5.4a Evidence of Evolution

09/05/2013 § Leave a comment

Let’s talk about evolution. Evolution in a biological context means the cumulative change in the heritable characteristics of a population. The idea that living organisms formed gradually from previous organisms was introduced by Charles Darwin, who proposed the concept of natural selection. Evidence for evolution by natural selection he presented were:

  • breeding of domesticated animals and crop plants
  • fossils
  • homologous structures
  • geographical distributions of animals and plants

With domesticated breeds, we know that they didn’t always look the way they look today. This is because we artificially select the individuals that are most suited to the tasks we need them to do. Humans literally choose the individual animals that have performed the best for what they are needed for – whether they are taller, smaller, faster (notice that the individual doesn’t necessarily have to be stronger) – and let those individuals reproduce so that the offspring and next generation would share the qualities and such traits would be inherited into further generations.

The fossils geologists have found have been known to hold evidence for evolution when it became clear that the sequence of the fossils were different. Fossils have shown the sequence in which organisms develop and evolve: bacteria and simple algae, the fungi and worms, then land vertebrae, and later, bony finish, amphibians, reptiles, birds, and placental mammals. Some fossils link some organisms today with unknown organisms that don’t exist anymore, which could most likely be their ancestors. The horse, for example, are very closely related to rhinoceroses and tapirs.

Finally, scientists, Darwin in particular, have noticed that the structure of some organisms are incredibly similar. I don’t mean that dugongs, whales, fish and dolphins all have fins. Those limbs are actually quite different from one another, if we look at the bone structure. I’m talking about homologous structures, like the forelimbs of horses, moles, humans, porpoises and bats. A closer look shows that all of the organisms have the same bones in generally the same positions, even if on the outside, they look quite different. This is called adaptive radiation and is a strong piece of evidence that suggests that organisms today come from a common ancestor. Other homologous structures don’t prove much about common ancestries and evolution but are really difficult to explain without evolution in that some structures lose their function and are not naturally selected for.

Essay Questions
  1. Outline what is meant by the trophic level of an organism with three examples from one named habitat. (4 max)
  2. Compare the ways in which autotrophic, heterotrophic and saprotrophic organisms obtain energy. (6 max)
  3. Draw a labelled sigmoid population growth curve. 4 marks
  4. Explain the factors that cause a population to follow the sigmoid ( S-shaped) growth curve. (8 max)
  5. Apply the concept of carrying capacity to the struggle for survival resulting from overproduction of offspring. (5 max)
  6. Outline the international system used for naming species of living organisms. (4 max)
  7. Discuss the definition of the term species. (8 max)
  8. Name the levels and the specific taxa in the hierachy of classification using humans as an example. (2 max)
  9. Describe the relationship between the rise in the concentration of atmospheric carbon dioxide and the enhanced greenhouse effect. 5 marks
  10. Outline the consequences of a global temperature rise on arctic ecosystems. 6 marks
  11. Outline the precautionary principle. 5 marks
  12. Outline the structural differences which characterize bryophytes, filicinophytes, coniferophytes and angiospermophytes. 9 marks
  13. List the structural differences between bryophytes and angiospermophytes. 5 marks
  14. Briefly explain Darwin`s theory of evolution. 4 marks
  15. Outline five types of evidence which support the theory of evolution by natural selection. 6 marks
  16. Outline one modern example of observed evolution by natural selection. 2 marks
  17. Explain the evidence from homologous anatomical structures that supports the theory of evolution. 6 marks
  18. Outline how antibiotic resistance in bacteria can arise in response to environmental change. 5 marks
  19. Antibiotic resistance in bacteria is an example of evolution in response to environmental change. Using another example, explain how an environmental change can lead to evolution. 8 marks



Page 194, domestication of corn

1. Calculate the percentage difference in length between teosinte and Silver Queen. —> 170 – 14 = 156 ÷ 14 = 11.142 x 100% = 1114.2%

2. Calculate the percentage difference in yield between teosinte and world average yields of corn. —> 4100 – 150 = 3950 ÷ 150 = 26.3333 x 100% = 2633.3%

3. Suggest factors apart from cob length, selected for by farmers. —> Size of the kernel, taste of the kernel, colour of the kernel, whether the kernel is smooth or round. 

4. Explain why improvement slows down over generations of selection. —> Like most everything else, the most improvement starts at the beginning and as time passes, less improvement is needed to an already advanced species.

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