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Parsimony (5 of 5) Comparison of two hypotheses

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The parsimony principle tells us to choose the simplest scientific explanation that fits the evidence. Hypothesis 1 requires six evolutionary changes and Hypothesis 2 requires seven evolutionary changes, with a bony skeleton evolving independently, twice. Although both fit the available data, the parsimony principle says that Hypothesis 1 is better — since it does not hypothesize unnecessarily complicated changes.

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Parsimony (1 of 5) Vertebrate character matrix
Character data for some major vertebrate lineages. Characters were limited to characters that are likely homologous (note that many vertebrate lineages and many characters were excluded from this example for the sake of simplicity).

Parsimony (2 of 5) Vertebrate ancestor characters
From studying fossils and lineages closely related to the vertebrate clade, we hypothesize that the ancestor of vertebrates had none of these features.

Parsimony (3 of 5) Amniotic egg clade and phylogeny
We focus in on the group of lineages that share the derived form of the egg character, an amniotic egg (A), and hypothesize that they form a clade (B.)

Parsimony (4 of 5) All clades and phylogeny
If we go through the whole table like this, grouping clades according to shared derived characters (C) we get the following hypothesis (D).