Homology:
Humans and whales are primarily homologs and are more related than it may seem.
Humans or homo sapiens, being classified
in genus homo and species sapiens, are reproductive mammals that does not
necessarily have a specimen, but we recognize human beings as homo sapiens.
Additionally, humans are nested in the primate category within also the great
ape family. On the other hand, whales are marine aquatic mammals who nurse
their young. Also, whales have a thick layer of fat on them called a blubber
that insulates them and provides heat and warmth from the cold waters and
temperatures. Most whales have teeth, such as the beluga or sperm whales,
whereas some have special structures in their mouth called baleen to strain
food, such as blue, gray, and bowhead whales. All in all, both these mammals
may sound different but they have evolved with some of the same
structures.
The flipper of a whale and an arm of human are
closely related and have the same bones almost. However, if not evident in the
photos below, both humans and whales have bones that are structurally the same,
but they are sized differently. For instance, the humerus of a human is
probably three times longer than a whale's humerus. Also, the shape of the
bones of the whale have a slight tilt to match the shape of the flipper, while
the human's bones are more longer and not as bent. Although they both have very
similar bones, whales use there flippers and the limbs themselves for swimming
and guiding themselves in the water. On the contrary, humans use their arms and
their limbs in their arms to bend it and basically do anything we can possibly
do, whether it would be writing notes, washing dishes, controlling the steering
wheel while driving and etc. Due to evolution and habitual differences, the homologous
trait of the similar limb in the arm exhibit different functions and have
evolved to different sizes and alternate shapes in order to be compatible for
that function; whales for swimming with their flippers and humans for using
their arm on a daily basis. Lastly, in order for the whale to use its flipper
to navigate through the waters and flap it, the shape of the limbs has evolved
to provide that functions, whereas for humans the shape of the limbs has
evolved to fit the function of being able to bend the arm in many ways to do
daily tasks needed for humans and their survival.
Generally speaking, the common
ancestor of both humans and whales was most likely a four-legged insect-eater
that lived hundred of thousands years after the dinosaurs were extinct. As you
may imagine, this creature was small and scurrying, but by having these
structures as they are studying now, this insect-eater is the most recent
common ancestor for these two species.
Analogy:
Who would have thought that us humans can have similar qualities with an octopus?
To begin with, as described before,
humans are called homo sapiens and they are mammals and primates closely
related to the primate and apes family. Humans are one of more than 200 species
that belong to the order of Primates. The most common ancestor for homo
sapiens is the neanderthals who are extinct. On the other hand, octopi are
cephalopod mollusks that have two eyes, four pairs of arms, and are bilaterally
symmetric. Most octopi live along the ocean floor in all of the world's oceans,
especially in warmer tropical waters. If they are threatened, they will
disperse an inky black fluid that darkens the water as a defense mechanism.
They can also communicate with each other by changing colors. Now, how they
have similar eyes if they are so different?
The analogous trait that humans share
with octopi is the similarity in eye structures, but having no evolution with
the similar structures in the eye. They both have a lens, retina, eyelid,
cornea, pupil, iris, muscles, optic nerve, and optic ganglion. However, the
only differences would be focusing and resolution due to the absence of the
blind spot in the octopus, which humans have. On the contrary, both fill the
function of providing great eyesight for both octopi and humans. Also, they
both contain the Pax6 gene that directs the formation of the eye, and in
order to create complex structures to fill different environments, the number
of directions from the single gene evolved. Because they lived in related
environment in a way, filled similar equal ecological tasks, through natural
selection that type of structure was favored in different ancestors, thus
displaying the evolution and similarities in both these eyes of both
species.
Since the octopi and humans are very far from
each other on the phylogenic tree, there has not yet been a common ancestor
found that these two could share. The only hypothetical assumption of the last
common ancestor these two may share is the urbilaterian, in which has bilateral
symmetry, but also possesses the Pax6 gene that directs the formation of
the eye, which may be where these two species evolved from. However, since they
are very far from each other, this is an assumption, but it is the most
probable ancestor with the similar genes that later evolved to create the
complex eyes of humans, octopi, etc.
Works Cited:
By Comparing the Traits of Species That Are Both Closely and Distantly Related to Each Other, We Can Begin to Understand Their Evolutionary History. "Evidence of Evolution: Homology Sometimes a Discussion of Evolution Needs to Consider How Evolution Does NOT Happen." BIL 160. N.p., n.d. Web. 03 Nov. 2016. <http://www.bio.miami.edu/dana/160/160S13_5.html>.
