Evolution is the reason behind the greatest transformations of simple organisms into the
everyday creatures of the world today. It all started with Charles Darwin’s foundation of
different species evolving over time. From that he developed the process of natural selection. His
idea of simpler species inheriting special traits and gradually changing to become more complex
species over time, in order to adapt and reproduce, dramatically changed the way we see and
think about the world. With that said, I believe the species that best demonstrates Darwin’s
theory of evolution in our dissection lab is the freshwater mussel, the grasshopper, and the frog.
To clarify, from my point of view the freshwater mussel (Ellipsaria lineolata) portrays a
great example of evolution from a simpler organism. For instance, scientific evidence states that
the mussel evolved from a mollusk with two hinged shells which is a bivalve ancestor such as an
oyster, clam, or other mollusks under the “Bivalvia” class during the Paleozoic era. Some fossil
shells also indicate that they coexisted with dinosaurs during the Mesozoic era about 65-245
million years ago. In the dissection lab we discovered that the mussel’s digestive system contains
a mouth, stomach, and anus. The circulatory system of the mussel is an open system. The open
circulatory system is commonly evolved in crustaceans, insects, mollusks and other
invertebrates. Unlike in the closed circulatory system, the open circulatory system pumps more
blood into the body cavities. The freshwater mussel has a decentralized nervous system and does
not have a brain. The mussel is one of the simpler organisms and lacks more complex
characteristics.
Furthermore, I personally believe the animal from our dissection lab that best exhibits the
next step in the evolutionary staircase is the grasshopper (Chloealtis conspersa). The grasshopper
is under the “Arthropoda” phylum and class “Insecta”. The grasshopper is a complex insect and
consists of more specific body functions than the mussel. The grasshopper, like all insects, has
three parts, the head, thorax, and abdomen. In addition to having walking legs it also has another
pair of legs to jump and a set of wings. It has a shell made of chitin which is a fibrous substance
to create an exoskeleton for protection of the insect’s organs. The exoskeleton is divided into
sections with flexible joints that allow movement more easily. The digestion system is made up
of a mouth, esophagus, stomach, anus, gizzard, and pyloric valve, which allows the passage of
only the thoroughly digested food into the stomach and prevents regurgitation. Like the mussel,
the grasshopper also has an open circulatory system. The blood starts at the hemolymph and
consists of sinuses that have four chambers similar to the human heart. However, unlike humans,
the grasshopper’s blood transfers food and waste and does not carry oxygen or carbon dioxide
throughout the body, this is why its blood is green. The process of carrying oxygen and carbon
dioxide through the body happens in the tracheal system found in the respiratory system. The
grasshopper does have a brain and is extremely sensitive to sound. The grasshopper is one of the
more complex species of organisms in our lab.
Finally, I think the animal that is the most evolved and complex species in our dissection
lab is the frog (Rana tigrina). They belong to the “Chordata” phylum and class of “Amphibia”.
According to scientific research the frogs and other amphibians have been around for about 360
million years. The frog is a very complex organism and has a highly specialized body structure.
Frogs breathe through the pores of their skin when underwater and use their lungs while on land.
In contrast to the mussel and grasshopper, the frog has a closed circulatory system. It is made up
of a three-chambered heart, two atria which are chambers that collect the blood, and a ventricle,
which receives and pumps blood into the arteries. It also has a spiral valve within the heart that
directs the flow of blood to prevent oxygenated and de-oxygenated blood from combining or
mixing together. During the dissection it seemed that the frog’s digestive system displayed more
detailed features. For example, it had a small intestine, large intestine, cloaca (waste filter),
stomach, bladder, kidneys, and spleen. Frogs have a highly developed nervous system and sense
of hearing. They can detect high-pitched sounds with their ears and low-pitched sounds through
their skin. They also have a highly developed sense of sight and smell. The frog is a very
complex and fully-developed organism.
Overall, Charles Darwin’s theory of evolution has greatly impacted the natural and
scientific world. It opens the doorway of classifying and predicting the different characteristics
of plants, animals, and all living things from the past. It might even help us predict the future by
identifying clues using present day features of organism and environmental study to indicate
where the evolutionary staircase will lead us next. But using the animals from the dissection lab I
believe that the species mentioned above specified how dramatic and amazing evolution can be
in altering the simplest of organisms into a more evolved and intricate creature.