variation and evolution

• organisms of the same species have...

  differences
• variation


  any difference between individuals of the same species
• what are an organism's characteristics determined by?

  the genes inherited from their parents
• genes


  coded DNA instructions that control the production of proteins within the cell
• how are genes passed on from the parents of an organism to the organism?

  in gametes, from which the offspring develop
• genetic variation


  differences among individuals in the composition of their genes or other DNA segments
• what characteristics are determined by genes?

  - eye colour

  - blood group

  - inherited disorders (e.g. cystic fibrosis)
• environmental variation


  differences between organisms caused by environmental factors
• what characteristics are determined by environment?

  - bodily blemishes (e.g. scars)

  - tattoos

  - language spoken
• what characteristics are due to genes and the environment?

  - height

  - weight

  - human hair/skin colour

  - size/colour of plant
• what introduces variation?

  mutations
• mutations


  a random error in gene replication that leads to a change
• theory of evolution


  states that organisms change and develop over time to adapt an increase rate of survival
• evolution


  change in a kind of organism over time; process by which modern organisms have descended from ancient organisms
• survival of the fittest

  process by which individuals that are better suited to their environment survive and reproduce most successfully; also called natural selection
• natural selection


  a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits
• Charles Darwin


  - English natural scientist who formulated a theory of evolution by natural selection (1809-1882)

  - he studied the plants and animals of South America and the Pacific islands, and in his book On the Origin of Species by Means of Natural Selection (1859) set forth his theory of evolution.
• phenotypic variation


  differences in appearance or function that are passed from generation to generation
• steps of evolution


  1. variation always present

  2. variations can be good or bad

  3. those with good variations survive and reproduce.

  4. they reproduce diverse offspring - more born than will survive due to competition for resources

  5. best fit survive and reproduce
• speciation


  the formation of new and distinct species in the course of evolution
• why does speciation occur?

  when populations of the same species become reproductively isolated
• reproductive isolation


  separation of species or populations so that they cannot interbreed and produce fertile offspring
• extinction


  the complete disappearance of a species from Earth, meaning no living individuals of that species exist anywhere
• causes of extinction


  - destruction of habitat

  - extreme changes in the environment

  - excessive hunting or extraction

  - a new predator or disease kills them all

  - inability to compete with another (new) species for food or habitat

  - natural disaster occurs that kills them all (e.g. volcanic eruption, asteroid collision)
• how did dodos go extinct?

  humans hunted them, destroyed their forest and introduced other animals to their island, Mauritius, which ate all their eggs - they were also flightless birds
• why was there opposition to Darwin's ideas?

  - it went against common religious beliefs about how life on Earth developed: it was the first plausible explanation for the existence of life on earth without the need for a "creator"

  - Darwin was unable to explain why these new, useful characteristics appeared and how they were passed on

  - there wasn't enough evidence to convince many scientists, because not many other studies had been done into how organisms change over time

  - genes and mutations were discovered 50 years after the publishing of his theory
• Jean-Bapitise Lamarck


  - French naturalist

  - argued that changed that an organism acquires during its lifetime will be passed onto its offspring

  - he thought that if a characteristic was used a lot by an organism, then it would be more developed during its lifetime, and the organism's offspring would inherit the acquired characteristic
• why was Lamarck's hypothesis rejected?

  experiments did not support his arguments, as an animal with dyed fur would not produce an offspring with fur of that dyed colour
• why was Darwin's hypothesis eventually accepted?

  - the discovery of genetics supported Darwin's idea because it produced an explanation of how organisms born with beneficial characteristics can pass them on (i.e. via their genes)

  - the fossil record allowed scientists to observe how the changes in organisms developed slowly over time

  - the discovery of how bacteria are able to evolve to become resistant to antibiotics also further supports evolution by natural selection