Homologous Traits: Dogs and Humans
Has anybody ever come up to you and said that you share some similarities to your pet dog? I haven't either. It may seem absurd, but dogs and humans share more similar bone structures then you think. This bone structure, came from one common ancestor. Lets take a look at this pairing!
A. Dogs and humans within their anatomy possess a radial bone and ulna bone. Humans and dogs are both mammals, yet act vastly different in behavioral terms. Dogs or, 'canis lupis familiaris' are said to be closely to the wolf, 'canis lupis,' and the coyote, 'canis latrans. On the other hand, humans or, 'homo sapiens,' are said to be once closely intertwined with apes or, 'hominoidea.'
B. From the great contrast, you may be wondering how dogs and humans could possibly share similar bone structure. In humans, the radial and ulna bones are the two largest bones within the forearm. The radial bone extends from the laternal side of the elbow to the thumb side of the wrist and stands parallel to the Ulna. The Ulna joins with the humerous on the larger end to make the elbow joint, and joins with the carpal bones of the hand at the smaller end. The site, Healthline states the functioning as follows, "Together with the raidus the ulna enables the wrist joint to rotate." Conversely, Bluepearl a vet site explains the functions and location of these bones within canines, "The forelimb has two bones between the wrist, or carpus, and the elbow join, the radius and ulna. The radius is the main weight-supporting bone of the forelimb; whereas, the ulna supports only 20% of the weight." While the two structures seem greatly similar, they each provide different utilization for both species. Firstly, it must be noted that the ulna and radius within the human are located in the forearm, while these bones in dogs are located in the foreleg. Animals who possess arms use them in order to prefer different functions such as using the these bones to aide in rotating the wrist, in order to grasp objects or food easier. To add, human wrists also have more access to flexibility then the paws of a dog do since the structure starts to differentiate in the surrounding bones. Dogs use these bones in their forelimbs for walking and running. Dogs cannot pick up objects like humans, neither do they run similarly to humans.
C. So, how where does this structure come from and how could these two differing species share a common ancestor? I wondered this too as I was studying this subject. The answer lies in the what scientists believe was the first placental mammal, according to an article on National Geographic. The placentals include all living mammals except marsupials and monotremes.
If this mammal possessed the radius and ulna human and dogs shared, it would likely appear in the foreleg in a much smaller and weaker form.
Analogous Traits: Bees and Ducks
Like above, you might be wondering how two species that seem vastly different could possibly share something in common. Ducks and bees may be derived from vastly different organism, but that doesn't mean they don't share a body part without a common function.
A. Bees or, 'Anthophila' originate from the 'insecta' family. On the other hand, ducks or, 'Anas platyrhynchos,' come from the, 'Aves' family. Both species provide different services within the food chain and environment. However, their wings provide the function of flight.
B. HowStuffWorks explains that bee wings are made up of, "Movable plates of Chitin." Chitin is commonly found in the exoskeletons of insects and is a fibrous substance consisting of polysaccharides. Ducks do not possess an exoskeleton like bees do. Their structure actually possesses an ulna and radial bone within the wing that aide them in flying. Though, these bones are much lighter in weight and size compared to how they're found in humans and dogs. These structures differentiate in order to compensate for the weight and anatomical structure of the animal. Chitin is an easily breakable substance in comparison to the solidity of the duck wing. The bee only needs its wings built like this because its' body is much smaller then that of the duck's.
C. The common ancestor of these two beings likely was derived from an organism that probably had a significant lesser amount of shells. By looking through images that display, 'the tree of life,' I was able to draw that the the common ancestor likely did not have the wings or any form of flight. These traits are not genetically related because insects possess an exoskeleton that ducks do not have in any shape or form.
Works Cited
Yong, Ed. “Meet the Ancestor of Every Human, Bat, Cat, Whale and Mouse.” Phenomena, National Geographic | Phenomena, 7 Feb. 2013, phenomena.nationalgeographic.com/2013/02/07/meet-the-ancestor-of-every-human-bat-cat-whale-and-mouse/.
“Radius and Ulna Fractures in Dogs and Cats | BluePearl Vet.” Blue Pearl Specialty and Emergency Pet Hospital, 11 July 2016, bluepearlvet.com/medical-articles/fractures-of-the-radius-and-ulna/.
“Ulna Bone Anatomy, Diagram & Function | Body Maps.” Healthline, Healthline Media, www.healthline.com/human-body-maps/ulna-bone.
Wilson, Tracy V. “How Bees Work.” HowStuffWorks, HowStuffWorks, 30 May 2007, animals.howstuffworks.com/insects/bee1.htm.
Hello Kathleen,
ReplyDeleteFirst, I have heard many times, of people saying, "you look like your pet"! and I really do think some people do! :) I was so close to using dogs and humans as my example of homologous traits as well, but wound up going a different route. When it comes to animals, wolves are my 1st love so I love that you chose the dog and humans and noted that dogs are closely related to canis lupis. I am curious though, did you find the idea of dogs (wolves) having a dewclaw was also similar to humans? You provided great visuals of examples of the structures you discussed. For your analogous traits, I never knew that the wings of bees were so small and simply because they didn't need to be so "strong", in order to support the body of bees. That is so interesting! They can be fibrous and fragile because bees don't need stronger? Fascinating! I also often find myself forgetting that ducks can fly because I rarely ever see it. What a great example. Thank you.
Good supporting images.
ReplyDeleteThe opening section in both the homologous and analogous areas asked for a description of your species, not just identification. This would help your reader understand the environment and behavior of the species to better understand why their traits evolved the way they did. Needed to be expanded.
Good, thorough discussion on the differences in structure, function and environmental pressures for your homologous comparison.
We don't need to get quite that specific in terms of a common ancestor. That may well be the "first mammal" but the actual common mammalian ancestor between humans and dogs may be more recent. So to keep it simple:
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 mammalian limb structure 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.
For your analogy comparison, what we needed here was a discussion on the *similarities* in structure due to similarities in function and environment. You are very thorough about differences, but we needed our focus on similarities. Differences aren't surprising in analogs... they are not genetically related. It is the similarities we need to explain.
" I was able to draw that the the common ancestor likely did not have the wings or any form of flight."
That is possibly true, but do we need to draw that conclusion to confirm that these are analogs? Don't we just need to confirm that the traits arose independently in at least one of these species?
It is difficult to guess at what the common ancestor of the bird and bee looked like some 100's of millions of years ago... it may have possessed wings or it may not have, but fortunately, we don't need to know that to confirm that these traits are analogous. While it is possible that the bee inherited its wings from that common ancestor, what about the bird? We know quite a bit about bird and bird-wing evolution. Birds evolved wings as they split from reptiles, and this occurred long, long after the split with that common ancestor with the bee. This means bird wing evolution occurred independently from that common ancestor with the butterfly. That is sufficient to confirm that these are not the product of common descent and are indeed analogous.
Good images.