Analogy vs. Homology

Homologous

When comparing two very different creatures it is interesting to find several homologous similarities between them. Dolphins and humans for example, are very different at first glance, but after a second take it is interesting to find exactly how much they have in common. Dolphins are marine mammals in close relation to porpoises and whales. They can be found in warm water such as tropical oceans. To communicate they use a clicking sound that can be heard underwater, and are often very social. Humans, are defined as homo-sapiens closely related to primates. They can be found in all seven continents of the world and communicate in various ways using language.  The human arm and Bottlenose dolphin flipper are very similar, and developed from a common ancestral structure. Though at first glance they are quite different, underneath, their structures both include a humerus, ulna, and radius. The humerus in humans, functions to connect the ulna as the forearms radical bone, to the wrist, and at the shoulder it connects the body to the scapula. The humerus also includes muscular insertion and origination. This all works together to allow humans to successfully move their arms such as reaching for an apple off of a tree. In a dolphin flipper however, all of the said bones are more compact and small. This allows for functions to be more swift and sharper, such as pushing through water. Millions of years ago dolphins and humans must have shared a common ancestor that lived in water and was forced out of sea, onto land. This might have been a dinosaur creature such as the   Thalattoarchon Saurophagis which was essentially a water dinosaur that closely resembles a half lizard half dolphin. While it is weird to think that today's humans could have evolved from a water dinosaur species, it is definitely an interesting theory. 

                              

             

Analogous

Penguins and fish though very different in appearance, share the same analogous trait of fins. Penguins and fish both have the same fin-like structures that help them navigate through aquatic environments. Emperor penguins are flightless birds found in Antarctica. They reside along arctic waters and survive harsh conditions by hunting nearby fish. Covina fish are saltwater fish found in the tropical waters of the southeastern Pacific. It can also be referred to as the croaking fish because of the sound it makes when it head comes above water. A penguins wings are much like a human arm or dolphin fin. They include a humerus, ulna, radius, and phalanges to help them navigate through the treacherous arctic waters. While they are still technically wings, they cannot be used for flight because they are too thin and cannot support the weight of the penguin. This is an example of an analogous trait itself because the wings of the penguin have evolved from their initial use of flight to their present use of swimming. The fins of a fish however, have the same use as the wings of a penguin. While their structures are different, they are still used the same way. Pectoral, anal, and pelvic fins can be found on almost all fish and contributed to the movement of said fish. A fish's fins for example, are comprised of small thin bones, and a webbing to protect them. The principle function of the fin is to help the fish swim. Depending on their location, different fins serve for different swimming purposes such as swimming left or right, or turning, or stopping. While most all species share some common ancestor, I believe that these analogous traits are based on the demands of the environment and not necessarily the ancestral lineage. 

analogous information: http://education-portal.com/academy/lesson/analogous-structures-definition-examples-quiz.html#lesson