Core Biology - Topic 1 Variation

Variation - differences in characteristics

• Some variation within species - much more between different species
• The variation within species makes classification difficult
• Ensure a 'new' species isn't just a hybrid or variation of another species
  • find more than one of the organism

Human variation

• Range in heights caused by inherited and environmental variation
• • example of continuous variation (any number within a certain range)
• Shoe size is an example of discontinuous variation (fixed set of values)

Biodiversity - measure of the total number of species in an area

• To count them you must identify them
  • tricky when many species are very similar to one another
  • more accurate classification system = easier identification
• Biodiversity is important for medicines and foods
  • the more species = the more choices
  • these areas also recover better from natural disasters
• Biodiversity hotspots should have the most time and money spent on conserving them
  • greater number of species will be conserved

• Adaptation - variation in characteristics that allow organisms to survive in their habitat 
  • all organisms adapt to their surroundings
  • most characteristics show variation between individuals of the same species
• Organisms from polar areas are adapted for the cold conditions
• Organisms from deep-sea hydrothermal vents are adapted for extreme heart (350°C+)
  • these organisms cope with extreme temperature changes, complete darkness and huge pressures
• Discontinuous variation e.g. blood group/gender
  • often caused by instructions in cells - GENETIC VARIATION
• Continuous variation e.g. height/weight
  • shows a normal distribution curve
  • most individuals measure within the middle part of the range
  • fewer individuals with measuremets at the extremes
  • often controlled by both genetic and envirornmental influences
• Being short from malnutrition would be an acquired characteristic
• • caused by environment therefore cause environmental variation between organisms

• Organisms generally produce more offspring than the environment can support
• Most die before adulthood because of lack of resources e.g. food/space
  • limited resources cause competition between individuals
  • the ones better adapted will be more likely to survive
  • SURVIVAL OF THE FITTEST - natural selection
• If these individuals breed they pass their variations onto their offspring
• Charles Darwin drew facts together about evolution into a new understandable theory
  • realised characteristics were inherited by offspring
• Evolution - range of variation gradually changing over generations
  • if environment changes, variations appear to suit new conditions
  • individuals with those variations survive and pass on the characterstics to offspring
• If the environment changes too rapidly species will become extinct
  • no time to adapt to new conditions and die out
• Darwin published book in 1859
  • theory was discussed and challenge - wasn't liked

• Warfarin 1940's/1950's
  • most rats died within days
  • after 10 years most rats were resistant
  • because of variations, always some rats were resistant
  • the poison killed the non resistant rats
  • only resistant ones were left to breed

• Darwin just used oservational characteristics to infer relationships
• Now new evidence is found for the theory from genetic information in species

• Darwin's theory helped him explain why neighbouring islands had their own species of mockingbird
• Guessed that the bird came from South America and inhabited the different islands
  • which had slightly different environmental conditions
  • the different adaptations made life more sucessful on each island
  • each island's population evolved in a different way
  • variations became so different that they cannot interbreed - NEW SPECIES!
• Process is called speciation