So, continuing on main vein of this thread, and going from post #239.
In this
material, we are still in section 2 of 7, titled "Patterns."
And in this post, I'm continuing with subsection titled, "Tree Building." This post will address the page titled, "Homologies and Analogies."
Homologies and Analogies
Since a phylogenetic tree is a hypothesis about evolutionary relationships, we want to use characters that are reliable indicators of common ancestry to build that tree. We use homologous characterscharacters in different organisms that are similar because they were inherited from a common ancestor that also had that character. An example of homologous characters is the four limbs of tetrapods. Birds, bats, mice, and crocodiles all have four limbs. Sharks and bony fish do not. The ancestor of tetrapods evolved four limbs, and its descendents have inherited that featureso the presence of four limbs is a homology.
1 - Model is a hypothesis (supposed explanation)
2 - Characters in model are desired to be reliable indicators of what is allegedly being explained (based on supposition)
3 - We use characters that appear the same / similar
4 - This is how we know there is common ancestry
How do you say, stacking the deck? Or, more accurately, preconceived notions being used as guide to have evidence tell you what you want to hear?
Not all characters are homologies. For example, birds and bats both have wings, while mice and crocodiles do not. Does that mean that birds and bats are more closely related to one another than to mice and crocodiles? No. When we examine bird wings and bat wings closely, we see that there are some major differences.
Yep, got that.
Bat wings consist of flaps of skin stretched between the bones of the fingers and arm. Bird wings consist of feathers extending all along the arm. These structural dissimilarities suggest that bird wings and bat wings were not inherited from a common ancestor with wings. This idea is illustrated by the phylogeny below, which is based on a large number of other characters.
Not sure I agree with what the dissimilarity suggests (to some, many). Pretty sure it won't matter to me in long run of what TOE aims at, and what this thread is about.
Again, this is about understanding patterns utilized within larger model (ancestral tree).
Bird and bat wings are analogousthat is, they have separate evolutionary origins, but are superficially similar because they evolved to serve the same function. Analogies are the result of convergent evolution.
Just a tad too simplistic for my tastes on first part of this quote, but again, not highly interested in discussing this, and so far no one on this thread cares to discuss this stuff, so I think I'm good to go.
Convergent evolution strikes me as very interesting concept. Saying, it is "acquisition of the same biological trait in unrelated lineages." (according to Wikipedia)
Same trait seems fairly significant. I'll even be glad to stick to 'fairly similar' instead.
And unrelated lineages seems huge, though admittedly I'm reading into that as if there isn't one common ancestor for all forms, for if there is or was, then all lineages would ultimately be related and this statement would be challenging to reconcile with that assertion of common ancestry.
But apart from all the mundane technicalities, it seems somewhere between oddly coincidental and plausibly design by conscious selection to have fairly similar designs in vastly different regions where lineages are determined not easily connected.
Interestingly, though bird and bat wings are analogous as wings, as forelimbs they are homologous. Birds and bats did not inherit wings from a common ancestor with wings, but they did inherit forelimbs from a common ancestor with forelimbs.
Too simplistic for my tastes, and not really telling me much other than we have these observable patterns in species, some of which are similar and believed to be traced to common ancestor and some of which are also similar but not believed to be from common ancestor.
Again, in this portion that I covered, the word "observe" or "observation" does not appear. But the words "see" and "examine" appeared in area that is bolded in above quotes. I think we are making some progress on that front.
Next up for this material is still in "Tree Building" and is section titled, "Recognizing Homologies," which I'll get to in next post.
