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You must email your answers to Mr. Widmer to complete the assessment tasks for this “Natural Selection” elective Chapter 3 Natural selection and evolution Name: ___________________________ In his book On the Origin of Species Charles Darwin drew a diagram he called a ‘Great Tree of Life’. The tree diagram showed how species should be related to each other if his theory of evolution was correct. Each branching of the tree showed where new species evolved because new structures appeared in the fossil record of the descendents. Phylogeny Darwin’s technique is still used today. Often hundreds of features are used to create the tree. Most of these are based on anatomy. However, now biologists also have molecular evidence such as DNA structure to help them. Consider Figure 1 on the following page which shows how tetrapods may have evolved. (Some of these species are also discussed in the Activity Book Activity 2.4.) This diagram shows the branching tree structure originally developed by Darwin. This type of diagram is now called a phylogeny. Phylogeny of tetrapods. To read the diagram, start at the far left-hand side where the label says ‘Bony skeleton, lungs’. You proceed through the diagram like you would use a biological key. The first line branches into two choices: ‘ray-finned fish’ and another branch that is labelled (with a small vertical line) ‘lobe fins’. What the diagram is saying here is that the ray-finned fish and the lobe-finned fish had an ancestor in common. That ancestor had a bony skeleton and also had structures similar to lungs. The ancestor split into fish that evolved into both ray finned fish and into lobe-finned fish. The lobe-finned fish eventually split into the Coelacanths and another group that then further split. This group evolved into lungfish and another group which evolved limb bones having a humerus, radius and ulna. Using a phylogeny like this, biologists are able to deduce which species should be the most closely related to each other. For example, consider which two of the following are the most closely related – ray-finned fish, Coelacanth or lungfish. The answer is the Coelacanth and the lungfish. This is because at one point in time (about 425 million years ago based on the timeline at the top) there were no Coelacanths or lungfish, only a common ancestor of both. This common ancestor was a lobe-finned fish that lived at the same time as ray-finned fish. Ref:769859221 Page 1 You must email your answers to Mr. Widmer to complete the assessment tasks for this “Natural Selection” elective Questions 1 Explain what Darwin’s Great Tree of Life diagram showed. __________________________________________________________________ 2 Identify a new type of evidence used by modern biologists to create phylogenies. __________________________________________________________________ 3 a Deduce which two of the following are most closely related: Eusthenopteron, Panderichthys and Tiktaalik. __________________________________________________________________ b Justify your answer. __________________________________________________________________ __________________________________________________________________ 4 a Deduce which two of the following are most closely related: lungfish, Tiktaalik, Ichthyostega and Tulerpeton. __________________________________________________________________ b Justify your answer. __________________________________________________________________ __________________________________________________________________ 5 Describe some features of the most recent ancestor of Acanthostega and Ichthyostega. __________________________________________________________________ __________________________________________________________________ 6 Describe some features that were different between Acanthostega and Ichthyostega. __________________________________________________________________ __________________________________________________________________ Ref:769859221 Page 2