Unit D: Changes in Living Systems

Lesson 2.5: Evolutionary Theory


In 2003, the spacecraft Mars Express was launched to orbit Mars and explore the planet. On board was a smaller vehicle designed to land on the planet’s surface. This lander, called “Beagle 2,” was to search for evidence of life on Mars. Beagle 2 was named after the sailing ship HMS Beagle. This ship was originally made famous for its round-the-world voyage with naturalist Charles Darwin more than a century before the launch of Beagle 2 into space. On Darwin’s historic voyage, he encountered thousands of animal and plant species and noted the adaptations that enabled life to thrive in a variety of conditions. From his observations, Darwin developed a profound new theory.

1.  Explain why Darwin thought varieties of finches came from a common ancestor
2.  Define Natural Selection
3.  Investigate how environment affects finch morphology over time.
4.  Compare the theories of Darwin and Lamarck
5.  List 7 kinds of evidence of evolution
6.  Explain natural selection using the example of the Peppered Moth
7.  Define asexual reproduction and sexual reproduction
8.  Give advantages of asexual and sexual reproduction



Figure 1:  Darwin's Finches












Darwin found many types of Finches on the Galapagos Islands.  He suspected that they were all descendants of seed eating Finches that came to the island long ago, but had changed over time to specialize to a limited local diet.  For example, narrow billed Finches ate insects, while thick billed Finches ate hard seeds.
Explore the Rainfall and Bird Beaks Gizmo to explore how the morphology of Finches changes as climate changes.  When rain is plentiful, Finches eat caterpillars and insects, which are plentiful.  In times of drought, Finches will live off of large, hard seeds.  Create different climates and look at the two graphs to see how populations, and Beak depth change with time.



  • Read pages 497 and 498 of the textbook, ending at the investigation. Answer the questions as you encounter them and check below.

     

    Science 20 Textbook.  Alberta Education

It might be fun try the next investigation.  You will learn the connection between beak types and their suitability in terms of food sources. The study will be based on a simulation in which you and several other people will use plastic forks and small food items to take the role of birds.

You should be doing this investigation with at least three other people. If you are working in a non-classroom environment, you may adapt the steps of Procedure on pages 498 and 499 of the textbook so that the investigation can be done by just a few participants. Choose some friends or family members to take the role of parent birds, and let each cup itself be a chick.


Be sure to wear protective goggles and gloves when breaking plastic tines off the forks.



There should be just one chick for each parent and its nest. The chicks must be placed equal distances from the bowl of food.
Modify the plastic forks so the number and placement of tines vary. Use Figure D2.37 on page 498 of the textbook as an example.

Before doing the simulation, predict which fork variation will be most successful at acquiring food.

  • Read the investigation on pages 498 and 499 of the textbook. Follow the directions, and answer the questions. Check your answers below.

     

    Science 20 Textbook.  Alberta Education


  • Read pages 499 to 503 of the textbook, starting at “Darwin’s Theory of Evolution”. Answer the questions as you encounter them and check the answers below.

 

Science 20 Textbook.  Alberta Education


Darwin's Theory of Evolution was controversial when it was proposed.  His Theory on Natural Section, which explains why species change over time, is still controversial, maybe because it is poorly understood.  
Mutations that cause variation happen by chance.  When people look at the amazing adaptations in the natural world it is difficult to believe they could come about by chance, but this 'trial and error' process has had more than 3.5 billion years to work!  
Darwinian Fitness is a problematic term.  It is often assumed that the strongest and fastest (most physically fit) species survive, but his is not the meaning of fitness.  Fitness describe how suited a species is in its environment.  For example, a sloth is very slow;  its slow metabolism helps it survive very well in its environment.  Species with adaptations that help them survive and reproduce in an environment, will pass on the genes for that adaptation to their offspring.  The offspring will also be well suited to the environment.

  • Do question 35 on page 500 and check your answer.
Jean-Baptist Lamarck believed that genes could change during the lifetime of an organism.  Then these changed genes could be passed on to offspring.  For example, a Grizzly bear that digs up marmots would develop larger shoulder muscles, so the offspring would have genes for larger shoulder muscles.   We now know that this is not the way that genes work.


This information adds to your understanding of page 502, which is just a quick survey of several kinds of evidence.
Biochemical evidence refers to DNA.  This is the clearest, most direct evidence for evolution.  We can see that the changes between parents and offspring occur because of the changes in genes.  
A characteristic of good theories is that they can predict something that will happen in the future.  Modern science is using knowledge of genes to make predictable changes in the structures of living things.  gene therapy is an example of this.
Companies investigate your ancestry by mapping out the mutations in your DAN and comparing them to people in different parts of the world.


This video uses the example of whales to explain many of the other kinds of evidence of evolution.  Its a cool video.



Natural Selection Case Study:  The Peppered Moth

This is an example of a change in environment that changed the morphology of a species.
Want to see how an adaptation helps a species survive?  Try this Natural Selection Gizmo and hunt some Peppered Moths
  

Review:  Two Kinds of Reproduction

Sexual reproduction requires genetic material from two individuals.  Offspring are a mix of genes from both parents, so there is a lot of variation in offspring because mutations ore more frequent.  Variation is an advantage in a changing environment because some offspring will be well suited, and will survive and pass on their genes. 

Asexual material requires genetic material from only one individual.  Offspring are exact genetic copies of the parent, and are called clones.  This kind of reproduction does not require much energy, so many more offspring can be produced.  This is better in an environment that is not changing, but there are few mutations and little variation in offspring, so when the environment changes the species may end.

  • Read page 503 - 504.  Do questions 42 - 46 and check your answers.  Check your answers below.

 

Science 20 Textbook.  Alberta Education

  • Read “2.5 Summary” on page 504 of the textbook. Then, complete “2.5 Questions 1 - 3”.   Check your answers below.

     

    Science 20 Textbook.  Alberta Education

Check Yourself
species with mutations (adaptions) best suited to their environment will live, reproduce and pass on the mutated genes to their offspring

They are structures in organisms that are very similar.  they seem to indicate a common ancestry

There is greater variety in offspring of sexually reproducing organisms, so some offspring are always better suited in a changed environment. 

Go to Assignment 2.5: Evolutionary Theory.