Evolution 101- part 5: These Homologous Limbs Were Made for Walkin’

Remember, normal text is copied from Evolution 101 by the Understanding Evolution team! (formerly the Understanding Evolution? team) http://evolution.berkeley.edu/

BOLD font is me, Rent A Friend 2000, being Bold.

Homologies and analogies

 phylogeny 4

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 characters — characters in different organisms that are similar because they were inherited from a common ancestor that also had that character.

If you’ll take out your Debate for Dummies book and look up Circular Reasoning, you’ll find Homologous Characters. How do we know these two creatures are descended from a common ancestor? They have homologous features. How do we know these are Homologous and not just coincidentally similar? Because they descended from a common ancestor.  

Later they will bring up what they call “Convergent Evolution,” meaning two creatures evolve a similar trait, when their most recent common ancestor did not have that trait. So how do they know the homologous features from the convergences? They check the phylogenetic trees! Yes, the trees they are going to try and confirm with this data is the foundation on which the data is built. Is the room spinning yet?

Again, imagine a lawyer pulling this one: “We found shoe prints which were made at the time of the crime. We know these are the defendants shoe prints at the scene of the crime, which proves he is guilty.”
“How do you know those are HIS shoe prints and not the prints of a similar shoe?”
“We know they are his, because he was there committing the crime, therefore those MUST be his shoe prints.”

And on CSI Darwin, that’s good enough to convict a man.

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 feature — so the presence of four limbs is a homology.

Translation: If you presume evolution to be true, and you presume the ancestor of all four legged animals was itself a four legged animal, then you can assume that four limbs is a homology. Yet, even after all of the required assumptions, these homologies will be delivered as PROOF of the evolution which has to be presumed to decide these are homologies. Dizzy yet? We’re just getting started.

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.limbs

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.

Not only did flight supposedly evolve in separate ways unrelated to a common ancestor, but the very similar radar that bats and dolphins have supposedly evolved separately and were not from a common ancestor (Because apparently it’s more likely that a rodent would develop its own radar system than a creature with a radar would develop rodent like teeth, I suppose), and the same is said of the ability to see or breathe air. One problem which instantly comes to the surface is trying to pick WHICH similarities mean a common ancestor, but even more than that is the necessity to have AMAZINGLY improbable events, such as the accidental increase in genetic information to cause the development of sight or flight from an unguided, accidental process happen not just ONCE in the history of life, but MULTIPLE TIMES. If I manage to get all four aces in one hand, it’s pretty unlikely, but not impossible. But if it keeps happening, how long until you pull your six shooter and demand to take a look up my sleeves?

This idea is illustrated by the phylogeny below, which is based on a large number of other characters.phylogeny 5

Bird and bat wings are analogous — that is, they have separate evolutionary origins, but are superficially similar because they have both experienced natural selection that shaped them to play a key role in flight. Analogies are the result of convergent evolution.

Here is an amazing slight of hand- Convergent Evolution. Because mice and bats are similar in their teeth and toes, we say they are from a common ancestor. Because bats and dolphins have a similar radar, but no common ancestor with that radar, then this is NOT an example of evolution. So how do we use this to sell evolution? We say this is evolution which is NOT the result of decent with modification (Another reason why the original definition failed) but the result of two different lineages creating similar (But not Homologous!) features. So, if they had a common ancestor with that trait, it’s garden variety evolution! If they don’t, it’s “Convergent” evolution! As you will come to see, they have created a veritable 31 flavors of evolution so that no matter what happens (Or doesn’t happen) they can label it Evolution- despite thereby contradicting the original definition of evolution that was provided. Check out IAN JUBY discussing this in more detail here. In the mean time, OH LOOK! I just dealt myself ANOTHER ace. What are the odds? Unlikely I know, but this hand is not homologous to that last hand with an ace I dealt me, it’s analogous because it’s the ace of SPADES this time. These are CONVERGENT hands. Unguided, random chance. Yup. Just put that gun down and let’s play the game…

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.

Let me clarify this: Wings, not homologous. Limbs, Homologous. How do we know? Because we believe the birds are dinosaurs, which are lizards, which used to be fish. Uh oh. Fish don’t have legs. OK, so we believe fish grew legs and became four legged animals (Frogs?) which then became lizards and mammals, each of which developed flight over non-homologous pathways (Which is still evolution! The convergent kind!) and then evolved into birds and rodents, some of which developed flight. How do we know all of this? Because…well, didn’t you see that chart a few pages back? It’s all on there. How did gills become lungs and a one chambered heart become a two chambered and then a three and then a four chambered heart without killing the creatures? And how did the lungs change from the hold your breath underwater for two hours kind to the fly nonstop for three days kind? And how did egg laying creatures become placental live birthers?

Stop asking questions and get back to work!

No we don’t HAVE the transitional creatures which this story demands a thousand times over, but OBVIOUSLY they must have lived at some point because birds and lizards and rats all have a common ancestor! Do you know what happens to our phylogenic tree if we ONLY put in the creatures we KNOW about?

It goes AWAY. For more on upsetting the Darwinian Tree of Life with actual data, watch this: LIVING FOSSILS

Join me next week for more.



About rentafriend2000
Rocking my 40's with a heart full of love and muffins, science and technology. Jesus loves me and wants me to totally rock! And I am here to help.

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