1. I picked Humans and Household Cats for the Homologous part of this project.
The trait which they both share is the tail bone or Coccyx, while in humans it ends and does not stem out, in cats it forms an entire tail, but the bone shaping is almost identical in both species. Their common ancestor had a well developed tail bone and passed it on to them.
The first image is a cats tailbone and the second is a humans.
While our spines work very differently as humans use Bipedal-ism and cats use Quadrupedal-ism. These words just mean that while humans walk on two legs; Cats usually walk on four. "While our coccyx or tailbone has become a vestigial structure, cats and dogs still have their tails intact."(Analogy V.S. Homology) The similarities in both cases come from a shared ancestor, which caused this trait to appear in both species. As this was very early in evolution this ancestor does not have a name, but is the common ancestor of not only primates(humans) and Carnivora (cats), but also many more, which I thought would be interesting to share considering the common trait came from the ancestor.
Human
House Cat
2. For the Analogous part of this project I will compare Whales and Fish. The analogous trait they share is Fins. Even though one is a mammal and one is a fish because of their common ancestor who also had this trait, it was passed on to one of them (fish). Then through many generations of evolution the whale also developed fins do to evolutionary stress.
First picture is a Killer Whale or Orca (Cetecea) and the second picture is a Crappie (Actinopterygii)
The common ancestor (Osteichthyes) that these two shared did have fins and lived underwater. I can say this because the family tree displays it. Their common ancestor would have had fins, the fins would have been later changed by these two species in order to survive evolution or natural selection. However because of all the evolving that happened before Whales came to exist, the fins are an analogous trait. The whales received the trait through evolution instead of through the ancestor that the two share.
Sources: http://evolution.about.com/od/evidence/a/Analogy-Vs-Homology.htm
http://tolweb.org/Eutheria/15997 Tree containing the ancestor of cats and humans.
http://tolweb.org/Gnathostomata/14843 Tree containing Fish and Whale ancestors.
Hi Zoey,
ReplyDeleteI also posted about the shared traits between an aquatic mammal and a fish, but I did this for the analogous trait. Even though the animals do share a common ancestor, they did not evolve to have fin and flipper from the same ancestor. All animal life began under water, but eventually some of the fish began to move on to land, it was there that they lost the fish-like structure and became terrestrial.
Some of these terrestrial animals, specifically the Mesonychid, which someone else mentioned on a different post, moved back into the water. It was then that they went from having legs, like a cat or dog, to flippers. this means that, even though their limbs to come from the same ancestor, the traits that evolved to serve the purpose of underwater locomotion were not from a common ancestor, but from similar environmental pressure.
The trait you chose for the analogous post, I believe is also flipped. The tailbone, being a vestigial structure means that humans evolved to not need it for survival anymore, the trait was evolved not through need but because a common ancestor between us and cats had the structure. On the evolutionary tree you can imagine that from this common ancestor that also had a tailbone cats branched to one side to continue to use the tail, and humans to another side without the tail.
Very good choice of traits and nice information and comparisons. The two posts should be switched though!
Thank you I have fixed the issue after further research I discovered you were correct.
DeleteHi Zoey!
ReplyDeleteI always find myself interested by other people's posts! To be honest, I found it so difficult to find a good example for analogous traits (that was not about wings), but I liked your example. I always kind of knew that the structure of human tail bones were somewhat similar to those of other animals, but I never knew much about it, so I'm happy you used this example.
I will have to slightly agree with Gustavo's above comment, as I suppose it is true that humans no longer rely on their tail bones for survival. But the very fact that we share a similar trait with a cat yet don't necessarily come from a similar ancestor, I think automatically implies a phylogenic relationship, so I still count your example as viable.
I did my analogous trait on fins, and it's just crazy, because every creature on earth I'm noticing has some sort of similarity that helps them to survive their environment, but we're also so different and we've evolved so much! I mean, even the picture you posted of the human tail bone shows how much humans have evolved. The structure of our tail bone seems to tuck in towards our hips instead of growing outward like that of a cat. I wonder what happened so long ago that made our tails so useless? Hmm... something to ponder!
Good work!
Bekah
Thank you I have fixed the issue after further research I discovered you were correct.
DeleteGood choice of homologous traits (and thanks to your two student commenters for helping you make your corrections/adjustments), and I appreciate your explanation as to why the tail expression is so different in humans and cats. I would have liked a little more explanation into why the tail is so important for quadrupedalism and not for bipeds? That is an interesting idea. Does the tail get in the way for bipeds? Does it not provide the benefit received in bipeds? To be honest, this is a persistent question in human evolution, but it is worthwhile asking it!
ReplyDeleteWith regard to ancestry, we don't need to know a specific ancestor but we can figure out a bit more. Since both cats and humans are mammals, we know that the ancestor was an archaic mammal. The absence of a tail is a derived (unique) trait and possessing a tail is an ancestral trait, so this is what we would expect to see in this early mammal. This trait was then passed through common descent from this archaic mammal to the cat line and to the primate line, with the tail receding in apes to our current expression.
By the way, contrary to popular belief, the tailbone still serves a function in humans, serving as a muscle insertion point for many of our pelvic floor muscles and helps to stabilize us when we sit.
Good choice of analogous trait and good explanation as two why these traits are analogous instead of homologous, even though the common ancestor was also an early fish. This can be difficult concept to grasp.
I'm glad to see the Tree of Life sites were useful! Good images.
Hi Zoe
ReplyDeleteI like the pictures that you used especially the human and cat tail bone that is really interesting. Also does this mean that humans also have a common ancestor with big cats like tigers? Also it was interesting to know that whales were able to get fins because of stress. I like your posting it was different and great to read.
Hey Zoey! I found it very interesting that humans and household cats both share a same trait from a common ancestor. You did a very great job explaining the traits. You also chose good pictures which help visualize what you are talking about.
ReplyDelete