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Unformatted text preview: Legs
+ Legs MRCA w/o legs 68
68 Principle of parsimony allows us
to arrive at the most likely scenario • Only some of these groups have legs
• What different ways could this pattern could have arisen? + Legs – Legs + Legs – Legs + Legs MRCA w/o legs 69
Most likely hypothesis is the one that
needs the least amount of change to explain actual results.
Aka Occam’s Razor:
Start with the simplest explanation that’s consistent with the data + Legs 70
Can be applied to almost any kind of data Chromosome
(each color is
a diff. gene) What is the simplest explanation that may have led to this pattern? 71
Due to analogies parsimony doesn’t always work • Analogies: streamlined body, long jaws, flippers
• Do not reflect true evolutionary history 72
72 Parsimony For best results, base relationships on many different characters. Based on many other characters:
Dolphins = mammals
Ichthyosaur = reptile 74
For best results, use many different characters. 79
79 New information continues to revise
our understanding of the tree of life Figure 26.21 Campbell et al (9th ed) Figure 26.23 Campbell et al (9th ed) 80
80 Readings on which you will NOT be tested • Figure 26.6 (Inquiry)
• Figure 26....
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