Looking at pandas you would never know that they posses 6 digits. One digit is considered to be a"false thumb" however you can only see this in their skeleton. On the surface pandas only show 5 digits. This sixth digit is homologous to a humans wrist bone (see first visual). They may be shaped differently but both are hiding beneath the surface.What is interesting is you can also make the argument that the pandas opposable thumb could be analogous of humans opposable thumbs (see second visual). Both humans and pandas reside in the carnivora order.
Analogy
Two different species with analogous traits, would be the koala bear and the panda bear. Koalas live in the coastal regions of Australia spending most of their time in the Eucalyptus trees eating their leaves. The koala has evolved to having opposable digits to make climbing trees and eating leaves easier. Their feet consist of the first 2 digits are opposable to the other 3 digits. Pandas have also evolved an extra "thumb" that is opposable to help with eating bamboo. Pandas are known to live in China. Both opposable digits for the panda and the koala are specifically to assist with food intake. Pandas are in the carnivora order and koalas are in a sub order within the group.
Correct, you can consider the panda's thumb both homologous and analogous to structures in the human hand, just different structures.
ReplyDeleteVery good description of the homologous pairing. Well explained. This is a classic example of adaptive evolutionary theory.
Need a little more information on ancestry. Remember that we are trying to confirm that these structures share a common evolutionary origin, arising from common descent. Both the panda and the human are mammals and inherited their limb and hand structure from an archaic mammals. Both the human and the panda have since experienced changes in the hand structure, but since they both started from the same source, we can see the similarities there due to ancestry.
Very interesting analogous pairing, but I'm having difficulty with the idea that these may actually be homologous. The bones that make up the "thumbs" of these two creatures all originate from the same set of carpals, metacarpals and phalanges, so the underlying structures is homologous. But the trait have "having thumbs", without focusing on the underlying structure, is analogous. Neither species inherited their thumbs from a common ancestor but developed them independently. Hence, analogous. Do you see my dilemma? Regardless, this was a creative and interesting pairing and it made my brain work. Well done.
Again, more information was needed for ancestry, and I covered this in the last paragraph. In order to confirm that these are analogs, you need to be sure they arose independently in at least one species from the common ancestor. If you are looking at the bones, this doesn't work since the bones came from the common ancestor. If you look from the perspective of the thumb structure themselves, these are analogs.
Good images.
I see your dilemma quite clearly actually. This was the dilemma that went around and around in my head confusing me. I spent the 5 hours Monday and another 5 Tuesday. My issue was I understand homology and analogy. You can give me examples and I can easily tell you which is which. I just couldn't produce an example on my own. Then when I thought I had one, start developing on it more, the more I thought it was wrong. There were plenty of examples I found on line, but I wanted to give my own example, thus showing my true understanding of the assignment. Unfortunately, all this back and forth, and research took up most of my time. When it came down to the rest of the assignment I didn't have time to look into that part as much as I needed too. I also found this part of the assignment difficult. I think that with the way I was taught about animals was always so cut and dry. A reptile is a reptile and is in no relationship to a mammal. I kept feeling this feeling that every time the blind fold was coming off and my mind was opening, the blind fold would quickly return and my brain was left sore and hurting.
ReplyDeleteAny how I did learn much from this assignment, mostly about the animals we see today (unfortunately not where they came from). I am almost reconsidering my major and becoming a zoologist.
I thought of some other possible homology/analogy traits, but I am not sure it would work, and the internet wouldn't answer my question, so here are some if you care to let me know if they are or not homology:
- The echidna is one of 5 monotreme (the other 4 are 1 platypus and 3 other types of echidna). The echidna has a spiky like fur that is similar to the porcupine, however, not as sharp. These two creatures are completely separate on the life tree, in different parts of the world, but developed this outer spiky fur to protect themselves from predators. (analogy?)
- The echidna also has a similar mouth/tongue as an anteater. They have the same type of diet, they live in different parts of the world, and are not at all directly related. They were still able to evolve their mouth and tongue to more easily catch and eat ants and termites. (analogy?)
-Shockingly the panda has a pouch, but is not a marsupial. Even though by now I should know better than to be surprised at this after all my research on platypuses and echidna. If you look at lets say a panda having a pouch and the panda carries her offspring within her womb, but after birthing her offspring, continues the gestational period for another 2 years, could you then consider this to be a homologous trait a normal mammal, like a dog?
- I will admit I did find this on wikapedia, so I am hesitant to take it seriously, and since it wasn't something I ended up using I didn't go back and correctly research this. Horses had paws similar to that of a dog, but it was better for the horse to harden its feet to run faster away from predator and lessen the likely hood of injury. The hippo and the elephant are also closely related to the horse and are also considered to have hooves. Elephants have hardened feet. (analogy?)
Some other fun facts that I learned and hoped that I could use:
*Dolphins are said to have also developed opposable "thumbs" to increase speed and maneuver more efficiently.
*Platypuses were first thought of as a hoax do to the oddity of their physical make up. After finding more, they realized that this was in fact a real species. The theory is that the platypus and the echidna are the least evolved species. Scientist believe that these animals are a glance into prehistoric times. Maybe the platypus or the echidna (or another animal like this) is the answer to the ancestors of the koala, panda, and human.
Lots to respond to!