Conversation_, By Malcolm Campbell_ The. "How Humans And Squid Evolved To Have The Same Eyes." Popular Science. N.p., n.d. Web. 04 Nov. 2016. <http://www.popsci.com/article/science/how-humans-and-squid-evolved-have-same-eyes>.
"Difference between Homologous and Analogous Structures." Difference Between. N.p., 08 Oct. 2016. Web. 03 Nov. 2016. <http://www.differencebtw.com/difference-between-homologous-and-analogous-structures/>.
"Octopus." Nationalgeographic.com. N.p., 01 Mar. 2014. Web. 04 Nov. 2016. <http://kids.nationalgeographic.com/animals/octopus/#octopus.jpg>.
"The Search for the Urbilaterian Ancestor." Developmental Biology 10e Online:. N.p., n.d. Web. 03 Nov. 2016. <http://10e.devbio.com/article.php?id=305>.
Smithsonian's National Museum of Natural History. "Homo Sapiens | The Smithsonian Institution's Human Origins Program." Homo Sapiens | The Smithsonian Institution's Human Origins Program. N.p., 01 Mar. 2010. Web. 03 Nov. 2016. <http://humanorigins.si.edu/evidence/human-fossils/species/homo-sapiens>.
"Whale." WorldWildlife.org. World Wildlife Fund, n.d. Web. 04 Nov. 2016. <http://www.worldwildlife.org/species/whale>.
"What Are Homologous Structures?" About.com Education. N.p., 02 Jan. 2016. Web. 04 Nov. 2016. <http://evolution.about.com/od/evidence/a/Homologous-Structures.htm>.
Hey Armine! I found your post to be really interesting and easy to read. The set up of the post was easy to follow and organized. I found the homologous trait between humans and wakes to be really interesting. I had no idea that we shared a similar structure in the arm and flipper. Looking at them from the outside, it is definitely hard to believe that they have a similar structure. Also, it's funny that though humans and octopus have a similar eye turner,it is just by coincidence. Since humans and octopi are very different, I like how you made an educated guess as to what the common ancestor is. I found with my post as well, that it is hard to find a common ancestor of two species that are so different and only share analogous traits. Great job!!
ReplyDeleteThanks you so much Brenna! I was shocked as much as you were for the similarities in the eyes of octopi and humans and also the arm and the flipper; it is so interesting how evolution works. Thank you for the great feedback ;)
DeleteVery good opening description of your two homologous species pairings.
ReplyDeleteYou also did well with your discussion of the homologous traits themselves, focusing on the differences in the structures and how that reflected differences in function. One caution: Don't get too wrapped up in the difference in size. Remember that this will all be relative to overall body size and size differences in bones may exist because the body size is also different. The shape (morphology) and the relative lengths of bones (such as the greater relative length of long bones in humans compared to the relatively short "long" bone lengths in whales) will tell you more about their function then straight size observations.
With regard to ancestry, the point is not to identify a specific ancestor, but how we can use ancestry to confirm that these traits are indeed homologous by demonstrating that the traits arose via common descent. In the case of humans and whales, as both are mammals, we know that the common ancestor was also an archaic mammal. We know from fossil evidence that early mammals possessed the primitive form of that mammalian limb structure, passing it onto these to extant species, with changes occurring as a result of different environments, producing divergent evolution of the traits. That is what we need to knwo to confirm homology.
Thank you for using the eye for your analogous pairing! One of my favorites and a classic example of analogy. Well described and explained. Well done in your section on ancestry talking about the Pax6 gene, but you are correct that this isn't evidence of homology. This may just suggest that the Pax6 gene itself is far older and may have just been "turned on" independently in the octopus line and in the line leading to humans. The eye has independently evolved several times on earth and the question of how it gets started is very interesting. Note that one key piece of evidence to support the fact that these two eyes are analogs is that the octopus eye is "designed" in reverse to the human eye. The human eye is actually a rather dumb design, with the attachment of the optic nerve causing us to have a blind spot. The octopus eyes has a superior layout and doesn't possess the blind spot.
Other than a few points in your homology section, good post. Great sources and good images.
Thank you so much for the great feedback Professor Rodriguez, I understand the points made of the differences and the ancestor for the homology portion.
ReplyDelete