creationist theory was widely taught and believed by many people. darwin's ideas challenged creationism and therefore the religious beliefs of many people
• darwin + evidence

  darwin had a lack of evidence. fossils didn't show a continuous record of change. changes are too slow to demonstrate in one life time
• darwin + genetics

  darwin had no knowledge of genetics so he could not explain a mechanism for passing on the favourable characteristics between generations
• species: two organisms that reproduce to produce fertile offspring
• speciation - the way in which 2 or more new species can arise from a pre-existing ancestor species
• to prove 2 animals are 2 different species:

  breed them together and see if they produce fertile offspring
• speciation model answer:

  1. two ancestral populations seperaed by a geographical barrier
  2. genetic variation occurs in each population
  3. under different environments
  4. natural selection occurs
  5. so favourable alleles passed on in each population
  6. the two types cannot interbreed to produce fertile offspring
• fossils are the 'remains' of organisms from millions of years ago, which are found in rocks
• fossils have provided evidence for the theory of evolution via the process of natural selection. this is because fossils can show us how species have changed over time
• mineralisation: parts of the organism are replaced by minerals from the rock as they slowly decay
• preservation (no decay): fossils form from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
• trace fossils: there are preserved traces of organism such as footprints, burrows and rootlet traces
• why very few organisms have been found as fossils:

  1. many early forms of life were soft-bodied, which means that they have left few traces behind
  2. what traces there were have been mainly destroyed by geological activity e.g volcanoes
  3. the conditions needed for fossilisation to occur are rare (conditions that prevent decay). few organisms become fossils
• five reasons why organisms may go extinct:

  • new predators
  • new diseases
  • better competitors
  • environmental change
  • catastrophic events (mass extinction)