DeleteCorrect, the spiky "fur" in the echinda and the porcupine arose, not from a common ancestor, but independently in each creature, so these are analogous traits.
Any time you compare a marsupial (or nearly any other organism from Australia) to another organism you are more than likely comparing analogous traits. Australian animals crossed a rare land bridge that popped up now and then between Asia and Australia and then underwent adaptive radiation, developing many of the same adaptations we see elsewhere because, frankly, they work. ;-) So the tongue of the echidna is analogous to the tongue of the anteater.
Not sure which trait you are referring to in the panda? The pouch is analogous to the pouches in marsupials. What were you referring to with the dog?
Early horses (and camels and cows and wild pigs and elephants) were all much smaller (large sizes only developed after the fall of the larger dinosaurs when niches opened up) and had the archaic mammalian foot structure that arose from ancestral reptiles, so they had the five toed structure. The loss of toes is just as you describe, for both the benefits of speed, stability and support. If you compare the horse with the elephant, two distantly related species, the traits are going to be analogs because the common ancestor between these two organisms lived very early in mammalian evolution and still had the five toes. If you compare to closely related species, such as the horse and the zebra, then the common ancestor probably already had hooves, so the trait would be homologous, passed down from a common ancestor with differences arising due to environmental differences.. See how that works?
Never heard about the dolphin thumbs. Have to look that up.
Who said the platypus and the echidna are the "least evolved species"?? That is a very judgemental statement that should not be coming out of the minds of a scientist, but what they may mean is that these species have not changed much over their evolutionary history. That doesn't mean they are "least evolved', it just means that whatever they are doing works for them. So why change? I actually would argue the the most "archiac" of organisms is the shark, which has been around pretty much unchanged for 100's of millions of years. It if ain't broke, don't fix it.
The platypus and the echidna are isolated to australia, so they couldn't be the ancestor of panda, who arose in Asia. We also know a lot about human evolution, enough to know they didn't arise from Echidna's or from Australia. Humans originated in Africa... we also know that humans evolved from archaic primates who arose from rodents who rose from reptiles, etc). I am not inclined to think that an archaic Echidna could be an ancestor of koalas either, mainly because Echidna's are egg-laying and koala's are placental animals. Completely different evolutionary line of reproduction. But it is an interesting idea of which came first, the egg-laying mammals (like ancestral lizards?), leading to placental mammals Possibly. Placental reproduction had to come from somewhere.
Thanks for the interesting questions!
Thank you for getting back to me! As you can see I have learned a lot and have a lot to say! My co-workers and family are tired of hearing me talk about such things! haha
DeleteFor this assignment (as we discussed in emails) I can get the analogy, it is the homology examples I have difficulty with. However, you did verify one theory I was going on, but I will get to that later (going in order of response).
Panda pouch is what I was referring to. What I was trying to say is if a mammal, such as a panda, evolved to have natural birth as well as prolong the gestational period for her offspring in her pouch, she is no longer like other mammals, such as a dog. A dog will give birth naturally but will not keep offspring in a pouch. I could be completely off my rocker here on this point... but I think there is something to be said about a mammal that develops a pouch for her offspring.
So now we are at the point of where I finally got a homology trait right! I started researching horses and thought I could use a horse and a giraffe (or an elephant) having hooves as analogy, and a horse and a zebra homologous traits for their hooves However, in my research it was showing that there was the early horses with paws and how they evolved, then it was showing the branch off of other species like zebras. At that point I thought I was going crazy. Here I am, yet again comparing two species that are too close in the life tree, who most likely had a very close relative that gave them the trait. But instead this time I am picking THE ancestor. I trashed that project and started over. I am very proud of myself for coming up with a homology example!
So the dolphin thumb article was on a site for scientist who subscribe, so I couldn't read the whole article. It seems like it could be "fake" but I am not entirely sure. I am one of those gullible people. When I was a little girl my mother hit a deer and I cried for the deer. My mother told me that deers have an amazing ability! They can stop their heart when they are scared so they can't feel pain. I went to high school repeating that to people!
The "least evolved species" statement is poorly worded on my part, with my ignorance. I believe that what I read was similar to what you said "not changed much over their evolutionary history". I reworded that into my own bias statement without knowing I was doing that. Interesting about the shark! I had no idea! Sharks are interesting in that they can't stop moving. They need to keep moving to breathe. Except when they sleep, they go into this odd paralysis state. I watched a documentary on how scientist were using sharks to study sleep in humans and sleep disorders (I may not have gotten that 100% but it was something to that extent).
Ancestor relations to the panda and koala. Yeah it was grasping at straws. I had the hardest time coming up with an ancestor, but after reading other peoples blogs I learned it wasn't a question of their is one out there find the answer. It could be that there isn't one that we could relate back to. I was trying to find the answer that was as simple as we don't know that far back. But how cool would it be to know about other animals like the platypus or the echidna? It is the perfect question, which came first!
You know to be completely honest with this assignment I was about to start using fictional characters. I was thinking of reptiles with wings and all I could think of was dragons. Then I was thinking of unicorns and horses.I think I finally got to the point of my brain shutting down.
With that being said, this is one of the best exercise because it not only forces the student to understand the material, but you have to also put it to practical use. That is the kind of assignment that you will remember.
The article needs a thorough proofread as it is riddled with errors that ought to have been put right before publication.
ReplyDelete