In systematics, a popular method of determining the right tree and the state of a common ancestor is parsimony.
Quotein the absence of any reason to think otherwise, favour the explanation that is the most straightforward, and (in the case of inferring evolutionary history) requires the least number of changes. Parsimony is a popular tool because it's straightforward, relatively easy to apply, and it makes a great deal of intuitive sense - if a red animal occupies a deeply nested position in a clade of blue animals, then it seems fairly obvious that the ancestral animal was blue. However, like all analytical tools, the principle of parsimony is based on certain assumptions, and can be misleading if those assumptions are violated. Parsimony assumes that when comparing changes in a character between two states, change in either direction is equally likely. If, for whatever reason, a change is more likely to happen in one direction than another, then a parsimony analysis might be mislead about the ancestral condition.
Stick insect wings are an excellent example of when parsimony can go wrong. The rest of the article is below.
http://catalogue-of-organisms.blogspot.com/2008/12/when-parsimony-goes-wrong-wings-of.html (http://catalogue-of-organisms.blogspot.com/2008/12/when-parsimony-goes-wrong-wings-of.html)
:mittens:
Kai, you should have a regular "When Scientism is FAIL" column in Intermittens ;-)
Quote from: Ratatosk on December 19, 2008, 08:01:06 PM
:mittens:
Kai, you should have a regular "When Scientism is FAIL" column in Intermittens ;-)
Except in this case (lol) it DIDN'T go wrong. They actually found out that a single gene turns wing expression on or off in stick insects, meaning the genes for wings are present in ALL families, just that they are turned OFF in the wingless ones and turned ON in the winged ones. This was something we discussed in morphology class, but I was surprised not to see it discussed in this blog post. On the other hand there are people that have evidence for an ancestral wingless form, and like the blogpost, have evidence for a winged ancestral form.
Who knows what is right at this point? I actually emailed the blogpost to my Morphology professor and committee member to see what he thought.
http://www.nature.com/nature/journal/v421/n6920/full/nature01313.html (http://www.nature.com/nature/journal/v421/n6920/full/nature01313.html)
One of the articles supporting ancestral wings with subsequent loss and then recovery. I am trying to find the article where the gene is demonstrated.