Variation and adaption

• variation - eren though plants and animals can be the same spieces and they are simular in many ways, they are never the exact same:

  These differences are called variations
• Discontinuous variation - characteristic being measured fits into 2 or more separate groups or categories with no immediate alternatives e.g - tongue roller / hand dominance
• When discontinuous variations are measured they are recorded in a bar chart with spaces between the bars / pie chart
• Continuous variation - characteristic being measured varies gradually across a range ( height / weight )
• When continuous variations are presented they are usually presented as a histogram with the characteristic arranged into convenient classes
• variation can either be caused by genetic or environmental factors
• Variation can be caused by genetic factors because they are caused by genes individuals have developed . Sexual reproduction endures that offspring show variation because they get different alleles from each parent. mutations that change genetic makeup of organisms also causes variation.
• Variation can be caused by environmental factors depending on the conditions that the individual was developed
• Natural selection -In the natural world adaptions in living organisms are essential for survival and success in their habitat (the best adapted organisms survive) - (survival of one fittest:)
• charles darwin (1809 -1882) was a naturalist who devoted his life to scienilfic research he spent 5 years on the HMS beagle as it travelled to south America. Darwin was influenced by the animals of the Galapogos Islands.

  Darwin published his account "the origin of spieces" in 1859.

  He realised that there are varlations within phenotypes which might change the chance of survival
• Charles Darwin’s main conclusion of natural selection was that there is variation within phenotypes in a population. resources are often limited and this leads to competition in a population and this leads to different rates of survival
• The best adapted individuals survive and they are more likely to reproduce and pass their desirable genes and characteristics to the next generation ( this is the basis of evolution ) ( natural selection )
• The least well adapted individuals will die or fail to reproduce and this will lead to reduction in the number of poorer adapted individuals and this may result in extinction.(natural selection)
• Darwin’s theory of evolution - natural selection is a continuous process which can lead to gradual changes in organisms over time and this could result in the formation of new species
• EXAMPLES OF NATURAL SELECTION IN ACTION - antibiotic resistance bacteria

  1.a few bacteria mutate so they have resistance to an an antibiotic such as penicillin

  2.population is treated with antibiotic

  3.normal bacteria die

  4. resistant bacteria survive ( best adapted / fitted )

  5. The resistant bacteria reproduce and numbers increase
• Antibiotic resistant bacteria diagram -

  stage 1: bacteria reproduce

  stage 2: treated with antibiotic

  stage 3: offspring of survivors (mutation resistant to antibiotic )

  
• a different antibiotic is needed to eliminate the bacteria resistant to penicillin : many will be destroyed , but a number will survive this new antibiotic. If the sequence continues - superbugs , resistant to antibiotics develop
• An example of a superbug is MRSA
• An example of natural selection is neck length of giraffes which happened over million of years. the process of natural selection has produced giraffes with longer necks because there was variation in neck length and there was competition for food on high branches so the small neck giraffes could not compete and therefore starved to death and failed to reproduce
• The fossil record is evidence of evolution
• Fossils are the remains of dead plants and animals buried in sedimentary rocks. The plants and animals were buried on the rock as it formed, tens of thousands of years ago
• Most evidence of evolution is from the fossil record . Fossils show how much or how little organisms have changed overtime. one of the problems with fossil record is it contain gaps because not all organisms fossilise well and many fossils were destroyed by the movements of the earth/ have not been discovered.
• One of the few animals with a fairly complete evolutionary record is the horse because all of the main stages have been preserved in fossil form
• Horses evolved from a small animal called Eohippus (47-56 mya) that had four toes on its front feet and three on its back feet. It weighed about 20kg and lived in forests

  
• Extinction - Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those that are well adapted. Simularly it is possible that spieces mat are poorly adapted to its environment will not survire and will become extinct
• factars that cause extinction

  • changes to the environment (change in climate)
  • new diseases
  • new predators
  • new competitors
  • loss of habitat
• The fossil record shows that many spieces have become extinct since life on Earth began extrinction is still happening. and a lot of it occus because of human activities - we compete with other living things for space, food and water and we are successful predators
• The dodo is a large flightless bird that lived on Mauritius which is an island in the Indian Ocean. The island was uninhabited so the dodo had no predators. Mauritius was then colonised by the Dutch so the dodos where hunted for food and easy to catch.(not afraid of people ). New animals also came such as pigs/ cats / rats that ate the dodos eggs and their young so within 80 years it went extinct.