Analogy and Homology
Analogy and Homology Blog Post
Homologous Trait: Tailbone
The two different species are a human and a monkey. Human are a primate, known as being one of the most intelligent living things on the planet. The monkey is also a primate, however, it's better known for living in trees and often being resourceful in the wild. There are about 93 different classifications for monkeys.
For the human, the tailbone is pretty pointless to have. It's called the coccyx, and is defined as a triangular arrangement of bone that makes up the very bottom portion of the spine below the sacrum.The tailbone in the human body represents a vestigial tail. On the other hand, the tailbone in monkeys is quite useful. These bones are used to make their tail, which can be used for many different uses. It can help swing from different branches, keep their balance, and hold onto food.
The common ancestor of humans and monkeys would've most likely been an older monkey no longer living, or adapted to become the monkeys we know today. This is due to the common ancestors often being a monkey, to then an ape, to then early forms of human.
Analogous Trait: Laying Eggs
The two different species are a platypus and a duck. The platypus is a mammal, looking like a cross between a beaver, raccoon and duck. The duck is a type of bird, known for it's overall friendly nature and spending most of it's time by or in fresh water.
The analogous trait is both species laying eggs. Even though the platypus is a mammal, it stills lays eggs of it's young. It's well known that birds lay eggs for their young. The trait is similar in both structure and function. Both are trying to reproduce for having young, and they both lay their eggs in similar fashion. The similarities were both likely due to both of their environments; both animals live around or in water for most of their lives.
I don't believe that these two species shared a common ancestor. It's believed that the platypus split from the reptile family, due to the males having venomous spokes coming out of their hind legs during their mating season. Because of this, it is most likely that these two species would've not crossed paths with a common ancestor.
I think it's very interesting that humans and monkeys evolved from each other. I agree that they must of came from a common ancestor a long time ago which was probably another type of monkey. I used the same analogous example as you, that being ducks and platypus. Platypi are fascinating creatures and it intrigues me that they lay eggs even though they are a mammal!!
ReplyDeleteLove this comparison was going to use the same one but did not want to use an example someone else had used. Do you think that the human tailbone can be used as a way of balance as well? We as humans do depend on our stability of our back which is connected to the tailbone. The Platypus is one of the most fascinating mammals and I forgot that they were egg laying mammals. Your blog was well layed out and easy to understand. Thank you for your insight.
ReplyDeleteHomology:
ReplyDelete"known as being one of the most intelligent living things on the planet"
Does this really, objectively "describe" us from a biological perspective? Is this useful in understanding the adaptation you discuss? Are you letting your own bias come into play here? This is a discussion on biological adaptations, so let's stick with biology. Describe based upon our anatomy, our diet, our environment, and our social systems. Don't describe us *relative* to any other organism.
Okay on "monkey" but, as you point out, there are a lot of different types of monkeys. Could you have been more specific here?
Good analogous trait, but is the human tailbone actually "useless"? It serves as a muscle attachment for some pretty important perineal muscles, which serve important excretory and reproductive functions. Few physical traits have no function.
Another question arises from this... why did apes lose their tails? There are a lot of different suggested answers, and anthropologists don't yet have a definitive answer, but it would have been good to question why this change happened. What environmental conditions encouraged this?
On the right track, but make sure your language is accurate. It isn't just an "older monkey" who is the common ancestor. It is an archaic ancestor of both monkeys and apes from millions of years ago. And how does this help us confirm that these traits are indeed homologous? Both humans and monkeys are anthropoids (monkeys and apes), so we know that the common ancestor would be an archaic anthropoid. We also know from the fossil record that early anthropoids possessed that generalized tail structure and passed that onto these two descendant species, with changes concurring over time due to differences in the environment (which is, as I said above, is still an open question). That is what we need to know to confirm common genetic origin and confirm homology.
Good images.
Analogy:
Much better, non-judgemental description of your two species. Do you see the difference?
Good description of your analogous traits, but one question is raised:
"both animals live around or in water for most of their lives."
Why is egg-laying adaptive aquatic environments? Is that the environmental stress that resulted in this trait developing in both species? I'm not saying you are are wrong. I'm asking you to continue the explanation.
"I don't believe that these two species shared a common ancestor. "
As explained in the guidelines, ALL organisms share a common ancestor if you go back far enough. The question is, did the trait you highlight here arise from that common ancestor? Or did it rise independently in at least one of these species (which is required if it is analogous)? So how do we figure this out?
We start by identifying the possible common ancestor. The platypus arose from mammals, who arose from reptiles. Birds also arose from reptiles, and they actually inherited the egg-laying trait from reptiles. So is it possible that the egg-laying trait is homologous, not analogous? Well, that depends upon how it arose in the platypus. We know that the platypus developed it's trait after it split off from mammals, who are generally placental in nature. That means this trait arose independently in the platypus relative to that common ancestor with birds. That's what we need to know to confirm that these traits are, indeed, analogous.
Good images.