Homologous and Analogous, Can You Figure Out the Difference?
The two species I chose to compare for homologous traits are a human and a dog. Humans stand on
two legs and walk upright while dogs walk and all four of their limbs and their spine is not developed
in the same way human spines are that give them the ability to walk and stand straight up and down.
Humans and dogs are both part of the mammalian species and both possess the homologous trait of
a tailbone. Although humans and dogs both have the tailbone trait, there is a clear difference on its
function for either species. Human tailbones are immobile and do not usually extend out of their body.
Dog tailbones extend out and it allows them to wag their tails. Human tailbones are called vestigial tails
and it means that they are an “evolutionary leftover”. The animals ancestors of humans and dogs are
believed by scientists to have tails and the reason is because animals that walked on four legs were in
need of an extended tailbone to serve as a structure of balance, to brush away insects, etc. Scientist
believe that the reason humans no longer have the looks of a tail is because we became bipedal which
means we walk on two legs. This gave humans the use of two extra limbs, no longer needing the tail to
serve for those extra purposes that arms and hands can do. This is called divergent evolution which
shows that the two species share this genetic relationship but the traits has two different functions in
each species.
two legs and walk upright while dogs walk and all four of their limbs and their spine is not developed
in the same way human spines are that give them the ability to walk and stand straight up and down.
Humans and dogs are both part of the mammalian species and both possess the homologous trait of
a tailbone. Although humans and dogs both have the tailbone trait, there is a clear difference on its
function for either species. Human tailbones are immobile and do not usually extend out of their body.
Dog tailbones extend out and it allows them to wag their tails. Human tailbones are called vestigial tails
and it means that they are an “evolutionary leftover”. The animals ancestors of humans and dogs are
believed by scientists to have tails and the reason is because animals that walked on four legs were in
need of an extended tailbone to serve as a structure of balance, to brush away insects, etc. Scientist
believe that the reason humans no longer have the looks of a tail is because we became bipedal which
means we walk on two legs. This gave humans the use of two extra limbs, no longer needing the tail to
serve for those extra purposes that arms and hands can do. This is called divergent evolution which
shows that the two species share this genetic relationship but the traits has two different functions in
each species.
The two species that have the analogous trait of an extended tail bone that moves and provides a purpose are a dog and an alligator. The dog is a mammal with an extended tail bone that serves a purpose while an alligator is a reptile with an extended and mobile tailbone. The reason this trait proves a similarity between the two is that, although they are two completely different species, they both have a part of their body (tail) that helps them survive. The dog tail moves when experiencing different emotions, helps provide balance, and can help swat away insects. Alligator tails also move in ways to help them, their tails help them swim, for example, when they are trying to catch prey. Yes, a common ancestor of these two different species possessed this trait of an extended tail bone because they were their for a purpose and were needed to survive. We know this trait of a mobile and extended tail is analogous because they are two different species, one is a mammal and one is a reptile. This is called parallel or convergent evolution, this shows the animals adapting over time to their environment and not an actual genetic relationship.
Hey Ayla, I like the species you decided to compare in your post. I really like the comparison of human beings and dogs. In a way we as human beings are similar to dogs like the tailbone you mentioned. Its very interesting to think about if we weren't walking on two legs what would we look like. maybe have a tail like dogs to bush away insects like you said. I agree with what you said about the tails of a dog and a alligator help them survive because it help to protect themselves and show what they are feeling. Great Post.
ReplyDeleteHey Ayla! It's really interesting that your comparison was between dogs and humans in the homologous portion. It's a great comparison because it shows that there are similarities across a numerous amount of species without being directly genetically related. The tail bone was a great example because human tailbones function completely differently from dog tailbones yet still exist on a human body. It shows that we all at one point were a related species but over millions and billions of years of evolution, we evolved more due to environmental pressures and natural selection. Evolution is a strange concept yet is so fascinating because it exists also to remind us our mutual traits with the other animals we share this earth with. Great Job!
ReplyDeleteOkay on your description of your homologous species, though I am confused as to why you focused on locomotion? Is that the only difference between these two organisms?
ReplyDeleteThe tail is a classic example of a homologous trait. a Couple of questions:
Does the tail of the dog serve any other function other than wagging?
While I understand that the human tailbone is sometimes labled as "vestigial", that is not the same as "non-functional". What function does the tailbone serve in humans?
I really like how you made a good attempt to explain why humans have lost their tail. This is still in debate among anthropologists. I do want to challenge you on the argument that it was bipedalism that caused the loss of our tail. Tail loss actually occurred in all apes, not just humans, so the tail was lost before bipedalism even developed. It actually starts to disappear in Old World Monkeys, such as the Baboon and the Gelada, both of with have very tiny tails. It's only in the New World monkeys where we see a grasping prehensile tail that you discuss. So the tail structure began to shrink as the Old World monkeys began to evolve. That is where we need to start the search for the answer to this question.
You touch on the issue of ancestry but don't completely explain how this confirms that these traits are homologous. Both humans and dogs are mammals, so we know that the common ancestor would be an archaic mammal. We also know from the fossil record that early mammals possessed that generalized tail structure found in nearly all mammals in some form and passed that onto these two descendant species, with changes concurring over time due to differences in the environment. That is what we need to know to confirm common genetic origin and confirm homology.
Analogy:
You leave out your description of your species here and just jump straight into a description of your analogous traits. Knowing some background on these species will help your reader understand what may have driven the divergent evolution on this trait.
For these tails to be analogous, that means they did not arise from common descent but due to independent evolution. Is that the case here?
The ancestry of tails in dogs and alligators is not that different from the ancestry of humans and dogs. Dogs are mammals, who arose from reptiles. Alligators are reptiles, so we know that the common ancestor was an archaic reptile. We also know from the fossil record that early reptiles (all of them) possessed a tail structure and passed it onto both of these descendant species. That means this trait is the product of common descent, which means it is NOT analogous.
You even mention this in your section on ancestry:
"Yes, a common ancestor of these two different species possessed this trait of an extended tail bone because they were their for a purpose and were needed to survive."
That should have been a big glaring warning light that these traits were not analogous.
"We know this trait of a mobile and extended tail is analogous because they are two different species, one is a mammal and one is a reptile"
No, that doesn't define "analogous". Genetic distance is not a guarantee of analogous status. For example, the tiny ear bones of humans are actually homologous to the branchial arches of archaic fish. Really. So genetic distance alone does not confirm analogy.
Take a look at some of the other student posts to understand what it means to be "analogous"... Basically we are looking for traits that did NOT arise from common descent (i.e., they have no common genetic origin) but evolved because those species were trying to solve the same problem and developed similar traits to address that problem.
Good images.
I love your choice between the dog and a human. I never really gave it thought on how we are similar. I guess that why a dog is a man's best friend. I found out that men actually have a longer tailbone than women which you might want to consider while doing your research on how dogs and humans are alike.
ReplyDelete