Homologous
Homologous animals are include species which are related to
each other and they share a trait due to common ancestry. For clarification, these homologous
structures don’t necessarily have the same function. Let’s study some evidence and evaluate two
species, the giraffe and human indicating these two species may have arisen by a
common descent. Primarily, the embryonic
structures of both species reflect the same skeletal structure of both the giraffe
and human. Both structures look
strikingly different on the outside however they vary in purpose.
The cervical spine of a giraffe is made of seven bones just
as the neck of a human. In contrast the
giraffe neck is slinky; the cervical vertebrae are bound together with
ball-and-socket joints, allowing the giraffe to extend its head virtually
perpendicular to the ground. Humans’ thoracic vertebrae are joined at the
middle providing stability and our cervical vertebrae are also fused at the
front and back for more mobility with less flexibility. The result of the giraffes ball-and-socket
joints we see the neck move back and
forth when it walks because of their weight and motion of the neck to balance the
giraffe's center of gravity. In addition,
their neck flips back and forth assist them in when standing. In contrast, we swing our arms up over a
chair or table to support us out from a sitting position. Lastly, the spotting on the giraffes coat and
or skin provides camouflage as the purpose of spots on human skins is not quite
clear yet.
The giraffe and human have a common general ancestors which are vertebrates and we know that ancestors possessed this trait are derived at the early stages of development. The skeletal evidence and biochemistry reveal the similarities between the organisms such as the DNA, hormones, bones and tissues, and the respiratory breathing pattern to rid of waste products, such as carbon dioxide.
vs
Analogous
Anologous traits are similar due to reasons other than
relatedness and are governed by structural genes and regulatory genes. The similarities among anologous species can
result from random chance or as a result of the organisms ability to adapt to their
environments.
As described by Berkeley University (2014) dolphins and sharks
both share similarities as they both a streamlined body, a triangular fin on
their back, and two side fins.
Sharks Dolphins
skeleton made of cartilage
skeleton
made of bone
use gills to get oxygen from the water go to the
surface and breathe atmospheric air in
through their blowholes
don't nurse their young do nurse their young
don't have hair born
with hair around their "noses"
The Pakicetus which is the earliest Cetacean is the ancestor
to both species the dolphin and the shark.
This ancestor possesses the same analogous trait as the dolphin and
shark’s based on skeletons found in the Punjab region of Pakistan. With the fossils researchers excavated they
were able to analyze skeletal structures and they surmise the forelimbs of the
Pakicetus were later formed into flippers.
Understanding Evolution. (2014).
http://evolution.berkeley.edu/evolibrary/home.php
Your post was well informed and the information looked correct according to what I researched myself. The only suggestions I can make is to fix your sentence structure and the font display on your blog. Even with the information I learned, with your I continued to learn more detail and information I had not read. It helped me clarify what I learned and some questions that have left me partly curious. I myself also compared humans but instead of comparing it to giraffes, I compared it too chimpanzees. Either way I enjoyed reading your blog and knowing more information I could have missed.
ReplyDeleteGreat discussion on your homologous trait! Good specifics. The only criticism is that you can get more specific on your ancestry than simply "vertebrates", which would include all organisms with a vertebral column: mammals, birds, reptiles, amphibians, and fish. Both humans and giraffes are mammals, so we can narrow it down and say that the common ancestor was a mammal and all mammals have 7 cervical vertebrae. This is an ancestral trait.
ReplyDeleteCan you think of analogous traits that are do solely to "random chance"? I can't. All adaptive traits are the result of environmental pressures, not due to chance alone.
You have found the similarities in structure between the dolphin and the shark, but you haven't explained why those similarities exist.
Regarding ancestry: Sharks are fish. They evolved millions of years before mammals ever appeared on the evolutionary scene and it isn't possible for the mammal you have identified to have been the ancestor of the shark. To find the common ancestor of these organisms, you have to go back many millions of years to the era when there were no land animals, only life in the seas, to the age of fish. More than likely, that common ancestor possessed the traits you highlight here, passing them onto their shark descendents.
So why aren't these traits homologs if the common ancestor possessed these traits? Because the dolphin developed those traits independently after it's mammalian ancestor returned to the water environment from the land. As long as one of these organisms developed the traits independently from the common ancestor, these traits are analogs.
Thank you very much L Rodriguez for your clarification on my post I will make it a point to verify my resources from other than university.edu sites.
DeleteI really enjoyed your analysis of the giraffe. It had never occurred to me that one of the other function of its neck is to assist standing up. In such case the neck's other function acts very much like our limbs. It will have to be strong and be able to move in different angels. I have always imagined that the bones in a giraffe's neck is very similar to that of a humans. However, for what they use for, it makes sense that their cervical bones looks such as so. I would have imagines that a shark fin and a dolphin fin are homologous. It is interesting how, as it turns out that they are made differently. However, I failed to made the connection to the Pakicetu. I would hope that maybe you can elaborate on that a little more. It is hypothesized that all living things came from the same origin from a long time ago. Perhaps their ancestors, at one point did look somewhat like the Pakicetu, before it formed legs instead of fins. Or perhaps the ancestor of the Pakicetu is the missing link between the animals.
ReplyDeleteI really enjoyed your comparison of the giraffe and human. Its very informing to make the connections about the way the giraffe swings its neck and we swing our arms, and how many bones make up the neck. I don't believe that the spotting on a humans skin is similar to the pattern of the giraffe's skin.
ReplyDeleteThe analogous trait, between the shark and the dolphin makes absolute sense. But one statement I do not agree with is the random change. Bodies evolve because it beneficial to their survival. If i knew nothing about evolution i would not believe that the Pakicetu is a common ancestor, because it is a land animal. After some research i learned that animals came from the sea to land, and back to the sea. It's just fascinating.